| 0/0 |
2026/06/01 10:12 |
flow |
assessment-security |
57m
Results: map[DenialOfService:true Explanation:The bug report indicates a memory leak of a `struct pid` object. Based on the
provided reproducer and kernel source code, the leak occurs in the
`clock_nanosleep` system call when dealing with CPU clocks of specific
processes.
### Root Cause Analysis
When `clock_nanosleep()` is invoked with a CPU clock targeting a specific
process (e.g., encoded in the `clockid_t`), it eventually calls
`do_cpu_nanosleep()` in `kernel/time/posix-cpu-timers.c`.
1. `do_cpu_nanosleep()` initializes a temporary `struct k_itimer` on the stack
and calls `posix_cpu_timer_create(&timer)`.
2. `posix_cpu_timer_create()` looks up the target `struct pid` based on the
`clockid_t` and takes a reference to it via `get_pid(pid)`, storing it in
`timer->it.cpu.pid`.
3. Next, `do_cpu_nanosleep()` attempts to arm this temporary timer by calling
`posix_cpu_timer_set()`.
4. If the target process has concurrently exited and been reaped,
`posix_cpu_timer_set()` fails to find the associated task (as `pid_task()`
returns `NULL`) and returns `-ESRCH`.
5. When `posix_cpu_timer_set()` returns an error, `do_cpu_nanosleep()` handles
it as follows:
```c
spin_lock_irq(&timer.it_lock);
error = posix_cpu_timer_set(&timer, flags, &it, NULL);
if (error) {
spin_unlock_irq(&timer.it_lock);
return error; // <--- BUG: timer is not deleted
}
```
Because it directly returns the error, it skips calling
`posix_cpu_timer_del(&timer)`. Since `posix_cpu_timer_del()` is the only place
that drops the `struct pid` reference (via `put_pid()`) for CPU timers, the
reference is permanently leaked.
### Security Impact
* **Exploitable:** No. This is a pure reference counting leak of a `struct pid`.
It does not lead to use-after-free, memory corruption, or privilege escalation.
* **Denial of Service:** Yes. An attacker can repeatedly spawn threads, target
them with `clock_nanosleep()`, and exit them concurrently to leak `struct pid`
objects. This will eventually exhaust kernel memory and cause a system-wide
Denial of Service (OOM).
* **Accessible From Unprivileged Processes / User Namespaces:** Yes. Any local
unprivileged user can create threads and call `clock_nanosleep()` on them. No
special capabilities are required.
* **Remote / Network / Peripheral / Filesystem Trigger:** No. The bug requires
local system call execution (`clock_nanosleep`). Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/06/01 10:12 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// rt_tgsigqueueinfo arguments: [
// gid: pid (resource)
// tid: pid (resource)
// sig: int32 = 0x1d (4 bytes)
// info: nil
// ]
syscall(__NR_rt_tgsigqueueinfo, /*gid=*/0, /*tid=*/(intptr_t)-1, /*sig=*/0x1d, /*info=*/0ul);
// socketpair$unix arguments: [
// domain: const = 0x1 (8 bytes)
// type: unix_socket_type = 0x2 (8 bytes)
// proto: const = 0x0 (4 bytes)
// fds: ptr[out, unix_pair] {
// unix_pair {
// fd0: sock_unix (resource)
// fd1: sock_unix (resource)
// }
// }
// ]
res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=SOCK_DGRAM*/2ul, /*proto=*/0, /*fds=*/0x200000000300ul);
if (res != -1)
r[0] = *(uint32_t*)0x200000000304;
// sendmmsg$unix arguments: [
// fd: sock_unix (resource)
// mmsg: ptr[in, array[send_mmsghdr_un]] {
// array[send_mmsghdr_un] {
// }
// }
// vlen: len = 0x651 (8 bytes)
// f: send_flags = 0x0 (8 bytes)
// ]
syscall(__NR_sendmmsg, /*fd=*/r[0], /*mmsg=*/0x200000000000ul, /*vlen=*/0x651ul, /*f=*/0ul);
// clock_nanosleep arguments: [
// id: clock_id = 0xfffffdfc (8 bytes)
// flags: timer_flags = 0x0 (8 bytes)
// rqtp: ptr[in, timespec] {
// timespec {
// sec: time_sec (resource)
// nsec: time_nsec (resource)
// }
// }
// rmtp: nil
// ]
*(uint64_t*)0x200000000080 = 0x77359400;
*(uint64_t*)0x200000000088 = 0;
syscall(__NR_clock_nanosleep, /*id=CLOCK_MONOTONIC_RAW|0xfffffdf8*/0xfffffdfcul, /*flags=*/0ul, /*rqtp=*/0x200000000080ul, /*rmtp=*/0ul);
return 0;
}
]
|
| 2/1 |
2026/06/01 10:12 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/01783f133a850ed9827804286d5bb9887f4242a2]
|
| 3/1 |
2026/06/01 10:14 |
action |
kernel-builder |
23m
Results: map[KernelObj:/app/workdir/cache/build/e734cbc40bc4b5e29f7c6fc6da70bc7474199212]
|
| 4/1 |
2026/06/01 10:38 |
action |
codesearch-prepare |
23m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/06/01 11:01 |
agent |
expert |
8m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Instruction: You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by grepping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completely wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control transfers, that also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidential Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
2026/04/26 03:03:57 executed programs: 19
2026/04/26 03:04:06 executed programs: 21
BUG: memory leak
unreferenced object 0xffff888103405f00 (size 184):
comm "syz.0.37", pid 6027, jiffies 4294951278
hex dump (first 32 bytes):
01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................
de 07 00 00 00 00 00 00 58 2e aa 02 81 88 ff ff ........X.......
backtrace (crc 2e4fcb10):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4574 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_noprof+0x36c/0x480 mm/slub.c:4905
alloc_pid+0xdf/0x880 kernel/pid.c:188
copy_process+0x1e3f/0x2cf0 kernel/fork.c:2278
kernel_clone+0xde/0x700 kernel/fork.c:2723
__do_sys_clone3+0x18c/0x210 kernel/fork.c:3027
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xee/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
connection error: failed to recv *flatrpc.ExecutorMessageRawT: EOF
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000ul, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000ul, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// rt_tgsigqueueinfo arguments: [
// gid: pid (resource)
// tid: pid (resource)
// sig: int32 = 0x1d (4 bytes)
// info: nil
// ]
syscall(__NR_rt_tgsigqueueinfo, /*gid=*/0, /*tid=*/(intptr_t)-1, /*sig=*/0x1d, /*info=*/0ul);
// socketpair$unix arguments: [
// domain: const = 0x1 (8 bytes)
// type: unix_socket_type = 0x2 (8 bytes)
// proto: const = 0x0 (4 bytes)
// fds: ptr[out, unix_pair] {
// unix_pair {
// fd0: sock_unix (resource)
// fd1: sock_unix (resource)
// }
// }
// ]
res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=SOCK_DGRAM*/2ul, /*proto=*/0, /*fds=*/0x200000000300ul);
if (res != -1)
r[0] = *(uint32_t*)0x200000000304;
// sendmmsg$unix arguments: [
// fd: sock_unix (resource)
// mmsg: ptr[in, array[send_mmsghdr_un]] {
// array[send_mmsghdr_un] {
// }
// }
// vlen: len = 0x651 (8 bytes)
// f: send_flags = 0x0 (8 bytes)
// ]
syscall(__NR_sendmmsg, /*fd=*/r[0], /*mmsg=*/0x200000000000ul, /*vlen=*/0x651ul, /*f=*/0ul);
// clock_nanosleep arguments: [
// id: clock_id = 0xfffffdfc (8 bytes)
// flags: timer_flags = 0x0 (8 bytes)
// rqtp: ptr[in, timespec] {
// timespec {
// sec: time_sec (resource)
// nsec: time_nsec (resource)
// }
// }
// rmtp: nil
// ]
*(uint64_t*)0x200000000080 = 0x77359400;
*(uint64_t*)0x200000000088 = 0;
syscall(__NR_clock_nanosleep, /*id=CLOCK_MONOTONIC_RAW|0xfffffdf8*/0xfffffdfcul, /*flags=*/0ul, /*rqtp=*/0x200000000080ul, /*rmtp=*/0ul);
return 0;
}
Reply: The bug report indicates a memory leak of a `struct pid` object. Based on the provided reproducer and kernel source code, the leak occurs in the `clock_nanosleep` system call when dealing with CPU clocks of specific processes.
### Root Cause Analysis
When `clock_nanosleep()` is invoked with a CPU clock targeting a specific process (e.g., encoded in the `clockid_t`), it eventually calls `do_cpu_nanosleep()` in `kernel/time/posix-cpu-timers.c`.
1. `do_cpu_nanosleep()` initializes a temporary `struct k_itimer` on the stack and calls `posix_cpu_timer_create(&timer)`.
2. `posix_cpu_timer_create()` looks up the target `struct pid` based on the `clockid_t` and takes a reference to it via `get_pid(pid)`, storing it in `timer->it.cpu.pid`.
3. Next, `do_cpu_nanosleep()` attempts to arm this temporary timer by calling `posix_cpu_timer_set()`.
4. If the target process has concurrently exited and been reaped, `posix_cpu_timer_set()` fails to find the associated task (as `pid_task()` returns `NULL`) and returns `-ESRCH`.
5. When `posix_cpu_timer_set()` returns an error, `do_cpu_nanosleep()` handles it as follows:
```c
spin_lock_irq(&timer.it_lock);
error = posix_cpu_timer_set(&timer, flags, &it, NULL);
if (error) {
spin_unlock_irq(&timer.it_lock);
return error; // <--- BUG: timer is not deleted
}
```
Because it directly returns the error, it skips calling `posix_cpu_timer_del(&timer)`. Since `posix_cpu_timer_del()` is the only place that drops the `struct pid` reference (via `put_pid()`) for CPU timers, the reference is permanently leaked.
### Security Impact
* **Exploitable:** No. This is a pure reference counting leak of a `struct pid`. It does not lead to use-after-free, memory corruption, or privilege escalation.
* **Denial of Service:** Yes. An attacker can repeatedly spawn threads, target them with `clock_nanosleep()`, and exit them concurrently to leak `struct pid` objects. This will eventually exhaust kernel memory and cause a system-wide Denial of Service (OOM).
* **Accessible From Unprivileged Processes / User Namespaces:** Yes. Any local unprivileged user can create threads and call `clock_nanosleep()` on them. No special capabilities are required.
* **Remote / Network / Peripheral / Filesystem Trigger:** No. The bug requires local system call execution (`clock_nanosleep`).
|
| 6/2 |
2026/06/01 11:01 |
llm |
expert |
0m
Model:
Tokens:
input: 7251
output: 37
thoughts: 968
Thoughts: **Analyzing a Syzkaller-Reported Memory Leak in `alloc_pid`**
Okay, so I've got a syzkaller bug report screaming "BUG: memory leak" in `alloc_pid`. The backtrace points directly to `alloc_pid`, which is concerning, especially since `kmemleak` is flagging it. The stack trace looks like a normal allocation path: `kmemleak_alloc_recursive` -> `slab_post_alloc_hook` -> `slab_alloc_node` -> `kmem_cache_alloc_noprof` -> `alloc_pid`. It's happening during `copy_process`, indicating it's related to process creation through the `clone` system call. Now, the reproducer uses `rt_tgsigqueueinfo`, `socketpair`, `sendmmsg`, and `clock_nanosleep`, which seems a bit odd, as it doesn't involve `clone3` which is what I would expect for this type of issue.
My first thought is always, is this exploitable? Probably not. Memory leaks are usually more of a denial-of-service risk, but still, a leak is a leak. Let's see if this is about a `struct pid` itself leaking. I quickly search for existing reports with similar keywords. And then, I'm thrown a curveball, syzkaller reports a connection error: `failed to recv *flatrpc.ExecutorMessageRawT: EOF`. This suggests the VM or the executor crashed, which could be related, or a red herring. However, I need to focus on the leak, as a `kmemleak` report is an indication of a leak, it periodically scans the memory for unreferenced objects. `alloc_pid` is called during process creation via `clone`, so, ordinarily, when a process exits, its `struct pid` should be freed. So why is this leaking? Is this a false positive by kmemleak, or something real is happening?
Let's look at the reproducer provided and understand what is it doing.
```c
syscall(__NR_rt_tgsigqueueinfo, /*gid=*/0, /*tid=*/(intptr_t)-1, /*sig=*/0x1d, /*info=*/0ul);
res = syscall(__NR_socketpair, /*domain=*/1ul, /*type=SOCK_DGRAM*/2ul, /*proto=*/0, /*fds=*/0x200000000300ul);
if (res != -1)
r[0] = *(uint32_t*)0x200000000304;
syscall(__NR_sendmmsg, /*fd=*/r[0], /*mmsg=*/0x200000000000ul, /*vlen=*/0x651ul, /*f=*/0ul);
*(uint64_t*)0x200000000080 = 0x77359400;
*(uint64_t*)0x200000000088 = 0;
syscall(__NR_clock_nanosleep, /*id=CLOCK_MONOTONIC_RAW|0xfffffdf8*/0xfffffdfcul, /*flags=*/0ul, /*rqtp=*/0ul);
```
Ah! `sendmmsg` on a unix socket. The `vlen` argument is 1617. I'm wondering if `sendmmsg` is doing something odd, like... leaking an object. Specifically the `struct pid` of the sender! If `sendmmsg` sends SCM_CREDENTIALS, it might attach a `struct pid` to the skb. It's a plausible theory. Let's check `unix_dgram_sendmsg` and `scm_send`. That's where I need to look.
|
| 7/2 |
2026/06/01 11:01 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:scm_send SourceTreePrefix:net/unix]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_dgram_sendmsg SourceFile:net/unix/af_unix.c SourceLine:2099] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_stream_sendmsg SourceFile:net/unix/af_unix.c SourceLine:2392]] TruncatedOutput:false]
|
| 8/2 |
2026/06/01 11:01 |
llm |
expert |
0m
Model:
Tokens:
input: 9254
output: 36
thoughts: 19
Thoughts: Here's a summary of my thought process:
**Diving into the SCM Details**
Okay, time to get my hands dirty. I need to understand how these SCM credentials are being handled at a low level. My first instinct is to check out the definition of `scm_send`. Given that it's related to the Socket Credentials Mechanism, the logical place to start is the `include/net/scm.h` file. I'm hoping to find the function prototype, potentially some inline documentation, and maybe even some clues about where it's called and how it's used within the networking stack. This will give me a good handle on its purpose and how it fits into the broader picture of socket operations. From there I can branch out to the functions which consume or rely upon `scm_send`.
|
| 9/2 |
2026/06/01 11:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:scm_send]
Results: map[SourceCode: 91: static __inline__ int scm_send(struct socket *sock, struct msghdr *msg,
92: struct scm_cookie *scm, bool forcecreds)
93: {
94: memset(scm, 0, sizeof(*scm));
95: scm->creds.uid = INVALID_UID;
96: scm->creds.gid = INVALID_GID;
97: if (forcecreds)
98: scm_set_cred(scm, task_tgid(current), current_uid(), current_gid());
99: unix_get_peersec_dgram(sock, scm);
100: if (msg->msg_controllen <= 0)
101: return 0;
102: return __scm_send(sock, msg, scm);
103: }
SourceFile:include/net/scm.h]
|
| 10/2 |
2026/06/01 11:01 |
llm |
expert |
0m
Model:
Tokens:
input: 9736
output: 36
thoughts: 15
Thoughts: Here's my understanding of the thought process, from my expert perspective:
**Debugging the `scm_set_cred` Function**
Okay, so I'm digging into this `scm_set_cred` function, and the key realization just hit me. This function, *specifically*, is responsible for setting the `scm->pid` member. This means that's the point where the process ID is being assigned or updated within the `scm` structure. That's crucial. I need to understand *why* and *how* it does this, now. I know that if I understand this function, I can trace back where this value originates, which will tell me precisely which process ID is being associated with the `scm`. This is likely a critical piece of information for the current debugging task at hand. It immediately suggests that I need to examine the context around the function's calls and the data it's handling with an even finer tooth comb. Understanding the PID assignment is now the most salient thing about this function, and that understanding may lead directly to the bug.
|
| 11/2 |
2026/06/01 11:01 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/net/scm.h Name:scm_set_cred]
Results: map[SourceCode: 69: static __inline__ void scm_set_cred(struct scm_cookie *scm,
70: struct pid *pid, kuid_t uid, kgid_t gid)
71: {
72: scm->pid = get_pid(pid);
73: scm->creds.pid = pid_vnr(pid);
74: scm->creds.uid = uid;
75: scm->creds.gid = gid;
76: }
SourceFile:include/net/scm.h]
|
| 12/2 |
2026/06/01 11:01 |
llm |
expert |
0m
Model:
Tokens:
input: 10169
output: 35
thoughts: 150
Thoughts: **Analyzing the Potential for Credential Leakage in Unix Domain Sockets**
Okay, so I'm looking at this code and trying to understand how credentials might be passed unexpectedly through Unix domain datagram sockets. I see `scm->pid` β that's a reference to the `struct pid`, so far so good. Now, `unix_dgram_sendmsg` calls `scm_send` with `forcecreds` set to false. That's what I'd expect; it shouldn't be forcing credential passing. Unless... wait, *unless* `SOCK_PASSCRED` is set on the socket. That's the crucial condition.
But hold on, isn't `socketpair` the function creating the initial socket? And isn't `SOCK_PASSCRED` *not* set by default when using `socketpair`? Right, it's not. Okay, so that should prevent it.
However... I need to consider `msg->msg_controllen`. If that's non-zero, then `__scm_send` is called, and it *parses* control messages. That's where things get interesting, because control messages could include `SCM_CREDENTIALS`. We've got to dig into `__scm_send` and verify that the handling of `SCM_CREDENTIALS` matches our assumptions regarding `forcecreds`. The key is whether or not `__scm_send` respects the state of the socket (namely, if `SOCK_PASSCRED` is enabled) when processing the `SCM_CREDENTIALS` control message. Let's see...
|
| 13/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/net/scm.h Name:__scm_send]
Results: map[SourceCode: 166: int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
167: {
168: const struct proto_ops *ops = READ_ONCE(sock->ops);
169: struct cmsghdr *cmsg;
170: int err;
171:
172: for_each_cmsghdr(cmsg, msg) {
173: err = -EINVAL;
174:
175: /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
176: /* The first check was omitted in <= 2.2.5. The reasoning was
177: that parser checks cmsg_len in any case, so that
178: additional check would be work duplication.
179: But if cmsg_level is not SOL_SOCKET, we do not check
180: for too short ancillary data object at all! Oops.
181: OK, let's add it...
182: */
183: if (!CMSG_OK(msg, cmsg))
184: goto error;
185:
186: if (cmsg->cmsg_level != SOL_SOCKET)
187: continue;
188:
189: switch (cmsg->cmsg_type)
190: {
191: case SCM_RIGHTS:
192: if (!ops || ops->family != PF_UNIX)
193: goto error;
194: err=scm_fp_copy(cmsg, &p->fp);
195: if (err<0)
196: goto error;
197: break;
198: case SCM_CREDENTIALS:
199: {
200: struct ucred creds;
201: kuid_t uid;
202: kgid_t gid;
203: if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
204: goto error;
205: memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
206: err = scm_check_creds(&creds);
207: if (err)
208: goto error;
209:
210: if (!p->pid || pid_vnr(p->pid) != creds.pid) {
211: struct pid *pid;
212: err = -ESRCH;
213: pid = find_get_pid(creds.pid);
214: if (!pid)
215: goto error;
216:
217: /* pass a struct pid reference from
218: * find_get_pid() to scm_replace_pid().
219: */
220: err = scm_replace_pid(p, pid);
221: if (err) {
222: put_pid(pid);
223: goto error;
224: }
225: }
226:
227: err = -EINVAL;
228: uid = make_kuid(current_user_ns(), creds.uid);
229: gid = make_kgid(current_user_ns(), creds.gid);
230: if (!uid_valid(uid) || !gid_valid(gid))
231: goto error;
232:
233: p->creds.uid = uid;
234: p->creds.gid = gid;
235: break;
236: }
237: default:
238: goto error;
239: }
240: }
241:
242: if (p->fp && !p->fp->count)
243: {
244: kfree(p->fp);
245: p->fp = NULL;
246: }
247: return 0;
248:
249: error:
250: scm_destroy(p);
251: return err;
252: }
SourceFile:net/core/scm.c]
|
| 14/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 11934
output: 36
thoughts: 44
Thoughts: Okay, let me think this through.
**Analyzing the PID Replacement Logic**
Okay, so I'm looking at this code and it seems like `scm_replace_pid` is the function that actually handles replacing a process ID. The comment says that it modifies the `p->pid` field with a new PID. Hmm, let me just double-check that by quickly examining the `scm_replace_pid` function itself. I need to understand how exactly it's doing this substitution, if there are any side effects I should know about. This is critical to ensure proper process management. Gotta be thorough.
|
| 15/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/scm.c Name:scm_replace_pid]
Results: map[SourceCode: 150: static inline int scm_replace_pid(struct scm_cookie *scm, struct pid *pid)
151: {
152: int err;
153:
154: /* drop all previous references */
155: scm_destroy_cred(scm);
156:
157: err = pidfs_register_pid(pid);
158: if (unlikely(err))
159: return err;
160:
161: scm->pid = pid;
162: scm->creds.pid = pid_vnr(pid);
163: return 0;
164: }
SourceFile:net/core/scm.c]
|
| 16/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 12364
output: 37
thoughts: 30
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Kernel PID File System - Entry Point Analysis**
Okay, here we go... I see `pidfs_register_pid(pid)` is being called. That's the signal, the entry point into this kernel-level PID file system registration. Good. Now, let's just hold on a moment... what's this function actually *doing*? I need to quickly refresh my mental model of `pidfs_register_pid`. I'm going to need to look up its implementation. Is it creating a new entry in the PIDFS data structures? Does it involve allocating and initializing resources? Is it interacting with the process table in any way to manage those new entries? Or, is it perhaps simply mapping a pid to existing resources in a separate PID-aware data structure? Need to determine which data structure the function is interfacing with. Right, time to dive into the code... got to understand the mechanics here, before I can analyze its implications.
|
| 17/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/scm.c Name:pidfs_register_pid]
Results: map[SourceCode: 993: /**
994: * pidfs_register_pid - register a struct pid in pidfs
995: * @pid: pid to pin
996: *
997: * Register a struct pid in pidfs.
998: *
999: * Return: On success zero, on error a negative error code is returned.
1000: */
1001: int pidfs_register_pid(struct pid *pid)
1002: {
1003: struct pidfs_attr *new_attr __free(kfree) = NULL;
1004: struct pidfs_attr *attr;
1005:
1006: might_sleep();
1007:
1008: if (!pid)
1009: return 0;
1010:
1011: attr = READ_ONCE(pid->attr);
1012: if (unlikely(attr == PIDFS_PID_DEAD))
1013: return PTR_ERR(PIDFS_PID_DEAD);
1014: if (attr)
1015: return 0;
1016:
1017: new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
1018: if (!new_attr)
1019: return -ENOMEM;
1020:
1021: /* Synchronize with pidfs_exit(). */
1022: guard(spinlock_irq)(&pid->wait_pidfd.lock);
1023:
1024: attr = pid->attr;
1025: if (unlikely(attr == PIDFS_PID_DEAD))
1026: return PTR_ERR(PIDFS_PID_DEAD);
1027: if (unlikely(attr))
1028: return 0;
1029:
1030: pid->attr = no_free_ptr(new_attr);
1031: return 0;
1032: }
SourceFile:fs/pidfs.c]
|
| 18/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 13228
output: 39
thoughts: 45
Thoughts: Okay, here's my take on those thoughts, framed as my own mental processing:
**Digging into PID Attribute Management**
Alright, hang on a second. I'm focusing on `pidfs_register_pid` and I'm seeing it allocates this `new_attr` and then *directly* assigns it to `pid->attr`. That's standard practice, but it's a critical moment for memory management. So... when exactly is that `pid->attr` memory being deallocated? I need to be sure the lifecycle is clean to avoid leaks or use-after-free issues. Let's see... the most obvious candidate for freeing the attribute is the `free_pid` function. I'll need to check the code there to see if it's explicitly handling the `pid->attr` pointer. That's the logical place to look for the matching `kfree`. Let's confirm this to ensure that all memory is being handled as expected.
|
| 19/2 |
2026/06/01 11:02 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:free_pid SourceTreePrefix:kernel/pid.c]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:alloc_pid SourceFile:kernel/pid.c SourceLine:340] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:free_pids SourceFile:kernel/pid.c SourceLine:156]] TruncatedOutput:false]
|
| 20/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 13629
output: 32
thoughts: 11
Thoughts: Here's my take on the thought process, as if it were my own:
**Investigating `free_pid`**
Alright, I need to understand this `free_pid` definition. Let's dig in and make sure I know what's going on. This is likely a key component for managing process IDs, and I need to be absolutely solid on its implementation to understand how this system manages and reuses those resources. I need to be sure the semantics match my understanding of best practice in this kind of situation.
|
| 21/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/pid.c Name:free_pid]
Results: map[SourceCode: 110: void free_pid(struct pid *pid)
111: {
112: int i;
113: struct pid_namespace *active_ns;
114:
115: lockdep_assert_not_held(&tasklist_lock);
116:
117: active_ns = pid->numbers[pid->level].ns;
118: ns_ref_active_put(active_ns);
119:
120: spin_lock(&pidmap_lock);
121: for (i = 0; i <= pid->level; i++) {
122: struct upid *upid = pid->numbers + i;
123: struct pid_namespace *ns = upid->ns;
124: switch (--ns->pid_allocated) {
125: case 2:
126: case 1:
127: /* When all that is left in the pid namespace
128: * is the reaper wake up the reaper. The reaper
129: * may be sleeping in zap_pid_ns_processes().
130: */
131: wake_up_process(READ_ONCE(ns->child_reaper));
132: break;
133: case PIDNS_ADDING:
134: /* Only possible if the 1st fork fails */
135: WARN_ON(READ_ONCE(ns->child_reaper));
136: break;
137: }
138:
139: idr_remove(&ns->idr, upid->nr);
140: }
141: spin_unlock(&pidmap_lock);
142:
143: pidfs_remove_pid(pid);
144: call_rcu(&pid->rcu, delayed_put_pid);
145: }
SourceFile:kernel/pid.c]
|
| 22/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 14335
output: 35
thoughts: 31
Thoughts: Here's my thought process, as if I were analyzing this code:
**Digging into PID Release**
Okay, so I see `pidfs_remove_pid` being called from within `free_pid`. That's interesting, and it immediately sets off some flags for me. I need to understand the relationship between these two functions and what `pidfs_remove_pid` actually *does*. There's likely some kind of filesystem interaction happening here related to process IDs, and it's intimately tied to the release of a PID. Let's get to the bottom of this. I need to examine `pidfs_remove_pid` and see exactly how it's integrated with PID management.
|
| 23/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/pid.c Name:pidfs_remove_pid]
Results: map[SourceCode: 183: void pidfs_remove_pid(struct pid *pid)
184: {
185: if (likely(pid->ino))
186: rhashtable_remove_fast(&pidfs_ino_ht, &pid->pidfs_hash,
187: pidfs_ino_ht_params);
188: }
SourceFile:fs/pidfs.c]
|
| 24/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 14677
output: 44
thoughts: 51
Thoughts: Okay, here's my thought process on that code snippet, presented from a first-person expert perspective:
**Finding a Memory Leak in PID File System Removal**
Right, something's nagging me. I'm looking at `pidfs_remove_pid`, and I'm realizing something potentially critical. I don't see any explicit deallocation of `pid->attr` within this function. That's a red flag. Where's the memory for that attribute structure actually getting freed? I know this code, and that's usually allocated, isn't it?
Okay, time to systematically track this down. I need to figure out where `pid->attr` is being freed (or not). My first approach is to use my tools to search for related code. So, let's start with a search. I'll search for either instances of `pidfs_attr_cachep`, since that likely deals with the cache, or directly look for where `pid->attr` itself is being accessed and freed. It's time to follow the trail. I'll go back and review the related functions and search through the surrounding code. This *could* be a serious leak!
|
| 25/2 |
2026/06/01 11:02 |
tool |
codesearch-find-references |
0m
Error:
Args: map[IncludeSnippetLines:0 Name:pidfs_attr_cachep SourceTreePrefix:fs/pidfs.c]
Results: map[References:<nil> TruncatedOutput:false]
|
| 26/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 15044
output: 21
thoughts: 22
Thoughts: Here's my thought process, as requested:
**Deconstructing `pidfs_attr_cachep`**
Okay, so `pidfs_attr_cachep`... that's a variable. I need to understand what it's used for. It's likely involved in caching attributes related to the `pidfs` filesystem, but I need more context. Let's see... a simple `grep` should quickly reveal where this variable is declared, used, and modified within the codebase. That's the best first step. Knowing its context within the system will help me formulate the right questions. Let's dig in and see what we find.
|
| 27/2 |
2026/06/01 11:02 |
tool |
grepper |
0m
Args: map[Expression:pidfs_attr_cachep]
Results: map[Output:fs/pidfs.c-35-
fs/pidfs.c:36:static struct kmem_cache *pidfs_attr_cachep __ro_after_init;
fs/pidfs.c-37-
--
fs/pidfs.c=1001=int pidfs_register_pid(struct pid *pid)
--
fs/pidfs.c-1016-
fs/pidfs.c:1017: new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
fs/pidfs.c-1018- if (!new_attr)
--
fs/pidfs.c=1167=void __init pidfs_init(void)
--
fs/pidfs.c-1171-
fs/pidfs.c:1172: pidfs_attr_cachep = kmem_cache_create("pidfs_attr_cache", sizeof(struct pidfs_attr), 0,
fs/pidfs.c-1173- (SLAB_HWCACHE_ALIGN | SLAB_RECLAIM_ACCOUNT |
]
|
| 28/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 15511
output: 28
thoughts: 21
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into Kernel Memory Allocation**
Alright, so I need to track down something related to memory management within the kernel, specifically concerning the `pidfs_attr_cachep` object. The quickest way to get a handle on where it's being freed is probably a good old `grep`. I'm going to start with a broad search, looking for instances of `kmem_cache_free`, because that's the kernel function typically used to release objects that were allocated with `kmem_cache_alloc`. The `.*` is crucial here; it gives me flexibility to account for function arguments. I am going to limit the scope to within the code base with the search term `pidfs_attr_cachep`. This approach should quickly pinpoint the code sections where `pidfs_attr_cachep` is being deallocated. This should give me my starting point to see what's going on.
|
| 29/2 |
2026/06/01 11:02 |
tool |
grepper |
0m
Error:
Args: map[Expression:kmem_cache_free.*pidfs_attr_cachep]
Results:
|
| 30/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 15785
output: 30
thoughts: 25
Thoughts: Here's my thought process, as if I were considering this code:
**Checking for Memory Leaks in `pid->attr`**
Okay, first thought: I need to make sure that the memory allocated for `pid->attr` isn't being leaked. A classic oversight! Let's get right to the point: Is there a corresponding `free()` somewhere, or some other mechanism releasing this memory?
I need to quickly search the code base for where `pid->attr` is released. A quick `grep` will be faster than manually scanning the code, so I will start there. I'm going to search for instances where that field gets freed.
|
| 31/2 |
2026/06/01 11:02 |
tool |
grepper |
0m
Args: map[Expression:kfree.*attr PathPrefix:fs/pidfs.c]
Results: map[Output:fs/pidfs.c=192=static void pidfs_free_attr_work(struct work_struct *work)
--
fs/pidfs.c-202- simple_xattrs_free(xattrs, NULL);
fs/pidfs.c:203: kfree(xattrs);
fs/pidfs.c-204- }
fs/pidfs.c:205: kfree(attr);
fs/pidfs.c-206- }
--
fs/pidfs.c=211=void pidfs_free_pid(struct pid *pid)
--
fs/pidfs.c-232- if (likely(!attr->xattrs))
fs/pidfs.c:233: kfree(attr);
fs/pidfs.c-234- else if (llist_add(&attr->pidfs_llist, &pidfs_free_list))
]
|
| 32/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 16221
output: 36
thoughts: 27
Thoughts: Here's my thought process, summarized as you requested:
**Deconstructing `pidfs_free_pid`**
Okay, so I'm digging into this code, and it seems like the function `pidfs_free_pid` is responsible for freeing up the `attr` data structure. That makes sense, but I need to be absolutely certain. My immediate next step is to dive right into the definition of `pidfs_free_pid` and verify precisely what it's doing with `attr`. Gotta confirm my initial hunch before moving on. We can't have any memory leaks, right?
|
| 33/2 |
2026/06/01 11:02 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/pidfs.c Name:pidfs_free_pid]
Results: map[SourceCode: 211: void pidfs_free_pid(struct pid *pid)
212: {
213: struct pidfs_attr *attr = pid->attr;
214:
215: /*
216: * Any dentry must've been wiped from the pid by now.
217: * Otherwise there's a reference count bug.
218: */
219: VFS_WARN_ON_ONCE(pid->stashed);
220:
221: /*
222: * This if an error occurred during e.g., task creation that
223: * causes us to never go through the exit path.
224: */
225: if (unlikely(!attr))
226: return;
227:
228: /* This never had a pidfd created. */
229: if (IS_ERR(attr))
230: return;
231:
232: if (likely(!attr->xattrs))
233: kfree(attr);
234: else if (llist_add(&attr->pidfs_llist, &pidfs_free_list))
235: schedule_work(&pidfs_free_work);
236: }
SourceFile:fs/pidfs.c]
|
| 34/2 |
2026/06/01 11:02 |
llm |
expert |
0m
Model:
Tokens:
input: 16797
output: 42
thoughts: 14
Thoughts: Here's my thought process, as if I were considering this myself:
**Delving into `pidfs_free_pid`**
Okay, so I'm thinking about `pidfs_free_pid`... what's the triggering mechanism here? When *exactly* is that function called in the lifecycle of this pidfs implementation? I need to understand the conditions leading up to its execution. I have to trace the calls. Is it a cleanup routine? Related to exit handlers? Process termination? Resource reclamation? I need to be precise. I'm visualizing the code flow now, trying to pinpoint the relevant scenarios. I'm going to quickly review the data structures and see if that reveals anything, I'm thinking about the allocation and deallocation lifecycle of the relevant PIDs. It's crucial to know its context to avoid unexpected behavior or memory leaks, especially when dealing with such fundamental process management concepts. Understanding this will highlight potential race conditions or resource leaks. Let's dig in.
|
| 35/2 |
2026/06/01 11:03 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:pidfs_free_pid SourceTreePrefix:kernel/pid.c]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:put_pid SourceFile:kernel/pid.c SourceLine:97]] TruncatedOutput:false]
|
| 36/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 17125
output: 32
thoughts: 9
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in this field, and rendered in the first person:
**Checking `put_pid`**
Alright, time to dive in. "Let's check `put_pid`." That's the mental trigger. I need to get a handle on what's happening with the process ID, probably for inter-process communication, resource management, or logging. I'm immediately thinking about the context. What problem am I trying to solve? What's the overall architecture? Am I looking at a specific bug report, debugging a live system, or just reviewing code?
I'm mentally running through the likely scenarios β is this a standard library function, a custom utility, or something specific to the operating system? Is it atomic? Does it handle race conditions correctly? Does it validate inputs? What's the error handling like? I'm already formulating questions: What does it *do*? Where is it called? What data does it take as input and output? What are its side effects? This is a critical function, so I need to understand it thoroughly to ensure everything is working as expected. This will be where I begin.
|
| 37/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/pid.c Name:put_pid]
Results: map[SourceCode: 88: void put_pid(struct pid *pid)
89: {
90: struct pid_namespace *ns;
91:
92: if (!pid)
93: return;
94:
95: ns = pid->numbers[pid->level].ns;
96: if (refcount_dec_and_test(&pid->count)) {
97: pidfs_free_pid(pid);
98: kmem_cache_free(ns->pid_cachep, pid);
99: put_pid_ns(ns);
100: }
101: }
SourceFile:kernel/pid.c]
|
| 38/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 17626
output: 36
thoughts: 680
Thoughts: **Debugging a PID Leak**
Okay, so `pidfs_free_pid` is the function that frees a `pid` when its reference count (`pid->count`) hits zero. But the bug report is screaming "memory leak," specifically mentioning a leaked `struct pid`. That's not good. The backtrace shows `alloc_pid` and `copy_process`, so this is a standard `pid` allocation. If a `struct pid` is leaked, then `put_pid` isn't being called enough. Why would a `struct pid` leak?
Let's look at `scm_replace_pid`. This function seems like a potential culprit. It takes a `struct pid *pid`, and my first thought is that it must be incrementing the reference count somewhere, but it's not. No, it doesn't! It looks like it is consuming a reference. But, I need to know where `pid` comes from. It came from `find_get_pid`. So, `find_get_pid` is incrementing the refcount, but `scm_replace_pid` is just using that already-incremented reference, not adding another one. So that is not it.
Okay, let's look at the caller of `scm_replace_pid`, which is `__scm_send`. Here it is. Aha! It does a check to see if `p->pid` is already set. If it isn't set, then it calls `find_get_pid`, does a bunch of checks, and *then* calls `scm_replace_pid`. Critically, it calls `put_pid` on the `pid` if `scm_replace_pid` fails. So, if `scm_replace_pid` fails, then `put_pid` gets called. But, what if it succeeds?
If `scm_replace_pid` *succeeds*, it returns zero, assigns `pid` to `p->pid`, and... that's it! It's just replacing the old `pid` reference. It also has a comment saying: `/* pass a struct pid reference from find_get_pid() to scm_replace_pid(). */`. Wait, I think I see it.
The important point is: What happens if `p->pid` *was* already set, so this whole section is skipped? And `scm_replace_pid` calls `scm_destroy_cred(scm)`. It looks like it will destroy the credentials, and likely there's a missing `put_pid` call there!
|
| 39/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/scm.c Name:scm_destroy_cred]
Results: map[SourceCode: 78: static __inline__ void scm_destroy_cred(struct scm_cookie *scm)
79: {
80: put_pid(scm->pid);
81: scm->pid = NULL;
82: }
SourceFile:include/net/scm.h]
|
| 40/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 18990
output: 34
thoughts: 699
Thoughts: **Analyzing SCM_CREDENTIALS Handling in Unix Domain Sockets**
Alright, let's break this down. My initial thought is that `scm_replace_pid` is responsible for updating the `scm->pid` field and handling the old `pid` properly, which is good. However, I need to understand the full lifecycle.
Looking deeper, `scm_send` is the key. It seems to initialize `scm->pid` using `scm_set_cred`, which calls `get_pid` on a potentially existing pid. Specifically, if `forcecreds` is true, the current task's thread group ID (`task_tgid(current)`) is used. Now, `unix_dgram_sendmsg` calls `scm_send` with `forcecreds` set to *false*.
This is where things get interesting. If `forcecreds` is false, `scm->pid` isn't explicitly set during the initial `scm_send` call! The code explicitly zeros the `scm` structure and sets uid/gid to INVALID_UID/GID. This means `scm->pid` starts as NULL.
Later, `__scm_send` processes the `SCM_CREDENTIALS` message. And *this* is where the actual `pid` assignment happens. It checks if the current `p->pid` matches the incoming credentials' pid value. If the pids don't match (or if the initial `p->pid` is NULL, which is the case when `forcecreds` is false), it finds the pid using `find_get_pid` and calls `scm_replace_pid`. That's where the swap happens.
Crucially, `__scm_send` iterates through *all* control message headers. So, *multiple* `SCM_CREDENTIALS` messages could potentially be processed. I've got to consider that the `scm_replace_pid` function could be called multiple times!
Good. `scm_replace_pid` calls `scm_destroy_cred`, and that calls `put_pid`. Thus, the kernel is correctly handling reference counting and preventing leaks, ensuring the previous PID is released. This is exactly what I'd expect.
What happens if `__scm_send` errors out *after* processing some `SCM_CREDENTIALS` messages, but *before* processing all of them? Well, it looks like it calls `scm_destroy(p)`. Let me go confirm how that cleans up. I need to make sure there are no leaks.
|
| 41/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/net/scm.h Name:scm_destroy]
Results: map[SourceCode: 84: static __inline__ void scm_destroy(struct scm_cookie *scm)
85: {
86: scm_destroy_cred(scm);
87: if (scm->fp)
88: __scm_destroy(scm);
89: }
SourceFile:include/net/scm.h]
|
| 42/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 20374
output: 40
thoughts: 77
Thoughts: Okay, let's break this down.
**Analyzing Potential Resource Leakage in SCM Handling**
Right, so `scm_destroy_cred` calls `put_pid(scm->pid)`. Makes sense, we're releasing a resource, the Process ID. The key here is, if `__scm_send` fails at any point, that `scm->pid` is immediately released via `put_pid`. That's good defensive programming. But hold on... what happens if `__scm_send` *succeeds*? Where does `scm->pid` go?
Ah, right, `unix_dgram_sendmsg` gets called after a successful `__scm_send`. That's where the SCM is actually *used*. My immediate concern now is to see how `unix_dgram_sendmsg` utilizes, or potentially neglects to properly handle, that `scm` structure and, critically, `scm->pid`. I need to dig into `unix_dgram_sendmsg` now to ensure we haven't created a subtle resource leak somewhere. This is a potential vulnerability, and I need to explore it to ensure the code is robust.
|
| 43/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_dgram_sendmsg]
Results: map[SourceCode:2087: static int unix_dgram_sendmsg(struct socket *sock, struct msghdr *msg,
2088: size_t len)
2089: {
2090: struct sock *sk = sock->sk, *other = NULL;
2091: struct unix_sock *u = unix_sk(sk);
2092: struct scm_cookie scm;
2093: struct sk_buff *skb;
2094: int data_len = 0;
2095: int sk_locked;
2096: long timeo;
2097: int err;
2098:
2099: err = scm_send(sock, msg, &scm, false);
2100: if (err < 0)
2101: return err;
2102:
2103: if (msg->msg_flags & MSG_OOB) {
2104: err = -EOPNOTSUPP;
2105: goto out;
2106: }
2107:
2108: if (msg->msg_namelen) {
2109: err = unix_validate_addr(msg->msg_name, msg->msg_namelen);
2110: if (err)
2111: goto out;
2112:
2113: err = BPF_CGROUP_RUN_PROG_UNIX_SENDMSG_LOCK(sk,
2114: msg->msg_name,
2115: &msg->msg_namelen,
2116: NULL);
2117: if (err)
2118: goto out;
2119: }
2120:
2121: if (unix_may_passcred(sk) && !READ_ONCE(u->addr)) {
2122: err = unix_autobind(sk);
2123: if (err)
2124: goto out;
2125: }
2126:
2127: if (len > READ_ONCE(sk->sk_sndbuf) - 32) {
2128: err = -EMSGSIZE;
2129: goto out;
2130: }
2131:
2132: if (len > SKB_MAX_ALLOC) {
2133: data_len = min_t(size_t,
2134: len - SKB_MAX_ALLOC,
2135: MAX_SKB_FRAGS * PAGE_SIZE);
2136: data_len = PAGE_ALIGN(data_len);
2137:
2138: BUILD_BUG_ON(SKB_MAX_ALLOC < PAGE_SIZE);
2139: }
2140:
2141: skb = sock_alloc_send_pskb(sk, len - data_len, data_len,
2142: msg->msg_flags & MSG_DONTWAIT, &err,
2143: PAGE_ALLOC_COSTLY_ORDER);
2144: if (!skb)
2145: goto out;
2146:
2147: err = unix_scm_to_skb(&scm, skb, true);
2148: if (err < 0)
2149: goto out_free;
2150:
2151: skb_put(skb, len - data_len);
2152: skb->data_len = data_len;
2153: skb->len = len;
2154: err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, len);
2155: if (err)
2156: goto out_free;
2157:
2158: timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);
2159:
2160: if (msg->msg_namelen) {
2161: lookup:
2162: other = unix_find_other(sock_net(sk), msg->msg_name,
2163: msg->msg_namelen, sk->sk_type, 0);
2164: if (IS_ERR(other)) {
2165: err = PTR_ERR(other);
2166: goto out_free;
2167: }
2168: } else {
2169: other = unix_peer_get(sk);
2170: if (!other) {
2171: err = -ENOTCONN;
2172: goto out_free;
2173: }
2174: }
2175:
2176: if (sk_filter(other, skb) < 0) {
2177: /* Toss the packet but do not return any error to the sender */
2178: err = len;
2179: goto out_sock_put;
2180: }
2181:
2182: err = unix_maybe_add_creds(skb, sk, other);
2183: if (err)
2184: goto out_sock_put;
2185:
2186: restart:
2187: sk_locked = 0;
2188: unix_state_lock(other);
2189: restart_locked:
2190:
2191: if (!unix_may_send(sk, other)) {
2192: err = -EPERM;
2193: goto out_unlock;
2194: }
2195:
2196: if (unlikely(sock_flag(other, SOCK_DEAD))) {
2197: /* Check with 1003.1g - what should datagram error */
2198:
2199: unix_state_unlock(other);
2200:
2201: if (sk->sk_type == SOCK_SEQPACKET) {
2202: /* We are here only when racing with unix_release_sock()
2203: * is clearing @other. Never change state to TCP_CLOSE
2204: * unlike SOCK_DGRAM wants.
2205: */
2206: err = -EPIPE;
2207: goto out_sock_put;
2208: }
2209:
2210: if (!sk_locked)
2211: unix_state_lock(sk);
2212:
2213: if (unix_peer(sk) == other) {
2214: unix_peer(sk) = NULL;
2215: unix_dgram_peer_wake_disconnect_wakeup(sk, other);
2216:
2217: WRITE_ONCE(sk->sk_state, TCP_CLOSE);
2218: unix_state_unlock(sk);
2219:
2220: unix_dgram_disconnected(sk, other);
2221: sock_put(other);
2222: err = -ECONNREFUSED;
2223: goto out_sock_put;
2224: }
2225:
2226: unix_state_unlock(sk);
2227:
2228: if (!msg->msg_namelen) {
2229: err = -ECONNRESET;
2230: goto out_sock_put;
2231: }
2232:
2233: sock_put(other);
2234: goto lookup;
2235: }
2236:
2237: if (other->sk_shutdown & RCV_SHUTDOWN) {
2238: err = -EPIPE;
2239: goto out_unlock;
2240: }
2241:
2242: if (UNIXCB(skb).fp && !other->sk_scm_rights) {
2243: err = -EPERM;
2244: goto out_unlock;
2245: }
2246:
2247: if (sk->sk_type != SOCK_SEQPACKET) {
2248: err = security_unix_may_send(sk->sk_socket, other->sk_socket);
2249: if (err)
2250: goto out_unlock;
2251: }
2252:
2253: /* other == sk && unix_peer(other) != sk if
2254: * - unix_peer(sk) == NULL, destination address bound to sk
2255: * - unix_peer(sk) == sk by time of get but disconnected before lock
2256: */
2257: if (other != sk &&
2258: unlikely(unix_peer(other) != sk &&
2259: unix_recvq_full_lockless(other))) {
2260: if (timeo) {
2261: timeo = unix_wait_for_peer(other, timeo);
2262:
2263: err = sock_intr_errno(timeo);
2264: if (signal_pending(current))
2265: goto out_sock_put;
2266:
2267: goto restart;
2268: }
2269:
2270: if (!sk_locked) {
2271: unix_state_unlock(other);
2272: unix_state_double_lock(sk, other);
2273: }
2274:
2275: if (unix_peer(sk) != other ||
2276: unix_dgram_peer_wake_me(sk, other)) {
2277: err = -EAGAIN;
2278: sk_locked = 1;
2279: goto out_unlock;
2280: }
2281:
2282: if (!sk_locked) {
2283: sk_locked = 1;
2284: goto restart_locked;
2285: }
2286: }
2287:
2288: if (unlikely(sk_locked))
2289: unix_state_unlock(sk);
2290:
2291: if (sock_flag(other, SOCK_RCVTSTAMP))
2292: __net_timestamp(skb);
2293:
2294: scm_stat_add(other, skb);
2295: skb_queue_tail(&other->sk_receive_queue, skb);
2296: unix_state_unlock(other);
2297: READ_ONCE(other->sk_data_ready)(other);
2298: sock_put(other);
2299: scm_destroy(&scm);
2300: return len;
2301:
2302: out_unlock:
2303: if (sk_locked)
2304: unix_state_unlock(sk);
2305: unix_state_unlock(other);
2306: out_sock_put:
2307: sock_put(other);
2308: out_free:
2309: consume_skb(skb);
2310: out:
2311: scm_destroy(&scm);
2312: return err;
2313: }
SourceFile:net/unix/af_unix.c]
|
| 44/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 23914
output: 41
thoughts: 90
Thoughts: Okay, let's see. My mind is racing a bit here, focusing on this `unix_dgram_sendmsg` function.
**Analyzing Potential Memory Management Issues in `unix_dgram_sendmsg`**
First, I need to confirm something. Ah, yes, right here! `unix_dgram_sendmsg` *does* call `scm_destroy(&scm)` at the very end. Crucially, it does this whether the function succeeds *or* encounters an error. Okay, good. That's the baseline.
Now, let's break down `scm_destroy`. Yes, it calls `scm_destroy_cred(&scm)`. And within *that*, we have `put_pid(scm->pid)`. Okay, that's what I needed to see. The PID, `scm->pid`, is getting properly released. That's a key point and a common source of bugs in this kind of code. We can check that one off.
But...wait. Now I'm thinking about the intermediary function `unix_scm_to_skb`. I need to review what that function does. It's the one that converts the ancillary data into an SKB. There might be some sneaky things going on there that could still lead to issues. I need to investigate that part further.
|
| 45/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_scm_to_skb]
Results: map[SourceCode:1987: static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb, bool send_fds)
1988: {
1989: int err = 0;
1990:
1991: UNIXCB(skb).pid = get_pid(scm->pid);
1992: UNIXCB(skb).uid = scm->creds.uid;
1993: UNIXCB(skb).gid = scm->creds.gid;
1994: UNIXCB(skb).fp = NULL;
1995: unix_get_secdata(scm, skb);
1996: if (scm->fp && send_fds)
1997: err = unix_attach_fds(scm, skb);
1998:
1999: skb->destructor = unix_wfree;
2000: return err;
2001: }
SourceFile:net/unix/af_unix.c]
|
| 46/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 24614
output: 40
thoughts: 84
Thoughts: **Analyzing the Lifecycle of a PID Reference in UNIX Domain Sockets**
Okay, so I'm looking at `unix_scm_to_skb`, and it's grabbing the PID from the `scm` (control message) structure and assigning it to the `skb` (socket buffer): `UNIXCB(skb).pid = get_pid(scm->pid)`. This `get_pid()` function is critical; it strongly suggests that the `skb` is now *referencing* the PID held within `scm->pid`. Makes sense β we need to track that.
My primary concern now is the lifecycle. When this `skb` is eventually freed, does the system correctly decrement the reference count on that PID? If not, we have a memory leak situation. I need to figure out which function is responsible for releasing the resources associated with the socket buffer when it's no longer needed.
Logically, I'd expect the cleanup to happen either in `unix_wfree` β when we free the write buffer β or potentially in `unix_destruct_scm` β when we're tearing down the control message structure. Time to dive into the code and confirm this. I need to track down exactly how this reference is being handled. I can't let a simple oversight like this introduce a subtle PID leak.
|
| 47/2 |
2026/06/01 11:03 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:unix_destruct_scm SourceTreePrefix:net/unix]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_orphan_scm SourceFile:net/unix/af_unix.c SourceLine:2079] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_wfree SourceFile:net/unix/af_unix.c SourceLine:1983]] TruncatedOutput:false]
|
| 48/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 25144
output: 39
thoughts: 12
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Checking `unix_destruct_scm`**
Right, let's dive in. The mental checklist starts with `unix_destruct_scm`. It's likely I'm thinking about a specific use case where this function, or macro, is relevant. I need to refresh my memory on the underlying implementation, or perhaps I'm looking for a particular optimization opportunity within that code block. I may be recalling a recent bug report or performance bottleneck that might relate to how `unix_destruct_scm` handles data structures within a UNIX environment. Could be a memory management issue, a synchronization problem, or even a subtle race condition related to its atomic operations. My initial thought process is to quickly verify the assumptions or potential gotchas embedded within that specific piece of code before going deeper.
|
| 49/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_destruct_scm]
Results: map[SourceCode:1969: static void unix_destruct_scm(struct sk_buff *skb)
1970: {
1971: struct scm_cookie scm = {};
1972:
1973: swap(scm.pid, UNIXCB(skb).pid);
1974:
1975: if (UNIXCB(skb).fp)
1976: unix_detach_fds(&scm, skb);
1977:
1978: scm_destroy(&scm);
1979: }
SourceFile:net/unix/af_unix.c]
|
| 50/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 25558
output: 37
thoughts: 82
Thoughts: Okay, let me break this down.
**Understanding the PID Release in UNIX Socket Destruction**
Alright, so `unix_destruct_scm` is the key function here. My initial thought process is: it appears that it's handling the cleanup of a Socket Control Message (`scm`). It does a PID swap between `scm.pid` and `UNIXCB(skb).pid`. That's interesting, makes me think that the `skb` (socket buffer) and the `scm` are somehow sharing or transferring ownership of a Process ID. The fact that it calls `scm_destroy(&scm)` immediately afterwards is crucial. I know `scm_destroy` is the function that is ultimately going to release the resources associated with that SCM, and specifically the part that gets my attention is `put_pid(scm.pid)`. This implies that `scm.pid` is a reference to a PID, and `put_pid()` is how we dereference it, which frees it up.
So basically, the `skb` releases the PID when it's destroyed, and the swap, if i understand it correctly, is just to make sure we're not leaking the PID, even if the buffer is no longer associated with the `scm`!
Aha, wait, I remember `unix_wfree` from my code reviews! It's likely involved in the destruction of waiting queue entries. And `unix_destruct_scm` is being called from there. So, `unix_wfree` has to be calling `unix_destruct_scm` in order to free those PIDs! I need to double-check the locking and reference counting around this section, but the general flow seems logical.
|
| 51/2 |
2026/06/01 11:03 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_wfree]
Results: map[SourceCode:1981: static void unix_wfree(struct sk_buff *skb)
1982: {
1983: unix_destruct_scm(skb);
1984: sock_wfree(skb);
1985: }
SourceFile:net/unix/af_unix.c]
|
| 52/2 |
2026/06/01 11:03 |
llm |
expert |
0m
Model:
Tokens:
input: 26141
output: 40
thoughts: 46
Thoughts: Okay, let me think this through.
**Analyzing SKB Destructor Timing**
Hmm, so `skb->destructor` is triggered whenever an `skb` is freed, that's clear enough. But the key question here is, *when* exactly does that happen in various scenarios? What I'm really trying to understand is the lifecycle. Specifically, what happens when an `skb` comes in over the network? That's where it gets interesting, and potentially tricky.
I need to dig deeper. I'll check `unix_dgram_recvmsg`. That function's got to be the place to figure out the receiving end and, therefore, the implications for the destructor call. It'll be the key to understanding if there is anything special related to a receiver.
|
| 53/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_dgram_recvmsg]
Results: map[SourceCode:2675: static int unix_dgram_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
2676: int flags)
2677: {
2678: struct sock *sk = sock->sk;
2679:
2680: #ifdef CONFIG_BPF_SYSCALL
2681: const struct proto *prot = READ_ONCE(sk->sk_prot);
2682:
2683: if (prot != &unix_dgram_proto)
2684: return prot->recvmsg(sk, msg, size, flags);
2685: #endif
2686: return __unix_dgram_recvmsg(sk, msg, size, flags);
2687: }
SourceFile:net/unix/af_unix.c]
|
| 54/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 26633
output: 41
thoughts: 14
Thoughts: Here's a first-person summary, tailored for an expert audience, of the thought process described:
**Diving into `__unix_dgram_recvmsg`**
Okay, so we're looking at `__unix_dgram_recvmsg`. That function name itself is a pretty good indicator of what we're dealing with: low-level Unix-domain datagram socket reception. This is where the magic happens, or more accurately, where things often *break* in a lot of tricky networking scenarios. I immediately start thinking about potential race conditions related to buffer management, particularly with the `recvmsg` system call's ability to handle multiple buffers via `iovec`. I wonder if there are any subtle issues regarding memory alignment and how the kernel interacts with user-space buffers here. Specifically, I'm thinking about potential vulnerabilities or performance bottlenecks arising from data copying within the kernel or from synchronization issues if this call is heavily multithreaded. I will be looking out for any non-obvious interactions with the control messages and flags passed via `msghdr`, and how they change behavior. I need to see what assumptions about buffer sizes, flags, and potential errors the code makes. I should also check the error handling; are there any critical errors that are handled inadequately, which could lead to resource leaks or even security vulnerabilities? Finally, I need to understand the implications of different socket options that can modify `recvmsg`'s behavior within this function, such as socket buffer sizes, timeouts, or specific control message handling. This is going to be interesting.
|
| 55/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:__unix_dgram_recvmsg]
Results: map[SourceCode:2566: int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
2567: int flags)
2568: {
2569: struct scm_cookie scm;
2570: struct socket *sock = sk->sk_socket;
2571: struct unix_sock *u = unix_sk(sk);
2572: struct sk_buff *skb, *last;
2573: long timeo;
2574: int skip;
2575: int err;
2576:
2577: err = -EOPNOTSUPP;
2578: if (flags&MSG_OOB)
2579: goto out;
2580:
2581: timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
2582:
2583: do {
2584: mutex_lock(&u->iolock);
2585:
2586: skip = sk_peek_offset(sk, flags);
2587: skb = __skb_try_recv_datagram(sk, &sk->sk_receive_queue, flags,
2588: &skip, &err, &last);
2589: if (skb) {
2590: if (!(flags & MSG_PEEK))
2591: scm_stat_del(sk, skb);
2592: break;
2593: }
2594:
2595: mutex_unlock(&u->iolock);
2596:
2597: if (err != -EAGAIN)
2598: break;
2599: } while (timeo &&
2600: !__skb_wait_for_more_packets(sk, &sk->sk_receive_queue,
2601: &err, &timeo, last));
2602:
2603: if (!skb) { /* implies iolock unlocked */
2604: /* Signal EOF on disconnected non-blocking SEQPACKET socket. */
2605: if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
2606: (READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN))
2607: err = 0;
2608: goto out;
2609: }
2610:
2611: if (wq_has_sleeper(&u->peer_wait))
2612: wake_up_interruptible_sync_poll(&u->peer_wait,
2613: EPOLLOUT | EPOLLWRNORM |
2614: EPOLLWRBAND);
2615:
2616: if (msg->msg_name) {
2617: unix_copy_addr(msg, skb->sk);
2618:
2619: BPF_CGROUP_RUN_PROG_UNIX_RECVMSG_LOCK(sk,
2620: msg->msg_name,
2621: &msg->msg_namelen);
2622: }
2623:
2624: if (size > skb->len - skip)
2625: size = skb->len - skip;
2626: else if (size < skb->len - skip)
2627: msg->msg_flags |= MSG_TRUNC;
2628:
2629: err = skb_copy_datagram_msg(skb, skip, msg, size);
2630: if (err)
2631: goto out_free;
2632:
2633: if (sock_flag(sk, SOCK_RCVTSTAMP))
2634: __sock_recv_timestamp(msg, sk, skb);
2635:
2636: memset(&scm, 0, sizeof(scm));
2637:
2638: unix_skb_to_scm(skb, &scm);
2639:
2640: if (!(flags & MSG_PEEK)) {
2641: if (UNIXCB(skb).fp)
2642: unix_detach_fds(&scm, skb);
2643:
2644: sk_peek_offset_bwd(sk, skb->len);
2645: } else {
2646: /* It is questionable: on PEEK we could:
2647: - do not return fds - good, but too simple 8)
2648: - return fds, and do not return them on read (old strategy,
2649: apparently wrong)
2650: - clone fds (I chose it for now, it is the most universal
2651: solution)
2652:
2653: POSIX 1003.1g does not actually define this clearly
2654: at all. POSIX 1003.1g doesn't define a lot of things
2655: clearly however!
2656:
2657: */
2658:
2659: sk_peek_offset_fwd(sk, size);
2660:
2661: if (UNIXCB(skb).fp)
2662: unix_peek_fds(&scm, skb);
2663: }
2664: err = (flags & MSG_TRUNC) ? skb->len - skip : size;
2665:
2666: scm_recv_unix(sock, msg, &scm, flags);
2667:
2668: out_free:
2669: skb_free_datagram(sk, skb);
2670: mutex_unlock(&u->iolock);
2671: out:
2672: return err;
2673: }
SourceFile:net/unix/af_unix.c]
|
| 56/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 28657
output: 41
thoughts: 17
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into the `unix_skb_to_scm` Function**
Hmm, `unix_skb_to_scm`...right, that's where things get interesting. I need to refresh my memory and think this through. The purpose is to essentially transform a raw SKB (Socket Buffer) into something manageable for the SCM (Socket Control Message) path. So, I see now that `unix_skb_to_scm` is responsible for setting up the `scm` structure. That's a crucial step. Itβs what bridges the gap between the incoming network data and the control messages that need to be processed by the application. It's the heart of how we get all the data and associated metadata from the kernel to userspace efficiently, isn't it? Okay, so understanding how *exactly* it sets up `scm` is key here. Time to dig deeper into the code to really understand the implications of that setup.
|
| 57/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_skb_to_scm]
Results: map[SourceCode:2003: static void unix_skb_to_scm(struct sk_buff *skb, struct scm_cookie *scm)
2004: {
2005: scm_set_cred(scm, UNIXCB(skb).pid, UNIXCB(skb).uid, UNIXCB(skb).gid);
2006: unix_set_secdata(scm, skb);
2007: }
SourceFile:net/unix/af_unix.c]
|
| 58/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 29078
output: 38
thoughts: 51
Thoughts: Here's my take on the thought process, as if it were my own:
**Analyzing the SCM Credential Handling**
Okay, so I'm looking at how credentials are managed in this SCM context. It appears that `scm_set_cred` is the key function here. It does a straightforward assignment: `scm->pid = get_pid(pid)`. Essentially, the SCM structure, specifically `scm->pid`, is taking a reference to whatever `pid` represents β likely a process ID. And, crucially, it looks like that `pid` originates as `UNIXCB(skb).pid`. So, the SCM now holds a reference to that.
The next thing that triggers this chain of events is then `scm_recv_unix`, which is a key function to explore next. That will likely be where that process ID (and, therefore, the credential information it represents) is put to use. I need to dig into `scm_recv_unix` to see how that PID is used in the context of receiving data over a UNIX socket. I need to figure out what that reference to the PID means in the grand scheme of things!
|
| 59/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:scm_recv_unix]
Results: map[SourceCode: 542: void scm_recv_unix(struct socket *sock, struct msghdr *msg,
543: struct scm_cookie *scm, int flags)
544: {
545: if (!__scm_recv_common(sock->sk, msg, scm, flags))
546: return;
547:
548: if (sock->sk->sk_scm_pidfd)
549: scm_pidfd_recv(msg, scm);
550:
551: scm_destroy_cred(scm);
552: }
SourceFile:net/core/scm.c]
|
| 60/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 29612
output: 37
thoughts: 64
Thoughts: Okay, let me think this through.
**Analyzing the Reference Counting in Unix Domain Socket Credential Handling**
Alright, so `scm_recv_unix` is calling `scm_destroy_cred(scm)`. And that function, in turn, calls `put_pid(scm->pid)`. So, that seems straightforward β we're releasing the reference held by `unix_skb_to_scm` if there was one, right? The reference taken is handled. But hold on a second... what if `scm_pidfd_recv` gets into the mix? I need to consider that interaction and the potential flow here. I wonder how that influences reference counts.
|
| 61/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/scm.c Name:scm_pidfd_recv]
Results: map[SourceCode: 465: static void scm_pidfd_recv(struct msghdr *msg, struct scm_cookie *scm)
466: {
467: struct file *pidfd_file = NULL;
468: int len, pidfd;
469:
470: /* put_cmsg() doesn't return an error if CMSG is truncated,
471: * that's why we need to opencode these checks here.
472: */
473: if (msg->msg_flags & MSG_CMSG_COMPAT)
474: len = sizeof(struct compat_cmsghdr) + sizeof(int);
475: else
476: len = sizeof(struct cmsghdr) + sizeof(int);
477:
478: if (msg->msg_controllen < len) {
479: msg->msg_flags |= MSG_CTRUNC;
480: return;
481: }
482:
483: if (!scm->pid)
484: return;
485:
486: pidfd = pidfd_prepare(scm->pid, PIDFD_STALE, &pidfd_file);
487:
488: if (put_cmsg(msg, SOL_SOCKET, SCM_PIDFD, sizeof(int), &pidfd)) {
489: if (pidfd_file) {
490: put_unused_fd(pidfd);
491: fput(pidfd_file);
492: }
493:
494: return;
495: }
496:
497: if (pidfd_file)
498: fd_install(pidfd, pidfd_file);
499: }
SourceFile:net/core/scm.c]
|
| 62/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 30387
output: 35
thoughts: 40
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into `pidfd_prepare`**
Right, so I'm thinking about how `pidfd_prepare` works, specifically in the context of `scm->pid`. I need to understand this better. My initial thought is, "Does this function, `pidfd_prepare`, actually grab a direct reference to `scm->pid`?" or is it making a copy? This is a crucial detail for thread safety and resource management, especially when dealing with process identifiers. I need to get this figured out so let's check `pidfd_prepare` and review the source code. Let's see how that routine actually handles the process ID (`pid`).
|
| 63/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/core/scm.c Name:pidfd_prepare]
Results: map[SourceCode:1838: /**
1839: * pidfd_prepare - allocate a new pidfd_file and reserve a pidfd
1840: * @pid: the struct pid for which to create a pidfd
1841: * @flags: flags of the new @pidfd
1842: * @ret_file: return the new pidfs file
1843: *
1844: * Allocate a new file that stashes @pid and reserve a new pidfd number in the
1845: * caller's file descriptor table. The pidfd is reserved but not installed yet.
1846: *
1847: * The helper verifies that @pid is still in use, without PIDFD_THREAD the
1848: * task identified by @pid must be a thread-group leader.
1849: *
1850: * If this function returns successfully the caller is responsible to either
1851: * call fd_install() passing the returned pidfd and pidfd file as arguments in
1852: * order to install the pidfd into its file descriptor table or they must use
1853: * put_unused_fd() and fput() on the returned pidfd and pidfd file
1854: * respectively.
1855: *
1856: * This function is useful when a pidfd must already be reserved but there
1857: * might still be points of failure afterwards and the caller wants to ensure
1858: * that no pidfd is leaked into its file descriptor table.
1859: *
1860: * Return: On success, a reserved pidfd is returned from the function and a new
1861: * pidfd file is returned in the last argument to the function. On
1862: * error, a negative error code is returned from the function and the
1863: * last argument remains unchanged.
1864: */
1865: int pidfd_prepare(struct pid *pid, unsigned int flags, struct file **ret_file)
1866: {
1867: struct file *pidfs_file;
1868:
1869: /*
1870: * PIDFD_STALE is only allowed to be passed if the caller knows
1871: * that @pid is already registered in pidfs and thus
1872: * PIDFD_INFO_EXIT information is guaranteed to be available.
1873: */
1874: if (!(flags & PIDFD_STALE)) {
1875: /*
1876: * While holding the pidfd waitqueue lock removing the
1877: * task linkage for the thread-group leader pid
1878: * (PIDTYPE_TGID) isn't possible. Thus, if there's still
1879: * task linkage for PIDTYPE_PID not having thread-group
1880: * leader linkage for the pid means it wasn't a
1881: * thread-group leader in the first place.
1882: */
1883: guard(spinlock_irq)(&pid->wait_pidfd.lock);
1884:
1885: /* Task has already been reaped. */
1886: if (!pid_has_task(pid, PIDTYPE_PID))
1887: return -ESRCH;
1888: /*
1889: * If this struct pid isn't used as a thread-group
1890: * leader but the caller requested to create a
1891: * thread-group leader pidfd then report ENOENT.
1892: */
1893: if (!(flags & PIDFD_THREAD) && !pid_has_task(pid, PIDTYPE_TGID))
1894: return -ENOENT;
1895: }
1896:
1897: CLASS(get_unused_fd, pidfd)(O_CLOEXEC);
1898: if (pidfd < 0)
1899: return pidfd;
1900:
1901: pidfs_file = pidfs_alloc_file(pid, flags | O_RDWR);
1902: if (IS_ERR(pidfs_file))
1903: return PTR_ERR(pidfs_file);
1904:
1905: *ret_file = pidfs_file;
1906: return take_fd(pidfd);
1907: }
SourceFile:kernel/fork.c]
|
| 64/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 31807
output: 35
thoughts: 22
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**File Allocation Deep Dive**
Alright, let's break this down. `pidfs_alloc_file`β¦ right, that's our file allocation function. My immediate question is about the parameter passing. Does this function, when allocating a new file structure, actually take a *reference* to the `pid`? It's a fundamental question. The implications are significant. Does it maintain a link back to the process? Or is the `pid` simply used for some kind of initial setup or metadata assignment, and then potentially discarded?
If it keeps the `pid` reference, we need to think about reference counting, the lifetime of the process, and what happens if the process terminates or forks. We'll be dealing with memory management complexities and potential dangling pointers if we're not very careful with how the reference is handled. On the other hand, if it *doesn't* retain a live reference, we need to be clear on how the system associates a given file with a particular process after the allocation. We might be relying on something like a filesystem's namespace for association. Knowing how the association is established is critical to ensure proper file access and cleanup when the associated process is done.
|
| 65/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/fork.c Name:pidfs_alloc_file]
Results: map[SourceCode:1135: struct file *pidfs_alloc_file(struct pid *pid, unsigned int flags)
1136: {
1137: struct file *pidfd_file;
1138: struct path path __free(path_put) = {};
1139: int ret;
1140:
1141: /*
1142: * Ensure that internal pidfd flags don't overlap with each
1143: * other or with uapi pidfd flags.
1144: */
1145: BUILD_BUG_ON(hweight32(PIDFD_THREAD | PIDFD_NONBLOCK |
1146: PIDFD_STALE | PIDFD_AUTOKILL) != 4);
1147:
1148: ret = path_from_stashed(&pid->stashed, pidfs_mnt, get_pid(pid), &path);
1149: if (ret < 0)
1150: return ERR_PTR(ret);
1151:
1152: VFS_WARN_ON_ONCE(!pid->attr);
1153:
1154: flags &= ~PIDFD_STALE;
1155: flags |= O_RDWR;
1156: pidfd_file = dentry_open(&path, flags, current_cred());
1157: /*
1158: * Raise PIDFD_THREAD and PIDFD_AUTOKILL explicitly as
1159: * do_dentry_open() strips O_EXCL and O_TRUNC.
1160: */
1161: if (!IS_ERR(pidfd_file))
1162: pidfd_file->f_flags |= (flags & (PIDFD_THREAD | PIDFD_AUTOKILL));
1163:
1164: return pidfd_file;
1165: }
SourceFile:fs/pidfs.c]
|
| 66/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 32658
output: 36
thoughts: 284
Thoughts: **My Analysis of PID Reference Management**
Okay, so I'm diving into this pidfd code, and here's what I'm thinking. `pidfs_alloc_file` is doing a `get_pid(pid)`. Alright, that's straightforward; the file descriptor is taking a reference to the `pid` itself. That makes sense for tracking the process.
Now, let's see how `scm_pidfd_recv` handles this... hmm, it calls `pidfd_prepare`, gets a file. Then, it tries `put_cmsg`. The interesting part is what happens on failure. If `put_cmsg` *succeeds*, it installs the file descriptor, so the file keeps the `pid` reference. But, if `put_cmsg` *fails*, it calls `fput(pidfd_file)`. And *that* is the key point. `fput` releases the file, which in turn releases the reference to the `pid`. So, as I understand it, `scm_pidfd_recv` won't leak the `pid` under those failure conditions. That's good.
But hang on⦠What if `pidfs_alloc_file` itself fails? We're going to get an error there. What happens with `path_from_stashed`? It calls `get_pid(pid)` as well. If *that* fails, does it also release the `pid`? I need to check the error paths there. I need to make sure we're not leaking pids if `pidfs_alloc_file` doesn't work.
|
| 67/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/pidfs.c Name:path_from_stashed]
Results: map[SourceCode:2210: /**
2211: * path_from_stashed - create path from stashed or new dentry
2212: * @stashed: where to retrieve or stash dentry
2213: * @mnt: mnt of the filesystems to use
2214: * @data: data to store in inode->i_private
2215: * @path: path to create
2216: *
2217: * The function tries to retrieve a stashed dentry from @stashed. If the dentry
2218: * is still valid then it will be reused. If the dentry isn't able the function
2219: * will allocate a new dentry and inode. It will then check again whether it
2220: * can reuse an existing dentry in case one has been added in the meantime or
2221: * update @stashed with the newly added dentry.
2222: *
2223: * Special-purpose helper for nsfs and pidfs.
2224: *
2225: * Return: On success zero and on failure a negative error is returned.
2226: */
2227: int path_from_stashed(struct dentry **stashed, struct vfsmount *mnt, void *data,
2228: struct path *path)
2229: {
2230: struct dentry *dentry, *res;
2231: const struct stashed_operations *sops = mnt->mnt_sb->s_fs_info;
2232:
2233: /* See if dentry can be reused. */
2234: res = stashed_dentry_get(stashed);
2235: if (IS_ERR(res))
2236: return PTR_ERR(res);
2237: if (res) {
2238: sops->put_data(data);
2239: goto make_path;
2240: }
2241:
2242: /* Allocate a new dentry. */
2243: dentry = prepare_anon_dentry(stashed, mnt->mnt_sb, data);
2244: if (IS_ERR(dentry))
2245: return PTR_ERR(dentry);
2246:
2247: /* Added a new dentry. @data is now owned by the filesystem. */
2248: if (sops->stash_dentry)
2249: res = sops->stash_dentry(stashed, dentry);
2250: else
2251: res = stash_dentry(stashed, dentry);
2252: if (IS_ERR(res)) {
2253: dput(dentry);
2254: return PTR_ERR(res);
2255: }
2256: if (res != dentry)
2257: dput(dentry);
2258:
2259: make_path:
2260: path->dentry = res;
2261: path->mnt = mntget(mnt);
2262: VFS_WARN_ON_ONCE(path->dentry->d_fsdata != stashed);
2263: VFS_WARN_ON_ONCE(d_inode(path->dentry)->i_private != data);
2264: return 0;
2265: }
SourceFile:fs/libfs.c]
|
| 68/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 34267
output: 36
thoughts: 50
Thoughts: Okay, let me break this down.
**Diving into the `pidfs` Data Handling**
Alright, so I'm focusing on the interaction within `path_from_stashed`, and it seems like the reuse of a dentry triggers a call to `sops->put_data(data)`. The key here is that the `sops->put_data` for a `pidfs` file system is actually the function `pidfs_put_data`. This makes sense; I need to understand what happens to the underlying data when a PID entry is reused. So `pidfs_put_data` is the function that determines how data associated with a PID is managed upon reuse of the Dentry. Got it. Now I need to figure out the actual behavior of that function in the context of the underlying system data.
|
| 69/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/pidfs.c Name:pidfs_put_data]
Results: map[SourceCode: 987: static void pidfs_put_data(void *data)
988: {
989: struct pid *pid = data;
990: put_pid(pid);
991: }
SourceFile:fs/pidfs.c]
|
| 70/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 34621
output: 37
thoughts: 56
Thoughts: Okay, here's my interpretation of that.
**My Analysis of Dentry Lifecycle in this Scenario**
Alright, let's break this down from a systems perspective. My initial thought process is this: when a process interacts with a dentry, there are a couple of key points where ownership and lifecycle management become critical.
First, if the system reuses an existing dentry, the code is using `put_pid`. This is consistent with how I'd expect PID management to function in a kernel environment. We're likely dealing with reference counting or a similar mechanism for managing the lifetime of the PID associated with the dentry.
However, if a *new* dentry is allocated, it means the filesystem now has ownership of the `data`. This implies a more granular allocation strategy on the file system side. It's a reminder that we can have a wide variety of strategies for how we manage the data associated with a dentry.
Finally, the function `pidfs_evict_inode` is triggered when the dentry or the inode is freed. This makes perfect sense; the "eviction" step represents a critical juncture for releasing resources or performing any necessary cleanup related to the pid. This is the stage where the file system likely deallocates any data it owns, as the dentry or inode is no longer in use. It is a key cleanup step that prevents dangling references, memory leaks, or general system instability.
|
| 71/2 |
2026/06/01 11:04 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/pidfs.c Name:pidfs_evict_inode]
Results: map[SourceCode: 834: static void pidfs_evict_inode(struct inode *inode)
835: {
836: struct pid *pid = inode->i_private;
837:
838: clear_inode(inode);
839: put_pid(pid);
840: }
SourceFile:fs/pidfs.c]
|
| 72/2 |
2026/06/01 11:04 |
llm |
expert |
0m
Model:
Tokens:
input: 35131
output: 36
thoughts: 213
Thoughts: **Analyzing Inode Eviction and Potential Resource Leaks**
Okay, so I'm tracing the execution path and it looks like `put_pid` gets invoked during inode eviction. But a critical question pops up: what happens if `prepare_anon_dentry` fails? The code indicates it returns `PTR_ERR(dentry)` in that scenario. My intuition is immediately piqued by this.
Let's see, does `path_from_stashed` handle a failure here by calling `put_data`? I see the snippet:
```c
/* Allocate a new dentry. */
dentry = prepare_anon_dentry(stashed, mnt->mnt_sb, data);
if (IS_ERR(dentry))
return PTR_ERR(dentry);
```
Wait a minute... If `prepare_anon_dentry` errors out, it just returns a pointer to an error! Critically, it *doesn't* call `sops->put_data(data)`! That's a red flag. Now, recall that `data` here is actually `get_pid(pid)`. If the dentry preparation fails, who's responsible for freeing that `pid` reference? I need to check `prepare_anon_dentry`'s implementation to be certain; this could be a memory leak waiting to happen.
|
| 73/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/libfs.c Name:prepare_anon_dentry]
Results: map[SourceCode:2147: static struct dentry *prepare_anon_dentry(struct dentry **stashed,
2148: struct super_block *sb,
2149: void *data)
2150: {
2151: struct dentry *dentry;
2152: struct inode *inode;
2153: const struct stashed_operations *sops = sb->s_fs_info;
2154: int ret;
2155:
2156: inode = new_inode_pseudo(sb);
2157: if (!inode) {
2158: sops->put_data(data);
2159: return ERR_PTR(-ENOMEM);
2160: }
2161:
2162: inode->i_flags |= S_IMMUTABLE;
2163: inode->i_mode = S_IFREG;
2164: simple_inode_init_ts(inode);
2165:
2166: ret = sops->init_inode(inode, data);
2167: if (ret < 0) {
2168: iput(inode);
2169: return ERR_PTR(ret);
2170: }
2171:
2172: /* Notice when this is changed. */
2173: WARN_ON_ONCE(!S_ISREG(inode->i_mode));
2174:
2175: dentry = d_alloc_anon(sb);
2176: if (!dentry) {
2177: iput(inode);
2178: return ERR_PTR(-ENOMEM);
2179: }
2180:
2181: /* Store address of location where dentry's supposed to be stashed. */
2182: dentry->d_fsdata = stashed;
2183:
2184: /* @data is now owned by the fs */
2185: d_instantiate(dentry, inode);
2186: return dentry;
2187: }
SourceFile:fs/libfs.c]
|
| 74/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 36271
output: 33
thoughts: 657
Thoughts: **Analyzing Resource Management in pidfd Code**
Okay, let's break this down. My initial concern was about resource leaks in the `pidfd` code, specifically around the allocation and freeing of various structures. I started by looking at `prepare_anon_dentry`. It seemed like failures could leave things dangling, but then I traced the call paths. I noticed that `sops->put_data(data)` gets called if `new_inode_pseudo` fails, which is good. If `sops->init_inode` fails, `iput(inode)` is called. And `iput` will eventually call `evict_inode`, which itself calls `put_pid(pid)`. The same pattern happens with a failed `d_alloc_anon`. So, it seems `prepare_anon_dentry` *does* free `data` on failure, as desired.
Next, I considered `path_from_stashed`. That one looked a little tricky. `sops->stash_dentry` or `stash_dentry` is called, and upon failure it calls `dput(dentry)`. And like with the inode, `dput` eventually calls `evict_inode`, which also calls `put_pid(pid)`. This seems to be correct.
The real tricky bit is if `pidfs_alloc_file` fails *after* a successful `path_from_stashed`. That's where things can get interesting. Now, I see that `path` is declared as `struct path path __free(path_put) = {};`. The function `path_from_stashed` is supposed to return a `path`, and if it succeeds it then calls `dentry_open`. Critically, if `dentry_open` fails, the function returns a pointer to an error. However, `path_put` is called regardless.
And here it gets interesting. `dentry_open` is passed the path. So if `dentry_open` *succeeds*, what happens to the path? Because it's declared `__free(path_put)`, `path_put(&path)` is going to be called on *success* as well! Let me verify that the `path` isn't duplicated anywhere and is still valid to be put. It seems like a potential double-free situation, but with careful review of the code I can make sure I'm not missing anything. I need to dive into the `dentry_open` function. Let's see what's happening there.
|
| 75/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/open.c Name:dentry_open]
Results: map[SourceCode:1091: struct file *dentry_open(const struct path *path, int flags,
1092: const struct cred *cred)
1093: {
1094: int error;
1095: struct file *f;
1096:
1097: /* We must always pass in a valid mount pointer. */
1098: BUG_ON(!path->mnt);
1099:
1100: f = alloc_empty_file(flags, cred);
1101: if (!IS_ERR(f)) {
1102: error = vfs_open(path, f);
1103: if (error) {
1104: fput(f);
1105: f = ERR_PTR(error);
1106: }
1107: }
1108: return f;
1109: }
SourceFile:fs/open.c]
|
| 76/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 37773
output: 35
thoughts: 44
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience:
**Dentry, Path, and the VFS: A Quick Recap**
Alright, let me just solidify my understanding of how this all slots together. Hang on... `dentry_open`. Right, right, it *doesn't* consume the `path`! It's passed a *constant* pointer to a `struct path`. That's important. I need to remember that the path itself isn't being modified or absorbed by that function. It's working on a reference, a read-only view, essentially. Okay, good.
Now, let's step back a bit and look at the bigger picture. `vfs_open` is the broader entry point. Ah, yes! And, as I recall, within `vfs_open`, we see `do_dentry_open`. So, `do_dentry_open` is clearly the workhorse function handling the actual low-level details of opening a file, dealing with the dentry structure, and I'd bet the path is getting evaluated and maybe traversed somewhere in there too... that makes sense. It's the point where the actual open operation happens, given all of that context. Okay, this is all coming back to me. Good to be refreshed.
|
| 77/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/open.c Name:do_dentry_open]
Results: map[SourceCode: 885: static int do_dentry_open(struct file *f,
886: int (*open)(struct inode *, struct file *))
887: {
888: static const struct file_operations empty_fops = {};
889: struct inode *inode = f->f_path.dentry->d_inode;
890: int error;
891:
892: path_get(&f->f_path);
893: f->f_inode = inode;
894: f->f_mapping = inode->i_mapping;
895: f->f_wb_err = filemap_sample_wb_err(f->f_mapping);
896: f->f_sb_err = file_sample_sb_err(f);
897:
898: if (unlikely(f->f_flags & O_PATH)) {
899: f->f_mode = FMODE_PATH | FMODE_OPENED;
900: file_set_fsnotify_mode(f, FMODE_NONOTIFY);
901: f->f_op = &empty_fops;
902: return 0;
903: }
904:
905: if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
906: i_readcount_inc(inode);
907: } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
908: error = file_get_write_access(f);
909: if (unlikely(error))
910: goto cleanup_file;
911: f->f_mode |= FMODE_WRITER;
912: }
913:
914: /* POSIX.1-2008/SUSv4 Section XSI 2.9.7 */
915: if (S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode))
916: f->f_mode |= FMODE_ATOMIC_POS;
917:
918: f->f_op = fops_get(inode->i_fop);
919: if (WARN_ON(!f->f_op)) {
920: error = -ENODEV;
921: goto cleanup_all;
922: }
923:
924: error = security_file_open(f);
925: if (unlikely(error))
926: goto cleanup_all;
927:
928: /*
929: * Call fsnotify open permission hook and set FMODE_NONOTIFY_* bits
930: * according to existing permission watches.
931: * If FMODE_NONOTIFY mode was already set for an fanotify fd or for a
932: * pseudo file, this call will not change the mode.
933: */
934: error = fsnotify_open_perm_and_set_mode(f);
935: if (unlikely(error))
936: goto cleanup_all;
937:
938: error = break_lease(file_inode(f), f->f_flags);
939: if (unlikely(error))
940: goto cleanup_all;
941:
942: /* normally all 3 are set; ->open() can clear them if needed */
943: f->f_mode |= FMODE_LSEEK | FMODE_PREAD | FMODE_PWRITE;
944: if (!open)
945: open = f->f_op->open;
946: if (open) {
947: error = open(inode, f);
948: if (error)
949: goto cleanup_all;
950: }
951: f->f_mode |= FMODE_OPENED;
952: if ((f->f_mode & FMODE_READ) &&
953: likely(f->f_op->read || f->f_op->read_iter))
954: f->f_mode |= FMODE_CAN_READ;
955: if ((f->f_mode & FMODE_WRITE) &&
956: likely(f->f_op->write || f->f_op->write_iter))
957: f->f_mode |= FMODE_CAN_WRITE;
958: if ((f->f_mode & FMODE_LSEEK) && !f->f_op->llseek)
959: f->f_mode &= ~FMODE_LSEEK;
960: if (f->f_mapping->a_ops && f->f_mapping->a_ops->direct_IO)
961: f->f_mode |= FMODE_CAN_ODIRECT;
962:
963: f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
964: f->f_iocb_flags = iocb_flags(f);
965:
966: file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
967:
968: if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
969: return -EINVAL;
970:
971: /*
972: * XXX: Huge page cache doesn't support writing yet. Drop all page
973: * cache for this file before processing writes.
974: */
975: if (f->f_mode & FMODE_WRITE) {
976: /*
977: * Depends on full fence from get_write_access() to synchronize
978: * against collapse_file() regarding i_writecount and nr_thps
979: * updates. Ensures subsequent insertion of THPs into the page
980: * cache will fail.
981: */
982: if (filemap_nr_thps(inode->i_mapping)) {
983: struct address_space *mapping = inode->i_mapping;
984:
985: filemap_invalidate_lock(inode->i_mapping);
986: /*
987: * unmap_mapping_range just need to be called once
988: * here, because the private pages is not need to be
989: * unmapped mapping (e.g. data segment of dynamic
990: * shared libraries here).
991: */
992: unmap_mapping_range(mapping, 0, 0, 0);
993: truncate_inode_pages(mapping, 0);
994: filemap_invalidate_unlock(inode->i_mapping);
995: }
996: }
997:
998: return 0;
999:
1000: cleanup_all:
1001: if (WARN_ON_ONCE(error > 0))
1002: error = -EINVAL;
1003: fops_put(f->f_op);
1004: put_file_access(f);
1005: cleanup_file:
1006: path_put(&f->f_path);
1007: f->__f_path.mnt = NULL;
1008: f->__f_path.dentry = NULL;
1009: f->f_inode = NULL;
1010: return error;
1011: }
SourceFile:fs/open.c]
|
| 78/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 40281
output: 39
thoughts: 3581
Thoughts: **Deep Dive into SCM and PID Reference Counting**
Alright, let's break this down systematically. I've been tracing the reference counts related to `pid` and SCM credentials in the Linux kernel, particularly focusing on potential memory leaks. It looks like the core issue revolves around the `scm_cookie` and how `pid` references are managed during message sending and reception.
The initial thought was the open and close of files. The path management around file opens seems solid. The file object, dentry, inode and PID have the correct references. But then I looked at a corner case with `pidfs_alloc_file`, and a potential error path, again it looked correct.
Then I focused on `scm_pidfd_recv`. The scenario seemed a bit tricky: if `pidfd_prepare` fails, it should NOT send a `pidfd` value. The code initialized `pidfd_file` to `NULL` so no file or fd is installed if `pidfd_prepare` fails. However, I had to ensure that the error code wasn't erroneously placed in the SCM message. The code correctly handles this situation by not placing the error code in the SCM message if `pidfd_prepare` fails. There are several cases to consider with `pidfd_prepare` and `put_cmsg`, but they all appear leak-free.
Next, I shifted to `scm_replace_pid`. This function's behavior is critical. It takes a `pid` reference, which it gets from `find_get_pid`. `scm_replace_pid` is used in `__scm_send` to replace the `pid` inside of the SCM. Crucially, it **doesn't** take an extra reference on its own. `scm_replace_pid` can potentially fail, but if it does, `__scm_send` correctly calls `put_pid` on the input `pid` argument before returning the error. So all previous references are released and managed.
`unix_dgram_sendmsg` and `unix_scm_to_skb` looked next. The good thing here is that `unix_scm_to_skb` takes a new reference on `scm->pid`. Then `scm_destroy` is always called afterward, which releases the original reference taken by `find_get_pid`, leaving only the reference on the `skb`. So there are no leaks. Several failure paths can exist in `unix_dgram_sendmsg`. No matter where it fails, `scm_destroy` is always called, which releases the references. I also considered multiple calls to `scm_replace_pid`, each time it's carefully de-referenced. `pidfs_register_pid` can fail and that is also handled correctly and no leaks occur.
`scm_send` had some further considerations. It may call `unix_get_peersec_dgram`, and set `scm->secid`. The core idea is that even if `__scm_send` fails, `scm_destroy` is called within `__scm_send`, ensuring the deallocation of any acquired references. Finally, I confirmed that `unix_dgram_sendmsg` and `unix_stream_sendmsg` always call `scm_destroy` which correctly release any references taken within `scm_send`. Even if the message control length is zero, the cleanup occurs.
|
| 79/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_stream_sendmsg]
Results: map[SourceCode:2381: static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
2382: size_t len)
2383: {
2384: struct sock *sk = sock->sk;
2385: struct sk_buff *skb = NULL;
2386: struct sock *other = NULL;
2387: struct unix_sock *otheru;
2388: struct scm_cookie scm;
2389: bool fds_sent = false;
2390: int err, sent = 0;
2391:
2392: err = scm_send(sock, msg, &scm, false);
2393: if (err < 0)
2394: return err;
2395:
2396: if (msg->msg_flags & MSG_OOB) {
2397: err = -EOPNOTSUPP;
2398: #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
2399: if (len)
2400: len--;
2401: else
2402: #endif
2403: goto out_err;
2404: }
2405:
2406: if (msg->msg_namelen) {
2407: err = READ_ONCE(sk->sk_state) == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
2408: goto out_err;
2409: }
2410:
2411: other = unix_peer(sk);
2412: if (!other) {
2413: err = -ENOTCONN;
2414: goto out_err;
2415: }
2416:
2417: otheru = unix_sk(other);
2418:
2419: if (READ_ONCE(sk->sk_shutdown) & SEND_SHUTDOWN)
2420: goto out_pipe;
2421:
2422: while (sent < len) {
2423: int size = len - sent;
2424: int data_len;
2425:
2426: if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
2427: skb = sock_alloc_send_pskb(sk, 0, 0,
2428: msg->msg_flags & MSG_DONTWAIT,
2429: &err, 0);
2430: } else {
2431: /* Keep two messages in the pipe so it schedules better */
2432: size = min_t(int, size, (READ_ONCE(sk->sk_sndbuf) >> 1) - 64);
2433:
2434: /* allow fallback to order-0 allocations */
2435: size = min_t(int, size, SKB_MAX_HEAD(0) + UNIX_SKB_FRAGS_SZ);
2436:
2437: data_len = max_t(int, 0, size - SKB_MAX_HEAD(0));
2438:
2439: data_len = min_t(size_t, size, PAGE_ALIGN(data_len));
2440:
2441: skb = sock_alloc_send_pskb(sk, size - data_len, data_len,
2442: msg->msg_flags & MSG_DONTWAIT, &err,
2443: get_order(UNIX_SKB_FRAGS_SZ));
2444: }
2445: if (!skb)
2446: goto out_err;
2447:
2448: /* Only send the fds in the first buffer */
2449: err = unix_scm_to_skb(&scm, skb, !fds_sent);
2450: if (err < 0)
2451: goto out_free;
2452:
2453: fds_sent = true;
2454:
2455: err = unix_maybe_add_creds(skb, sk, other);
2456: if (err)
2457: goto out_free;
2458:
2459: if (unlikely(msg->msg_flags & MSG_SPLICE_PAGES)) {
2460: skb->ip_summed = CHECKSUM_UNNECESSARY;
2461: err = skb_splice_from_iter(skb, &msg->msg_iter, size);
2462: if (err < 0)
2463: goto out_free;
2464:
2465: size = err;
2466: refcount_add(size, &sk->sk_wmem_alloc);
2467: } else {
2468: skb_put(skb, size - data_len);
2469: skb->data_len = data_len;
2470: skb->len = size;
2471: err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
2472: if (err)
2473: goto out_free;
2474: }
2475:
2476: unix_state_lock(other);
2477:
2478: if (sock_flag(other, SOCK_DEAD) ||
2479: (other->sk_shutdown & RCV_SHUTDOWN))
2480: goto out_pipe_unlock;
2481:
2482: if (UNIXCB(skb).fp && !other->sk_scm_rights) {
2483: unix_state_unlock(other);
2484: err = -EPERM;
2485: goto out_free;
2486: }
2487:
2488: scm_stat_add(other, skb);
2489:
2490: spin_lock(&other->sk_receive_queue.lock);
2491: WRITE_ONCE(otheru->inq_len, otheru->inq_len + skb->len);
2492: __skb_queue_tail(&other->sk_receive_queue, skb);
2493: spin_unlock(&other->sk_receive_queue.lock);
2494:
2495: unix_state_unlock(other);
2496: READ_ONCE(other->sk_data_ready)(other);
2497: sent += size;
2498: }
2499:
2500: #if IS_ENABLED(CONFIG_AF_UNIX_OOB)
2501: if (msg->msg_flags & MSG_OOB) {
2502: err = queue_oob(sk, msg, other, &scm, fds_sent);
2503: if (err)
2504: goto out_err;
2505: sent++;
2506: }
2507: #endif
2508:
2509: scm_destroy(&scm);
2510:
2511: return sent;
2512:
2513: out_pipe_unlock:
2514: unix_state_unlock(other);
2515: out_pipe:
2516: if (!sent && !(msg->msg_flags & MSG_NOSIGNAL))
2517: send_sig(SIGPIPE, current, 0);
2518: err = -EPIPE;
2519: out_free:
2520: consume_skb(skb);
2521: out_err:
2522: scm_destroy(&scm);
2523: return sent ? : err;
2524: }
SourceFile:net/unix/af_unix.c]
|
| 80/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 46816
output: 35
thoughts: 573
Thoughts: **Analyzing `unix_stream_sendmsg` and `sendmmsg` for Potential PID Leaks**
Okay, let's break this down. My initial observation is focused on `unix_stream_sendmsg`. It's clear that the loop `while (sent < len)` is central to how data is sent. Inside this loop, `unix_scm_to_skb` is called multiple times, once for each chunk of data. This function is key.
Each time `unix_scm_to_skb` gets invoked, it sets `UNIXCB(skb).pid = get_pid(scm->pid)`. This means each `skb` (socket buffer) gets a reference to the process ID (`pid`) associated with the `scm` (SCM cookie). The crucial part here is the balanced nature of this operation: when an `skb` is freed, `unix_wfree` is called, which in turn calls `unix_destruct_scm`. That eventually calls `scm_destroy` which ends in a `put_pid` call. Each `skb` releases its reference to the `pid` when it is freed. This seems perfectly balanced so far, with references incremented and decremented as expected.
I have to consider the case where `len` is zero. If `len` is zero, the loop is skipped entirely. However, even in this scenario, `scm_destroy(&scm)` gets called directly. This also releases the reference, keeping things balanced.
However, the reproducer uses `sendmmsg`, which sends multiple messages at once. Now, this is where I need to focus my attention. It could be possible that the `sendmmsg` system call contains an issue. The concern is whether the system call's behavior with regards to `pid` and reference counting can lead to leaks if `sendmmsg` is mishandled. Let me check the code.
|
| 81/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/socket.c Name:__sys_sendmmsg]
Results: map[SourceCode:2796: int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
2797: unsigned int flags, bool forbid_cmsg_compat)
2798: {
2799: int err, datagrams;
2800: struct socket *sock;
2801: struct mmsghdr __user *entry;
2802: struct compat_mmsghdr __user *compat_entry;
2803: struct msghdr msg_sys;
2804: struct used_address used_address;
2805: unsigned int oflags = flags;
2806:
2807: if (forbid_cmsg_compat && (flags & MSG_CMSG_COMPAT))
2808: return -EINVAL;
2809:
2810: if (vlen > UIO_MAXIOV)
2811: vlen = UIO_MAXIOV;
2812:
2813: datagrams = 0;
2814:
2815: CLASS(fd, f)(fd);
2816:
2817: if (fd_empty(f))
2818: return -EBADF;
2819: sock = sock_from_file(fd_file(f));
2820: if (unlikely(!sock))
2821: return -ENOTSOCK;
2822:
2823: used_address.name_len = UINT_MAX;
2824: entry = mmsg;
2825: compat_entry = (struct compat_mmsghdr __user *)mmsg;
2826: err = 0;
2827: flags |= MSG_BATCH;
2828:
2829: while (datagrams < vlen) {
2830: if (datagrams == vlen - 1)
2831: flags = oflags;
2832:
2833: if (MSG_CMSG_COMPAT & flags) {
2834: err = ___sys_sendmsg(sock, (struct user_msghdr __user *)compat_entry,
2835: &msg_sys, flags, &used_address, MSG_EOR);
2836: if (err < 0)
2837: break;
2838: err = __put_user(err, &compat_entry->msg_len);
2839: ++compat_entry;
2840: } else {
2841: err = ___sys_sendmsg(sock,
2842: (struct user_msghdr __user *)entry,
2843: &msg_sys, flags, &used_address, MSG_EOR);
2844: if (err < 0)
2845: break;
2846: err = put_user(err, &entry->msg_len);
2847: ++entry;
2848: }
2849:
2850: if (err)
2851: break;
2852: ++datagrams;
2853: if (msg_data_left(&msg_sys))
2854: break;
2855: cond_resched();
2856: }
2857:
2858: /* We only return an error if no datagrams were able to be sent */
2859: if (datagrams != 0)
2860: return datagrams;
2861:
2862: return err;
2863: }
SourceFile:net/socket.c]
|
| 82/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 48839
output: 34
thoughts: 51
Thoughts: Okay, here's my interpretation of those thoughts, presented as if they're my own:
**Analyzing `__sys_sendmmsg` and Message Sending**
Alright, let's break this down. `__sys_sendmmsg` β that's the multi-message send system call, right? I'm immediately thinking, "how efficient is this?" It seems like it's just calling `___sys_sendmsg` for *every single* message. That's... potentially a lot of overhead. I need to keep that in mind.
Then, `___sys_sendmsg` goes down to `sock_sendmsg`. Okay, so we're getting down to the socket level. That's the core functionality, where the actual data transmission happens.
But wait a minute... Now I'm getting a little uneasy. Let me rewind and look more closely. My concern is, is there any possibility of a resource leak introduced *inside* the `___sys_sendmsg` function? Could there be an issue that happens in that intermediate step which is replicated for each message sent via the multi-send system call? I'm going to have to dive into that function and scrutinize it to ensure it does not hold a potential vulnerability. It is worth digging into how resources are handled there, memory specifically, and whether there are any corner cases I need to consider with the multi-send setup.
|
| 83/2 |
2026/06/01 11:05 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/socket.c Name:___sys_sendmsg]
Results: map[SourceCode:2737: static int ___sys_sendmsg(struct socket *sock, struct user_msghdr __user *msg,
2738: struct msghdr *msg_sys, unsigned int flags,
2739: struct used_address *used_address,
2740: unsigned int allowed_msghdr_flags)
2741: {
2742: struct sockaddr_storage address;
2743: struct iovec iovstack[UIO_FASTIOV], *iov = iovstack;
2744: ssize_t err;
2745:
2746: msg_sys->msg_name = &address;
2747:
2748: err = sendmsg_copy_msghdr(msg_sys, msg, flags, &iov);
2749: if (err < 0)
2750: return err;
2751:
2752: err = ____sys_sendmsg(sock, msg_sys, flags, used_address,
2753: allowed_msghdr_flags);
2754: kfree(iov);
2755: return err;
2756: }
SourceFile:net/socket.c]
|
| 84/2 |
2026/06/01 11:05 |
llm |
expert |
0m
Model:
Tokens:
input: 49560
output: 41
thoughts: 536
Thoughts: **My Analysis of a Potential `sendmmsg` Vulnerability**
Okay, so I'm diving into this `sendmmsg` issue. Initially, `____sys_sendmsg` calls `sock_sendmsg`, which seems straightforward, no immediate red flags there. But then I see this repro with `sendmmsg` using `vlen=0x651` (1617). The code's using a syscall for `__NR_sendmmsg`, and that's where things get interesting. The repro sets up a mapping at `0x200000000000` with a size of `0x1000000`. Crucially, it *doesn't* initialize that memory!
So, the `mmsg` pointer in `sendmmsg` points to zeroed memory. If `mmsg` is zeroed, then `msg_controllen` will be zero. Looking at `scm_send`, it bails out early if `msg->msg_controllen <= 0`. It just returns 0 immediately.
But hang on! If `msg_controllen` is 0, that means `scm_send` *won't* parse any `SCM_CREDENTIALS` control messages. That's a key point. This is where I have to zoom in again. It *does* seem to have a default:
```c
memset(scm, 0, sizeof(*scm));
scm->creds.uid = INVALID_UID;
scm->creds.gid = INVALID_GID;
if (forcecreds)
scm_set_cred(scm, task_tgid(current), current_uid(), current_gid());
unix_get_peersec_dgram(sock, scm);
if (msg->msg_controllen <= 0)
return 0;
```
`unix_dgram_sendmsg` is what's calling `scm_send(sock, msg, &scm, false)`, so the `forcecreds` flag is *false* in this case. So it's not going to force creds. But what about `SOCK_PASSCRED`?
I need to figure out where the `SOCK_PASSCRED` is being handled. I can see that `unix_dgram_sendmsg` is doing this call to `scm_send`, but I don't see the conditional check for `SOCK_PASSCRED`. It's calling it directly:
```c
err = scm_send(sock, msg, &scm, false);
```
Okay, now I have to check `unix_maybe_add_creds` to see how that's handled. That's where I need to focus next.
|
| 85/2 |
2026/06/01 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:unix_maybe_add_creds]
Results: map[SourceCode:2009: /**
2010: * unix_maybe_add_creds() - Adds current task uid/gid and struct pid to skb if needed.
2011: * @skb: skb to attach creds to.
2012: * @sk: Sender sock.
2013: * @other: Receiver sock.
2014: *
2015: * Some apps rely on write() giving SCM_CREDENTIALS
2016: * We include credentials if source or destination socket
2017: * asserted SOCK_PASSCRED.
2018: *
2019: * Context: May sleep.
2020: * Return: On success zero, on error a negative error code is returned.
2021: */
2022: static int unix_maybe_add_creds(struct sk_buff *skb, const struct sock *sk,
2023: const struct sock *other)
2024: {
2025: if (UNIXCB(skb).pid)
2026: return 0;
2027:
2028: if (unix_may_passcred(sk) || unix_may_passcred(other) ||
2029: !other->sk_socket) {
2030: struct pid *pid;
2031: int err;
2032:
2033: pid = task_tgid(current);
2034: err = pidfs_register_pid(pid);
2035: if (unlikely(err))
2036: return err;
2037:
2038: UNIXCB(skb).pid = get_pid(pid);
2039: current_uid_gid(&UNIXCB(skb).uid, &UNIXCB(skb).gid);
2040: }
2041:
2042: return 0;
2043: }
SourceFile:net/unix/af_unix.c]
|
| 86/2 |
2026/06/01 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 51295
output: 42
thoughts: 4605
Thoughts: **Deep Dive into Unix Domain Socket Credential Management**
Okay, let's break this down. My initial observation is focused on how credentials are handled within Unix domain sockets, specifically regarding process IDs (PIDs) and how they're associated with socket buffers (`skb`s). The core function, `unix_maybe_add_creds`, is clearly designed to inject credential information, but a careful examination reveals that it doesn't always manage the lifecycle of references on its own.
My immediate thought is that `pidfs_register_pid` and `get_pid` are key. `pidfs_register_pid` presumably handles the registration of a PID with a filesystem, and `get_pid` increments a reference count. The crucial part is how these references are released. If `pidfs_register_pid` fails, we exit and the buffer is freed, so there's no leak. If it succeeds, the `pid` is stored in the `skb` and it seems like the reference is balanced by the `put_pid` call within `unix_destruct_scm` as part of the `skb` cleanup.
The code's structure checks if `UNIXCB(skb).pid` is already set, preventing multiple registrations for a single `skb`. That's good defensive programming.
The error paths within `unix_stream_sendmsg` and `unix_dgram_sendmsg` appear well-managed. If `unix_maybe_add_creds` fails, the `skb` is freed, and the NULL `UNIXCB(skb).pid` will be handled gracefully by `unix_destruct_scm` with a `put_pid(NULL)`. Similarly, if these sendmsg functions error out after `unix_maybe_add_creds` succeeds, it looks balanced too, because `unix_wfree`, called by the buffer destructor, takes care of the reference released.
I need to focus on potential reference leaks. The `pidfs_free_pid` function itself doesn't free the PID structure, the reference is handled by `put_pid`, which does deallocate the PID structure, which includes releasing any related attributes via a list or a workqueue in case of xattrs.
Now I am going through the `unix_dgram_sendmsg` function. The code's interaction with `skb_copy_datagram_from_iter` is a point of concern. A failure in that function could lead to an early exit. If `unix_scm_to_skb` succeeded, we *should* have a valid reference to the PID, but the early exit could trigger a `consume_skb` call, and I need to check that the destructor is called. Then I see that `unix_scm_to_skb` *does* set `skb->destructor = unix_wfree;`, so it looks balanced. The `scm` local variable is cleaned up correctly, too, with the correct reference counting.
Next point is to understand what happens if a datagram is received. `unix_skb_to_scm` appears to be responsible for copying credentials from the `skb` into the `scm` (SCM stands for Socket Control Message). Here, it seems the `scm` takes its own reference to the `skb`'s PID. The received datagram's handling is balanced and the `scm`'s reference is released. This includes scenarios where `MSG_PEEK` is used which does *not* consume the SKB. This is good because `__skb_try_recv_datagram` increments the `skb`'s refcount in the peek case, so there's no leak.
I also have to check that when the socket is closed while packets are in the queue, `skb_queue_purge` will trigger the proper cleanup through the destructor.
The sendmsg cases also need a bit more digging. If the queuing itself fails in `unix_dgram_sendmsg`, which queues the skb at the very end. The packets are cleaned correctly on error. The function checks for `sock_flag(other, SOCK_DEAD)` which will potentially return a -ECONNRESET error, and I have to make sure that the `consume_skb` call cleans the skb, which it does.
Now let's go back and examine `unix_maybe_add_creds` itself. If there's an issue there, it'll propagate. The crucial thing is that `unix_maybe_add_creds` doesn't set `skb->destructor`, so what function is setting the destructor? The call to `unix_scm_to_skb` sets this, which happens *before* `unix_maybe_add_creds` is
|
| 87/2 |
2026/06/01 11:06 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:unix_maybe_add_creds SourceTreePrefix:net/unix]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:queue_oob SourceFile:net/unix/af_unix.c SourceLine:2337] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_dgram_sendmsg SourceFile:net/unix/af_unix.c SourceLine:2182] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:unix_stream_sendmsg SourceFile:net/unix/af_unix.c SourceLine:2455]] TruncatedOutput:false]
|
| 88/2 |
2026/06/01 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 57145
output: 37
thoughts: 10
Thoughts: Okay, here's my summarized thought process, presented as if I'm the one thinking it:
**Checking `queue_oob`**
Alright, time to dive in. Let's start by taking a look at `queue_oob`. I need to ensure it's functioning as expected, and ideally, I'd like to identify any potential vulnerabilities or bottlenecks. I'll need to scrutinize the implementation, paying close attention to its boundary conditions and how it handles edge cases. Any subtle nuances in its logic could lead to out-of-bounds errors or performance degradation, so I'll be thorough. I'll need to consider how it interacts with other modules and components β dependencies can be a source of unexpected issues. Essentially, this is a deep dive into the code. I'm looking for anything that feels off, anything that might be a weak point. Let's get to it.
|
| 89/2 |
2026/06/01 11:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/unix/af_unix.c Name:queue_oob]
Results: map[SourceCode:2321: static int queue_oob(struct sock *sk, struct msghdr *msg, struct sock *other,
2322: struct scm_cookie *scm, bool fds_sent)
2323: {
2324: struct unix_sock *ousk = unix_sk(other);
2325: struct sk_buff *skb;
2326: int err;
2327:
2328: skb = sock_alloc_send_skb(sk, 1, msg->msg_flags & MSG_DONTWAIT, &err);
2329:
2330: if (!skb)
2331: return err;
2332:
2333: err = unix_scm_to_skb(scm, skb, !fds_sent);
2334: if (err < 0)
2335: goto out;
2336:
2337: err = unix_maybe_add_creds(skb, sk, other);
2338: if (err)
2339: goto out;
2340:
2341: skb_put(skb, 1);
2342: err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);
2343:
2344: if (err)
2345: goto out;
2346:
2347: unix_state_lock(other);
2348:
2349: if (sock_flag(other, SOCK_DEAD) ||
2350: (other->sk_shutdown & RCV_SHUTDOWN)) {
2351: err = -EPIPE;
2352: goto out_unlock;
2353: }
2354:
2355: if (UNIXCB(skb).fp && !other->sk_scm_rights) {
2356: err = -EPERM;
2357: goto out_unlock;
2358: }
2359:
2360: scm_stat_add(other, skb);
2361:
2362: spin_lock(&other->sk_receive_queue.lock);
2363: WRITE_ONCE(ousk->oob_skb, skb);
2364: WRITE_ONCE(ousk->inq_len, ousk->inq_len + 1);
2365: __skb_queue_tail(&other->sk_receive_queue, skb);
2366: spin_unlock(&other->sk_receive_queue.lock);
2367:
2368: sk_send_sigurg(other);
2369: unix_state_unlock(other);
2370: READ_ONCE(other->sk_data_ready)(other);
2371:
2372: return 0;
2373: out_unlock:
2374: unix_state_unlock(other);
2375: out:
2376: consume_skb(skb);
2377: return err;
2378: }
SourceFile:net/unix/af_unix.c]
|
| 90/2 |
2026/06/01 11:06 |
llm |
expert |
0m
Model:
Tokens:
input: 58273
output: 32
thoughts: 633
Thoughts: **Analyzing Potential Resource Leaks in the UNIX Domain Socket Code**
Okay, let's break this down. In the `queue_oob` function, it's immediately apparent that `unix_scm_to_skb` is called *before* `unix_maybe_add_creds`. This is significant because `unix_scm_to_skb` sets the `skb->destructor`, which is crucial.
But hold onβ¦ what happens if `unix_maybe_add_creds` is called, and then `pidfs_register_pid` *fails*? I need to trace the execution path. If `pidfs_register_pid` returns an error, `unix_maybe_add_creds` will propagate that error back. Then the caller will jump to `out_free` or `out`, which will inevitably call `consume_skb(skb)`. Since `UNIXCB(skb).pid` would still be `NULL` (or whatever `unix_scm_to_skb` set it to), `unix_destruct_scm` will be responsible for releasing the resources correctly. Okay, I think this part is fine β the destruction is handled gracefully. Good.
Now, my Spidey-Sense is tingling⦠I need to scrutinize `pidfs_register_pid` itself for any potential leaks. Specifically, I'm examining this code:
```c
int pidfs_register_pid(struct pid *pid)
{
struct pidfs_attr *new_attr __free(kfree) = NULL;
struct pidfs_attr *attr;
might_sleep();
if (!pid)
return 0;
attr = READ_ONCE(pid->attr);
if (unlikely(attr == PIDFS_PID_DEAD))
return PTR_ERR(PIDFS_PID_DEAD);
if (attr)
return 0;
new_attr = kmem_cache_zalloc(pidfs_attr_cachep, GFP_KERNEL);
if (!new_attr)
return -ENOMEM;
/* Synchronize with pidfs_exit(). */
guard(spinlock_irq)(&pid->wait_pidfd.lock);
attr = pid->attr;
if (unlikely(attr == PIDFS_PID_DEAD))
return PTR_ERR(PIDFS_PID_DEAD);
if (unlikely(attr))
return 0;
pid->attr = no_free_ptr(new_attr);
return 0;
}
```
Okay, `new_attr` is allocated using `kmem_cache_zalloc`. If `attr` is already set, the function returns early. But wait a minute⦠the declaration of `new_attr` includes `__free(kfree)`! That's a red flag. The allocation is coming from `pidfs_attr_cachep`, and I *know* `pidfs_attr_cachep` is a `kmem_cache`. Can I free an object allocated from a `kmem_cache` using `kfree`? I need to verify how `kfree` is implemented. This could be a very subtle and serious memory management bug if handled incorrectly. I need to check the source immediately.
|
| 91/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:mm/slub.c Name:kfree]
Results: map[SourceCode:6534: /**
6535: * kfree - free previously allocated memory
6536: * @object: pointer returned by kmalloc(), kmalloc_nolock(), or kmem_cache_alloc()
6537: *
6538: * If @object is NULL, no operation is performed.
6539: */
6540: void kfree(const void *object)
6541: {
6542: struct page *page;
6543: struct slab *slab;
6544: struct kmem_cache *s;
6545: void *x = (void *)object;
6546:
6547: trace_kfree(_RET_IP_, object);
6548:
6549: if (unlikely(ZERO_OR_NULL_PTR(object)))
6550: return;
6551:
6552: page = virt_to_page(object);
6553: slab = page_slab(page);
6554: if (!slab) {
6555: /* kmalloc_nolock() doesn't support large kmalloc */
6556: free_large_kmalloc(page, (void *)object);
6557: return;
6558: }
6559:
6560: s = slab->slab_cache;
6561: slab_free(s, slab, x, _RET_IP_);
6562: }
SourceFile:mm/slub.c]
|
| 92/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 60087
output: 34
thoughts: 519
Thoughts: **Analyzing Memory Management in the `pidfs` Module**
Okay, let's break this down systematically. My initial concern was about how objects allocated with `kmem_cache_alloc` are freed. Then I reminded myself that, yes, `kfree` *can* free objects allocated by `kmem_cache_alloc`. The documentation confirms this: "pointer returned by kmalloc(), kmalloc_nolock(), or kmem_cache_alloc()". So, using `__free(kfree)` is perfectly acceptable for `kmem_cache_zalloc`.
Now I'm looking at `pidfs_free_pid`. The code snippet shows:
```c
if (likely(!attr->xattrs))
kfree(attr);
```
So `kfree` is used. This is fine, that's expected.
Next, I need to check the different states when `pidfs_register_pid` is called. First, if `pid->attr` is already set, `new_attr` is freed by `__free(kfree)`. Makes sense, the old one is freed, the new one potentially takes its place. This is also fine.
If `pid->attr` is *not* set, the code does `pid->attr = no_free_ptr(new_attr);`. Ah, this is critical. `no_free_ptr` sets `pid->attr` and *prevents* `__free(kfree)` from freeing it. That's good, so it's handled correctly in this scenario. This is still fine.
If `pid->attr` is `PIDFS_PID_DEAD`, it returns `PTR_ERR(PIDFS_PID_DEAD)` and `new_attr` is freed by `__free(kfree)`. So that case is covered as well. This is still fine.
Now, if `pidfs_register_pid` is called and `pid->attr` is set to `new_attr`, the code then calls `pidfs_free_pid`. This is where I initially saw a potential issue.
```c
void pidfs_free_pid(struct pid *pid)
{
struct pidfs_attr *attr = pid->attr;
...
if (likely(!attr->xattrs))
kfree(attr);
else if (llist_add(&attr->pidfs_llist, &pidfs_free_list))
schedule_work(&pidfs_free_work);
}
```
My concern was: What if `pidfs_free_pid` is called MULTIPLE times? But, wait... I have to remember the context of the code. It's called from `put_pid` when `pid->count` drops to 0. Therefore, `pidfs_free_pid` is only called ONCE. That resolves my concern.
Finally, what about `pidfs_exit`? That case doesn't show any issue.
Ok, so it appears my analysis is complete. All the different scenarios are covered in the correct way. There are no memory leaks or double-frees, so all is well.
|
| 93/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/pidfs.c Name:pidfs_exit]
Results: map[SourceCode: 707: /*
708: * We're called from release_task(). We know there's at least one
709: * reference to struct pid being held that won't be released until the
710: * task has been reaped which cannot happen until we're out of
711: * release_task().
712: *
713: * If this struct pid has at least once been referred to by a pidfd then
714: * pid->attr will be allocated. If not we mark the struct pid as dead so
715: * anyone who is trying to register it with pidfs will fail to do so.
716: * Otherwise we would hand out pidfs for reaped tasks without having
717: * exit information available.
718: *
719: * Worst case is that we've filled in the info and the pid gets freed
720: * right away in free_pid() when no one holds a pidfd anymore. Since
721: * pidfs_exit() currently is placed after exit_task_work() we know that
722: * it cannot be us aka the exiting task holding a pidfd to itself.
723: */
724: void pidfs_exit(struct task_struct *tsk)
725: {
726: struct pid *pid = task_pid(tsk);
727: struct pidfs_attr *attr;
728: #ifdef CONFIG_CGROUPS
729: struct cgroup *cgrp;
730: #endif
731:
732: might_sleep();
733:
734: /* Synchronize with pidfs_register_pid(). */
735: scoped_guard(spinlock_irq, &pid->wait_pidfd.lock) {
736: attr = pid->attr;
737: if (!attr) {
738: /*
739: * No one ever held a pidfd for this struct pid.
740: * Mark it as dead so no one can add a pidfs
741: * entry anymore. We're about to be reaped and
742: * so no exit information would be available.
743: */
744: pid->attr = PIDFS_PID_DEAD;
745: return;
746: }
747: }
748:
749: /*
750: * If @pid->attr is set someone might still legitimately hold a
751: * pidfd to @pid or someone might concurrently still be getting
752: * a reference to an already stashed dentry from @pid->stashed.
753: * So defer cleaning @pid->attr until the last reference to @pid
754: * is put
755: */
756:
757: #ifdef CONFIG_CGROUPS
758: rcu_read_lock();
759: cgrp = task_dfl_cgroup(tsk);
760: attr->cgroupid = cgroup_id(cgrp);
761: rcu_read_unlock();
762: #endif
763: attr->exit_code = tsk->exit_code;
764:
765: /* Ensure that PIDFD_GET_INFO sees either all or nothing. */
766: smp_wmb();
767: set_bit(PIDFS_ATTR_BIT_EXIT, &attr->attr_mask);
768: }
SourceFile:fs/pidfs.c]
|
| 94/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 62314
output: 19
thoughts: 660
Thoughts: **Analyzing a Potential PIDFS Memory Leak**
Okay, let's break this down. My initial concern was centered around potential memory leaks within the `pidfs` subsystem, specifically during PID registration, exit, and possible race conditions.
First, I had to ensure I fully understood the logic. I reviewed how `pidfs_exit` handles the `attr` pointer. If `attr` is NULL, it sets `pid->attr` to `PIDFS_PID_DEAD`, which is an error pointer. Then, `pidfs_free_pid` bails out if it encounters an error pointer. That's good; no double free. If `attr` is not NULL, `pidfs_exit` modifies it with exit information, and then `pidfs_free_pid` frees it. Also good.
Next, I considered the scenario where `pidfs_register_pid` is called *after* `pidfs_exit`. I confirmed that `pidfs_register_pid` correctly checks `if (unlikely(attr == PIDFS_PID_DEAD))` and returns an error if it finds that condition. No problem there.
Then, I thought about concurrency. What if `pidfs_register_pid` and `pidfs_exit` are called concurrently? They are synchronized by `pid->wait_pidfd.lock`. Safe.
After verifying all the scenarios, I concluded that based on my review, `pidfs_register_pid` itself doesn't inherently leak memory in its logic.
Now, I need to investigate the bug report more deeply. The report indicates a memory leak: a "struct pid" of size 184. The backtrace points to `alloc_pid`. I'm going to double check the layout of the `struct pid`. That's where I need to focus my attention. It's time to check the definition of the struct and the `alloc_pid` function.
|
| 95/2 |
2026/06/01 11:07 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:count OffsetBits:0 SizeBits:32] map[Name:level OffsetBits:32 SizeBits:32] map[Name:lock OffsetBits:64 SizeBits:32] map[Name: OffsetBits:128 SizeBits:256] map[Name:tasks OffsetBits:384 SizeBits:256] map[Name:inodes OffsetBits:640 SizeBits:64] map[Name:wait_pidfd OffsetBits:704 SizeBits:192] map[Name:rcu OffsetBits:896 SizeBits:128] map[Name:numbers OffsetBits:1024 SizeBits:0]]]
|
| 96/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 63589
output: 30
thoughts: 166
Thoughts: **Analyzing the Reported Size of a Data Structure**
Okay, so I'm looking at this data structure, and the reported size is throwing me off. I know the base size is 1024 bits, or 128 bytes, plus the `numbers` array. But the `numbers` array isn't just a primitive type; it's an array of `struct upid`.
Let's see⦠`struct upid` is defined as containing an `int nr` and a pointer to `struct pid_namespace`. Considering a standard architecture, an `int` is typically 4 bytes, and a pointer would also be 8 bytes on a 64-bit system, which would make the total size 12 bytes, or 16 bytes for padding reasons, right? Therefore, `struct upid` should be 16 bytes.
Now, if `level` is 0, the `numbers` array only holds one element. So, 128 bytes (base) + 16 bytes (one `upid`) gives me 144 bytes. But the report says the size is 184 bytes! That's a discrepancy.
Perhaps `level` isn't 0. Let's try `level` equal to 2, which would give three elements in the `numbers` array. That would be 128 + (3 * 16) = 176 bytes. Still not 184. Where's the extra 8 bytes?
There has to be some other fields contributing to the reported size. It's time to dig deeper and investigate the `struct pid` definition to see what else might be lurking in there.
|
| 97/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/pid.c Name:pid]
Results: map[SourceCode: 58: struct pid {
59: refcount_t count;
60: unsigned int level;
61: spinlock_t lock;
62: struct {
63: u64 ino;
64: struct rhash_head pidfs_hash;
65: struct dentry *stashed;
66: struct pidfs_attr *attr;
67: };
68: /* lists of tasks that use this pid */
69: struct hlist_head tasks[PIDTYPE_MAX];
70: struct hlist_head inodes;
71: /* wait queue for pidfd notifications */
72: wait_queue_head_t wait_pidfd;
73: struct rcu_head rcu;
74: struct upid numbers[];
75: };
SourceFile:include/linux/pid.h]
|
| 98/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 64400
output: 38
thoughts: 814
Thoughts: **Analyzing a Potential Kernel Memory Leak**
Okay, let's break this down. First, I'm looking at the `struct pid` structure in the kernel. I see it has an anonymous struct inside, and I'm quickly calculating its size. `ino`, `pidfs_hash`, `stashed`, and `attr` β that anonymous struct is 40 bytes. Then there's `count`, `level`, `lock`, and some padding, another 16 bytes. So far, we're at 56 bytes. Adding the other members like `tasks`, `inodes`, `wait_pidfd`, and `rcu` brings the total to 136 bytes. Ah, right, `numbers`! That size depends on the `level`. If the `level` is 2, meaning 3 namespaces, then `numbers` will be 48 bytes. That brings the entire structure size to a hefty 184 bytes!
And yes, I see it! The leaked object in Syzkaller *is* a `struct pid` with `level == 2`. The fact that Syzkaller is running in a nested pid namespace is key. This means that the nested pid namespace is leaking. I'm going to look at why.
Let's revisit the reproducer and see if there are any clues to explain this. I'm focusing on the system calls and their arguments. I'm looking at this `rt_tgsigqueueinfo` call.
```c
syscall(__NR_rt_tgsigqueueinfo, /*gid=*/0, /*tid=*/(intptr_t)-1, /*sig=*/0x1d, /*info=*/0ul);
```
The call is with `gid=0` and `tid=-1`. `rt_tgsigqueueinfo` takes tgid, tid, sig, and info. If I understand the system call correctly, using 0 for the group ID and -1 for the thread ID will almost certainly result in either `-EINVAL` or `-ESRCH` errors. The key question is, *does* this specific call somehow leak the `pid` structure even in error cases? This is where the root of the leak has to be.
|
| 99/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:kernel/signal.c Name:sys_rt_tgsigqueueinfo]
Results: map[SourceCode: SourceFile:]
|
| 100/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 65762
output: 38
thoughts: 15
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of kernel debugging or performance analysis:
**Diving into the Real-Time Signal Queue Information**
Alright, time to dig into this. "Let's check `do_rt_tgsigqueueinfo`." Hmm, that command immediately signals I'm focusing on the real-time signal queue information. I'm probably troubleshooting something related to signal handling, real-time priorities, or perhaps some sort of blocking or latency issue within the signal delivery mechanism. I need to understand what's happening at the core level within the real-time thread group signal queue data structures, to identify any potential bottlenecks, overruns, or unexpected behaviors in the real-time system. This function is likely the entry point to analyze the state of this system, and thus likely the place to start.
|
| 101/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/signal.c Name:do_rt_tgsigqueueinfo]
Results: map[SourceCode:4236: static int do_rt_tgsigqueueinfo(pid_t tgid, pid_t pid, int sig, kernel_siginfo_t *info)
4237: {
4238: /* This is only valid for single tasks */
4239: if (pid <= 0 || tgid <= 0)
4240: return -EINVAL;
4241:
4242: /* Not even root can pretend to send signals from the kernel.
4243: * Nor can they impersonate a kill()/tgkill(), which adds source info.
4244: */
4245: if ((info->si_code >= 0 || info->si_code == SI_TKILL) &&
4246: (task_pid_vnr(current) != pid))
4247: return -EPERM;
4248:
4249: return do_send_specific(tgid, pid, sig, info);
4250: }
SourceFile:kernel/signal.c]
|
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2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 66285
output: 42
thoughts: 167
Thoughts: **Debugging a Nanosleep Mystery**
Okay, so I'm looking at this system call result. It returned `-EINVAL`. No obvious memory leaks, that's good. But what's going on with this `clock_nanosleep` call? I see the arguments... Specifically, I'm concerned with the `id` argument, which is `0xfffffdfc`.
Hang on, let me convert that. `0xfffffdfc`... that's `-516`. Hmmm, that's definitely not a standard clock ID. Could this be related to a PID clock? I seem to recall PID clocks being encoded in a specific way, something involving a bitwise operation like `(~pid << 3) | 2`, or something similar.
Time to look into this `clockid_to_pid` function. Hopefully, that will shed some light on this unexpected ID. I need to figure out what `-516` *means* in the context of this system call!
|
| 103/2 |
2026/06/01 11:07 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:clockid_to_pid]
Results: map[SourceCode: SourceFile:]
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| 104/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 66731
output: 18
thoughts: 15
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of kernel programming or systems internals, and you, the user, understand the context:
**Investigating Clock ID/Process ID Association**
Alright, I'm thinking I need to zero in on how the system's clock information is being linked to individual processes. It feels like there's a potential issue related to the relationship between the clock ID and the process ID (PID), or maybe something analogous to that association. I should really dive into the code and start by checking the `pid_of_clockid` function, or something functionally similar, if it exists. Thatβs probably the best first step to see if the mapping or association there is what I expect. I need to understand how the system's timekeeping and the process table are interacting here.
|
| 105/2 |
2026/06/01 11:07 |
tool |
grepper |
0m
Args: map[Expression:pid.*clockid]
Results: map[Output:kernel/time/posix-cpu-timers.c=42=int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
--
kernel/time/posix-cpu-timers.c-56- */
kernel/time/posix-cpu-timers.c:57:static struct pid *pid_for_clock(const clockid_t clock, bool gettime)
kernel/time/posix-cpu-timers.c-58-{
--
kernel/time/posix-cpu-timers.c=97=static inline int validate_clock_permissions(const clockid_t clock)
--
kernel/time/posix-cpu-timers.c-107-
kernel/time/posix-cpu-timers.c:108:static inline enum pid_type clock_pid_type(const clockid_t clock)
kernel/time/posix-cpu-timers.c-109-{
]
|
| 106/2 |
2026/06/01 11:07 |
llm |
expert |
0m
Model:
Tokens:
input: 67179
output: 41
thoughts: 11
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Assessing Clock Process Identification**
Alright, time to dive into this. The initial thought, "Let's check `pid_for_clock`," immediately signals a focused investigation. I need to determine the process ID (PID) specifically associated with the clock functionality. This isn't just a generic PID; it's a critical piece of information when dealing with timing and scheduling, especially in a system where timing is paramount. I'm likely gearing up to examine or troubleshoot a timing-related issue, analyze clock source behavior, or perhaps even optimize clock access. The precise reason is not explicit, but the direction is clear: my attention is centered on the precise process responsible for the system clock. The `pid_for_clock` variable presumably serves as a key identifier for me to investigate further. Now, what insights does it hold, and what's next in my investigation?
|
| 107/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:pid_for_clock]
Results: map[SourceCode: 54: /*
55: * Functions for validating access to tasks.
56: */
57: static struct pid *pid_for_clock(const clockid_t clock, bool gettime)
58: {
59: const bool thread = !!CPUCLOCK_PERTHREAD(clock);
60: const pid_t upid = CPUCLOCK_PID(clock);
61: struct pid *pid;
62:
63: if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
64: return NULL;
65:
66: /*
67: * If the encoded PID is 0, then the timer is targeted at current
68: * or the process to which current belongs.
69: */
70: if (upid == 0)
71: return thread ? task_pid(current) : task_tgid(current);
72:
73: pid = find_vpid(upid);
74: if (!pid)
75: return NULL;
76:
77: if (thread) {
78: struct task_struct *tsk = pid_task(pid, PIDTYPE_PID);
79: return (tsk && same_thread_group(tsk, current)) ? pid : NULL;
80: }
81:
82: /*
83: * For clock_gettime(PROCESS) allow finding the process by
84: * with the pid of the current task. The code needs the tgid
85: * of the process so that pid_task(pid, PIDTYPE_TGID) can be
86: * used to find the process.
87: */
88: if (gettime && (pid == task_pid(current)))
89: return task_tgid(current);
90:
91: /*
92: * For processes require that pid identifies a process.
93: */
94: return pid_has_task(pid, PIDTYPE_TGID) ? pid : NULL;
95: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 108/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 68034
output: 39
thoughts: 95
Thoughts: **Clock PID Investigation**
Okay, so I'm looking at this code and something's bugging me about `pid_for_clock`. It returns a `struct pid *`, but I'm questioning whether it takes a reference. This is a crucial distinction. Let me compare this with `find_vpid`. Ah, nope, `find_vpid` doesn't take a reference either, it just hands back the pointer directly. Now, I remember, `find_vpid` relies on RCU, which makes me wonder, is `pid_for_clock` also operating under RCU? That could have implications for how I need to handle the pointer. To be sure, I need to trace this back. Let me quickly examine `posix_cpu_clock_get` or potentially `posix_cpu_timer_create` to see if that answers the question.
|
| 109/2 |
2026/06/01 11:08 |
tool |
codesearch-find-references |
0m
Args: map[IncludeSnippetLines:0 Name:pid_for_clock SourceTreePrefix:kernel/time]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:posix_cpu_clock_get SourceFile:kernel/time/posix-cpu-timers.c SourceLine:365] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:posix_cpu_timer_create SourceFile:kernel/time/posix-cpu-timers.c SourceLine:392] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:validate_clock_permissions SourceFile:kernel/time/posix-cpu-timers.c SourceLine:102]] TruncatedOutput:false]
|
| 110/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 68543
output: 44
thoughts: 14
Thoughts: Okay, let's dive into this. Here's how I'd approach summarizing the "thoughts" process, assuming I'm an expert in the field and considering how I'd process it myself:
**Investigating `posix_cpu_timer_create`**
Alright, the initial prompt is pretty straightforward. I'm seeing `posix_cpu_timer_create` and my mind immediately jumps into action. I'm likely already familiar with the POSIX timers in general, so the first thing I do is mentally reconstruct my understanding of the landscape.
I start by thinking, "Okay, this function is responsible for creating a CPU timer, which likely means it's designed to measure and trigger events based on CPU time, rather than wall-clock time." I mentally file that away. Next, I begin considering the likely implementation details, or potential pitfalls. I immediately start asking myself questions about this API. Is this part of the POSIX realtime extensions? What are the typical use cases? Where does it fit within the context of other timing mechanisms like `getrusage()` or `clock_gettime()` and their related clock IDs? I'm probably recalling how it compares with other ways to achieve similar objectives, like interval timers or eventfd.
Then I am thinking about checking the underlying implementation details. I am thinking about checking the source code, maybe checking the man pages, or maybe reading an online tutorial. I am thinking about seeing how these timers are configured, what sorts of signals they're capable of generating (SIGALRM, SIGVTALRM, SIGPROF, etc.), and how they interact with signal handlers. "Is it thread-safe? How does it handle context switches?" are important details I would consider immediately.
In the back of my mind, I'm already formulating test cases. I'm thinking about potential edge cases, like what happens if the timer is very short or very long. I start thinking about potential performance implications. "How much overhead does this introduce compared to other methods?" is a key question in my mind. Ultimately, I am ready to delve further, and am ready to write an initial analysis and/or code to understand this routine.
|
| 111/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:posix_cpu_timer_create]
Results: map[SourceCode: 381: /*
382: * Validate the clockid_t for a new CPU-clock timer, and initialize the timer.
383: * This is called from sys_timer_create() and do_cpu_nanosleep() with the
384: * new timer already all-zeros initialized.
385: */
386: static int posix_cpu_timer_create(struct k_itimer *new_timer)
387: {
388: static struct lock_class_key posix_cpu_timers_key;
389: struct pid *pid;
390:
391: rcu_read_lock();
392: pid = pid_for_clock(new_timer->it_clock, false);
393: if (!pid) {
394: rcu_read_unlock();
395: return -EINVAL;
396: }
397:
398: /*
399: * If posix timer expiry is handled in task work context then
400: * timer::it_lock can be taken without disabling interrupts as all
401: * other locking happens in task context. This requires a separate
402: * lock class key otherwise regular posix timer expiry would record
403: * the lock class being taken in interrupt context and generate a
404: * false positive warning.
405: */
406: if (IS_ENABLED(CONFIG_POSIX_CPU_TIMERS_TASK_WORK))
407: lockdep_set_class(&new_timer->it_lock, &posix_cpu_timers_key);
408:
409: new_timer->kclock = &clock_posix_cpu;
410: timerqueue_init(&new_timer->it.cpu.node);
411: new_timer->it.cpu.pid = get_pid(pid);
412: rcu_read_unlock();
413: return 0;
414: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 112/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 69640
output: 43
thoughts: 66
Thoughts: **My Concerns Regarding CPU Timer Creation and PID References**
Okay, so looking at this `posix_cpu_timer_create` function, it's pretty straightforward, but a key point is immediately jumping out at me. The code assigns the PID of the target process using `new_timer->it.cpu.pid = get_pid(pid);`. Essentially, it's taking a reference. But, and this is a significant "but," where and *when* is that reference released? This is a memory management question that needs a very specific answer when it comes to kernel code, especially when dealing with PID structures. If this isn't handled correctly, we're staring down the barrel of a memory leak or, even worse, a use-after-free scenario.
The immediate call path, `posix_cpu_timer_create` from `do_cpu_nanosleep`, doesn't necessarily scream "problem," but the context of `do_cpu_nanosleep` is what's important. It's a sleep function, so there could potentially be timer operations in this module. I need to trace this back. Specifically, I need to know the entire life cycle of this timer, the PID reference, and the associated cleanup process, because if it's not handled cleanly, we could have some real trouble. Time to dig deeper into the timer subsystem code.
|
| 113/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:do_cpu_nanosleep]
Results: map[SourceCode:1478: static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
1479: const struct timespec64 *rqtp)
1480: {
1481: struct itimerspec64 it;
1482: struct k_itimer timer;
1483: u64 expires;
1484: int error;
1485:
1486: /*
1487: * Set up a temporary timer and then wait for it to go off.
1488: */
1489: memset(&timer, 0, sizeof timer);
1490: spin_lock_init(&timer.it_lock);
1491: timer.it_clock = which_clock;
1492: timer.it_overrun = -1;
1493: error = posix_cpu_timer_create(&timer);
1494: timer.it_process = current;
1495: timer.it.cpu.nanosleep = true;
1496:
1497: if (!error) {
1498: static struct itimerspec64 zero_it;
1499: struct restart_block *restart;
1500:
1501: memset(&it, 0, sizeof(it));
1502: it.it_value = *rqtp;
1503:
1504: spin_lock_irq(&timer.it_lock);
1505: error = posix_cpu_timer_set(&timer, flags, &it, NULL);
1506: if (error) {
1507: spin_unlock_irq(&timer.it_lock);
1508: return error;
1509: }
1510:
1511: while (!signal_pending(current)) {
1512: if (!cpu_timer_getexpires(&timer.it.cpu)) {
1513: /*
1514: * Our timer fired and was reset, below
1515: * deletion can not fail.
1516: */
1517: posix_cpu_timer_del(&timer);
1518: spin_unlock_irq(&timer.it_lock);
1519: return 0;
1520: }
1521:
1522: /*
1523: * Block until cpu_timer_fire (or a signal) wakes us.
1524: */
1525: __set_current_state(TASK_INTERRUPTIBLE);
1526: spin_unlock_irq(&timer.it_lock);
1527: schedule();
1528: spin_lock_irq(&timer.it_lock);
1529: }
1530:
1531: /*
1532: * We were interrupted by a signal.
1533: */
1534: expires = cpu_timer_getexpires(&timer.it.cpu);
1535: error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
1536: if (!error) {
1537: /* Timer is now unarmed, deletion can not fail. */
1538: posix_cpu_timer_del(&timer);
1539: } else {
1540: while (error == TIMER_RETRY) {
1541: posix_cpu_timer_wait_running_nsleep(&timer);
1542: error = posix_cpu_timer_del(&timer);
1543: }
1544: }
1545:
1546: spin_unlock_irq(&timer.it_lock);
1547:
1548: if ((it.it_value.tv_sec | it.it_value.tv_nsec) == 0) {
1549: /*
1550: * It actually did fire already.
1551: */
1552: return 0;
1553: }
1554:
1555: error = -ERESTART_RESTARTBLOCK;
1556: /*
1557: * Report back to the user the time still remaining.
1558: */
1559: restart = ¤t->restart_block;
1560: restart->nanosleep.expires = ns_to_ktime(expires);
1561: if (restart->nanosleep.type != TT_NONE)
1562: error = nanosleep_copyout(restart, &it.it_value);
1563: }
1564:
1565: return error;
1566: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 114/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 71340
output: 44
thoughts: 82
Thoughts: **Investigating a Potential Resource Leak**
Hold on a minute! I'm looking at this `do_cpu_nanosleep` function and something's bugging me. It calls `posix_cpu_timer_create(&timer)` to set up a CPU timer. And then, right after, it calls `posix_cpu_timer_del(&timer)`. My immediate thought is, did that `posix_cpu_timer_del` *actually* properly release the `timer.it.cpu.pid` resource? It's easy to assume things are handled, but I need to be certain. I need to dive into the source code for `posix_cpu_timer_del` to verify that it's doing the cleanup it should be. Let me check...
|
| 115/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:posix_cpu_timer_del]
Results: map[SourceCode: 465: /*
466: * Clean up a CPU-clock timer that is about to be destroyed.
467: * This is called from timer deletion with the timer already locked.
468: * If we return TIMER_RETRY, it's necessary to release the timer's lock
469: * and try again. (This happens when the timer is in the middle of firing.)
470: */
471: static int posix_cpu_timer_del(struct k_itimer *timer)
472: {
473: struct cpu_timer *ctmr = &timer->it.cpu;
474: struct sighand_struct *sighand;
475: struct task_struct *p;
476: unsigned long flags;
477: int ret = 0;
478:
479: rcu_read_lock();
480: p = cpu_timer_task_rcu(timer);
481: if (!p)
482: goto out;
483:
484: /*
485: * Protect against sighand release/switch in exit/exec and process/
486: * thread timer list entry concurrent read/writes.
487: */
488: sighand = lock_task_sighand(p, &flags);
489: if (unlikely(sighand == NULL)) {
490: /*
491: * This raced with the reaping of the task. The exit cleanup
492: * should have removed this timer from the timer queue.
493: */
494: WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
495: } else {
496: if (timer->it.cpu.firing) {
497: /*
498: * Prevent signal delivery. The timer cannot be dequeued
499: * because it is on the firing list which is not protected
500: * by sighand->lock. The delivery path is waiting for
501: * the timer lock. So go back, unlock and retry.
502: */
503: timer->it.cpu.firing = false;
504: ret = TIMER_RETRY;
505: } else {
506: disarm_timer(timer, p);
507: }
508: unlock_task_sighand(p, &flags);
509: }
510:
511: out:
512: rcu_read_unlock();
513:
514: if (!ret) {
515: put_pid(ctmr->pid);
516: timer->it_status = POSIX_TIMER_DISARMED;
517: }
518: return ret;
519: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 116/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 72465
output: 44
thoughts: 438
Thoughts: **My Concerns Regarding Potential PID Leaks in CPU Timer Implementation**
Okay, hold on a second! I'm seeing something potentially problematic in the way these CPU timers are handled. Specifically, I'm focusing on the interaction between `posix_cpu_timer_del` and the broader error handling within functions like `do_cpu_nanosleep`. My initial thought was that `posix_cpu_timer_del` should correctly decrement the PID reference count, especially if it returns zero, as that would seem to indicate success.
But, when I dug into `do_cpu_nanosleep`, there's a specific code path that immediately throws a flag. It shows that `posix_cpu_timer_del` *might* not always be called, even after a timer has been created. The code in `do_cpu_nanosleep` seems to handle errors from `posix_cpu_timer_set` and has a loop retry of `posix_cpu_timer_del`. However, it doesn't handle the failure before the call.
Now, here's the kicker: `posix_cpu_timer_set` *directly* returns an error code in a certain path of the code. If that happens, it means we *skip* the `posix_cpu_timer_del` call. Crucially, the `timer` structure is a local variable within the `do_cpu_nanosleep` stack frame. If an error occurs *before* calling `posix_cpu_timer_del`, the `timer` goes out of scope, right? That means the `timer.it.cpu.pid` is leaked, since it won't be decremented by the timer_del function!
I need to confirm this. I need to go back and check the implementation of `posix_cpu_timer_set` very carefully to determine under what conditions it can return an error directly. I'm worried we have a significant PID leak potential here!
|
| 117/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:posix_cpu_timer_set]
Results: map[SourceCode: 616: /*
617: * Guts of sys_timer_settime for CPU timers.
618: * This is called with the timer locked and interrupts disabled.
619: * If we return TIMER_RETRY, it's necessary to release the timer's lock
620: * and try again. (This happens when the timer is in the middle of firing.)
621: */
622: static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
623: struct itimerspec64 *new, struct itimerspec64 *old)
624: {
625: bool sigev_none = timer->it_sigev_notify == SIGEV_NONE;
626: clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
627: struct cpu_timer *ctmr = &timer->it.cpu;
628: u64 old_expires, new_expires, now;
629: struct sighand_struct *sighand;
630: struct task_struct *p;
631: unsigned long flags;
632: int ret = 0;
633:
634: rcu_read_lock();
635: p = cpu_timer_task_rcu(timer);
636: if (!p) {
637: /*
638: * If p has just been reaped, we can no
639: * longer get any information about it at all.
640: */
641: rcu_read_unlock();
642: return -ESRCH;
643: }
644:
645: /*
646: * Use the to_ktime conversion because that clamps the maximum
647: * value to KTIME_MAX and avoid multiplication overflows.
648: */
649: new_expires = ktime_to_ns(timespec64_to_ktime(new->it_value));
650:
651: /*
652: * Protect against sighand release/switch in exit/exec and p->cpu_timers
653: * and p->signal->cpu_timers read/write in arm_timer()
654: */
655: sighand = lock_task_sighand(p, &flags);
656: /*
657: * If p has just been reaped, we can no
658: * longer get any information about it at all.
659: */
660: if (unlikely(sighand == NULL)) {
661: rcu_read_unlock();
662: return -ESRCH;
663: }
664:
665: /* Retrieve the current expiry time before disarming the timer */
666: old_expires = cpu_timer_getexpires(ctmr);
667:
668: if (unlikely(timer->it.cpu.firing)) {
669: /*
670: * Prevent signal delivery. The timer cannot be dequeued
671: * because it is on the firing list which is not protected
672: * by sighand->lock. The delivery path is waiting for
673: * the timer lock. So go back, unlock and retry.
674: */
675: timer->it.cpu.firing = false;
676: ret = TIMER_RETRY;
677: } else {
678: cpu_timer_dequeue(ctmr);
679: timer->it_status = POSIX_TIMER_DISARMED;
680: }
681:
682: /*
683: * Sample the current clock for saving the previous setting
684: * and for rearming the timer.
685: */
686: if (CPUCLOCK_PERTHREAD(timer->it_clock))
687: now = cpu_clock_sample(clkid, p);
688: else
689: now = cpu_clock_sample_group(clkid, p, !sigev_none);
690:
691: /* Retrieve the previous expiry value if requested. */
692: if (old) {
693: old->it_value = (struct timespec64){ };
694: if (old_expires)
695: __posix_cpu_timer_get(timer, old, now);
696: }
697:
698: /* Retry if the timer expiry is running concurrently */
699: if (unlikely(ret)) {
700: unlock_task_sighand(p, &flags);
701: goto out;
702: }
703:
704: /* Convert relative expiry time to absolute */
705: if (new_expires && !(timer_flags & TIMER_ABSTIME))
706: new_expires += now;
707:
708: /* Set the new expiry time (might be 0) */
709: cpu_timer_setexpires(ctmr, new_expires);
710:
711: /*
712: * Arm the timer if it is not disabled, the new expiry value has
713: * not yet expired and the timer requires signal delivery.
714: * SIGEV_NONE timers are never armed. In case the timer is not
715: * armed, enforce the reevaluation of the timer base so that the
716: * process wide cputime counter can be disabled eventually.
717: */
718: if (likely(!sigev_none)) {
719: if (new_expires && now < new_expires)
720: arm_timer(timer, p);
721: else
722: trigger_base_recalc_expires(timer, p);
723: }
724:
725: unlock_task_sighand(p, &flags);
726:
727: posix_timer_set_common(timer, new);
728:
729: /*
730: * If the new expiry time was already in the past the timer was not
731: * queued. Fire it immediately even if the thread never runs to
732: * accumulate more time on this clock.
733: */
734: if (!sigev_none && new_expires && now >= new_expires)
735: cpu_timer_fire(timer);
736: out:
737: rcu_read_unlock();
738: return ret;
739: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 118/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 75259
output: 44
thoughts: 1363
Thoughts: **Memory Leak in posix_cpu_timer_set for CPU Clocks**
Okay, so I've been digging into this `posix_cpu_timer_set` function, and it seems like there's a potential memory leak scenario I need to investigate further. It's triggered when `posix_cpu_timer_set` returns `-ESRCH` (No such process), which happens when the target process (represented by `p`) has just been reaped.
The critical issue is this: `do_cpu_nanosleep`, when called from `clock_nanosleep`, calls `posix_cpu_timer_set`. If `posix_cpu_timer_set` returns `-ESRCH`, `do_cpu_nanosleep` simply returns the error code without cleaning up. Crucially, `posix_cpu_timer_create` takes a reference to the `pid` (process ID) passed to the function! Specifically, the `new_timer->it.cpu.pid = get_pid(pid);` line is the culprit. And the function that releases this reference, `posix_cpu_timer_del`, is *not* called if `posix_cpu_timer_set` fails. So, the reference to the PID is leaked.
My first thought was, where would we see this in action? Let's trace it back. `do_cpu_nanosleep` is called from the `clock_nanosleep` syscall. Looking at the syscall arguments, the clock ID seems to be `0xfffffdfc`. Let's unpack this! `-516` is represented by this hex number. `CPUCLOCK_PID(clock)` is `~clock >> 3`, so `~(-516) >> 3` evaluates to `515 >> 3 = 64`. So the clock ID is for PID 64! So this would be for CPU time of process 64. If PID 64 has been reaped, and `posix_cpu_timer_set` fails, then `put_pid` is never called, and we have a memory leak of the `pid` structure.
Now, let's verify this step by step. I verified `do_cpu_nanosleep`, if an error is returned by `posix_cpu_timer_set` then it just returns without freeing the memory. Going deeper in the functions, `posix_cpu_timer_create` does take a `get_pid()` reference to the process `pid` and stores it into `new_timer->it.cpu.pid`. And, `posix_cpu_timer_del` *is* the only function that releases this reference with a `put_pid()`.
So, in the scenario where `posix_cpu_timer_set` returns an error, specifically `-ESRCH` due to a reaped PID, then the `pid` reference is leaked because `posix_cpu_timer_del` is never called.
Now, I need to check whether the process `current` can ever cause this condition. Let's dig deeper into the code that validates the process ID!
|
| 119/2 |
2026/06/01 11:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-cpu-timers.c Name:cpu_timer_task_rcu]
Results: map[SourceCode: 113: static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer)
114: {
115: return pid_task(timer->it.cpu.pid, clock_pid_type(timer->it_clock));
116: }
SourceFile:kernel/time/posix-cpu-timers.c]
|
| 120/2 |
2026/06/01 11:08 |
llm |
expert |
0m
Model:
Tokens:
input: 77474
output: 39
thoughts: 864
Thoughts: **Analyzing a Concurrency-Induced PID Leak in `do_cpu_nanosleep`**
Okay, so I'm looking at this code, specifically how `cpu_timer_task_rcu` uses `timer->it.cpu.pid`. Interesting, it *doesn't* use `timer->it_process`. That's a key observation. The problem arises when `timer->it.cpu.pid` points to a task that has been reaped β meaning it's gone. Then, `pid_task` returns `NULL`, and that's when things go south.
`posix_cpu_timer_set` subsequently returns `-ESRCH`, and this propagates back to `do_cpu_nanosleep`, which... crucially, leaks the `pid`!
Now, the question is, *how* can `pid_task` return `NULL` after `pid_for_clock` returned a valid `pid`? Ah, right, `pid_for_clock` checks `pid_has_task` under an `rcu_read_lock`. Then, `posix_cpu_timer_create` drops the lock, and later, `do_cpu_nanosleep` calls `posix_cpu_timer_set`, which reacquires it. In that gap, the task can be reaped! It's a classic race condition. Even if the task hasn't exited at the first `pid_task` call, `lock_task_sighand` can return `NULL`, still resulting in `-ESRCH` from `posix_cpu_timer_set`. So, yeah, this is definitely possible.
Wait, are there any other errors that `posix_cpu_timer_set` can return? It can return `TIMER_RETRY`, but that's handled by the caller? No! `do_cpu_nanosleep` directly returns the error:
```c
error = posix_cpu_timer_set(&timer, flags, &it, NULL);
if (error) {
spin_unlock_irq(&timer.it_lock);
return error;
}
```
If it returns `TIMER_RETRY`, it also returns directly. But `TIMER_RETRY` only happens if `timer->it.cpu.firing` is true, and the timer's not firing when newly created, so that's not the issue.
Okay, so the bug is precisely this: `do_cpu_nanosleep` leaks the `timer.it.cpu.pid` if `posix_cpu_timer_set` returns an error. This occurs when the target task exits concurrently.
The reproducer calls `clock_nanosleep` with a PID of `-516`. This means PID 64. Syzkaller creates many tasks, and PID 64 is likely one of them. This is the source of the leak, because it's triggering the race.
So, this is a `struct pid` memory leak. Can we exploit it? Typically, a memory leak isn't a direct path to code execution or privilege escalation. It's more likely a Denial of Service (DoS) issue, leading to OOM (Out Of Memory) conditions. Can an unprivileged user trigger this? Yes, `clock_nanosleep` is accessible to unprivileged users, and it can be triggered from a user namespace too. Remote attack? No, local syscall execution is needed.
Let's double-check if `do_cpu_nanosleep` is the *only* place. What about `sys_timer_create`?
|
| 121/2 |
2026/06/01 11:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/time/posix-timers.c Name:do_timer_create]
Results: map[SourceCode: 457: /* Create a POSIX.1b interval timer. */
458: static int do_timer_create(clockid_t which_clock, struct sigevent *event,
459: timer_t __user *created_timer_id)
460: {
461: const struct k_clock *kc = clockid_to_kclock(which_clock);
462: timer_t req_id = TIMER_ANY_ID;
463: struct k_itimer *new_timer;
464: int error, new_timer_id;
465:
466: if (!kc)
467: return -EINVAL;
468: if (!kc->timer_create)
469: return -EOPNOTSUPP;
470:
471: /* Special case for CRIU to restore timers with a given timer ID. */
472: if (unlikely(current->signal->timer_create_restore_ids)) {
473: if (copy_from_user(&req_id, created_timer_id, sizeof(req_id)))
474: return -EFAULT;
475: /* Valid IDs are 0..INT_MAX */
476: if ((unsigned int)req_id > INT_MAX)
477: return -EINVAL;
478: }
479:
480: new_timer = alloc_posix_timer();
481: if (unlikely(!new_timer))
482: return -EAGAIN;
483:
484: spin_lock_init(&new_timer->it_lock);
485:
486: /*
487: * Add the timer to the hash table. The timer is not yet valid
488: * after insertion, but has a unique ID allocated.
489: */
490: new_timer_id = posix_timer_add(new_timer, req_id);
491: if (new_timer_id < 0) {
492: posixtimer_free_timer(new_timer);
493: return new_timer_id;
494: }
495:
496: new_timer->it_clock = which_clock;
497: new_timer->kclock = kc;
498: new_timer->it_overrun = -1LL;
499:
500: if (event) {
501: scoped_guard (rcu)
502: new_timer->it_pid = get_pid(good_sigevent(event));
503: if (!new_timer->it_pid) {
504: error = -EINVAL;
505: goto out;
506: }
507: new_timer->it_sigev_notify = event->sigev_notify;
508: new_timer->sigq.info.si_signo = event->sigev_signo;
509: new_timer->sigq.info.si_value = event->sigev_value;
510: } else {
511: new_timer->it_sigev_notify = SIGEV_SIGNAL;
512: new_timer->sigq.info.si_signo = SIGALRM;
513: new_timer->sigq.info.si_value.sival_int = new_timer->it_id;
514: new_timer->it_pid = get_pid(task_tgid(current));
515: }
516:
517: if (new_timer->it_sigev_notify & SIGEV_THREAD_ID)
518: new_timer->it_pid_type = PIDTYPE_PID;
519: else
520: new_timer->it_pid_type = PIDTYPE_TGID;
521:
522: new_timer->sigq.info.si_tid = new_timer->it_id;
523: new_timer->sigq.info.si_code = SI_TIMER;
524:
525: if (copy_to_user(created_timer_id, &new_timer_id, sizeof (new_timer_id))) {
526: error = -EFAULT;
527: goto out;
528: }
529: /*
530: * After successful copy out, the timer ID is visible to user space
531: * now but not yet valid because new_timer::signal low order bit is 1.
532: *
533: * Complete the initialization with the clock specific create
534: * callback.
535: */
536: error = kc->timer_create(new_timer);
537: if (error)
538: goto out;
539:
540: /*
541: * timer::it_lock ensures that __lock_timer() observes a fully
542: * initialized timer when it observes a valid timer::it_signal.
543: *
544: * sighand::siglock is required to protect signal::posix_timers.
545: */
546: scoped_guard (spinlock_irq, &new_timer->it_lock) {
547: guard(spinlock)(¤t->sighand->siglock);
548: /*
549: * new_timer::it_signal contains the signal pointer with
550: * bit 0 set, which makes it invalid for syscall operations.
551: * Store the unmodified signal pointer to make it valid.
552: */
553: WRITE_ONCE(new_timer->it_signal, current->signal);
554: hlist_add_head_rcu(&new_timer->list, ¤t->signal->posix_timers);
555: }
556: /*
557: * After unlocking @new_timer is subject to concurrent removal and
558: * cannot be touched anymore
559: */
560: return 0;
561: out:
562: posix_timer_unhash_and_free(new_timer);
563: return error;
564: }
SourceFile:kernel/time/posix-timers.c]
|
| 122/2 |
2026/06/01 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 80929
output: 66
thoughts: 2126
Thoughts: **Analysis of a Kernel CPU Timer Memory Leak**
Okay, let's break this down systematically. I'm focusing on the `do_cpu_nanosleep` function and how it interacts with CPU timers. The core issue seems to be a potential leak of a `struct pid` reference under specific error conditions.
First, I see that `do_timer_create` indirectly calls `posix_cpu_timer_create` for CPU clocks. That function can fail, and the code handles those failure cases gracefully, releasing resources and returning an error. Specifically, the error handling path (`out:`) in the code calls `posix_timer_unhash_and_free(new_timer)`, which should clean up anything that went wrong, so that path looks safe.
The real problem arises within `do_cpu_nanosleep`. I see the `posix_cpu_timer_create` call succeeded, and crucially, it sets `new_timer->it.cpu.pid = get_pid(pid)`. This `get_pid` call *increments* the reference count of the `struct pid`. Now I'm looking at what happens if a `copy_to_user` fails; it bails before the call to `posix_cpu_timer_create`, which means no leak there.
However, if `posix_cpu_timer_set` *fails* after the `posix_cpu_timer_create` call succeeds, there's a problem. The code simply returns the error directly, *without* calling `posix_cpu_timer_del(&timer)` which would release the `pid` reference. The timer struct is allocated on the stack. Boom! We have a leak. It's a clear memory leak of `struct pid`!
I'm now thinking about what conditions could lead to `posix_cpu_timer_set` failing. The code mentions it returns `-ESRCH` if the target task is reaped. Let me confirm this behavior. Yes, `-ESRCH` is returned when `pid_task` returns `NULL`. That happens if the task is exiting (or already exited). So, if the target task of `clock_nanosleep` is concurrently exiting, the `pid_task` call in `posix_cpu_timer_set` can return NULL and lead to the leak. The code checks `pid_has_task` so the task must be alive, but can be reaped after this check.
It is a simple and straightforward memory leak. It can't be exploited for privilege escalation or code execution, just DoS by leaking memory until the system is OOM. It is accessible to unprivileged processes and even within user namespaces. This leak is not remotely exploitable - local syscalls are required.
To check for similar problems, let me verify the same leak doesn't exist for timers created via `timer_create` and used with `timer_settime`. If `kc->timer_set` returns `-ESRCH`, the timer isn't destroyed immediately, so the process still holds a reference. But on process exit, `exit_itimers` will clean up and call `kc->timer_del`, which would call `posix_cpu_timer_del` and release the pid reference in that case. So, it's NOT a general problem, it is specific to the local timer in `do_cpu_nanosleep`.
The fix is clear: if `posix_cpu_timer_set` returns an error, we MUST call `posix_cpu_timer_del(&timer)` to release the `pid` reference. Let's make sure the calls are compatible. The timer is already locked at the moment of the error return, which satisfies the `posix_cpu_timer_del` requirement.
So, the proposed fix: within `do_cpu_nanosleep`, if `posix_cpu_timer_set` fails, then `posix_cpu_timer_del(&timer)` must be called before returning.
The `posix_cpu_timer_del` can return `TIMER_RETRY`, but newly created timers can never be in the firing state, so it doesn't matter. The only possible return from `posix_cpu_timer_set` is `-ESRCH` which does not require a retry.
I am pretty confident in this analysis.
|
| 123/2 |
2026/06/01 11:09 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 124/2 |
2026/06/01 11:09 |
llm |
expert |
0m
Model:
Tokens:
input: 84122
output: 645
thoughts: 399
Thoughts: **My Analysis Concluded: The Memory Leak in `do_cpu_nanosleep()`**
Alright, the analysis is done, and it's time to craft the final response. My findings are quite specific: we've got a memory leak in the kernel, stemming from the `do_cpu_nanosleep()` function. Specifically, it's a leak of the `struct pid` object.
The root cause lies in how `clock_nanosleep()` handles CPU clocks tied to specific processes. When a call with a process ID is made (like `CLOCK_MONOTONIC_RAW | 0xfffffdf8`), the system spins up a temporary POSIX CPU timer on the stack using `posix_cpu_timer_create()`. Crucially, this function grabs a reference to the target process's `struct pid` using `get_pid()`.
Here's where it goes sideways. `do_cpu_nanosleep()` then tries to set up the timer using `posix_cpu_timer_set()`. The vulnerability creeps in when the target process exits and is reaped *concurrently*. `posix_cpu_timer_set()` might fail in this case, returning `-ESRCH` (No such process).
The key problem? The function immediately returns that error code without cleaning up the temporary timer. This is the critical code path:
```c
error = posix_cpu_timer_set(&timer, flags, &it, NULL);
if (error) {
spin_unlock_irq(&timer.it_lock);
return error; // LEAK!
}
```
Because `posix_cpu_timer_del(&timer)` is never called on this error path, the reference to the `struct pid` is never released ( `put_pid()` isn't called). Thus, that `struct pid` is leaked, leading to memory bloat.
The good news is that it can't be used for code execution or privilege escalation. But the bad news is that any unprivileged user can trigger this by repeatedly calling `clock_nanosleep()` on a CPU clock for a concurrently exiting thread. This can be exploited to exhaust kernel memory and cause an Out-Of-Memory condition, resulting in a local Denial of Service. Now that I have summarized all of my thoughts and findings I am confident that I have provided you with a sufficient explanation.
|
| 125/1 |
2026/06/01 11:09 |
action |
format-explanation |
0m
Results: map[Explanation:The bug report indicates a memory leak of a `struct pid` object. Based on the
provided reproducer and kernel source code, the leak occurs in the
`clock_nanosleep` system call when dealing with CPU clocks of specific
processes.
### Root Cause Analysis
When `clock_nanosleep()` is invoked with a CPU clock targeting a specific
process (e.g., encoded in the `clockid_t`), it eventually calls
`do_cpu_nanosleep()` in `kernel/time/posix-cpu-timers.c`.
1. `do_cpu_nanosleep()` initializes a temporary `struct k_itimer` on the stack
and calls `posix_cpu_timer_create(&timer)`.
2. `posix_cpu_timer_create()` looks up the target `struct pid` based on the
`clockid_t` and takes a reference to it via `get_pid(pid)`, storing it in
`timer->it.cpu.pid`.
3. Next, `do_cpu_nanosleep()` attempts to arm this temporary timer by calling
`posix_cpu_timer_set()`.
4. If the target process has concurrently exited and been reaped,
`posix_cpu_timer_set()` fails to find the associated task (as `pid_task()`
returns `NULL`) and returns `-ESRCH`.
5. When `posix_cpu_timer_set()` returns an error, `do_cpu_nanosleep()` handles
it as follows:
```c
spin_lock_irq(&timer.it_lock);
error = posix_cpu_timer_set(&timer, flags, &it, NULL);
if (error) {
spin_unlock_irq(&timer.it_lock);
return error; // <--- BUG: timer is not deleted
}
```
Because it directly returns the error, it skips calling
`posix_cpu_timer_del(&timer)`. Since `posix_cpu_timer_del()` is the only place
that drops the `struct pid` reference (via `put_pid()`) for CPU timers, the
reference is permanently leaked.
### Security Impact
* **Exploitable:** No. This is a pure reference counting leak of a `struct pid`.
It does not lead to use-after-free, memory corruption, or privilege escalation.
* **Denial of Service:** Yes. An attacker can repeatedly spawn threads, target
them with `clock_nanosleep()`, and exit them concurrently to leak `struct pid`
objects. This will eventually exhaust kernel memory and cause a system-wide
Denial of Service (OOM).
* **Accessible From Unprivileged Processes / User Namespaces:** Yes. Any local
unprivileged user can create threads and call `clock_nanosleep()` on them. No
special capabilities are required.
* **Remote / Network / Peripheral / Filesystem Trigger:** No. The bug requires
local system call execution (`clock_nanosleep`).]
|