| 0/0 |
2026/07/30 00:00 |
flow |
assessment-security |
42m
Results: map[DenialOfService:true Explanation:**Bug Analysis:**
The bug is located in the `f_uac2_opts_p_srate_store` function (and similarly in
other rate attribute store functions like `c_srate` in `f_uac1.c` and
`f_uac2.c`), which is generated by the `UAC2_RATE_ATTRIBUTE` macro.
When a user writes a comma-separated list of sample rates to the configfs
attribute, the code duplicates the input string using `kstrdup` and parses it
using `strsep`:
```c
split_page = kstrdup(page, GFP_KERNEL);
while ((token = strsep(&split_page, ",")) != NULL) {
ret = kstrtou32(token, 0, &num);
if (ret)
goto end;
// ...
};
end:
kfree(split_page);
```
The `strsep` function modifies the `split_page` pointer to point to the
beginning of the *next* token.
This leads to two severe issues:
1. **Memory Leak:** If the string is parsed successfully to the end,
`split_page` becomes `NULL`. The subsequent `kfree(NULL)` does nothing, and the
original pointer returned by `kstrdup` is leaked. This is the issue caught by
the syzkaller report.
2. **Invalid Free (Memory Corruption):** If an invalid token is encountered in
the middle of the string (e.g., writing `"44100,invalid,more"`), `kstrtou32`
will fail and the code will jump to the `end` label. At this point, `split_page`
has been advanced by `strsep` and points to the middle of the allocated buffer
(e.g., pointing to `"more"`). Calling `kfree()` on this interior pointer will
corrupt the SLUB allocator's freelist. This allows an attacker to obtain
overlapping object allocations, which is a powerful primitive for privilege
escalation and arbitrary code execution.
**Accessibility:**
Despite the severe nature of the bug, it is highly restricted in terms of
accessibility. The vulnerable code is only reachable via the USB Gadget Configfs
interface (typically mounted at `/sys/kernel/config/usb_gadget/`).
- Configfs directories and files are owned by `root` and are created with
restricted permissions (e.g., `0644` for attributes, meaning only the owner can
write to them).
- Configfs does not have the `FS_USERNS_MOUNT` flag, meaning it cannot be
mounted inside an unprivileged user namespace. Even if a user namespace could
access the host's mounted configfs, the files are owned by the global root
(`kuid 0`), preventing write access.
- Therefore, the bug can only be triggered by the global root user.
**Conclusion:**
- **Exploitable:** Yes. The interior pointer free corrupts the SLUB freelist,
leading to overlapping allocations and memory corruption.
- **Denial of Service:** Yes. The memory leak can exhaust system memory, and the
invalid free will crash the kernel or corrupt memory.
- **Accessible From Unprivileged Processes:** No. Requires global root
privileges to write to configfs.
- **Accessible From User Namespaces:** No. Configfs cannot be mounted or written
to from unprivileged user namespaces.
- **Other Triggers:** No. This is a local configuration interface, not reachable
via network, malicious USB hosts, or malicious filesystems. Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/07/30 00:00 |
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=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*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=*/0x1000, /*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)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 00} (length 0xb)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000140, "./myconfig\000", 11);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000140ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 00} (length 0xb)
// }
// type: ptr[in, buffer] {
// buffer: {63 6f 6e 66 69 67 66 73 00} (length 0x9)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x2000000001c0, "./myconfig\000", 11);
memcpy((void*)0x200000000200, "configfs\000", 9);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x2000000001c0ul, /*type=*/0x200000000200ul, /*flags=*/0ul, /*data=*/0ul);
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 00} (length 0x19)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000240, "./myconfig/usb_gadget/g1\000", 25);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000240ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 2f 66 75 6e 63 74 69 6f 6e 73 2f 75 61 63 32 2e 75 73 62 30 00} (length 0x2d)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x2000000003c0, "./myconfig/usb_gadget/g1/functions/uac2.usb0\000", 45);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x2000000003c0ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 2f 66 75 6e 63 74 69 6f 6e 73 2f 75 61 63 32 2e 75 73 62 30 2f 70 5f 73 72 61 74 65 00} (length 0x35)
// }
// flags: open_flags = 0x1 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000400, "./myconfig/usb_gadget/g1/functions/uac2.usb0/p_srate\000", 53);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000400ul, /*flags=O_WRONLY*/1, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {34 34 31 30 30 2c 34 38 30 30 30 2c 38 38 32 30 30 2c 39 36 30 30 30 2c 31 37 36 34 30 30 2c 31 39 32 30 30 30 2c 33 35 32 38 30 30 2c 33 38 34 30 30 30 2c 37 30 35 36 30} (length 0x39)
// }
// count: len = 0x39 (8 bytes)
// ]
memcpy((void*)0x200000000440, "44100,48000,88200,96000,176400,192000,352800,384000,70560", 57);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x200000000440ul, /*count=*/0x39ul);
return 0;
}
]
|
| 2/1 |
2026/07/30 00:00 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/a43694d4bed4bc357b0c64e52341ff394417331e]
|
| 3/1 |
2026/07/30 00:01 |
action |
kernel-builder |
22m
Results: map[KernelObj:/app/workdir/cache/build/e2d185ac96847fcbf6e12143580e9916221d817b]
|
| 4/1 |
2026/07/30 00:23 |
action |
codesearch-prepare |
14m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/07/30 00:38 |
agent |
expert |
4m
Model:
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false 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, elevated privileges, or an information leak.
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.
Information leaks are exploitable on their own and should be classified as such. A bug that copies kernel
memory contents to userspace (e.g. an out-of-bounds read whose result is returned to the caller, or
uninitialized stack/heap bytes written to a user buffer) is exploitable: it can reveal kernel pointer
values and defeat KASLR, expose sensitive data such as cryptographic keys or other processes' memory, and
serves as a necessary building block in most modern kernel privilege-escalation exploit chains. Do not classify
an information leak as non-exploitable solely because it does not directly cause a memory write or control-flow
hijack; the leak itself is the exploit primitive.
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:
2026/07/29 19:24:36 executed programs: 7
BUG: memory leak
unreferenced object 0xffff888112f1fd80 (size 64):
comm "syz.0.21", pid 5964, jiffies 4294942888
hex dump (first 32 bytes):
34 34 31 30 30 00 34 38 30 30 30 00 38 38 32 30 44100.48000.8820
30 00 39 36 30 30 30 00 31 37 36 34 30 30 00 31 0.96000.176400.1
backtrace (crc 6cdecf20):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4597 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
__do_kmalloc_node mm/slub.c:5333 [inline]
__kmalloc_node_track_caller_noprof+0x3d3/0x570 mm/slub.c:5471
__kmemdup_nul mm/util.c:64 [inline]
kstrdup+0x3c/0x80 mm/util.c:84
f_uac2_opts_p_srate_store+0xbb/0x170 drivers/usb/gadget/function/f_uac2.c:2087
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x3ac/0x720 fs/read_write.c:687
ksys_write+0xa5/0x170 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf8/0x610 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
BUG: memory leak
unreferenced object 0xffff888113454dc0 (size 64):
comm "syz.0.23", pid 5967, jiffies 4294943452
hex dump (first 32 bytes):
34 34 31 30 30 00 34 38 30 30 30 00 38 38 32 30 44100.48000.8820
30 00 39 36 30 30 30 00 31 37 36 34 30 30 00 31 0.96000.176400.1
backtrace (crc 6cdecf20):
kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline]
slab_post_alloc_hook mm/slub.c:4597 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
__do_kmalloc_node mm/slub.c:5333 [inline]
__kmalloc_node_track_caller_noprof+0x3d3/0x570 mm/slub.c:5471
__kmemdup_nul mm/util.c:64 [inline]
kstrdup+0x3c/0x80 mm/util.c:84
f_uac2_opts_p_srate_store+0xbb/0x170 drivers/usb/gadget/function/f_uac2.c:2087
flush_write_buffer fs/configfs/file.c:207 [inline]
configfs_write_iter+0x10d/0x1a0 fs/configfs/file.c:229
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x3ac/0x720 fs/read_write.c:687
ksys_write+0xa5/0x170 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf8/0x610 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=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*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=*/0x1000, /*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)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 00} (length 0xb)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000140, "./myconfig\000", 11);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000140ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 00} (length 0xb)
// }
// type: ptr[in, buffer] {
// buffer: {63 6f 6e 66 69 67 66 73 00} (length 0x9)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x2000000001c0, "./myconfig\000", 11);
memcpy((void*)0x200000000200, "configfs\000", 9);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x2000000001c0ul, /*type=*/0x200000000200ul, /*flags=*/0ul, /*data=*/0ul);
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 00} (length 0x19)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000240, "./myconfig/usb_gadget/g1\000", 25);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000240ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 2f 66 75 6e 63 74 69 6f 6e 73 2f 75 61 63 32 2e 75 73 62 30 00} (length 0x2d)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x2000000003c0, "./myconfig/usb_gadget/g1/functions/uac2.usb0\000", 45);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x2000000003c0ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 6d 79 63 6f 6e 66 69 67 2f 75 73 62 5f 67 61 64 67 65 74 2f 67 31 2f 66 75 6e 63 74 69 6f 6e 73 2f 75 61 63 32 2e 75 73 62 30 2f 70 5f 73 72 61 74 65 00} (length 0x35)
// }
// flags: open_flags = 0x1 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000400, "./myconfig/usb_gadget/g1/functions/uac2.usb0/p_srate\000", 53);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000400ul, /*flags=O_WRONLY*/1, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {34 34 31 30 30 2c 34 38 30 30 30 2c 38 38 32 30 30 2c 39 36 30 30 30 2c 31 37 36 34 30 30 2c 31 39 32 30 30 30 2c 33 35 32 38 30 30 2c 33 38 34 30 30 30 2c 37 30 35 36 30} (length 0x39)
// }
// count: len = 0x39 (8 bytes)
// ]
memcpy((void*)0x200000000440, "44100,48000,88200,96000,176400,192000,352800,384000,70560", 57);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x200000000440ul, /*count=*/0x39ul);
return 0;
}
Reply: **Bug Analysis:**
The bug is located in the `f_uac2_opts_p_srate_store` function (and similarly in other rate attribute store functions like `c_srate` in `f_uac1.c` and `f_uac2.c`), which is generated by the `UAC2_RATE_ATTRIBUTE` macro.
When a user writes a comma-separated list of sample rates to the configfs attribute, the code duplicates the input string using `kstrdup` and parses it using `strsep`:
```c
split_page = kstrdup(page, GFP_KERNEL);
while ((token = strsep(&split_page, ",")) != NULL) {
ret = kstrtou32(token, 0, &num);
if (ret)
goto end;
// ...
};
end:
kfree(split_page);
```
The `strsep` function modifies the `split_page` pointer to point to the beginning of the *next* token.
This leads to two severe issues:
1. **Memory Leak:** If the string is parsed successfully to the end, `split_page` becomes `NULL`. The subsequent `kfree(NULL)` does nothing, and the original pointer returned by `kstrdup` is leaked. This is the issue caught by the syzkaller report.
2. **Invalid Free (Memory Corruption):** If an invalid token is encountered in the middle of the string (e.g., writing `"44100,invalid,more"`), `kstrtou32` will fail and the code will jump to the `end` label. At this point, `split_page` has been advanced by `strsep` and points to the middle of the allocated buffer (e.g., pointing to `"more"`). Calling `kfree()` on this interior pointer will corrupt the SLUB allocator's freelist. This allows an attacker to obtain overlapping object allocations, which is a powerful primitive for privilege escalation and arbitrary code execution.
**Accessibility:**
Despite the severe nature of the bug, it is highly restricted in terms of accessibility. The vulnerable code is only reachable via the USB Gadget Configfs interface (typically mounted at `/sys/kernel/config/usb_gadget/`).
- Configfs directories and files are owned by `root` and are created with restricted permissions (e.g., `0644` for attributes, meaning only the owner can write to them).
- Configfs does not have the `FS_USERNS_MOUNT` flag, meaning it cannot be mounted inside an unprivileged user namespace. Even if a user namespace could access the host's mounted configfs, the files are owned by the global root (`kuid 0`), preventing write access.
- Therefore, the bug can only be triggered by the global root user.
**Conclusion:**
- **Exploitable:** Yes. The interior pointer free corrupts the SLUB freelist, leading to overlapping allocations and memory corruption.
- **Denial of Service:** Yes. The memory leak can exhaust system memory, and the invalid free will crash the kernel or corrupt memory.
- **Accessible From Unprivileged Processes:** No. Requires global root privileges to write to configfs.
- **Accessible From User Namespaces:** No. Configfs cannot be mounted or written to from unprivileged user namespaces.
- **Other Triggers:** No. This is a local configuration interface, not reachable via network, malicious USB hosts, or malicious filesystems.
|
| 6/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 9491
output: 32
thoughts: 311
Thoughts: **Memory Leak Debugging: A Deep Dive**
Okay, so I've got a memory leak report specifically targeting `f_uac2_opts_p_srate_store` within `drivers/usb/gadget/function/f_uac2.c`. The backtrace is pretty clear, pointing directly to the root cause: a leak triggered within that function. I can see the trail starting with `kmemleak_alloc_recursive`, moving through the `slab` allocator (`slab_post_alloc_hook`, `slab_alloc_node`, etc.), and culminating in `f_uac2_opts_p_srate_store` itself. The crucial function for me to focus on here, based on the backtrace, is likely `kstrdup`.
My analysis starts with line 2087 within `f_uac2_opts_p_srate_store`. It looks like it is calling `kstrdup`, which means itβs duplicating a string. If this memory is allocated and never freed, that's exactly where the leak will be. I need to figure out where that duplicated string is being used and whether the memory is appropriately released, especially if error conditions are present or if the string is only needed temporarily. I need to meticulously examine the context of the `kstrdup` call to understand the allocation and deallocation lifecycle of the string, checking for missed `kfree` calls, or improper error handling. This backtrace provides a great starting point.
|
| 7/2 |
2026/07/30 00:38 |
tool |
codesearch-definition-source |
0m
Args: map[Name:f_uac2_opts_p_srate_store]
Results: map[SourceCode:2087: UAC2_RATE_ATTRIBUTE(p_srate);
SourceFile:drivers/usb/gadget/function/f_uac2.c]
|
| 8/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 10210
output: 25
thoughts: 22
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience:
**Analyzing the Macro: UAC2_RATE_ATTRIBUTE**
Right, this is definitely a macro. Let's see... the mention of `UAC2_RATE_ATTRIBUTE` immediately triggers my interest. I need to understand what this macro is doing within the context. Is it a defined constant? An inline function? Is it likely part of an Audio Class 2 (UAC2) implementation? If so, this probably defines or refers to a specific attribute related to sample rates or clock rates within a USB Audio Class 2 device's descriptors. Depending on the architecture, this macro could be expanding to a structure member, bitfield, or a value. I'll need to dig into the relevant header files or the encompassing source code to decipher its precise function and purpose within this system, especially in relation to audio data transfer and synchronization. I'll be particularly interested in whether it relates to clock frequency, sampling rate negotiation, or even potential rate limiting mechanisms. The potential implication is it could be critical in managing and setting the device's clock rate properly.
|
| 9/2 |
2026/07/30 00:38 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[Name:UAC2_RATE_ATTRIBUTE]
Results: map[SourceCode: SourceFile:]
|
| 10/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 10516
output: 21
thoughts: 14
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Grasping for the UAC2 Rate Attribute**
Okay, so I'm thinking... I need to find something specific related to the UAC2 audio interface rate. My mental search immediately brings up the `UAC2_RATE_ATTRIBUTE`. That's the key. I need to dive into the codebase and quickly locate all instances of this term. I'm imagining a `grep` operation is going to be my best friend right now. It'll allow me to rapidly pinpoint any configurations, definitions, or code sections that are interacting with the sampling rate within the UAC2 framework. This is the starting point to understand the specifics.
|
| 11/2 |
2026/07/30 00:38 |
tool |
grepper |
0m
Args: map[Expression:UAC2_RATE_ATTRIBUTE]
Results: map[Output:drivers/usb/gadget/function/f_uac2.c=1986=CONFIGFS_ATTR(f_uac2_opts_, name)
drivers/usb/gadget/function/f_uac2.c-1987-
drivers/usb/gadget/function/f_uac2.c:1988:#define UAC2_RATE_ATTRIBUTE(name) \
drivers/usb/gadget/function/f_uac2.c-1989-static ssize_t f_uac2_opts_##name##_show(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac2.c=2086=UAC2_ATTRIBUTE(u32, p_chmask);
drivers/usb/gadget/function/f_uac2.c:2087:UAC2_RATE_ATTRIBUTE(p_srate);
drivers/usb/gadget/function/f_uac2.c-2088-UAC2_ATTRIBUTE(u32, p_ssize);
--
drivers/usb/gadget/function/f_uac2.c=2090=UAC2_ATTRIBUTE(u32, c_chmask);
drivers/usb/gadget/function/f_uac2.c:2091:UAC2_RATE_ATTRIBUTE(c_srate);
drivers/usb/gadget/function/f_uac2.c-2092-UAC2_ATTRIBUTE_SYNC(c_sync);
]
|
| 12/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 11088
output: 45
thoughts: 30
Thoughts: Okay, let's dive into this. Here's my take on those lines in `f_uac2.c`:
**Analyzing `f_uac2.c` at Line 1988**
Alright, I'm heading over to `drivers/usb/gadget/function/f_uac2.c` and focusing around line 1988. I need to refresh my memory on how this audio gadget handles requests. I'm expecting to see something related to either setting up an audio stream, handling control requests for the device, or maybe even an interrupt related to an isochronous transfer. Based on the surrounding code, I'm anticipating this area to be critical in managing the data flow or configuration of the UAC2 device. Let me check the context, specifically what variables are involved and what functions are being called. I bet it's something about managing the endpoints, setting up buffers, or error handling around those isochronous transactions. Time to get to the core of this gadget driver!
|
| 13/2 |
2026/07/30 00:38 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/function/f_uac2.c FirstLine:1988 LineCount:50]
Results: map[Contents:1988: #define UAC2_RATE_ATTRIBUTE(name) \
1989: static ssize_t f_uac2_opts_##name##_show(struct config_item *item, \
1990: char *page) \
1991: { \
1992: struct f_uac2_opts *opts = to_f_uac2_opts(item); \
1993: int result = 0; \
1994: int i; \
1995: \
1996: mutex_lock(&opts->lock); \
1997: page[0] = '\0'; \
1998: for (i = 0; i < UAC_MAX_RATES; i++) { \
1999: if (opts->name##s[i] == 0) \
2000: break; \
2001: result += sprintf(page + strlen(page), "%u,", \
2002: opts->name##s[i]); \
2003: } \
2004: if (strlen(page) > 0) \
2005: page[strlen(page) - 1] = '\n'; \
2006: mutex_unlock(&opts->lock); \
2007: \
2008: return result; \
2009: } \
2010: \
2011: static ssize_t f_uac2_opts_##name##_store(struct config_item *item, \
2012: const char *page, size_t len) \
2013: { \
2014: struct f_uac2_opts *opts = to_f_uac2_opts(item); \
2015: char *split_page = NULL; \
2016: int ret = -EINVAL; \
2017: char *token; \
2018: u32 num; \
2019: int i; \
2020: \
2021: mutex_lock(&opts->lock); \
2022: if (opts->refcnt) { \
2023: ret = -EBUSY; \
2024: goto end; \
2025: } \
2026: \
2027: i = 0; \
2028: memset(opts->name##s, 0x00, sizeof(opts->name##s)); \
2029: split_page = kstrdup(page, GFP_KERNEL); \
2030: while ((token = strsep(&split_page, ",")) != NULL) { \
2031: ret = kstrtou32(token, 0, &num); \
2032: if (ret) \
2033: goto end; \
2034: \
2035: opts->name##s[i++] = num; \
2036: ret = len; \
2037: }; \
]
|
| 14/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 12234
output: 45
thoughts: 10
Thoughts: Okay, I'm ready to summarize my "thoughts" as a process. Here we go:
**Analyzing the Macro's Structure**
Alright, the instruction is clear: I need to delve into the remaining components of the macro. Let's see what's left to evaluate. I'm focusing on parsing the entire structure to identify the relationship of parts and determine it's function. I will examine how the components interact, and what the overall effect will be. Let's get to it.
|
| 15/2 |
2026/07/30 00:38 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/function/f_uac2.c FirstLine:2038 LineCount:20]
Results: map[Contents:2038: \
2039: end: \
2040: kfree(split_page); \
2041: mutex_unlock(&opts->lock); \
2042: return ret; \
2043: } \
2044: \
2045: CONFIGFS_ATTR(f_uac2_opts_, name)
2046:
2047: #define UAC2_ATTRIBUTE_STRING(name) \
2048: static ssize_t f_uac2_opts_##name##_show(struct config_item *item, \
2049: char *page) \
2050: { \
2051: struct f_uac2_opts *opts = to_f_uac2_opts(item); \
2052: int result; \
2053: \
2054: mutex_lock(&opts->lock); \
2055: result = sysfs_emit(page, "%s", opts->name); \
2056: mutex_unlock(&opts->lock); \
2057: \
]
|
| 16/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 12717
output: 31
thoughts: 1220
Thoughts: **Memory Leak in UAC2 Configuration Parsing**
Okay, so I've been looking at this `f_uac2_opts_p_srate_store` function, which is generated by the `UAC2_RATE_ATTRIBUTE(p_srate)` macro. My initial thought is that the core issue is within this `f_uac2_opts_##name##_store` function. Specifically, it seems like there's a memory leak stemming from how it parses the configuration data.
I see that it uses `kstrdup(page, GFP_KERNEL)` to duplicate the input string `page` into `split_page`. Then, it uses `strsep(&split_page, ",")` to tokenize the string, looking for comma-separated values. The problem is now clear, `strsep` is modifying the `split_page` pointer, advancing it with each call. After the loop completes, it's very possible (and likely, if the entire string is parsed) that `split_page` will be `NULL`. So `kfree(split_page)` frees the *wrong* pointer, or potentially a `NULL` pointer.
Now, that's where the leak is: `kstrdup` allocates memory at the beginning of the `split_page` pointer, and the `strsep` loop progresses this pointer to the end, or `NULL`. Then `kfree` is called, and a dangling pointer is lost, leaking the original allocated memory returned by `kstrdup`.
I need to confirm `strsep`'s behavior, I have to be sure it's updating `*s`. Yes, it does, `strsep` updates `*s` to point past the token. If the loop completes, `split_page` becomes `NULL`. Then `kfree(NULL)` does nothing (is safe). The original pointer returned by `kstrdup` is lost and never freed. This is definitely a classic memory leak.
So, the next question is, is this exploitable? It's a memory leak, which is concerning. A user can write to this configfs attribute, which means they can trigger the memory leak. The critical thing here is *who* can access configfs? Is it accessible to an unprivileged user? The default location is `/sys/kernel/config`. Is it owned by root, and what are the default permissions?
Now, let's see how syzkaller is reproducing the mount. They're making a mount in a user namespace. The key is in the mount syscall. They're making a call to `mount`, which means they likely have the permissions to do so (or are setting up a user namespace). They're creating a user namespace, and mounting configfs there, it appears. This suggests they can mount configfs if the system allows this. I need to investigate if configfs has `FS_USERNS_MOUNT` set, which would indicate if mounting is allowed in user namespaces.
|
| 17/2 |
2026/07/30 00:38 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/configfs]
Results:
|
| 18/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 14614
output: 36
thoughts: 22
Thoughts: Here's my thought process, as if I were considering this code:
**Diving into the ConfigFS Mount Code**
Okay, so I need to understand how ConfigFS mounts are handled. I immediately think to start with `fs/configfs/mount.c`. That's the logical place to find the core mounting logic. The crucial piece I'm going to be looking for is the `file_system_type` structure. It's the bread and butter of how the VFS sees and interacts with the filesystem. That structure will contain all the necessary details to register ConfigFS as a filesystem and define the operations that can be performed on it. Let's see how that's defined and used within this mounting context. I want to see how the system identifies the ConfigFS type and if there are any specific initialization steps or idiosyncrasies that might be relevant here. Let's dig in and see what we find.
|
| 19/2 |
2026/07/30 00:38 |
tool |
grepper |
0m
Args: map[Expression:struct file_system_type configfs_fs_type PathPrefix:fs/configfs]
Results: map[Output:fs/configfs/mount.c=109=static int configfs_init_fs_context(struct fs_context *fc)
--
fs/configfs/mount.c-114-
fs/configfs/mount.c:115:static struct file_system_type configfs_fs_type = {
fs/configfs/mount.c-116- .owner = THIS_MODULE,
]
|
| 20/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 14979
output: 36
thoughts: 21
Thoughts: Here's a summary of my thought process, as requested:
**Diving into the ConfigFS Mounting Code**
Alright, let's get down to brass tacks. I need to understand how ConfigFS handles mounts. Specifically, I'm thinking I need to refresh my understanding of the mount mechanics within the `fs/configfs/` subsystem. My mental map suggests that the critical code governing the mount process is likely centered around line 115 in `mount.c`. That area probably holds the core logic I'm interested in β how ConfigFS integrates with the VFS layer, sets up the mount point, and handles the nitty-gritty details of bringing a ConfigFS filesystem into the broader system. I'm especially keen to see how the mount options are handled here, as this is often where the tricky bits reside. Let's see if that's where the heart of the matter lies. Time to dig in and see what treasures that section reveals!
|
| 21/2 |
2026/07/30 00:38 |
tool |
read-file |
0m
Args: map[File:fs/configfs/mount.c FirstLine:110 LineCount:20]
Results: map[Contents: 110: {
111: fc->ops = &configfs_context_ops;
112: return 0;
113: }
114:
115: static struct file_system_type configfs_fs_type = {
116: .owner = THIS_MODULE,
117: .name = "configfs",
118: .init_fs_context = configfs_init_fs_context,
119: .kill_sb = kill_anon_super,
120: };
121: MODULE_ALIAS_FS("configfs");
122:
123: struct dentry *configfs_pin_fs(void)
124: {
125: int err = simple_pin_fs(&configfs_fs_type, &configfs_mount,
126: &configfs_mnt_count);
127: return err ? ERR_PTR(err) : configfs_mount->mnt_root;
128: }
129:
]
|
| 22/2 |
2026/07/30 00:38 |
llm |
expert |
0m
Model:
Tokens:
input: 15545
output: 43
thoughts: 327
Thoughts: **Analyzing Configfs Accessibility**
Okay, so I'm looking at this code and it's missing the `FS_USERNS_MOUNT` flag. That immediately tells me unprivileged users, even those within a user namespace, *shouldn't* be able to mount configfs. This is where it gets interesting...how did syzkaller manage to trigger this scenario then? Syzkaller runs a lot of tests, so let's backtrack and consider the environment.
Aha, syzkaller probably runs with elevated privileges, either as root directly or in a namespace with sufficient capabilities. If `FS_USERNS_MOUNT` isn't set, then even a 'root' user within a namespace is blocked from the mount operation, however. I need to make the distinction: Is the test environment using global root, or namespace root? If it's global root, then mounting configfs would be trivial.
The core question here is really about *accessibility*: can unprivileged processes touch this, and does that extend to user namespaces? If configfs *can't* be mounted within a user namespace, then it's effectively inaccessible from user namespaces β unless it's already mounted by the host, and therefore accessible. By default, it's mounted at `/sys/kernel/config`. I need to start digging into the permissions to understand what's actually possible.
Typically, `/sys/kernel/config` is `drwxr-xr-x root root`. Subdirectories are generally created by root, which means an unprivileged user can't just go in and make a directory like `/sys/kernel/config/usb_gadget/g1`. So the question is: can they still write to `p_srate` if it's already been created by root? That's the key question, and I need to check the exact permissions of the `p_srate` attribute to find out.
|
| 23/2 |
2026/07/30 00:39 |
tool |
grepper |
0m
Args: map[Expression:UAC2_RATE_ATTRIBUTE PathPrefix:drivers/usb/gadget/function/f_uac2.c]
Results: map[Output:drivers/usb/gadget/function/f_uac2.c=1986=CONFIGFS_ATTR(f_uac2_opts_, name)
drivers/usb/gadget/function/f_uac2.c-1987-
drivers/usb/gadget/function/f_uac2.c:1988:#define UAC2_RATE_ATTRIBUTE(name) \
drivers/usb/gadget/function/f_uac2.c-1989-static ssize_t f_uac2_opts_##name##_show(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac2.c=2086=UAC2_ATTRIBUTE(u32, p_chmask);
drivers/usb/gadget/function/f_uac2.c:2087:UAC2_RATE_ATTRIBUTE(p_srate);
drivers/usb/gadget/function/f_uac2.c-2088-UAC2_ATTRIBUTE(u32, p_ssize);
--
drivers/usb/gadget/function/f_uac2.c=2090=UAC2_ATTRIBUTE(u32, c_chmask);
drivers/usb/gadget/function/f_uac2.c:2091:UAC2_RATE_ATTRIBUTE(c_srate);
drivers/usb/gadget/function/f_uac2.c-2092-UAC2_ATTRIBUTE_SYNC(c_sync);
]
|
| 24/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 16704
output: 22
thoughts: 10
Thoughts: Okay, here's my interpretation of "Let's see `CONFIGFS_ATTR`", as an expert in my field.
**Diving into CONFIGFS_ATTR**
Alright, so the phrase "Let's see `CONFIGFS_ATTR`" sparks a specific train of thought. Immediately, I'm thinking about the low-level details, the plumbing, of `configfs`. It's a signal to investigate a *specific* attribute within the `configfs` framework. I understand this isn't about just any attribute; it's likely a critical one, otherwise, why isolate it like this?
`CONFIGFS_ATTR` implies we're dealing with the core attribute representation. It could be related to how attributes are defined, how their permissions are managed, their data types, or potentially their interaction with backing stores. I'm imagining the struct definition, likely a `struct configfs_attribute` or something similar, and the functions that operate on it: `configfs_get_attr`, `configfs_set_attr`, the validation routines...
I'm mentally preparing for a deep dive. The emphasis on *seeing* it means I'm probably going to need to look at the source code, perhaps some kernel documentation or commit logs related to the implementation. It could be part of an effort to fix a bug, optimize performance, or add a new feature. Based on the context, I could be:
* **Debugging:** Looking for a specific value, a possible leak, or incorrect permissions being applied.
* **Analyzing:** Trying to understand a specific implementation detail or the flow of data through the attribute handling.
* **Improving:** Perhaps refactoring something, adding comments, or proposing a change to enhance how this attribute works in a specific situation.
In summary, this phrase is a call to action. It's a starting point for an investigation that requires deep knowledge of the `configfs` internals. The level of curiosity is medium, I know a lot about the framework, so I want to know more, this will be an engaging experience. Let's see what we're actually looking at, then we can decide the true focus!
|
| 25/2 |
2026/07/30 00:39 |
tool |
codesearch-definition-source |
0m
Error:
Args:
Results: map[SourceCode: SourceFile:]
|
| 26/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 17214
output: 20
thoughts: 13
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Grasping for the `CONFIGFS_ATTR`**
Right, let's dive in. I need to get my hands dirty and understand this code a bit better. My immediate instinct is to pinpoint the definition of `CONFIGFS_ATTR`. It's a key structure or macro, I'm sure, and understanding *it* is crucial to understanding the behavior of this part of the system. I'll need to know its members, how it's used, how it's initialized - everything. So, the quickest path to that information is to do a good ol' fashioned `grep`. I'll use it to find exactly where and how `CONFIGFS_ATTR` is defined. This should give me the foundation I need for any more in-depth exploration. Let's see what we can find.
|
| 27/2 |
2026/07/30 00:39 |
tool |
grepper |
0m
Args: map[Expression:#define CONFIGFS_ATTR]
Results: map[Output:include/linux/configfs.h=115=struct configfs_attribute {
--
include/linux/configfs.h-122-
include/linux/configfs.h:123:#define CONFIGFS_ATTR_PERM(_pfx, _name, _perm) \
include/linux/configfs.h-124-static struct configfs_attribute _pfx##attr_##_name = { \
--
include/linux/configfs.h-131-
include/linux/configfs.h:132:#define CONFIGFS_ATTR(_pfx, _name) CONFIGFS_ATTR_PERM( \
include/linux/configfs.h-133- _pfx, _name, S_IRUGO | S_IWUSR \
--
include/linux/configfs.h-135-
include/linux/configfs.h:136:#define CONFIGFS_ATTR_RO(_pfx, _name) \
include/linux/configfs.h-137-static struct configfs_attribute _pfx##attr_##_name = { \
--
include/linux/configfs.h-143-
include/linux/configfs.h:144:#define CONFIGFS_ATTR_WO(_pfx, _name) \
include/linux/configfs.h-145-static struct configfs_attribute _pfx##attr_##_name = { \
--
lib/fault-inject.c=334=static ssize_t fault_atomic_t_attr_store(atomic_t *val, const char *page, size_t count)
--
lib/fault-inject.c-346-
lib/fault-inject.c:347:#define CONFIGFS_ATTR_NAMED(_pfx, _name, _attr_name) \
lib/fault-inject.c-348-static struct configfs_attribute _pfx##attr_##_name = { \
]
|
| 28/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 17923
output: 32
thoughts: 393
Thoughts: **Analyzing the Security Implications of `CONFIGFS_ATTR` and the `p_srate` Attribute**
Okay, so I'm looking at this `CONFIGFS_ATTR` definition and it's using `S_IRUGO | S_IWUSR`. That means everyone can *read*, but only the *owner* can *write*. And the owner of configfs files is always root. Alright, so straight away, that `p_srate` attribute, in particular, is only writable by root. No unprivileged processes are getting access.
Now, the question is, what about user namespaces? Can someone in a user namespace get at this? No, that's not possible. Configfs can't even be *mounted* within a user namespace because it lacks `FS_USERNS_MOUNT` capability. So, if it's already mounted by the host, the files are owned by the *global* root. A user namespace's root isn't the global root, so they can't write to anything owned by the global root unless, of course, they're mapped to it, which completely negates the point of user namespaces in the first place. Therefore, access from user namespaces is blocked.
The question then is, are there any other ways to reach this USB gadget configuration? This USB gadget is configured by the host system itself β things like Android init scripts, or systemd. It's really a peripheral configuration interface, so could some peripheral somehow *trigger* this? No, not really. This is triggered by writing to configfs, which the *local* system does to configure the USB gadget *before* it gets bound to a UDC.
The real issue here is the memory leak. The main question here is: is this memory leak actually exploitable? Typically, memory leaks are categorized as a Denial of Service (DoS) issue, mainly because they could potentially exhaust system memory. In general, they're not seen as a pathway for privilege escalation or executing code. So, the exploitability angle? No, that's not likely. But Denial of Service? Yes, definitely. It's a memory exhaustion vulnerability, no doubt.
Just to be absolutely sure, I'm going to double-check if there's any other way to get to the `f_uac2_opts_p_srate_store` function. It's a configfs store function, meaning it's only called when a user writes to the configfs attribute. Are there *any* other callers? That's the only path I see here.
|
| 29/2 |
2026/07/30 00:39 |
tool |
codesearch-find-references |
0m
Args: map[Name:f_uac2_opts_p_srate_store]
Results: map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:f_uac2_opts_attr_p_srate SourceFile:drivers/usb/gadget/function/f_uac2.c SourceLine:2087]] TruncatedOutput:false]
|
| 30/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 18985
output: 20
thoughts: 669
Thoughts: **Analyzing a Potential Memory Corruption Vulnerability**
Okay, so I'm digging into this code, specifically this snippet:
```c
split_page = kstrdup(page, GFP_KERNEL); \
while ((token = strsep(&split_page, ",")) != NULL) { \
ret = kstrtou32(token, 0, &num); \
if (ret) \
goto end; \
\
opts->name##s[i++] = num; \
ret = len; \
}; \
\
end: \
kfree(split_page); \
```
My initial thought is, this looks like a memory leak. If `strsep` succeeds and exhausts the string, `split_page` will be `NULL`, and `kfree(NULL)` is harmless. But the original allocated pointer from `kstrdup` is lost. But the bigger problem is the *other* path...
If `kstrtou32` fails, the code jumps to `end`. However, the `split_page` pointer, which was originally the start of the string allocated by `kstrdup`, has been advanced by `strsep`. And `strsep` is:
```c
char *strsep(char **s, const char *ct)
{
char *sbegin = *s;
char *end;
if (sbegin == NULL)
return NULL;
end = strpbrk(sbegin, ct);
if (end)
*end++ = '\0';
*s = end;
return sbegin;
}
```
Okay, so `strsep` updates `*s` (which is `split_page`) to point *past* the current token. That means `kfree(split_page)` is being called with an internal pointer! That's a huge red flag.
My immediate concern is: what does `kfree` do with an interior pointer? It's SLUB, so it will attempt to free an object. It seems obvious that `kfree` expects the original pointer from the allocation. So, passing an interior pointer is *definitely* a problem. I'm worried it will calculate a wrong object index.
Let's quickly verify that `kfree` doesn't handle interior pointers, just in case. Yup, `kfree` requires the exact pointer returned by `kmalloc`/`kstrdup`. It looks like it doesn't do any alignment checks.
So, when `kstrtou32` fails, we're passing an interior pointer to `kfree`, which is going to be `slab_free` in SLUB. And the resulting `slab_free` will attempt to use an incorrect offset into an allocated object. That's a recipe for either a kernel crash (BUG) or nasty memory corruption!
I need to confirm if SLUB does any special alignment checks, maybe masking the pointer to an object boundary. But I don't see that in SLUB's `kfree`.
Okay, so the conclusion is clear. This is *definitely* a memory corruption vulnerability. This is a big problem.
|
| 31/2 |
2026/07/30 00:39 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode:6665: /**
6666: * kfree - free previously allocated memory
6667: * @object: pointer returned by kmalloc(), kmalloc_nolock(), or kmem_cache_alloc()
6668: *
6669: * If @object is NULL, no operation is performed.
6670: */
6671: void kfree(const void *object)
6672: {
6673: struct page *page;
6674: struct slab *slab;
6675: struct kmem_cache *s;
6676: void *x = (void *)object;
6677:
6678: trace_kfree(_RET_IP_, object);
6679:
6680: if (unlikely(ZERO_OR_NULL_PTR(object)))
6681: return;
6682:
6683: page = virt_to_page(object);
6684: slab = page_slab(page);
6685: if (!slab) {
6686: /* kmalloc_nolock() doesn't support large kmalloc */
6687: free_large_kmalloc(page, (void *)object);
6688: return;
6689: }
6690:
6691: s = slab->slab_cache;
6692: slab_free(s, slab, x, _RET_IP_);
6693: }
SourceFile:mm/slub.c]
|
| 32/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 20799
output: 23
thoughts: 154
Thoughts: **My Concerns Regarding Slab Allocation and Deallocation**
Okay, so I'm tracing this `slab_free` path and it's hitting `do_slab_free`, which then goes into `__slab_free`. My main concern right now is what happens if the pointer `x` isn't properly aligned to an object boundary. We know that `slab_free_freelist_hook` might check KASAN. Now, inside `do_slab_free`, this `x` is being put onto the freelist. Specifically, the code does `set_freepointer(s, tail_obj, fp);`. This is where the alarm bells are ringing!
If `x` is an interior pointer β that is, a pointer *within* a slab object and *not* at the beginning β then this is a disaster waiting to happen. It will overwrite memory *inside* the slab object. The next time that memory is allocated, it'll return this same interior pointer! This is absolutely brutal memory corruption. We're talking about very severe and likely exploitable vulnerabilities. This could lead to overwritten metadata, compromised data, and, obviously, code execution.
Now, a question I need to answer, immediately, is whether `kfree` itself performs an alignment check. I'm going to jump into the `slab_free_hook` code right away and find out. This could be where any critical sanity checks are performed.
|
| 33/2 |
2026/07/30 00:39 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode:2569: /*
2570: * Hooks for other subsystems that check memory allocations. In a typical
2571: * production configuration these hooks all should produce no code at all.
2572: *
2573: * Returns true if freeing of the object can proceed, false if its reuse
2574: * was delayed by CONFIG_SLUB_RCU_DEBUG or KASAN quarantine, or it was returned
2575: * to KFENCE.
2576: *
2577: * For objects allocated via kmalloc_nolock(), only a subset of alloc hooks
2578: * are invoked, so some free hooks must handle asymmetric hook calls.
2579: *
2580: * Alloc hooks called for kmalloc_nolock():
2581: * - kmsan_slab_alloc()
2582: * - kasan_slab_alloc()
2583: * - memcg_slab_post_alloc_hook()
2584: * - alloc_tagging_slab_alloc_hook()
2585: *
2586: * Free hooks that must handle missing corresponding alloc hooks:
2587: * - kmemleak_free_recursive()
2588: * - kfence_free()
2589: *
2590: * Free hooks that have no alloc hook counterpart, and thus safe to call:
2591: * - debug_check_no_locks_freed()
2592: * - debug_check_no_obj_freed()
2593: * - __kcsan_check_access()
2594: */
2595: static __always_inline
2596: bool slab_free_hook(struct kmem_cache *s, void *x, bool init,
2597: bool after_rcu_delay)
2598: {
2599: /* Are the object contents still accessible? */
2600: bool still_accessible = (s->flags & SLAB_TYPESAFE_BY_RCU) && !after_rcu_delay;
2601:
2602: kmemleak_free_recursive(x, s->flags);
2603: kmsan_slab_free(s, x);
2604:
2605: debug_check_no_locks_freed(x, s->object_size);
2606:
2607: if (!(s->flags & SLAB_DEBUG_OBJECTS))
2608: debug_check_no_obj_freed(x, s->object_size);
2609:
2610: /* Use KCSAN to help debug racy use-after-free. */
2611: if (!still_accessible)
2612: __kcsan_check_access(x, s->object_size,
2613: KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT);
2614:
2615: if (kfence_free(x))
2616: return false;
2617:
2618: /*
2619: * Give KASAN a chance to notice an invalid free operation before we
2620: * modify the object.
2621: */
2622: if (kasan_slab_pre_free(s, x))
2623: return false;
2624:
2625: #ifdef CONFIG_SLUB_RCU_DEBUG
2626: if (still_accessible) {
2627: struct rcu_delayed_free *delayed_free;
2628:
2629: delayed_free = kmalloc_obj(*delayed_free, GFP_NOWAIT);
2630: if (delayed_free) {
2631: /*
2632: * Let KASAN track our call stack as a "related work
2633: * creation", just like if the object had been freed
2634: * normally via kfree_rcu().
2635: * We have to do this manually because the rcu_head is
2636: * not located inside the object.
2637: */
2638: kasan_record_aux_stack(x);
2639:
2640: delayed_free->object = x;
2641: call_rcu(&delayed_free->head, slab_free_after_rcu_debug);
2642: return false;
2643: }
2644: }
2645: #endif /* CONFIG_SLUB_RCU_DEBUG */
2646:
2647: /*
2648: * As memory initialization might be integrated into KASAN,
2649: * kasan_slab_free and initialization memset's must be
2650: * kept together to avoid discrepancies in behavior.
2651: *
2652: * The initialization memset's clear the object and the metadata,
2653: * but don't touch the SLAB redzone.
2654: *
2655: * The object's freepointer is also avoided if stored outside the
2656: * object.
2657: */
2658: if (unlikely(init)) {
2659: int rsize;
2660: unsigned int inuse, orig_size;
2661:
2662: inuse = get_info_end(s);
2663: orig_size = get_orig_size(s, x);
2664: if (!kasan_has_integrated_init())
2665: memset(kasan_reset_tag(x), 0, orig_size);
2666: rsize = (s->flags & SLAB_RED_ZONE) ? s->red_left_pad : 0;
2667: memset((char *)kasan_reset_tag(x) + inuse, 0,
2668: s->size - inuse - rsize);
2669: /*
2670: * Restore orig_size, otherwise kmalloc redzone overwritten
2671: * would be reported
2672: */
2673: set_orig_size(s, x, orig_size);
2674:
2675: }
2676: /* KASAN might put x into memory quarantine, delaying its reuse. */
2677: return !kasan_slab_free(s, x, init, still_accessible, false);
2678: }
SourceFile:mm/slub.c]
|
| 34/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 23042
output: 32
thoughts: 567
Thoughts: **My Assessment of the `kfree` Vulnerability**
Okay, hold on a second. I've got a problem here. It just hit me: `kfree` *doesn't* check if the pointer `x` is aligned to the object boundary, does it? That means if `x` is an interior pointer, calling `kfree(x)` is going to corrupt the SLUB freelist! This is potentially a really powerful exploit primitive!
Let me walk through the scenario. An attacker could craft a malicious string like `"44100,invalid"` and write it to `p_srate`. The `strsep` function would then parse "44100" and the pointer `split_page` would point to `&"invalid"`. Now, when `kstrtou32("invalid")` fails, returning `-EINVAL`, the code jumps to the `end:` label and executes `kfree(split_page)`. Since `split_page` points to the memory location of `"invalid"`, which is actually `original_ptr + 6`, this translates to `kfree(original_ptr + 6)`!
Essentially, we're calling `kfree` on an *interior pointer*! This creates an arbitrary (or unaligned) free in the `kmalloc-32` or `kmalloc-64` cache. This is seriously exploitable! An attacker could use this to overlap objects, corrupt freelist pointers, and much more.
But now, I need to consider accessibility. Is this reachable from an unprivileged process? We know `p_srate` is in configfs, which is owned by root and has `S_IWUSR` permission. That means only root can write to it. Can an unprivileged user even write to it? No. What about an unprivileged user in a user namespace? Nope. Configfs can't be mounted in a user namespace. The host's configfs is owned by the global root.
Hold on, is there *any* other way to trigger this? What if the USB gadget is configured via some other interface? No. Configfs is the standard way to configure USB gadgets. What about some Android or other system daemon exposing it to unprivileged users? Maybe, but we're focusing on the kernel bug itself. The bug lives in the configfs store function, which is protected by standard file permissions.
Wait! What if the user can use `usbfs` or some other USB interface? No, this is the gadget driver (device side), not the host side. The gadget driver is configured by the system administrator (root) to emulate a USB device. Only root can configure it.
Alright, conclusion: the bug is *NOT* accessible from unprivileged processes, and it's also *NOT* accessible from user namespaces.
I still want to be sure, though. Is there any other way to reach the `f_uac2_opts_p_srate_store` function? I should probably check if it's called from elsewhere just to be absolutely certain.
|
| 35/2 |
2026/07/30 00:39 |
tool |
codesearch-find-references |
0m
Args: map[Name:f_uac2_opts_p_srate_store]
Results: map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:f_uac2_opts_attr_p_srate SourceFile:drivers/usb/gadget/function/f_uac2.c SourceLine:2087]] TruncatedOutput:false]
|
| 36/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 24387
output: 32
thoughts: 47
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the Audio Sample Rate Configuration**
Right, so the question of where this sample rate configuration originates... it's looking like the answer is only from `f_uac2_opts_attr_p_srate`. I need to be absolutely sure about that. We need to rule out any other potential sources of the sample rate value. I'll need to double check how `f_uac2_opts_attr_p_srate` is used to confirm its scope. Let me start tracing the uses of this variable and make sure there are not any other places this value is set, read, or modified before being applied.
|
| 37/2 |
2026/07/30 00:39 |
tool |
codesearch-find-references |
0m
Args: map[Name:f_uac2_opts_attr_p_srate]
Results: map[References:<nil> TruncatedOutput:false]
|
| 38/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 24636
output: 28
thoughts: 12
Thoughts: Okay, let's see. My mind is jumping around a bit here, focusing on the core concept.
**Internal Reflection on Attribute Usage**
Hold on a second... I'm noticing it's being employed within an array of attributes. Not just a standalone instance. This detail is significant, as it suggests a more complex structure or relationship than initially assumed. It's not a singular, isolated property, but rather a component within a collection or group. This shifts the focus from an individual characteristic to its role within a broader system of attributes.
|
| 39/2 |
2026/07/30 00:39 |
tool |
grepper |
0m
Args: map[Expression:f_uac2_opts_attr_p_srate]
Results: map[Output:drivers/usb/gadget/function/f_uac2.c=2128=static struct configfs_attribute *f_uac2_attrs[] = {
drivers/usb/gadget/function/f_uac2.c-2129- &f_uac2_opts_attr_p_chmask,
drivers/usb/gadget/function/f_uac2.c:2130: &f_uac2_opts_attr_p_srate,
drivers/usb/gadget/function/f_uac2.c-2131- &f_uac2_opts_attr_p_ssize,
]
|
| 40/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 24962
output: 30
thoughts: 222
Thoughts: **My Assessment of Configfs Accessibility**
Okay, so I'm dealing with a configfs attribute here. Clearly, the primary access point is through configfs itself. My initial instinct is to verify if configfs can even be mounted within a user namespace. Let's dig into the code, specifically the `fs/configfs/mount.c` file. Right, I see the `configfs_fs_type` structure defined. Ah, but there's no `FS_USERNS_MOUNT` flag set there. That immediately tells me it's not possible to mount configfs within a user namespace.
Now, a more interesting question: even if unprivileged, can a user *access* a *pre-mounted* configfs? My focus shifts to the permissions involved when an unprivileged user accesses `/sys/kernel/config`. Given the standard mount point, `/sys/kernel/config`, and the core operations within configfs, I need to understand the permissions assigned to files and directories created there. Specifically, when a directory is created *within* configfs, what are its default permissions? I'll need to check the directory creation logic, probably in `fs/configfs/dir.c`. Understanding that is critical to assessing the security implications.
|
| 41/2 |
2026/07/30 00:39 |
tool |
grepper |
0m
Args: map[Expression:configfs_create_dir PathPrefix:fs/configfs]
Results: map[Output:fs/configfs/dir.c=271=static void configfs_remove_dirent(struct dentry *dentry)
--
fs/configfs/dir.c-283-/**
fs/configfs/dir.c:284: * configfs_create_dir - create a directory for an config_item.
fs/configfs/dir.c-285- * @item: config_itemwe're creating directory for.
--
fs/configfs/dir.c-292-
fs/configfs/dir.c:293:static int configfs_create_dir(struct config_item *item, struct dentry *dentry,
fs/configfs/dir.c-294- struct configfs_fragment *frag)
--
fs/configfs/dir.c-332- * Allow userspace to create new entries under a new directory created with
fs/configfs/dir.c:333: * configfs_create_dir(), and under all of its chidlren directories recursively.
fs/configfs/dir.c-334- * @sd configfs_dirent of the new directory to validate
--
fs/configfs/dir.c=857=static int configfs_attach_item(struct config_item *item,
--
fs/configfs/dir.c-862-
fs/configfs/dir.c:863: ret = configfs_create_dir(item, dentry, frag);
fs/configfs/dir.c-864- if (!ret) {
]
|
| 42/2 |
2026/07/30 00:39 |
llm |
expert |
0m
Model:
Tokens:
input: 25868
output: 36
thoughts: 14
Thoughts: Okay, let's dive into it.
**Examining `configfs_create_dir` Permissions**
Alright, I need to get a clear picture of how `configfs_create_dir` handles permissions. That's the core focus right now. Understanding the security implications is paramount. I need to know: what user, group, and permissions are assigned to a newly created directory by this function? Are they restrictive enough by default? Could a misconfiguration here create a security vulnerability, opening the door for unintended access or modification? Are there any potential race conditions I need to be aware of if multiple users or processes are creating directories concurrently? I need to analyze the code path to see if any aspects of it bypass standard permission checks, or provide a way to change permissions. Specifically, I'll need to know whether the function adheres to the Principle of Least Privilege. So, I need to start digging through the code and documentation, and cross-reference them with relevant security best practices. Let's start with a systematic code review and documentation search.
|
| 43/2 |
2026/07/30 00:40 |
tool |
read-file |
0m
Args: map[File:fs/configfs/dir.c FirstLine:293 LineCount:40]
Results: map[Contents: 293: static int configfs_create_dir(struct config_item *item, struct dentry *dentry,
294: struct configfs_fragment *frag)
295: {
296: int error;
297: umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
298: struct dentry *p = dentry->d_parent;
299: struct inode *p_inode = d_inode(p);
300: struct inode *inode;
301:
302: BUG_ON(!item);
303:
304: error = configfs_make_dirent(p->d_fsdata, dentry, item, mode,
305: CONFIGFS_DIR | CONFIGFS_USET_CREATING,
306: frag);
307: if (unlikely(error))
308: return error;
309:
310: configfs_set_dir_dirent_depth(p->d_fsdata, dentry->d_fsdata);
311: inode = configfs_create(dentry, mode);
312: if (IS_ERR(inode))
313: goto out_remove;
314:
315: inode->i_op = &configfs_dir_inode_operations;
316: inode->i_fop = &configfs_dir_operations;
317: /* directory inodes start off with i_nlink == 2 (for "." entry) */
318: inc_nlink(inode);
319: d_make_persistent(dentry, inode);
320: inc_nlink(p_inode);
321: inode_set_mtime_to_ts(p_inode, inode_set_ctime_current(p_inode));
322: item->ci_dentry = dentry;
323: return 0;
324:
325: out_remove:
326: configfs_put(dentry->d_fsdata);
327: configfs_remove_dirent(dentry);
328: return PTR_ERR(inode);
329: }
330:
331: /*
332: * Allow userspace to create new entries under a new directory created with
]
|
| 44/2 |
2026/07/30 00:40 |
llm |
expert |
0m
Model:
Tokens:
input: 26802
output: 23
thoughts: 2801
Thoughts: **Exploitation of a Kernel Memory Corruption Bug in ConfigFS**
Okay, so I've been looking at this configfs issue. The first thing I checked was access control. It looks like unprivileged users can't directly create the directory or write the `p_srate` file. User namespaces are also a no-go for exploitation because mounting configfs isn't allowed in a user namespace. So the initial impression is that this is not accessible from an unprivileged context.
Initially, I thought it was just a denial of service because of a potential memory leak. But, wait, I can see that this isn't just a simple leak: it frees an interior pointer within `kstrdup`. I've gone over the code again to verify. The bug lies in how `strsep` is used after calling `kstrdup` and how `kfree` is called in the error path. If `kstrtou32` fails, `kfree` is called with a pointer to the middle of the string, not the beginning. This appears to be a classic use-after-free issue.
I traced the execution with multiple different inputs. For the input `"44100,invalid,more"`, the code *does* free an interior pointer. I traced the string tokenization process using `strsep`, ensuring the incorrect `kfree` is called, and that the interior pointer is passed to `kfree`.
Now, if `kfree` is called with an interior pointer, that's a *huge* problem. I went back and looked at the `kfree` implementation within SLUB. The code calls `virt_to_page` to get the correct page and, in the fastpath, the `set_freepointer` function writes to an offset within the interior pointer. This sets up an object overlap in memory. If we can trigger the bug to free `ptr + 14` when we have a 32-byte object, the next allocation will return `ptr + 14`, allowing us to write out-of-bounds, potentially overwriting other adjacent objects in the slab! This is a textbook out-of-bounds write / object overlap condition. The bug is definitely exploitable!
The bug report mentions a memory leak. I re-examined the code. I then understand that a large list of comma-separated rates leads to a large memory leak, but it is also exploitable.
|
| 45/2 |
2026/07/30 00:40 |
tool |
grepper |
0m
Args: map[Expression:#define UAC_MAX_RATES]
Results: map[Output:drivers/usb/gadget/function/uac_common.h-7-
drivers/usb/gadget/function/uac_common.h:8:#define UAC_MAX_RATES 10 /* maximum number of rates configurable by f_uac1/2 */
drivers/usb/gadget/function/uac_common.h-9-#endif
]
|
| 46/2 |
2026/07/30 00:40 |
llm |
expert |
0m
Model:
Tokens:
input: 30234
output: 34
thoughts: 1042
Thoughts: **Analyzing the configfs USB Gadget Rate Handling**
Okay, so `UAC_MAX_RATES` is 10. The syzkaller input has 9 tokens, those sampling rates. That initially looked fine, but then... why did it leak? Let's trace through the problematic loop in the C code:
```c
while ((token = strsep(&split_page, ",")) != NULL) { \
ret = kstrtou32(token, 0, &num); \
if (ret) \
goto end; \
\
opts->name##s[i++] = num; \
ret = len; \
}; \
```
If that loop completes successfully, `split_page` becomes `NULL`. Aha! `kfree(NULL)` is a no-op, meaning the *original* pointer is leaked! That explains the memory leak report from syzkaller. Because syzkaller gave a valid list, the loop ran clean, `split_page` was `NULL` at the end, and the original pointer was lost.
Interesting. If syzkaller had provided an invalid token *in the middle* of the list, it would have been a nasty free β an invalid free of an interior pointer, probably leading to SLUB corruption or KASAN problems! But... what if the invalid token is the *last* one? Like `"44100,invalid"`? Let's check:
`split_page = ptr`
`token = strsep(&split_page, ",")` -> `token = ptr`, `split_page = ptr + 6`
`kstrtou32("44100")` succeeds.
`token = strsep(&split_page, ",")` -> `token = ptr + 6`, `split_page = NULL`
`kstrtou32("invalid")` fails.
`goto end;`
`kfree(split_page)` -> `kfree(NULL)`!
Still a leak! To get the *invalid* free, the invalid token *cannot* be the last one. It has to be in the middle, like `"44100,invalid,more"`. Let's confirm:
`split_page = ptr`
`token = strsep(&split_page, ",")` -> `token = ptr`, `split_page = ptr + 6`
`kstrtou32("44100")` succeeds.
`token = strsep(&split_page, ",")` -> `token = ptr + 6`, `split_page = ptr + 14`
`kstrtou32("invalid")` fails.
`goto end;`
`kfree(split_page)` -> `kfree(ptr + 14)`!
Yes! An invalid free! This means it's BOTH a memory leak AND an arbitrary unaligned free! That makes this *very* exploitable.
Now, is this accessible from an unprivileged process? Configfs is only writable by root, we know that. So, let's double-check if there's *any* other entry point. Is there a `chmod`? No. Another way to configure USB gadgets? Android might use `init`, which *is* root, so that's a different attack surface. Could an unprivileged app talk to a daemon to configure it? Then that is a vulnerability in the *daemon*, not the kernel.
So, the kernel bug itself is only accessible to root. Hmm, what about user namespaces? Could a user namespace root mount configfs? No, `FS_USERNS_MOUNT` is not set. Could a user namespace root write to a configfs file mounted by the host? No, it's owned by global root (`kuid 0`). A user namespace root has a different `kuid`, so it can't write.
So not accessible from user namespaces either... Wait, what if the gadget is *created* by a user namespace root? If configfs *could* be mounted inside a user namespace, then the files would belong to the user namespace root, and they *could* write to them. But configfs *cannot* be mounted there.
Okay, is there a *recent* change that might allow configfs to be mounted in user namespaces? Let's search for `FS_USERNS_MOUNT` changes in configfs.
|
| 47/2 |
2026/07/30 00:40 |
tool |
git-log |
0m
Args: map[CodeRegexp:FS_USERNS_MOUNT PathPrefix:fs/configfs]
Results:
|
| 48/2 |
2026/07/30 00:40 |
llm |
expert |
0m
Model:
Tokens:
input: 32285
output: 35
thoughts: 468
Thoughts: **My Assessment of the Bug**
Okay, so I'm looking at this bug, and the key question is, has this vulnerability ever been introduced anywhere else in the code? No, I'm pretty sure it hasn't. Now, let's see if we can trigger this in a different way. Is there any other path to `f_uac2_opts_p_srate_store`? Nope, we checked the references and it looks like it's exclusively used as a configfs attribute.
So, here's what we've got:
* **Exploitable:** Yes, absolutely. It's an invalid or unaligned free, which can lead to object overlap.
* **Denial of Service:** Yes, we're looking at a memory leak and SLUB corruption, which will cause a crash.
* **Privilege Level:** No, it requires root privileges.
* **User Namespaces:** Also, not accessible from user namespaces.
* **VM Guest Trigger:** Hold on... initially I thought it wasn't, but that's not quite right. This is a USB gadget driver, so it runs on the device side. However, the root user on the guest is writing to configfs, so it's a guest local root bug. It crashes the guest itself, and we're not talking about escaping to the host here. No host triggering.
* **VM Host Trigger (Confidential Computing):** Nope.
* **Ethernet Trigger:** No.
* **Other Remote Trigger:** Definitely not.
* **Peripheral Trigger:** No, it's triggered by a *local* configfs write, not by plugging in a USB device. The USB device is what the code actually implements.
* **Malicious Filesystem Trigger:** No.
But wait, is it possible that `f_uac2` is used in some other context? Can this be configured via a netlink interface, or something like that? It is possible? No, USB gadgets are configured via configfs or by legacy module parameters. I'll check if the legacy parameters of `g_audio` or `g_uac2` can cause this bug.
|
| 49/2 |
2026/07/30 00:40 |
tool |
grepper |
0m
Args: map[Expression:f_uac2_opts PathPrefix:drivers/usb/gadget/legacy]
Results: map[Output:drivers/usb/gadget/legacy/audio.c=253=static int audio_bind(struct usb_composite_dev *cdev)
--
drivers/usb/gadget/legacy/audio.c-255-#ifndef CONFIG_GADGET_UAC1
drivers/usb/gadget/legacy/audio.c:256: struct f_uac2_opts *uac2_opts;
drivers/usb/gadget/legacy/audio.c-257- int i;
--
drivers/usb/gadget/legacy/audio.c-282-#ifndef CONFIG_GADGET_UAC1
drivers/usb/gadget/legacy/audio.c:283: uac2_opts = container_of(fi_uac2, struct f_uac2_opts, func_inst);
drivers/usb/gadget/legacy/audio.c-284- uac2_opts->p_chmask = p_chmask;
]
|
| 50/2 |
2026/07/30 00:40 |
llm |
expert |
0m
Model:
Tokens:
input: 33504
output: 40
thoughts: 25
Thoughts: Here's a first-person summary, tailored for an expert audience, as requested:
**Diving into the Audio Gadget Driver**
Okay, time to get my hands dirty. Let's dig into the `drivers/usb/gadget/legacy/audio.c` file. I'm specifically interested in what's happening around line 283. I expect there's some interesting stuff going on in that area, likely related to the interaction between the USB audio gadget and the underlying hardware or the sound card abstraction. I'm hoping to understand how data is actually moved, potentially buffering mechanisms, or maybe some specific control transfers that set up the audio streams. This is the older "legacy" implementation, so I'm prepared for some potentially clunky code that might be ripe for refactoring, but that's what makes it interesting. Let's see what gems are hidden in there!
|
| 51/2 |
2026/07/30 00:40 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/legacy/audio.c FirstLine:270 LineCount:40]
Results: map[Contents: 270: if (IS_ERR(fi_uac2))
271: return PTR_ERR(fi_uac2);
272: #else
273: #ifndef CONFIG_GADGET_UAC1_LEGACY
274: fi_uac1 = usb_get_function_instance("uac1");
275: #else
276: fi_uac1 = usb_get_function_instance("uac1_legacy");
277: #endif
278: if (IS_ERR(fi_uac1))
279: return PTR_ERR(fi_uac1);
280: #endif
281:
282: #ifndef CONFIG_GADGET_UAC1
283: uac2_opts = container_of(fi_uac2, struct f_uac2_opts, func_inst);
284: uac2_opts->p_chmask = p_chmask;
285:
286: for (i = 0; i < p_srates_cnt; ++i)
287: uac2_opts->p_srates[i] = p_srates[i];
288:
289: uac2_opts->p_ssize = p_ssize;
290: uac2_opts->p_hs_bint = p_hs_bint;
291: uac2_opts->c_chmask = c_chmask;
292:
293: for (i = 0; i < c_srates_cnt; ++i)
294: uac2_opts->c_srates[i] = c_srates[i];
295:
296: uac2_opts->c_ssize = c_ssize;
297: uac2_opts->c_hs_bint = c_hs_bint;
298: uac2_opts->req_number = UAC2_DEF_REQ_NUM;
299: #else
300: #ifndef CONFIG_GADGET_UAC1_LEGACY
301: uac1_opts = container_of(fi_uac1, struct f_uac1_opts, func_inst);
302: uac1_opts->p_chmask = p_chmask;
303:
304: for (i = 0; i < p_srates_cnt; ++i)
305: uac1_opts->p_srates[i] = p_srates[i];
306:
307: uac1_opts->p_ssize = p_ssize;
308: uac1_opts->c_chmask = c_chmask;
309:
]
|
| 52/2 |
2026/07/30 00:40 |
llm |
expert |
0m
Model:
Tokens:
input: 34532
output: 31
thoughts: 686
Thoughts: **Analyzing the UAC2 Sample Rate Configuration Vulnerability**
Okay, here's what I'm thinking, breaking this down step by step:
First, it's immediately clear that the legacy module bypasses `f_uac2_opts_p_srate_store` and directly assigns the sample rates. That's a red herring for this vulnerability, since `f_uac2_opts_p_srate_store` is only used through configfs.
Now, let's re-examine that `kstrdup` and `strsep` code block. If we give it a malformed input like "44100,invalid,more", the `kstrtou32` fails on "invalid", but `strsep` is going to keep iterating. The critical thing here is that `kfree` gets passed an interior pointer β `"more"` in this scenario.
My first gut reaction is, is this *actually* exploitable? Freeing an interior pointer is usually a big deal. However, the catch is that this functionality is only accessible by root, through configfs. So, in terms of privilege escalation, we are technically not escalating privileges, since root already has them.
But the text says: "Memory safety issues are almost always exploitable... When kernel is crashing on a completely wild pointer access... that also usually implies possibility of exploitation." It's definitely a memory corruption vulnerability (invalid free). So, in theory, it's still exploitable.
Now, let's dig into the *mechanics* of how this memory corruption works, to prove it. Does this interior pointer free really corrupt the SLUB freelist? Let's check the code path:
1. `kfree` with an interior pointer: The `virt_to_page` function will correctly identify the page containing the interior pointer.
2. `page_slab` will correctly find the slab of the page containing the interior pointer.
3. `slab_free` is called, using the interior pointer as the object address.
4. Within `do_slab_free`, it writes the freelist pointer to `interior_pointer + offset`. So, yes, it overwrites *some* data within the object itself, and then sets the freelist head to `interior_pointer`.
The next `kmalloc` call from this slab will return `interior_pointer`. When the subsequent caller writes to this new allocation, it will overwrite the remainder of the original object, and likely the next object in the slab as well.
This is textbook object overlap and an out-of-bounds write! It looks highly exploitable.
But, a nagging question remains, does `kfree` or `slab_free` contain alignment checks? I should check to make sure. Let's see what the code in `mm/slub.c` shows...
|
| 53/2 |
2026/07/30 00:41 |
tool |
grepper |
0m
Args: map[Expression:check_valid_pointer PathPrefix:mm/slub.c]
Results: map[Output:mm/slub.c=998=static int disable_higher_order_debug;
--
mm/slub.c-1004-/* Verify that a pointer has an address that is valid within a slab page */
mm/slub.c:1005:static inline int check_valid_pointer(struct kmem_cache *s,
mm/slub.c-1006- struct slab *slab, void *object)
--
mm/slub.c=1218=static void object_err(struct kmem_cache *s, struct slab *slab,
--
mm/slub.c-1224- slab_bug(s, reason);
mm/slub.c:1225: if (!object || !check_valid_pointer(s, slab, object)) {
mm/slub.c-1226- print_slab_info(slab);
--
mm/slub.c=1470=static int check_object(struct kmem_cache *s, struct slab *slab,
--
mm/slub.c-1535- if ((freeptr_outside_object(s) || val != SLUB_RED_ACTIVE) &&
mm/slub.c:1536: !check_valid_pointer(s, slab, get_freepointer(s, p))) {
mm/slub.c-1537- object_err(s, slab, p, "Freepointer corrupt");
--
mm/slub.c=1584=static bool on_freelist(struct kmem_cache *s, struct slab *slab, void *search)
--
mm/slub.c-1594- return true;
mm/slub.c:1595: if (!check_valid_pointer(s, slab, fp)) {
mm/slub.c-1596- if (object) {
--
mm/slub.c=1722=static inline int alloc_consistency_checks(struct kmem_cache *s,
--
mm/slub.c-1727-
mm/slub.c:1728: if (!check_valid_pointer(s, slab, object)) {
mm/slub.c-1729- object_err(s, slab, object, "Freelist Pointer check fails");
--
mm/slub.c=1766=static inline int free_consistency_checks(struct kmem_cache *s,
--
mm/slub.c-1768-{
mm/slub.c:1769: if (!check_valid_pointer(s, slab, object)) {
mm/slub.c-1770- slab_err(s, slab, "Invalid object pointer 0x%p", object);
]
|
| 54/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 36554
output: 23
thoughts: 32
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into Pointer Validation**
Right, so `free_consistency_checks` ultimately calls `check_valid_pointer`. That's the key. I need to understand *exactly* how `check_valid_pointer` is implemented. I already know `free_consistency_checks` is involved in ensuring memory integrity when freeing memory, so `check_valid_pointer` must be crucial for validating those pointers before freeing to prevent double-frees, corruption, and all sorts of nastiness. Let's see how they've implemented that critical piece. Time to dig into the `check_valid_pointer` function itself. I need to see if it's relying on some standard library checks, custom metadata, or a combination. The specifics are important, as the quality and performance of memory management greatly depend on this.
|
| 55/2 |
2026/07/30 00:41 |
tool |
codesearch-definition-source |
0m
Args: map[Name:check_valid_pointer]
Results: map[SourceCode:1004: /* Verify that a pointer has an address that is valid within a slab page */
1005: static inline int check_valid_pointer(struct kmem_cache *s,
1006: struct slab *slab, void *object)
1007: {
1008: void *base;
1009:
1010: if (!object)
1011: return 1;
1012:
1013: base = slab_address(slab);
1014: object = kasan_reset_tag(object);
1015: object = restore_red_left(s, object);
1016: if (object < base || object >= base + slab->objects * s->size ||
1017: (object - base) % s->size) {
1018: return 0;
1019: }
1020:
1021: return 1;
1022: }
SourceFile:mm/slub.c]
|
| 56/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 37088
output: 23
thoughts: 70
Thoughts: **Analyzing Pointer Alignment in SLAB Allocator**
Okay, so I'm looking at this code and it's doing a modulo operation: `(object - base) % s->size`. My initial thought is, *yes, this is the crucial check!* It's actually verifying that the pointer is properly aligned to the object size, which is exactly what I'd expect. But then a little alarm bell goes off. This `free_consistency_checks` function...it's only invoked if `SLAB_DEBUG_FLAGS` is enabled. That's a bit concerning from a reliability standpoint, meaning the alignment check is only active during debug builds. Time to dive deeper and see where `free_consistency_checks` is being called to get the full picture.
|
| 57/2 |
2026/07/30 00:41 |
tool |
codesearch-find-references |
0m
Args: map[Name:free_consistency_checks]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:free_debug_processing SourceFile:mm/slub.c SourceLine:4194]] TruncatedOutput:false]
|
| 58/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 37413
output: 23
thoughts: 27
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating `free_debug_processing`**
Right, so I'm seeing this call to `free_debug_processing`. Immediately, I need to understand its context. Where is this function being invoked? A bit of code archaeology is in order. Let's trace back the calls to `free_debug_processing`. I need to figure out the calling hierarchy and what triggers its execution. Understanding the upstream logic is crucial. What are the preconditions? What data is being passed in? And, crucially, what *else* might it be freeing or affecting? This initial investigation is key to understanding its purpose and potential impact, especially in a debug context.
|
| 59/2 |
2026/07/30 00:41 |
tool |
codesearch-find-references |
0m
Args: map[Name:free_debug_processing]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:free_to_partial_list SourceFile:mm/slub.c SourceLine:5557]] TruncatedOutput:false]
|
| 60/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 37692
output: 23
thoughts: 97
Thoughts: **Analyzing the Memory Allocation Flow**
Okay, so I'm focusing on this `free_debug_processing` function. The key here is that it only gets invoked when `kmem_cache_debug_flags` returns true. In a real-world, production kernel environment, the `SLAB_DEBUG_FLAGS` aren't enabled for regular `kmalloc` caches. I mean, flags like `SLAB_RED_ZONE`, `SLAB_POISON`, and `SLAB_STORE_USER`? Those are development aids, not runtime essentials for normal allocations. Therefore, I need to understand when and why this debug processing is happening. My immediate next step is to examine the `do_slab_free` function; that's where the critical decision is made. I need to figure out the circumstances that lead to this debug path being taken because they seem highly specific.
|
| 61/2 |
2026/07/30 00:41 |
tool |
codesearch-definition-source |
0m
Error:
Args:
Results: map[SourceCode: SourceFile:]
|
| 62/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 38019
output: 25
thoughts: 12
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing Memory Management in the Kernel**
Alright, let's get down to brass tacks. I'm thinking about memory allocation and deallocation within the kernel, specifically the slab allocator. The first thing that comes to mind when I need to understand the freeing process is to zero in on the function that handles that core operation. That leads me to a good search target.
I'm mentally formulating a plan to start digging into the `do_slab_free` function. I anticipate it will be the central point to understand how slabs are managed when objects are returned to the pool. I'm expecting this will quickly lead me down paths to analyze the underlying data structures, slab cache management, and synchronization primitives used to ensure thread safety. This could go as far as looking at the interactions between CPU caches and how the free objects are maintained. My primary goal here is to determine how efficiently memory is being returned to the system when it's no longer needed, and this function is likely a critical piece of that puzzle.
|
| 63/2 |
2026/07/30 00:41 |
tool |
grepper |
0m
Error:
Args: map[Expression:static __always_inline void do_slab_free]
Results:
|
| 64/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 38298
output: 19
thoughts: 19
Thoughts: Here's my thought process, as requested:
**Investigating Slab Allocator Optimization**
Okay, so I'm thinking about digging into the slab allocator code again. Specifically, I'm trying to identify potential areas for optimization. The first thing I want to do is target a specific function: `do_slab_free`. I suspect it could be a performance bottleneck, and it's a good place to start my investigation.
But I don't want to get distracted by inline versions of the function, so I'll grep for every instance of `do_slab_free`, but I will explicitly exclude the `__always_inline` versions. This should give me a cleaner view of the non-inlined function calls and help me see where the core logic is being used. This could show me, as an expert, where the slab allocator is spending the most time.
|
| 65/2 |
2026/07/30 00:41 |
tool |
grepper |
0m
Error:
Args: map[Expression:do_slab_free]
Results:
|
| 66/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 38534
output: 21
thoughts: 39
Thoughts: **Kernel Memory Management Insights**
Okay, so I'm thinking, based on what I know about kernel memory management, especially in more recent kernels, the function I'm looking for to free memory from the slab allocator is likely `slab_free` or possibly `__slab_free`. The naming convention makes sense in that context. To be absolutely sure, and to understand the specific implementation, I need to check the source code. I know that the core of the SLUB allocator is in `mm/slub.c`, so that's the first place I'll dive into to find the definition of `slab_free` and get a clear picture of what's happening under the hood. Time to get my hands dirty.
|
| 67/2 |
2026/07/30 00:41 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode:6370: static __fastpath_inline
6371: void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
6372: unsigned long addr)
6373: {
6374: memcg_slab_free_hook(s, slab, &object, 1);
6375: alloc_tagging_slab_free_hook(s, slab, &object, 1);
6376:
6377: if (unlikely(!slab_free_hook(s, object, slab_want_init_on_free(s), false)))
6378: return;
6379:
6380: if (likely(can_free_to_pcs(slab)) && likely(free_to_pcs(s, object, true)))
6381: return;
6382:
6383: __slab_free(s, slab, object, object, 1, addr);
6384: stat(s, FREE_SLOWPATH);
6385: }
SourceFile:mm/slub.c]
|
| 68/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 39052
output: 22
thoughts: 10
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Diving into `__slab_free`**
Alright, time to dig into this. "Let's check `__slab_free`." I need to understand the memory management implications here, specifically how objects are returned to the slab allocator. My initial focus is on the mechanism β what steps are taken when an object is freed? What are the implications of the chosen algorithm on performance and fragmentation? I'm anticipating that this function is going to involve cache manipulations, potentially updating bitmaps, and maybe even moving objects around within the slabs. I'll need to look closely for any potential race conditions or locking issues, especially if this function is called concurrently. I'm also going to check for any potential subtle memory leaks or double-frees β it's crucial to ensure that all internal structures are correctly updated. I should also consider how this specific implementation handles partial frees or coalescing, given my existing knowledge. So, let's get started.
|
| 69/2 |
2026/07/30 00:41 |
tool |
codesearch-definition-source |
0m
Args:
Results: map[SourceCode:5630: /*
5631: * Slow path handling. This may still be called frequently since objects
5632: * have a longer lifetime than the cpu slabs in most processing loads.
5633: *
5634: * So we still attempt to reduce cache line usage. Just take the slab
5635: * lock and free the item. If there is no additional partial slab
5636: * handling required then we can return immediately.
5637: */
5638: static void __slab_free(struct kmem_cache *s, struct slab *slab,
5639: void *head, void *tail, int cnt,
5640: unsigned long addr)
5641:
5642: {
5643: bool was_full;
5644: struct freelist_counters old, new;
5645: struct kmem_cache_node *n = NULL;
5646: unsigned long flags;
5647: bool on_node_partial;
5648:
5649: if (IS_ENABLED(CONFIG_SLUB_TINY) || kmem_cache_debug(s)) {
5650: free_to_partial_list(s, slab, head, tail, cnt, addr);
5651: return;
5652: }
5653:
5654: do {
5655: if (unlikely(n)) {
5656: spin_unlock_irqrestore(&n->list_lock, flags);
5657: n = NULL;
5658: }
5659:
5660: old.freelist = slab->freelist;
5661: old.counters = slab->counters;
5662:
5663: was_full = (old.freelist == NULL);
5664:
5665: set_freepointer(s, tail, old.freelist);
5666:
5667: new.freelist = head;
5668: new.counters = old.counters;
5669: new.inuse -= cnt;
5670:
5671: /*
5672: * Might need to be taken off (due to becoming empty) or added
5673: * to (due to not being full anymore) the partial list.
5674: * Unless it's frozen.
5675: */
5676: if (!new.inuse || was_full) {
5677:
5678: n = get_node(s, slab_nid(slab));
5679: /*
5680: * Speculatively acquire the list_lock.
5681: * If the cmpxchg does not succeed then we may
5682: * drop the list_lock without any processing.
5683: *
5684: * Otherwise the list_lock will synchronize with
5685: * other processors updating the list of slabs.
5686: */
5687: spin_lock_irqsave(&n->list_lock, flags);
5688:
5689: on_node_partial = slab_test_node_partial(slab);
5690: }
5691:
5692: } while (!slab_update_freelist(s, slab, &old, &new, "__slab_free"));
5693:
5694: if (likely(!n)) {
5695: /*
5696: * We didn't take the list_lock because the slab was already on
5697: * the partial list and will remain there.
5698: */
5699: return;
5700: }
5701:
5702: /*
5703: * This slab was partially empty but not on the per-node partial list,
5704: * in which case we shouldn't manipulate its list, just return.
5705: */
5706: if (!was_full && !on_node_partial) {
5707: spin_unlock_irqrestore(&n->list_lock, flags);
5708: return;
5709: }
5710:
5711: /*
5712: * If slab became empty, should we add/keep it on the partial list or we
5713: * have enough?
5714: */
5715: if (unlikely(!new.inuse && n->nr_partial >= s->min_partial))
5716: goto slab_empty;
5717:
5718: /*
5719: * Objects left in the slab. If it was not on the partial list before
5720: * then add it.
5721: */
5722: if (unlikely(was_full)) {
5723: add_partial(n, slab, ADD_TO_TAIL);
5724: stat(s, FREE_ADD_PARTIAL);
5725: }
5726: spin_unlock_irqrestore(&n->list_lock, flags);
5727: return;
5728:
5729: slab_empty:
5730: /*
5731: * The slab could have a single object and thus go from full to empty in
5732: * a single free, but more likely it was on the partial list. Remove it.
5733: */
5734: if (likely(!was_full)) {
5735: remove_partial(n, slab);
5736: stat(s, FREE_REMOVE_PARTIAL);
5737: }
5738:
5739: spin_unlock_irqrestore(&n->list_lock, flags);
5740: stat(s, FREE_SLAB);
5741: discard_slab(s, slab);
5742: }
SourceFile:mm/slub.c]
|
| 70/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 40918
output: 21
thoughts: 141
Thoughts: Okay, here's my breakdown of this.
**Exploiting a Vulnerability in `__slab_free`**
Right, so `__slab_free` is setting the free pointer here:
```c
set_freepointer(s, tail, old.freelist);
new.freelist = head;
```
Interesting, it doesn't seem to have any alignment checks on `head` or `tail`. That's a classic setup for a memory corruption vulnerability. This means we should be able to trigger something by freeing an interior pointer, which is definitely exploitable.
Now, before I get too excited, let's make sure this is the only path. We know the direct call site using `f_uac2_opts_p_srate_store` has the problem, but we should make certain we're not missing something.
So, I need to double-check if `f_uac2_opts_p_srate_store` is reachable from other code paths, just in case there's another point of entry. I think we already looked, but it's worth a second. Nope, we already confirmed that's the only direct call.
Okay, let's shift gears slightly. I also need to scan the codebase to see if any other function uses `UAC2_RATE_ATTRIBUTE`. Maybe there's another route, or maybe we can leverage how this attribute is used in other places. This is a common pattern for digging around in memory corruption exploits. Gotta be thorough.
|
| 71/2 |
2026/07/30 00:41 |
tool |
grepper |
0m
Args: map[Expression:UAC2_RATE_ATTRIBUTE]
Results: map[Output:drivers/usb/gadget/function/f_uac2.c=1986=CONFIGFS_ATTR(f_uac2_opts_, name)
drivers/usb/gadget/function/f_uac2.c-1987-
drivers/usb/gadget/function/f_uac2.c:1988:#define UAC2_RATE_ATTRIBUTE(name) \
drivers/usb/gadget/function/f_uac2.c-1989-static ssize_t f_uac2_opts_##name##_show(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac2.c=2086=UAC2_ATTRIBUTE(u32, p_chmask);
drivers/usb/gadget/function/f_uac2.c:2087:UAC2_RATE_ATTRIBUTE(p_srate);
drivers/usb/gadget/function/f_uac2.c-2088-UAC2_ATTRIBUTE(u32, p_ssize);
--
drivers/usb/gadget/function/f_uac2.c=2090=UAC2_ATTRIBUTE(u32, c_chmask);
drivers/usb/gadget/function/f_uac2.c:2091:UAC2_RATE_ATTRIBUTE(c_srate);
drivers/usb/gadget/function/f_uac2.c-2092-UAC2_ATTRIBUTE_SYNC(c_sync);
]
|
| 72/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 41794
output: 21
thoughts: 44
Thoughts: Okay, here's my summarized thought process, presented as if I'm the one having these thoughts, targeting an expert audience:
**Investigating Sampling Rate Definitions Across UAC Implementations**
Alright, I'm digging into this UAC code and my immediate focus is on the sampling rate definitions. I've noted that `p_srate` and `c_srate` are defined *only* in `f_uac2.c`. That's the starting point. But, hang on a second... what about the earlier UAC implementation? The `f_uac1.c` file - I need to check it and make sure it doesn't have a *similar* set of macros. I'm wondering if there's a duplication, or an inconsistency, or perhaps a completely different method used there. This potential difference is the next logical step in the investigation.
|
| 73/2 |
2026/07/30 00:41 |
tool |
grepper |
0m
Args: map[Expression:UAC1_RATE_ATTRIBUTE]
Results: map[Output:drivers/usb/gadget/function/f_uac1.c=1568=CONFIGFS_ATTR(f_uac1_opts_, name)
drivers/usb/gadget/function/f_uac1.c-1569-
drivers/usb/gadget/function/f_uac1.c:1570:#define UAC1_RATE_ATTRIBUTE(name) \
drivers/usb/gadget/function/f_uac1.c-1571-static ssize_t f_uac1_opts_##name##_show(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac1.c=1665=UAC1_ATTRIBUTE(u32, c_chmask);
drivers/usb/gadget/function/f_uac1.c:1666:UAC1_RATE_ATTRIBUTE(c_srate);
drivers/usb/gadget/function/f_uac1.c-1667-UAC1_ATTRIBUTE(u32, c_ssize);
drivers/usb/gadget/function/f_uac1.c=1668=UAC1_ATTRIBUTE(u32, p_chmask);
drivers/usb/gadget/function/f_uac1.c:1669:UAC1_RATE_ATTRIBUTE(p_srate);
drivers/usb/gadget/function/f_uac1.c-1670-UAC1_ATTRIBUTE(u32, p_ssize);
]
|
| 74/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 42432
output: 45
thoughts: 23
Thoughts: Here's my thought process, as if I were considering this myself:
**Investigating `UAC1_RATE_ATTRIBUTE`**
Okay, time to dig into this. I need to refresh my memory on how `UAC1_RATE_ATTRIBUTE` is handled, and I know I'll find the relevant code in `f_uac1.c`. Let's pull that file up. I'm going to want to examine the context around that specific attribute to understand its purpose and how it influences the overall UAC1 implementation. I'll need to remember all the edge cases where this comes into play, as well as the initialization, access and update mechanisms. Let's start with a search for the identifier. From there, I'll need to trace its usage within the surrounding functions and data structures. I'll be looking for potential issues, bottlenecks, or areas for optimization. This will require a systematic review, but I'll make sure to note all my relevant thoughts along the way.
|
| 75/2 |
2026/07/30 00:41 |
tool |
read-file |
0m
Args: map[File:drivers/usb/gadget/function/f_uac1.c FirstLine:1570 LineCount:50]
Results: map[Contents:1570: #define UAC1_RATE_ATTRIBUTE(name) \
1571: static ssize_t f_uac1_opts_##name##_show(struct config_item *item, \
1572: char *page) \
1573: { \
1574: struct f_uac1_opts *opts = to_f_uac1_opts(item); \
1575: int result = 0; \
1576: int i; \
1577: \
1578: mutex_lock(&opts->lock); \
1579: page[0] = '\0'; \
1580: for (i = 0; i < UAC_MAX_RATES; i++) { \
1581: if (opts->name##s[i] == 0) \
1582: break; \
1583: result += sprintf(page + strlen(page), "%u,", \
1584: opts->name##s[i]); \
1585: } \
1586: if (strlen(page) > 0) \
1587: page[strlen(page) - 1] = '\n'; \
1588: mutex_unlock(&opts->lock); \
1589: \
1590: return result; \
1591: } \
1592: \
1593: static ssize_t f_uac1_opts_##name##_store(struct config_item *item, \
1594: const char *page, size_t len) \
1595: { \
1596: struct f_uac1_opts *opts = to_f_uac1_opts(item); \
1597: char *split_page = NULL; \
1598: int ret = -EINVAL; \
1599: char *token; \
1600: u32 num; \
1601: int i; \
1602: \
1603: mutex_lock(&opts->lock); \
1604: if (opts->refcnt) { \
1605: ret = -EBUSY; \
1606: goto end; \
1607: } \
1608: \
1609: i = 0; \
1610: memset(opts->name##s, 0x00, sizeof(opts->name##s)); \
1611: split_page = kstrdup(page, GFP_KERNEL); \
1612: while ((token = strsep(&split_page, ",")) != NULL) { \
1613: ret = kstrtou32(token, 0, &num); \
1614: if (ret) \
1615: goto end; \
1616: \
1617: opts->name##s[i++] = num; \
1618: ret = len; \
1619: }; \
]
|
| 76/2 |
2026/07/30 00:41 |
llm |
expert |
0m
Model:
Tokens:
input: 43563
output: 21
thoughts: 910
Thoughts: **Analyzing the USB Gadget Kernel Bug**
Okay, here's the deal. I've got this code, and it's definitely the culprit. The issue boils down to a memory leak and an invalid free operation β specifically, freeing an interior pointer. This is a classic vulnerability, and I need to figure out the full scope of its impact.
Right now, I'm confident that it *is* exploitable, but it's restricted to root access. It certainly causes a denial of service. The important part is that it is *not* accessible from unprivileged processes, user namespaces, any virtual machine guest or host triggers, nor over the network, or through peripheral or malicious filesystem interaction.
So, the next step is exhaustive: can anything else trigger this bug? Let's rule out some things. Can a malicious USB host somehow exploit this? Nope, because the USB host is limited to sending requests. The gadget configuration is controlled by the local device using configfs, which the host can't directly write to. So, no peripheral trigger here. Okay, what about a malicious filesystem interacting with configfs? Still no, configfs is a pseudo-filesystem.
Are there other ways to configure the gadget? What about a userspace daemon that takes input and configures the gadget for me? If there's a daemon that takes input from an unprivileged user or the network, *that* could be a vector, but then the vulnerability lies in the *daemon*, not the kernel code I'm analyzing. Back to the original bug.
Alright, let's revisit exploitability. Does this `kfree` immediately crash the kernel, or can it be exploited for something more subtle? If it crashes immediately, it's just a DoS. But I saw that `__slab_free` doesn't check alignment, so it writes a freelist pointer without error checking. That means it doesn't crash right away. Instead, it corrupts the freelist. When the corrupted freelist is used, it might crash, or it might just give back overlapping memory, allowing overwrite. So yes, this is *definitely* exploitable.
Wait. Is it *guaranteed* that `split_page` will be an interior pointer? It's true that `strsep` advances it, and if the loop breaks early (e.g., a `kstrtou32` failure), `split_page` will be an interior pointer. Okay, but what if `kstrdup` fails? If `kstrdup` fails, `split_page` is `NULL`. Then `strsep` returns `NULL`. The loop doesn't execute and `kfree(NULL)` is called. No crash. That case is safe.
Let's test edge cases. What if `page` is "44100,invalid"? `split_page` is initially `ptr`. The first `strsep` call makes `token = ptr` and `split_page = ptr + 6`. The `kstrtou32` call for "44100" succeeds. The second `strsep` call makes `token = ptr + 6`, and `split_page = NULL`. `kstrtou32` for "invalid" fails. Then the loop goes to `end`, which then calls `kfree(split_page)` which is `kfree(NULL)`. No crash, just a memory leak.
Okay, let's try "44100,invalid,more." The first `strsep` makes `token = ptr` and `split_page = ptr + 6`. "44100" succeeds. The second `strsep` makes `token = ptr + 6` and `split_page = ptr + 14`. "invalid" fails. Then we `goto end`, and execute `kfree(split_page)`, which becomes `kfree(ptr + 14)`. Aha! It frees an interior pointer. That's it!
So yes, it *is* an interior pointer free. Now, let's dig deeper: Is there any other place in the code that uses `strsep` in a similarly dangerous way?
|
| 77/2 |
2026/07/30 00:42 |
tool |
grepper |
0m
Args: map[Expression:strsep\(&split_page]
Results: map[Output:drivers/usb/gadget/function/f_uac1.c=1593=static ssize_t f_uac1_opts_##name##_store(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac1.c-1611- split_page = kstrdup(page, GFP_KERNEL); \
drivers/usb/gadget/function/f_uac1.c:1612: while ((token = strsep(&split_page, ",")) != NULL) { \
drivers/usb/gadget/function/f_uac1.c-1613- ret = kstrtou32(token, 0, &num); \
--
drivers/usb/gadget/function/f_uac2.c=2011=static ssize_t f_uac2_opts_##name##_store(struct config_item *item, \
--
drivers/usb/gadget/function/f_uac2.c-2029- split_page = kstrdup(page, GFP_KERNEL); \
drivers/usb/gadget/function/f_uac2.c:2030: while ((token = strsep(&split_page, ",")) != NULL) { \
drivers/usb/gadget/function/f_uac2.c-2031- ret = kstrtou32(token, 0, &num); \
]
|
| 78/2 |
2026/07/30 00:42 |
llm |
expert |
0m
Model:
Tokens:
input: 45748
output: 66
thoughts: 143
Thoughts: **My Assessment of the Vulnerability**
Okay, so I've narrowed it down to these two files. That's a good start; the scope is manageable. The core issue is well-defined: a memory leak leading to an invalid free β a classic recipe for trouble. And this one is exploitable, alright. Practically speaking, we're looking at a Denial of Service, likely impacting availability. Now, the crucial part: it's not accessible to unprivileged processes, and user namespaces are off-limits.
Let me break this down for a final answer:
* **Exploitable:** Yes. Confirmed.
* **DenialOfService:** Yes. We're looking at an availability issue.
* **Unprivileged:** No. Access is restricted.
* **UserNamespace:** No. Not accessible through that avenue either.
* **VMGuestTrigger:** No. Not a virtual machine guest trigger.
* **VMHostTrigger:** No. Not a virtual machine host trigger.
* **NetworkTrigger:** No. Not remotely triggered.
* **RemoteTrigger:** No. Not accessible remotely.
* **PeripheralTrigger:** No. Not dependent on peripherals.
* **FilesystemTrigger:** No. Not filesystem related.
I'm satisfied with this analysis. Time to call `set-results` and submit my findings.
|
| 79/2 |
2026/07/30 00:42 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 80/2 |
2026/07/30 00:42 |
llm |
expert |
0m
Model:
Tokens:
input: 46313
output: 761
thoughts: 484
Thoughts: **Final Thoughts on the USB Gadget Vulnerability**
Okay, the analysis is complete. Time to synthesize this into a final response. The core of the issue lies within the `f_uac2_opts_p_srate_store` and `f_uac1_opts_p_srate_store` functions, both generated by the `UAC2_RATE_ATTRIBUTE` macro. Specifically, the `strsep` function is the culprit when parsing the comma-separated list of sample rates.
Here's the problem: `strsep` modifies the pointer, `split_page`, to point to the next token. If the parsing completes *successfully*, `split_page` winds up being `NULL`, and the subsequent `kfree(split_page)` call is a no-op, leading to a memory leak of the original string allocated by `kstrdup`. Syzkaller flagged this, and it makes sense.
Things get far more interesting, and much worse, with invalid input. If we feed in something like `"44100,invalid,more"`, `kstrtou32` will choke on "invalid." The code then jumps to `end:` to `kfree(split_page)`. However, at this point, `split_page` is *not* the original allocated string, it's an interior pointer, pointing to the remainder of the string `"more"`. This is where the real trouble brews. Freeing an interior pointer leads to SLUB freelist corruption, which in turn means overlapping object allocations and, consequently, arbitrary memory corruption. This is a big deal.
Now, the saving grace (or at least, a limitation) is that this bug is only accessible via configfs, specifically the `/sys/kernel/config/usb_gadget/...` interface. And configfs files and directories are, by default, owned by root and have restricted permissions. Furthermore, configfs can't be mounted inside an unprivileged user namespace, because it lacks the `FS_USERNS_MOUNT` flag.
Therefore, although this is definitely exploitable, requiring global root privileges to write to configfs makes this inaccessible to unprivileged users, and also effectively prevents an attacker from triggering it from within a user namespace. Itβs still exploitable with those privileges, for sure, and causes memory leaks and potential denial of service, but the attack surface is limited. It's a local configuration interface for USB gadgets; no other triggers are relevant.
|
| 81/1 |
2026/07/30 00:42 |
action |
format-explanation |
0m
Results: map[Explanation:**Bug Analysis:**
The bug is located in the `f_uac2_opts_p_srate_store` function (and similarly in
other rate attribute store functions like `c_srate` in `f_uac1.c` and
`f_uac2.c`), which is generated by the `UAC2_RATE_ATTRIBUTE` macro.
When a user writes a comma-separated list of sample rates to the configfs
attribute, the code duplicates the input string using `kstrdup` and parses it
using `strsep`:
```c
split_page = kstrdup(page, GFP_KERNEL);
while ((token = strsep(&split_page, ",")) != NULL) {
ret = kstrtou32(token, 0, &num);
if (ret)
goto end;
// ...
};
end:
kfree(split_page);
```
The `strsep` function modifies the `split_page` pointer to point to the
beginning of the *next* token.
This leads to two severe issues:
1. **Memory Leak:** If the string is parsed successfully to the end,
`split_page` becomes `NULL`. The subsequent `kfree(NULL)` does nothing, and the
original pointer returned by `kstrdup` is leaked. This is the issue caught by
the syzkaller report.
2. **Invalid Free (Memory Corruption):** If an invalid token is encountered in
the middle of the string (e.g., writing `"44100,invalid,more"`), `kstrtou32`
will fail and the code will jump to the `end` label. At this point, `split_page`
has been advanced by `strsep` and points to the middle of the allocated buffer
(e.g., pointing to `"more"`). Calling `kfree()` on this interior pointer will
corrupt the SLUB allocator's freelist. This allows an attacker to obtain
overlapping object allocations, which is a powerful primitive for privilege
escalation and arbitrary code execution.
**Accessibility:**
Despite the severe nature of the bug, it is highly restricted in terms of
accessibility. The vulnerable code is only reachable via the USB Gadget Configfs
interface (typically mounted at `/sys/kernel/config/usb_gadget/`).
- Configfs directories and files are owned by `root` and are created with
restricted permissions (e.g., `0644` for attributes, meaning only the owner can
write to them).
- Configfs does not have the `FS_USERNS_MOUNT` flag, meaning it cannot be
mounted inside an unprivileged user namespace. Even if a user namespace could
access the host's mounted configfs, the files are owned by the global root
(`kuid 0`), preventing write access.
- Therefore, the bug can only be triggered by the global root user.
**Conclusion:**
- **Exploitable:** Yes. The interior pointer free corrupts the SLUB freelist,
leading to overlapping allocations and memory corruption.
- **Denial of Service:** Yes. The memory leak can exhaust system memory, and the
invalid free will crash the kernel or corrupt memory.
- **Accessible From Unprivileged Processes:** No. Requires global root
privileges to write to configfs.
- **Accessible From User Namespaces:** No. Configfs cannot be mounted or written
to from unprivileged user namespaces.
- **Other Triggers:** No. This is a local configuration interface, not reachable
via network, malicious USB hosts, or malicious filesystems.]
|