| 0/0 |
2026/08/01 00:55 |
flow |
assessment-security |
6m
Results: map[DenialOfService:true Explanation:**Exploitable:** Yes
**Denial Of Service:** Yes
**Accessible From Unprivileged Processes:** No
**Accessible From User Namespaces:** No
**VM Guest Trigger:** No
**VM Host Trigger in The Confidential Computing Context:** No
**Ethernet Network Trigger:** No
**Other Remote Trigger:** No
**Peripheral Trigger:** No
**Malicious Filesystem Trigger:** No
**Reasoning:**
The bug is a use-after-free in the ftrace ring buffer iterator code. It occurs
when an active iterator (e.g., a process reading from the `trace` or
`trace_pipe` files) races with a change to the sub-buffer size (e.g., writing to
`buffer_subbuf_size_kb`). The `ring_buffer_subbuf_order_set` function allocates
new pages, swaps them in, and frees the old pages, but it fails to update the
`head_page` pointer of any active iterators. As a result, the iterator continues
to use a freed `struct buffer_page`.
This is exploitable because the freed `struct buffer_page` is allocated from the
`kmalloc-64` cache, which is easy to spray and control. If an attacker
reallocates this memory and controls its contents, they can point
`iter->head_page->page` to an arbitrary memory address. When the iterator
advances, `rb_page_size` and `__rb_page_index` will read from this
attacker-controlled address, and `memcpy` will copy the data to `iter->event`,
which is subsequently returned to userspace via `seq_read`. This provides a
powerful arbitrary read primitive (information leak), which can be used to
bypass KASLR or read sensitive kernel memory. The use-after-free can also easily
lead to a kernel panic, causing a denial of service.
However, the bug is strictly restricted to privileged users. Triggering it
requires writing to `buffer_subbuf_size_kb` (or other tracefs files that
allocate/free snapshot buffers). These files are created with `TRACE_MODE_WRITE`
(mode `0640`) and are only writable by `root` (or users in the `tracing` group).
Furthermore, `tracefs` cannot be mounted inside a user namespace, meaning the
bug cannot be reached by an unprivileged user even within a container. Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/08/01 00:55 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/08/01 00:55 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/cde1b9ef9bc0fd8ebc2b773db8e023ba15b86bfc]
|
| 3/1 |
2026/08/01 00:55 |
action |
kernel-builder |
0m
Results: map[KernelObj:/app/workdir/cache/build/387161899d4d98525e72fbd25159a49cf5355674]
|
| 4/1 |
2026/08/01 00:55 |
action |
codesearch-prepare |
0m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/08/01 00:55 |
agent |
expert |
6m
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:
==================================================================
BUG: KASAN: slab-use-after-free in rb_page_size kernel/trace/ring_buffer.c:391 [inline]
BUG: KASAN: slab-use-after-free in rb_advance_iter+0x40e/0x460 kernel/trace/ring_buffer.c:6024
Read of size 8 at addr ffff88802d79b8b8 by task syz.4.389/6869
CPU: 0 UID: 0 PID: 6869 Comm: syz.4.389 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x13d/0x4b0 mm/kasan/report.c:482
kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
rb_page_size kernel/trace/ring_buffer.c:391 [inline]
rb_advance_iter+0x40e/0x460 kernel/trace/ring_buffer.c:6024
ring_buffer_iter_advance+0x69/0x90 kernel/trace/ring_buffer.c:6445
trace_find_next_entry_inc kernel/trace/trace.c:2679 [inline]
s_next+0x270/0x410 kernel/trace/trace.c:2711
seq_read_iter+0xac5/0x1270 fs/seq_file.c:263
seq_read+0x344/0x4d0 fs/seq_file.c:163
vfs_read+0x1e4/0xb40 fs/read_write.c:572
ksys_read+0x12a/0x250 fs/read_write.c:716
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f734c99df99
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f734d820028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f734cc25fa0 RCX: 00007f734c99df99
RDX: 0000000000001000 RSI: 0000200000000340 RDI: 0000000000000005
RBP: 00007f734ca34ec4 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f734cc26038 R14: 00007f734cc25fa0 R15: 00007ffcf813c748
</TASK>
Allocated by task 6869:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__do_kmalloc_node mm/slub.c:5334 [inline]
__kmalloc_node_noprof+0x339/0x830 mm/slub.c:5346
_kmalloc_node_noprof include/linux/slab.h:1197 [inline]
__rb_allocate_pages+0x399/0x10a0 kernel/trace/ring_buffer.c:2402
ring_buffer_subbuf_order_set+0x3ef/0x18a0 kernel/trace/ring_buffer.c:7379
buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221
vfs_write+0x2aa/0x1050 fs/read_write.c:685
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 6871:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2677 [inline]
slab_free mm/slub.c:6377 [inline]
kfree+0x22b/0x6c0 mm/slub.c:6692
free_buffer_page kernel/trace/ring_buffer.c:399 [inline]
ring_buffer_subbuf_order_set+0x116b/0x18a0 kernel/trace/ring_buffer.c:7439
buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221
vfs_write+0x2aa/0x1050 fs/read_write.c:685
ksys_write+0x12a/0x250 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff88802d79b880
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 56 bytes inside of
freed 64-byte region [ffff88802d79b880, ffff88802d79b8c0)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2d79b
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88813fe238c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 13416095140, free_ts 0
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3266 [inline]
allocate_slab mm/slub.c:3380 [inline]
new_slab+0xa2/0x640 mm/slub.c:3426
refill_objects+0xe3/0x410 mm/slub.c:7310
refill_sheaf mm/slub.c:2804 [inline]
__pcs_replace_empty_main+0x376/0x680 mm/slub.c:4675
alloc_from_pcs mm/slub.c:4773 [inline]
slab_alloc_node mm/slub.c:4905 [inline]
__do_kmalloc_node mm/slub.c:5333 [inline]
__kmalloc_noprof+0x66d/0x820 mm/slub.c:5359
_kmalloc_noprof include/linux/slab.h:992 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
handler_new_ref+0x1ab/0xc60 drivers/media/v4l2-core/v4l2-ctrls-core.c:1895
v4l2_ctrl_add_handler drivers/media/v4l2-core/v4l2-ctrls-core.c:2456 [inline]
v4l2_ctrl_add_handler+0x223/0x300 drivers/media/v4l2-core/v4l2-ctrls-core.c:2430
vivid_create_controls+0x33ce/0x3e80 drivers/media/test-drivers/vivid/vivid-ctrls.c:2072
vivid_create_instance drivers/media/test-drivers/vivid/vivid-core.c:1933 [inline]
vivid_probe.cold+0x4f1e/0x921e drivers/media/test-drivers/vivid/vivid-core.c:2095
platform_probe+0x106/0x1d0 drivers/base/platform.c:1439
call_driver_probe drivers/base/dd.c:628 [inline]
really_probe+0x241/0xa60 drivers/base/dd.c:706
__driver_probe_device+0x20e/0x450 drivers/base/dd.c:868
driver_probe_device+0x4a/0x140 drivers/base/dd.c:898
__driver_attach+0x21f/0x5b0 drivers/base/dd.c:1292
page_owner free stack trace missing
Memory state around the buggy address:
ffff88802d79b780: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
ffff88802d79b800: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff88802d79b880: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ffff88802d79b900: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
ffff88802d79b980: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
Reply: **Exploitable:** Yes
**Denial Of Service:** Yes
**Accessible From Unprivileged Processes:** No
**Accessible From User Namespaces:** No
**VM Guest Trigger:** No
**VM Host Trigger in The Confidential Computing Context:** No
**Ethernet Network Trigger:** No
**Other Remote Trigger:** No
**Peripheral Trigger:** No
**Malicious Filesystem Trigger:** No
**Reasoning:**
The bug is a use-after-free in the ftrace ring buffer iterator code. It occurs when an active iterator (e.g., a process reading from the `trace` or `trace_pipe` files) races with a change to the sub-buffer size (e.g., writing to `buffer_subbuf_size_kb`). The `ring_buffer_subbuf_order_set` function allocates new pages, swaps them in, and frees the old pages, but it fails to update the `head_page` pointer of any active iterators. As a result, the iterator continues to use a freed `struct buffer_page`.
This is exploitable because the freed `struct buffer_page` is allocated from the `kmalloc-64` cache, which is easy to spray and control. If an attacker reallocates this memory and controls its contents, they can point `iter->head_page->page` to an arbitrary memory address. When the iterator advances, `rb_page_size` and `__rb_page_index` will read from this attacker-controlled address, and `memcpy` will copy the data to `iter->event`, which is subsequently returned to userspace via `seq_read`. This provides a powerful arbitrary read primitive (information leak), which can be used to bypass KASLR or read sensitive kernel memory. The use-after-free can also easily lead to a kernel panic, causing a denial of service.
However, the bug is strictly restricted to privileged users. Triggering it requires writing to `buffer_subbuf_size_kb` (or other tracefs files that allocate/free snapshot buffers). These files are created with `TRACE_MODE_WRITE` (mode `0640`) and are only writable by `root` (or users in the `tracing` group). Furthermore, `tracefs` cannot be mounted inside a user namespace, meaning the bug cannot be reached by an unprivileged user even within a container.
|
| 6/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 9367
output: 35
thoughts: 569
Thoughts: **Analyzing a KASAN Slab-Use-After-Free in the Tracefs Subsystem**
Alright, let's break this down. I've got a KASAN slab-use-after-free report specifically in `rb_page_size`. The backtrace is pretty clear: it's hitting `rb_page_size` in `ring_buffer.c`, specifically line 391. The call chain leads through `rb_advance_iter`, `ring_buffer_iter_advance`, and down to the file system interface via `trace_find_next_entry_inc`, then `s_next`, eventually getting to `seq_read_iter`, and `vfs_read`. It's clearly a read operation on a sequence file.
Now, the allocation is happening via `__rb_allocate_pages` during the execution of `ring_buffer_subbuf_order_set`, and is ultimately triggered by a `vfs_write`, via `buffer_subbuf_size_write`. The free function is also `free_buffer_page` during the execution of `ring_buffer_subbuf_order_set` and ultimately triggered by `vfs_write`, again via `buffer_subbuf_size_write`. So, it looks like there's a race condition. It seems like we're potentially dealing with concurrent access from reads on trace files, like the `trace` or `trace_pipe` files, alongside a write to `buffer_subbuf_size` which ends up modifying sub-buffer sizes.
My focus should be on `buffer_subbuf_size_write` and `ring_buffer_subbuf_order_set`. These are the key players in this race. Access to the trace files is typically restricted to root or users with `CAP_SYS_ADMIN` or `CAP_TRACING`, right? Wait, does that hold true in all cases? Are tracefs files accessible to unprivileged users? No, tracefs is normally mounted at `/sys/kernel/tracing` and is restricted. So normally it is, I can't imagine this being exploitable by an unprivileged user...
Okay, I need to check something. Can `tracefs` be mounted within a user namespace? That's the angle I need to explore. Let me grep the code for `tracefs` and `fs_flags`. That's where I need to start digging to see if this is an issue that can be exploited in more common configurations.
|
| 7/2 |
2026/08/01 00:55 |
tool |
grepper |
0m
Error:
Args: map[Expression:fs_flags.*FS_USERNS_MOUNT PathPrefix:fs/tracefs]
Results:
|
| 8/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 10515
output: 39
thoughts: 64
Thoughts: **Investigating Tracefs Access in User Namespaces**
Okay, so Tracefs is proving problematic β apparently, you can't mount it within a user namespace. That's immediately a concern and I need to figure out the implications. My first thought is to check accessibility by unprivileged users; if it *can* be accessed, then there's an immediate security implication.
Digging deeper, the root of the issue seems to be reading from a trace file, which then triggers a write operation to `buffer_subbuf_size_kb`. Time to look closely at the write path there. I need to get a handle on the function `buffer_subbuf_size_write`. I suspect there's a vulnerability or misconfiguration in that function. It is likely that the bug is triggered by the interaction between reading and writing capabilities.
|
| 9/2 |
2026/08/01 00:55 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace.c Name:buffer_subbuf_size_write]
Results: map[SourceCode:8190: static ssize_t
8191: buffer_subbuf_size_write(struct file *filp, const char __user *ubuf,
8192: size_t cnt, loff_t *ppos)
8193: {
8194: struct trace_array *tr = filp->private_data;
8195: unsigned long val;
8196: int old_order;
8197: int order;
8198: int pages;
8199: int ret;
8200:
8201: ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
8202: if (ret)
8203: return ret;
8204:
8205: val *= 1024; /* value passed in is in KB */
8206:
8207: pages = DIV_ROUND_UP(val, PAGE_SIZE);
8208: order = fls(pages - 1);
8209:
8210: /* limit between 1 and 128 system pages */
8211: if (order < 0 || order > 7)
8212: return -EINVAL;
8213:
8214: /* Do not allow tracing while changing the order of the ring buffer */
8215: tracing_stop_tr(tr);
8216:
8217: old_order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer);
8218: if (old_order == order)
8219: goto out;
8220:
8221: ret = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, order);
8222: if (ret)
8223: goto out;
8224:
8225: #ifdef CONFIG_TRACER_SNAPSHOT
8226:
8227: if (!tr->allocated_snapshot)
8228: goto out_max;
8229:
8230: ret = ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, order);
8231: if (ret) {
8232: /* Put back the old order */
8233: cnt = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, old_order);
8234: if (WARN_ON_ONCE(cnt)) {
8235: /*
8236: * AARGH! We are left with different orders!
8237: * The max buffer is our "snapshot" buffer.
8238: * When a tracer needs a snapshot (one of the
8239: * latency tracers), it swaps the max buffer
8240: * with the saved snap shot. We succeeded to
8241: * update the order of the main buffer, but failed to
8242: * update the order of the max buffer. But when we tried
8243: * to reset the main buffer to the original size, we
8244: * failed there too. This is very unlikely to
8245: * happen, but if it does, warn and kill all
8246: * tracing.
8247: */
8248: tracing_disabled = 1;
8249: }
8250: goto out;
8251: }
8252: out_max:
8253: #endif
8254: (*ppos)++;
8255: out:
8256: if (ret)
8257: cnt = ret;
8258: tracing_start_tr(tr);
8259: return cnt;
8260: }
SourceFile:kernel/trace/trace.c]
|
| 10/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 11834
output: 52
thoughts: 18
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the Registration of `buffer_subbuf_size_write`**
Okay, so I need to trace how `buffer_subbuf_size_write` is actually hooked into the system. My first thought is to dive into the registration process. I'm going to look for the key elements that define this function and its associated data structures. I need to understand *where* and *how* it's integrated β is it a direct call, a part of a larger module, or handled by a more generic subsystem?
I'll be looking for clues like:
* **Symbol Table References**: I'll see if I can cross-reference the symbol name in the kernel to identify where it is declared.
* **Configuration Files**: Any kernel configuration options associated with this? I should look for configuration files that are connected to the subsystem that contains the write operation, specifically how the write operation is controlled.
* **Initialization Code**: I'll scour the initialization routines related to the relevant buffer or memory management framework. That's likely where the registration happens. I'm looking for function calls, macro expansions, or data structure assignments that explicitly link this function into the writing process.
* **Device Driver Interactions**: It could be a part of the driver itself, handling writes to specific device buffers, so, I will need to check those.
* **External References**: Are there other pieces of code calling or using this function? Is it being used as a callback, or is it used directly.
My primary goal is to form a full mental map of how this write function is associated within the dataflow, its dependency on data structures, and the context of its execution.
|
| 11/2 |
2026/08/01 00:55 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace.c IncludeSnippetLines:2 Name:buffer_subbuf_size_write SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:buffer_subbuf_size_fops SourceFile:kernel/trace/trace.c SourceLine:8265 SourceSnippet:8263: .open = tracing_open_generic_tr,
8264: .read = buffer_subbuf_size_read,
8265: .write = buffer_subbuf_size_write,
8266: .release = tracing_release_generic_tr,
8267: .llseek = default_llseek,
]] TruncatedOutput:false]
|
| 12/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 12457
output: 53
thoughts: 19
Thoughts: Here's my thought process, as if I were analyzing that code:
**Analyzing the Usage of `buffer_subbuf_size_fops`**
Okay, so I need to understand where this `buffer_subbuf_size_fops` thing is actually employed. Let's dig into the codebase and see what functions or modules are referencing it. This should give me a good handle on its purpose and how it's integrated into the larger system. I'm expecting this to be a key element in managing sub-buffers or chunks within a larger buffer structure. Depending on the context, this could be related to memory allocation, data transfers, or access control. Getting a clear picture of its usage is the first step towards understanding its overall role and potential optimizations. I'm going to start with a grep or code search, and then dive into the relevant calls to get the full picture.
|
| 13/2 |
2026/08/01 00:55 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace.c IncludeSnippetLines:2 Name:buffer_subbuf_size_fops SourceTreePrefix:]
Results: map[References:<nil> TruncatedOutput:false]
|
| 14/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 12733
output: 36
thoughts: 33
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Debugging a Missing Symbol**
Hmm, that's unexpected. The system can't seem to locate the symbol I was expecting. It's not a common function, but I remember it being critical in the trace buffer subsystem. Okay, let's drill down. My instinct is that this should be inside the kernel's tracing code, specifically within the `kernel/trace` directory. The function name itself, `buffer_subbuf_size_fops`, strongly hints at its purpose: file operations related to buffer sub-buffer sizing. That's a strong clue. I need to dive into `trace.c` and confirm that the function is correctly declared, defined, and exported. Perhaps there's a typo in the header, or a missing `EXPORT_SYMBOL` statement. Let's see what `trace.c` reveals.
|
| 15/2 |
2026/08/01 00:55 |
tool |
grepper |
0m
Args: map[Expression:buffer_subbuf_size_fops PathPrefix:kernel/trace/trace.c]
Results: map[Output:kernel/trace/trace.c=8191=buffer_subbuf_size_write(struct file *filp, const char __user *ubuf,
--
kernel/trace/trace.c-8261-
kernel/trace/trace.c:8262:static const struct file_operations buffer_subbuf_size_fops = {
kernel/trace/trace.c-8263- .open = tracing_open_generic_tr,
--
kernel/trace/trace.c=8876=init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
--
kernel/trace/trace.c-8917- trace_create_file("buffer_subbuf_size_kb", writable_mode, d_tracer,
kernel/trace/trace.c:8918: tr, &buffer_subbuf_size_fops);
kernel/trace/trace.c-8919-
]
|
| 16/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 13243
output: 30
thoughts: 88
Thoughts: Okay, here's my understanding, playing the role of an expert:
**Investigating a Tracefs Parameter**
Alright, I'm digging into this `buffer_subbuf_size_kb` setting within `tracefs`. I know that it's the specific parameter controlling that buffer size, and I also know where it's located: `/sys/kernel/tracing`. Of course, being a tracefs parameter, it's going to be restricted β likely only accessible to root or users within the 'tracing' group. That's standard practice for these trace-related controls.
Now, my immediate thought is to confirm the permissions. I'm pretty sure most of these writable tracefs nodes follow the `0644` pattern, meaning read/write for the owner (root, likely) and read-only for the group and others. Gotta verify this `writable_mode` though; just to be sure. It's always good to confirm those assumptions before I try to modify anything.
|
| 17/2 |
2026/08/01 00:55 |
tool |
grepper |
0m
Args: map[Expression:writable_mode PathPrefix:kernel/trace/trace.c]
Results: map[Output:kernel/trace/trace.c=8876=init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
kernel/trace/trace.c-8877-{
kernel/trace/trace.c:8878: umode_t writable_mode = TRACE_MODE_WRITE;
kernel/trace/trace.c-8879- int cpu;
--
kernel/trace/trace.c-8881- if (trace_array_is_readonly(tr))
kernel/trace/trace.c:8882: writable_mode = TRACE_MODE_READ;
kernel/trace/trace.c-8883-
--
kernel/trace/trace.c-8886-
kernel/trace/trace.c:8887: trace_create_file("current_tracer", writable_mode, d_tracer,
kernel/trace/trace.c-8888- tr, &set_tracer_fops);
kernel/trace/trace.c-8889-
kernel/trace/trace.c:8890: trace_create_file("tracing_cpumask", writable_mode, d_tracer,
kernel/trace/trace.c-8891- tr, &tracing_cpumask_fops);
--
kernel/trace/trace.c-8902-
kernel/trace/trace.c:8903: trace_create_file("buffer_size_kb", writable_mode, d_tracer,
kernel/trace/trace.c-8904- tr, &tracing_entries_fops);
--
kernel/trace/trace.c-8908-
kernel/trace/trace.c:8909: trace_create_file("trace_clock", writable_mode, d_tracer, tr,
kernel/trace/trace.c-8910- &trace_clock_fops);
--
kernel/trace/trace.c-8916-
kernel/trace/trace.c:8917: trace_create_file("buffer_subbuf_size_kb", writable_mode, d_tracer,
kernel/trace/trace.c-8918- tr, &buffer_subbuf_size_fops);
]
|
| 18/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 14138
output: 29
thoughts: 11
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience, presented in the first person:
**Checking `TRACE_MODE_WRITE`**
Alright, let's just make sure we're on the same page here. Before diving too deep, I need to confirm the current state of `TRACE_MODE_WRITE`. Depending on its setting, this simple check could have significant implications for the subsequent analysis. I'm thinking, is this set? Is it a binary flag, an enumerated value, or something more complex? The answer will dictate how the system logs and processes data, which is essential context. This variable is like the central nervous system of debugging, and any misunderstanding would lead to inaccurate conclusions and wasted time. I will confirm the implications for the system's logging and processing of data, before moving forward.
|
| 19/2 |
2026/08/01 00:55 |
tool |
grepper |
0m
Args: map[Expression:TRACE_MODE_WRITE PathPrefix:kernel/trace/]
Results: map[Output:kernel/trace/ftrace.c=1016=static __init void ftrace_profile_tracefs(struct dentry *d_tracer)
--
kernel/trace/ftrace.c-1049- trace_create_file("function_profile_enabled",
kernel/trace/ftrace.c:1050: TRACE_MODE_WRITE, d_tracer, NULL,
kernel/trace/ftrace.c-1051- &ftrace_profile_fops);
--
kernel/trace/ftrace.c=7486=void ftrace_create_filter_files(struct ftrace_ops *ops,
--
kernel/trace/ftrace.c-7489-
kernel/trace/ftrace.c:7490: trace_create_file("set_ftrace_filter", TRACE_MODE_WRITE, parent,
kernel/trace/ftrace.c-7491- ops, &ftrace_filter_fops);
kernel/trace/ftrace.c-7492-
kernel/trace/ftrace.c:7493: trace_create_file("set_ftrace_notrace", TRACE_MODE_WRITE, parent,
kernel/trace/ftrace.c-7494- ops, &ftrace_notrace_fops);
--
kernel/trace/ftrace.c=7517=static __init int ftrace_init_dyn_tracefs(struct dentry *d_tracer)
--
kernel/trace/ftrace.c-7534-#ifdef CONFIG_FUNCTION_GRAPH_TRACER
kernel/trace/ftrace.c:7535: trace_create_file("set_graph_function", TRACE_MODE_WRITE, d_tracer,
kernel/trace/ftrace.c-7536- NULL,
kernel/trace/ftrace.c-7537- &ftrace_graph_fops);
kernel/trace/ftrace.c:7538: trace_create_file("set_graph_notrace", TRACE_MODE_WRITE, d_tracer,
kernel/trace/ftrace.c-7539- NULL,
--
kernel/trace/ftrace.c=9029=void ftrace_init_tracefs(struct trace_array *tr, struct dentry *d_tracer)
kernel/trace/ftrace.c-9030-{
kernel/trace/ftrace.c:9031: trace_create_file("set_ftrace_pid", TRACE_MODE_WRITE, d_tracer,
kernel/trace/ftrace.c-9032- tr, &ftrace_pid_fops);
kernel/trace/ftrace.c:9033: trace_create_file("set_ftrace_notrace_pid", TRACE_MODE_WRITE,
kernel/trace/ftrace.c-9034- d_tracer, tr, &ftrace_no_pid_fops);
--
kernel/trace/rv/rv.h=4=struct rv_interface {
--
kernel/trace/rv/rv.h-12-
kernel/trace/rv/rv.h:13:#define RV_MODE_WRITE TRACE_MODE_WRITE
kernel/trace/rv/rv.h-14-#define RV_MODE_READ TRACE_MODE_READ
--
kernel/trace/trace.c=7634=tracing_init_tracefs_percpu(struct trace_array *tr, long cpu)
--
kernel/trace/trace.c-7654- /* per cpu trace */
kernel/trace/trace.c:7655: trace_create_cpu_file("trace", TRACE_MODE_WRITE, d_cpu,
kernel/trace/trace.c-7656- tr, cpu, &tracing_fops);
--
kernel/trace/trace.c-7663-
kernel/trace/trace.c:7664: trace_create_cpu_file("buffer_size_kb", TRACE_MODE_WRITE, d_cpu,
kernel/trace/trace.c-7665- tr, cpu, &tracing_entries_fops);
--
kernel/trace/trace.c-7671- if (!tr->range_addr_start) {
kernel/trace/trace.c:7672: trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu,
kernel/trace/trace.c-7673- tr, cpu, &snapshot_fops);
--
kernel/trace/trace.c=7887=create_trace_option_file(struct trace_array *tr,
--
kernel/trace/trace.c-7901-
kernel/trace/trace.c:7902: topt->entry = trace_create_file(opt->name, TRACE_MODE_WRITE,
kernel/trace/trace.c-7903- t_options, topt, &trace_options_fops);
--
kernel/trace/trace.c=8040=create_trace_option_core_file(struct trace_array *tr,
--
kernel/trace/trace.c-8048-
kernel/trace/trace.c:8049: return trace_create_file(option, TRACE_MODE_WRITE, t_options,
kernel/trace/trace.c-8050- (void *)&tr->trace_flags_index[index],
--
kernel/trace/trace.c=8876=init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
kernel/trace/trace.c-8877-{
kernel/trace/trace.c:8878: umode_t writable_mode = TRACE_MODE_WRITE;
kernel/trace/trace.c-8879- int cpu;
--
kernel/trace/trace.c-8893- /* Options are used for changing print-format even for readonly instance. */
kernel/trace/trace.c:8894: trace_create_file("trace_options", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8895- tr, &tracing_iter_fops);
kernel/trace/trace.c-8896-
kernel/trace/trace.c:8897: trace_create_file("trace", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8898- tr, &tracing_fops);
--
kernel/trace/trace.c-8943-
kernel/trace/trace.c:8944: trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8945- tr, &buffer_percent_fops);
kernel/trace/trace.c-8946-
kernel/trace/trace.c:8947: trace_create_file("syscall_user_buf_size", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8948- tr, &tracing_syscall_buf_fops);
kernel/trace/trace.c-8949-
kernel/trace/trace.c:8950: trace_create_file("tracing_on", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8951- tr, &rb_simple_fops);
--
kernel/trace/trace.c-8959- if (!tr->range_addr_start)
kernel/trace/trace.c:8960: trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8961- tr, &snapshot_fops);
--
kernel/trace/trace.c-8963-
kernel/trace/trace.c:8964: trace_create_file("error_log", TRACE_MODE_WRITE, d_tracer,
kernel/trace/trace.c-8965- tr, &tracing_err_log_fops);
--
kernel/trace/trace.c=9191=static __init void tracer_init_tracefs_work_func(struct work_struct *work)
--
kernel/trace/trace.c-9198-
kernel/trace/trace.c:9199: trace_create_file("tracing_thresh", TRACE_MODE_WRITE, NULL,
kernel/trace/trace.c-9200- &global_trace, &tracing_thresh_fops);
--
kernel/trace/trace.c-9207-
kernel/trace/trace.c:9208: trace_create_file("saved_cmdlines_size", TRACE_MODE_WRITE, NULL,
kernel/trace/trace.c-9209- NULL, &tracing_saved_cmdlines_size_fops);
--
kernel/trace/trace.h-33-
kernel/trace/trace.h:34:#define TRACE_MODE_WRITE 0640
kernel/trace/trace.h-35-#define TRACE_MODE_READ 0440
--
kernel/trace/trace_dynevent.c=274=static __init int init_dynamic_event(void)
--
kernel/trace/trace_dynevent.c-281-
kernel/trace/trace_dynevent.c:282: trace_create_file("dynamic_events", TRACE_MODE_WRITE, NULL,
kernel/trace/trace_dynevent.c-283- NULL, &dynamic_events_ops);
--
kernel/trace/trace_events.c=2912=static int system_callback(const char *name, umode_t *mode, void **data,
--
kernel/trace/trace_events.c-2923-
kernel/trace/trace_events.c:2924: *mode = TRACE_MODE_WRITE;
kernel/trace/trace_events.c-2925- return 1;
--
kernel/trace/trace_events.c=3048=static int event_callback(const char *name, umode_t *mode, void **data,
--
kernel/trace/trace_events.c-3066- if (call->class->reg && strcmp(name, "enable") == 0) {
kernel/trace/trace_events.c:3067: *mode = TRACE_MODE_WRITE;
kernel/trace/trace_events.c-3068- *fops = &ftrace_enable_fops;
--
kernel/trace/trace_events.c-3072- if (strcmp(name, "filter") == 0) {
kernel/trace/trace_events.c:3073: *mode = TRACE_MODE_WRITE;
kernel/trace/trace_events.c-3074- *fops = &ftrace_event_filter_fops;
--
kernel/trace/trace_events.c-3081- if (strcmp(name, "trigger") == 0) {
kernel/trace/trace_events.c:3082: *mode = TRACE_MODE_WRITE;
kernel/trace/trace_events.c-3083- *fops = &event_trigger_fops;
--
kernel/trace/trace_events.c=4521=static int events_callback(const char *name, umode_t *mode, void **data,
--
kernel/trace/trace_events.c-4524- if (strcmp(name, "enable") == 0) {
kernel/trace/trace_events.c:4525: *mode = TRACE_MODE_WRITE;
kernel/trace/trace_events.c-4526- *fops = &ftrace_tr_enable_fops;
--
kernel/trace/trace_events.c=4545=create_event_toplevel_files(struct dentry *parent, struct trace_array *tr)
--
kernel/trace/trace_events.c-4567- if (!trace_array_is_readonly(tr)) {
kernel/trace/trace_events.c:4568: entry = trace_create_file("set_event", TRACE_MODE_WRITE, parent,
kernel/trace/trace_events.c-4569- tr, &ftrace_set_event_fops);
--
kernel/trace/trace_events.c-4579-
kernel/trace/trace_events.c:4580: trace_create_file("set_event_pid", TRACE_MODE_WRITE, parent,
kernel/trace/trace_events.c-4581- tr, &ftrace_set_event_pid_fops);
--
kernel/trace/trace_events.c-4583- trace_create_file("set_event_notrace_pid",
kernel/trace/trace_events.c:4584: TRACE_MODE_WRITE, parent, tr,
kernel/trace/trace_events.c-4585- &ftrace_set_event_notrace_pid_fops);
--
kernel/trace/trace_events_synth.c=2411=static __init int trace_events_synth_init(void)
--
kernel/trace/trace_events_synth.c-2418-
kernel/trace/trace_events_synth.c:2419: entry = tracefs_create_file("synthetic_events", TRACE_MODE_WRITE,
kernel/trace/trace_events_synth.c-2420- NULL, NULL, &synth_events_fops);
--
kernel/trace/trace_events_user.c=2874=static int create_user_tracefs(void)
--
kernel/trace/trace_events_user.c-2877-
kernel/trace/trace_events_user.c:2878: edata = tracefs_create_file("user_events_data", TRACE_MODE_WRITE,
kernel/trace/trace_events_user.c-2879- NULL, NULL, &user_data_fops);
--
kernel/trace/trace_functions_graph.c=1799=static __init int init_graph_tracefs(void)
--
kernel/trace/trace_functions_graph.c-1806-
kernel/trace/trace_functions_graph.c:1807: trace_create_file("max_graph_depth", TRACE_MODE_WRITE, NULL,
kernel/trace/trace_functions_graph.c-1808- NULL, &graph_depth_fops);
--
kernel/trace/trace_hwlat.c=765=static int init_tracefs(void)
--
kernel/trace/trace_hwlat.c-777-
kernel/trace/trace_hwlat.c:778: hwlat_sample_window = tracefs_create_file("window", TRACE_MODE_WRITE,
kernel/trace/trace_hwlat.c-779- top_dir,
--
kernel/trace/trace_hwlat.c-784-
kernel/trace/trace_hwlat.c:785: hwlat_sample_width = tracefs_create_file("width", TRACE_MODE_WRITE,
kernel/trace/trace_hwlat.c-786- top_dir,
--
kernel/trace/trace_hwlat.c-791-
kernel/trace/trace_hwlat.c:792: hwlat_thread_mode = trace_create_file("mode", TRACE_MODE_WRITE,
kernel/trace/trace_hwlat.c-793- top_dir,
--
kernel/trace/trace_kprobe.c=2048=static __init int init_kprobe_trace(void)
--
kernel/trace/trace_kprobe.c-2056- /* Event list interface */
kernel/trace/trace_kprobe.c:2057: trace_create_file("kprobe_events", TRACE_MODE_WRITE,
kernel/trace/trace_kprobe.c-2058- NULL, NULL, &kprobe_events_ops);
--
kernel/trace/trace_osnoise.c=2739=static int init_timerlat_stack_tracefs(struct dentry *top_dir)
--
kernel/trace/trace_osnoise.c-2742-
kernel/trace/trace_osnoise.c:2743: tmp = tracefs_create_file("print_stack", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2744- &osnoise_print_stack, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c=2800=static int init_timerlat_tracefs(struct dentry *top_dir)
--
kernel/trace/trace_osnoise.c-2804-
kernel/trace/trace_osnoise.c:2805: tmp = tracefs_create_file("timerlat_period_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2806- &timerlat_period, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c-2809-
kernel/trace/trace_osnoise.c:2810: tmp = tracefs_create_file("timerlat_align_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2811- &timerlat_align_us, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c=2835=static int init_tracefs(void)
--
kernel/trace/trace_osnoise.c-2848-
kernel/trace/trace_osnoise.c:2849: tmp = tracefs_create_file("period_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2850- &osnoise_period, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c-2853-
kernel/trace/trace_osnoise.c:2854: tmp = tracefs_create_file("runtime_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2855- &osnoise_runtime, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c-2858-
kernel/trace/trace_osnoise.c:2859: tmp = tracefs_create_file("stop_tracing_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2860- &osnoise_stop_tracing_in, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c-2863-
kernel/trace/trace_osnoise.c:2864: tmp = tracefs_create_file("stop_tracing_total_us", TRACE_MODE_WRITE, top_dir,
kernel/trace/trace_osnoise.c-2865- &osnoise_stop_tracing_total, &trace_min_max_fops);
--
kernel/trace/trace_osnoise.c-2868-
kernel/trace/trace_osnoise.c:2869: tmp = trace_create_file("cpus", TRACE_MODE_WRITE, top_dir, NULL, &cpus_fops);
kernel/trace/trace_osnoise.c-2870- if (!tmp)
--
kernel/trace/trace_osnoise.c-2872-
kernel/trace/trace_osnoise.c:2873: tmp = trace_create_file("options", TRACE_MODE_WRITE, top_dir, NULL,
kernel/trace/trace_osnoise.c-2874- &osnoise_options_fops);
--
kernel/trace/trace_recursion_record.c=223=__init static int create_recursed_functions(void)
--
kernel/trace/trace_recursion_record.c-225-
kernel/trace/trace_recursion_record.c:226: trace_create_file("recursed_functions", TRACE_MODE_WRITE,
kernel/trace/trace_recursion_record.c-227- NULL, NULL, &recursed_functions_fops);
--
kernel/trace/trace_snapshot.c=398=void trace_create_maxlat_file(struct trace_array *tr,
--
kernel/trace/trace_snapshot.c-405- tr->d_max_latency = trace_create_file("tracing_max_latency",
kernel/trace/trace_snapshot.c:406: TRACE_MODE_WRITE,
kernel/trace/trace_snapshot.c-407- d_tracer, tr,
--
kernel/trace/trace_stack.c=552=static __init int stack_trace_init(void)
--
kernel/trace/trace_stack.c-559-
kernel/trace/trace_stack.c:560: trace_create_file("stack_max_size", TRACE_MODE_WRITE, NULL,
kernel/trace/trace_stack.c-561- &stack_trace_max_size, &stack_max_size_fops);
--
kernel/trace/trace_stack.c-566-#ifdef CONFIG_DYNAMIC_FTRACE
kernel/trace/trace_stack.c:567: trace_create_file("stack_trace_filter", TRACE_MODE_WRITE, NULL,
kernel/trace/trace_stack.c-568- &trace_ops, &stack_trace_filter_fops);
--
kernel/trace/trace_stat.c=290=static int init_stat_file(struct stat_session *session)
--
kernel/trace/trace_stat.c-296-
kernel/trace/trace_stat.c:297: session->file = tracefs_create_file(session->ts->name, TRACE_MODE_WRITE,
kernel/trace/trace_stat.c-298- stat_dir, session,
--
kernel/trace/trace_uprobe.c=1691=static __init int init_uprobe_trace(void)
--
kernel/trace/trace_uprobe.c-1702-
kernel/trace/trace_uprobe.c:1703: trace_create_file("uprobe_events", TRACE_MODE_WRITE, NULL,
kernel/trace/trace_uprobe.c-1704- NULL, &uprobe_events_ops);
]
|
| 20/2 |
2026/08/01 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 20039
output: 38
thoughts: 393
Thoughts: **Analyzing the Vulnerability: A Deep Dive**
Okay, so I'm looking at this `TRACE_MODE_WRITE` constant, which is defined as `0640`. That means the file, in this case, `buffer_subbuf_size_kb`, is root-owned and readable and writable by the owner, and readable by the group. But hold on, the group *can't* write; the file permissions say it's *readable* by the group. Hmm... the code uses `TRACE_MODE_WRITE` to create `buffer_subbuf_size_kb`. The owner is root, or potentially the `tracing` group if configured. So, unprivileged users can't touch it.
Can this be exploited from within a user namespace? Nope, tracefs is blocked there. So, this looks like a privilege escalation bug, limited to root access or users with the appropriate capabilities: `CAP_SYS_ADMIN` or `CAP_TRACING`. Wait a second⦠what if syzkaller somehow managed to trigger it without root? But it runs as root by default, unless it is configured with `sandbox=none`, where it will still have root access. The report says the `UID` is 0, so root is triggering this.
Let's make sure there aren't any other ways to trigger this. I need to think about alternatives. The core of this seems to be a race condition. It is occurring between reads from `trace` or `trace_pipe` and writes to `buffer_subbuf_size_kb`. Is there *any* other file that could change that subbuf size? Nope, `buffer_subbuf_size_kb` is the only one.
Okay, let's get into the bug itself. It's a slab-use-after-free, in `rb_page_size`. `rb_page_size` accesses `bpage->size`, where `bpage` is a `struct buffer_page`. That's freed by `free_buffer_page`. Okay, so let's dig into `free_buffer_page` and track where things go south.
|
| 21/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:free_buffer_page]
Results: map[SourceCode: 394: static void free_buffer_page(struct buffer_page *bpage)
395: {
396: /* Range pages are not to be freed */
397: if (!bpage->range)
398: free_pages((unsigned long)bpage->page, bpage->order);
399: kfree(bpage);
400: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 22/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 21067
output: 38
thoughts: 11
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Investigating `rb_page_size`**
Alright, let's dive in. First, I need to confirm the underlying page size, specifically by examining the `rb_page_size`. It's a fundamental parameter, and I'm treating this as a baseline step. Iβll need to understand this to determine if any unusual memory alignment or fragmentation is occurring, especially as it relates to whatever task this investigation is linked to. Knowing the page size will allow me to contextualize any observed performance anomalies within that framework. Depending on the architecture, there could be interesting implications for NUMA configurations, cache line interactions, and overall memory utilization if there are unusual values that are outside the norm. This is the first question I need answered to proceed.
|
| 23/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_page_size]
Results: map[SourceCode: 389: static __always_inline unsigned int rb_page_size(struct buffer_page *bpage)
390: {
391: return rb_data_page_size(bpage->page);
392: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 24/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 21387
output: 40
thoughts: 46
Thoughts: Okay, let's see...
**Analyzing the Memory Access**
Alright, hold on a second. It looks like `rb_data_page_size` is trying to get at `bpage->page`. Okay, that's fine, nothing inherently wrong there... but, the crash is happening *inside* `rb_page_size`. Hmm... I need to look into `rb_data_page_size` again. Something's not quite lining up. Let me trace that logic and see what's happening.
|
| 25/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_data_page_size]
Results: map[SourceCode: 379: static __always_inline long rb_data_page_size(struct buffer_data_page *dpage)
380: {
381: return rb_data_page_commit(dpage) & ~RB_MISSED_MASK;
382: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 26/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 21692
output: 40
thoughts: 32
Thoughts: Here's my thought process, as if I were analyzing that code:
**Diving into `rb_data_page_commit`**
Okay, so I'm seeing `rb_data_page_commit` and that immediately triggers a question: how exactly is this function interacting with the `dpage->commit` field? I need to understand this connection to fully grasp what's going on. Let's dig into the implementation of `rb_data_page_commit`. I need to see the details. I want to see this function's logic, to check the access and understand how `dpage->commit` is being used within the context of the data page management. Time to get down in the details.
|
| 27/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_data_page_commit]
Results: map[SourceCode: 374: static __always_inline long rb_data_page_commit(struct buffer_data_page *dpage)
375: {
376: return local_read(&dpage->commit);
377: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 28/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 22013
output: 42
thoughts: 138
Thoughts: **Analyzing a Kernel Crash in the Ring Buffer**
Okay, so I'm digging into this kernel crash. It looks like the issue is originating from `rb_page_size`, which is accessing `bpage->page->commit`, which is not great. The debugger pointed me right to it, and the crash is happening specifically at `kernel/trace/ring_buffer.c:391`. This line is calling `rb_data_page_size(bpage->page);`. That function call is likely the source of the trouble.
The kernel is attempting to read 8 bytes from address `ffff88802d79b8b8`, but there's a problem, as this is causing the kernel to halt. I see the related object is at `ffff88802d79b880`, and its size is only 64 bytes. The read is happening at offset 56. I should go over `struct buffer_page` now. I need to figure out what's causing this out-of-bounds read within the ring buffer. Something isn't right with that `bpage->page` pointer or the way we're calculating the size, it seems.
|
| 29/2 |
2026/08/01 00:56 |
tool |
codesearch-struct-layout |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c FieldOffset:56 Name:buffer_page]
Results: map[Fields:[map[Name:page OffsetBits:448 SizeBits:64]]]
|
| 30/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 22486
output: 38
thoughts: 54
Thoughts: Okay, here's my understanding, based on those breadcrumbs.
**Debugging a Potentially Freed Structure**
Right, so `page` is apparently located at an offset of 56. I'm seeing an attempt to read `bpage->page`, which suggests we're dealing with a `struct buffer_page` here. The critical clue is that this `bpage` has been *freed*. That's a classic memory corruption scenario. I need to figure out how we got into this state. The focus now shifts to how we are advancing the iterator, or how this structure is even being accessed in the first place, so I need to check `rb_advance_iter`. That's where the problem is probably originating. I'll focus on how it's dealing with the pointer to this `struct` now.
|
| 31/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_advance_iter]
Results: map[SourceCode:6006: static void rb_advance_iter(struct ring_buffer_iter *iter)
6007: {
6008: struct ring_buffer_per_cpu *cpu_buffer;
6009:
6010: cpu_buffer = iter->cpu_buffer;
6011:
6012: /* If head == next_event then we need to jump to the next event */
6013: if (iter->head == iter->next_event) {
6014: /* If the event gets overwritten again, there's nothing to do */
6015: if (rb_iter_head_event(iter) == NULL)
6016: return;
6017: }
6018:
6019: iter->head = iter->next_event;
6020:
6021: /*
6022: * Check if we are at the end of the buffer.
6023: */
6024: if (iter->next_event >= rb_page_size(iter->head_page)) {
6025: /* discarded commits can make the page empty */
6026: if (iter->head_page == cpu_buffer->commit_page)
6027: return;
6028: rb_inc_iter(iter);
6029: return;
6030: }
6031:
6032: rb_update_iter_read_stamp(iter, iter->event);
6033: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 32/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 23186
output: 43
thoughts: 61
Thoughts: **Analyzing a Memory Access Violation**
Okay, so I'm looking at this code and I've got a problem. `iter->head_page` β that's a pointer to a `struct buffer_page *` β it's being accessed, but the debugger is telling me it's been freed. That's a classic use-after-free scenario. This is definitely a bug I need to track down.
The critical piece here is *where* the free is happening. The error report pinpoints the freeing occurring within `ring_buffer_subbuf_order_set`. So, my immediate next step is to dive into *that* function. I need to understand what's happening in `ring_buffer_subbuf_order_set` and trace exactly how that `head_page` is getting freed. I'm going to follow the execution flow, step by step, and see where the invalid access is happening. Understanding the conditions that lead to the free, and then subsequently the access, is key to fixing this. This points towards an order of operations issue in memory management.
|
| 33/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:ring_buffer_subbuf_order_set]
Results: map[SourceCode:7298: /**
7299: * ring_buffer_subbuf_order_set - set the size of ring buffer sub page.
7300: * @buffer: The ring_buffer to set the new page size.
7301: * @order: Order of the system pages in one sub buffer page
7302: *
7303: * By default, one ring buffer pages equals to one system page. This API can be
7304: * used to set new size of the ring buffer page. The size must be order of
7305: * system page size, that's why the input parameter @order is the order of
7306: * system pages that are allocated for one ring buffer page:
7307: * 0 - 1 system page
7308: * 1 - 2 system pages
7309: * 3 - 4 system pages
7310: * ...
7311: *
7312: * Returns 0 on success or < 0 in case of an error.
7313: */
7314: int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
7315: {
7316: struct ring_buffer_per_cpu *cpu_buffer;
7317: struct buffer_page *bpage, *tmp;
7318: int old_order, old_size;
7319: int nr_pages;
7320: int psize;
7321: int err;
7322: int cpu;
7323:
7324: if (!buffer || order < 0)
7325: return -EINVAL;
7326:
7327: if (buffer->subbuf_order == order)
7328: return 0;
7329:
7330: psize = (1 << order) * PAGE_SIZE;
7331: if (psize <= BUF_PAGE_HDR_SIZE)
7332: return -EINVAL;
7333:
7334: /* Size of a subbuf cannot be greater than the write counter */
7335: if (psize > RB_WRITE_MASK + 1)
7336: return -EINVAL;
7337:
7338: old_order = buffer->subbuf_order;
7339: old_size = buffer->subbuf_size;
7340:
7341: /* prevent another thread from changing buffer sizes */
7342: guard(mutex)(&buffer->mutex);
7343: atomic_inc(&buffer->record_disabled);
7344:
7345: /* Make sure all commits have finished */
7346: synchronize_rcu();
7347:
7348: buffer->subbuf_order = order;
7349: buffer->subbuf_size = psize - BUF_PAGE_HDR_SIZE;
7350:
7351: /* Make sure all new buffers are allocated, before deleting the old ones */
7352: for_each_buffer_cpu(buffer, cpu) {
7353:
7354: if (!cpumask_test_cpu(cpu, buffer->cpumask))
7355: continue;
7356:
7357: cpu_buffer = buffer->buffers[cpu];
7358:
7359: if (cpu_buffer->mapped) {
7360: err = -EBUSY;
7361: goto error;
7362: }
7363:
7364: /* Update the number of pages to match the new size */
7365: nr_pages = old_size * buffer->buffers[cpu]->nr_pages;
7366: nr_pages = DIV_ROUND_UP(nr_pages, buffer->subbuf_size);
7367:
7368: /* we need a minimum of two pages */
7369: if (nr_pages < 2)
7370: nr_pages = 2;
7371:
7372: cpu_buffer->nr_pages_to_update = nr_pages;
7373:
7374: /* Include the reader page */
7375: nr_pages++;
7376:
7377: /* Allocate the new size buffer */
7378: INIT_LIST_HEAD(&cpu_buffer->new_pages);
7379: if (__rb_allocate_pages(cpu_buffer, nr_pages,
7380: &cpu_buffer->new_pages)) {
7381: /* not enough memory for new pages */
7382: err = -ENOMEM;
7383: goto error;
7384: }
7385: }
7386:
7387: for_each_buffer_cpu(buffer, cpu) {
7388: struct buffer_data_page *old_free_data_page;
7389: struct list_head old_pages;
7390: unsigned long flags;
7391:
7392: if (!cpumask_test_cpu(cpu, buffer->cpumask))
7393: continue;
7394:
7395: cpu_buffer = buffer->buffers[cpu];
7396:
7397: raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
7398:
7399: /* Clear the head bit to make the link list normal to read */
7400: rb_head_page_deactivate(cpu_buffer);
7401:
7402: /*
7403: * Collect buffers from the cpu_buffer pages list and the
7404: * reader_page on old_pages, so they can be freed later when not
7405: * under a spinlock. The pages list is a linked list with no
7406: * head, adding old_pages turns it into a regular list with
7407: * old_pages being the head.
7408: */
7409: list_add(&old_pages, cpu_buffer->pages);
7410: list_add(&cpu_buffer->reader_page->list, &old_pages);
7411:
7412: /* One page was allocated for the reader page */
7413: cpu_buffer->reader_page = list_entry(cpu_buffer->new_pages.next,
7414: struct buffer_page, list);
7415: list_del_init(&cpu_buffer->reader_page->list);
7416:
7417: /* Install the new pages, remove the head from the list */
7418: cpu_buffer->pages = cpu_buffer->new_pages.next;
7419: list_del_init(&cpu_buffer->new_pages);
7420: cpu_buffer->cnt++;
7421:
7422: cpu_buffer->head_page
7423: = list_entry(cpu_buffer->pages, struct buffer_page, list);
7424: cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
7425:
7426: cpu_buffer->nr_pages = cpu_buffer->nr_pages_to_update;
7427: cpu_buffer->nr_pages_to_update = 0;
7428:
7429: old_free_data_page = cpu_buffer->free_page;
7430: cpu_buffer->free_page = NULL;
7431:
7432: rb_head_page_activate(cpu_buffer);
7433:
7434: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
7435:
7436: /* Free old sub buffers */
7437: list_for_each_entry_safe(bpage, tmp, &old_pages, list) {
7438: list_del_init(&bpage->list);
7439: free_buffer_page(bpage);
7440: }
7441: free_pages((unsigned long)old_free_data_page, old_order);
7442:
7443: rb_check_pages(cpu_buffer);
7444: }
7445:
7446: atomic_dec(&buffer->record_disabled);
7447:
7448: return 0;
7449:
7450: error:
7451: buffer->subbuf_order = old_order;
7452: buffer->subbuf_size = old_size;
7453:
7454: atomic_dec(&buffer->record_disabled);
7455:
7456: for_each_buffer_cpu(buffer, cpu) {
7457: cpu_buffer = buffer->buffers[cpu];
7458:
7459: if (!cpu_buffer->nr_pages_to_update)
7460: continue;
7461:
7462: list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages, list) {
7463: list_del_init(&bpage->list);
7464: free_buffer_page(bpage);
7465: }
7466: }
7467:
7468: return err;
7469: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 34/2 |
2026/08/01 00:56 |
llm |
expert |
0m
Model:
Tokens:
input: 26109
output: 40
thoughts: 68
Thoughts: Okay, let's break this down.
**Diving Deep into Ring Buffer Page Swapping**
Alright, so `ring_buffer_subbuf_order_set` is doing the heavy lifting here, allocating fresh pages, deftly swapping them into the ring buffer, and then, crucially, releasing the obsolete pages. The core of this operation seems to be the page-swapping process. It's interesting they've chosen to acquire the `cpu_buffer->reader_lock` during the swap. That tells me they're very concerned about data consistency, which makes sense. Any read operations during that swap could potentially grab incomplete or inconsistent data. But I have a follow-up question. I now need to think about `rb_advance_iter`. I need to figure out what's going on there.
Let's shift gears and examine `ring_buffer_iter_advance` to see if there are any subtle interactions with the page swapping. I need to understand how iterators are handled during this potentially disruptive operation. How does it handle the iterator.
|
| 35/2 |
2026/08/01 00:56 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:ring_buffer_iter_advance]
Results: map[SourceCode:6431: /**
6432: * ring_buffer_iter_advance - advance the iterator to the next location
6433: * @iter: The ring buffer iterator
6434: *
6435: * Move the location of the iterator such that the next read will
6436: * be the next location of the iterator.
6437: */
6438: void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
6439: {
6440: struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
6441: unsigned long flags;
6442:
6443: raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
6444: iter->missed_events = 0;
6445: rb_advance_iter(iter);
6446:
6447: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
6448: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 36/2 |
2026/08/01 00:56 |
llm |
expert |
1m
Model:
Tokens:
input: 26747
output: 34
thoughts: 242
Thoughts: **My Concerns Regarding Iterator Safety in the Ring Buffer**
Okay, so I'm digging into this `ring_buffer_iter_advance` function, and something's bugging me. It's acquiring the `cpu_buffer->reader_lock`. That's fine, but it has me wondering about the lifecycle of `iter->head_page`. If that lock is held, how can `head_page` possibly be freed?
Ah, right, `ring_buffer_subbuf_order_set` is the culprit for freeing old pages. That's where the potential problem lies. It replaces all the pages, which is good for managing buffer size dynamically, but what about active iterators? They each hold a `head_page` pointer that references a page within the *old* ring buffer.
The issue is that `ring_buffer_subbuf_order_set` doesn't seem to update `iter->head_page` for any existing iterators after replacing the pages! This is a classic concurrency issue β a potential use-after-free situation, right?
Wait, hold on. `buffer_subbuf_size_write` *does* call `tracing_stop_tr(tr)` before it calls `ring_buffer_subbuf_order_set`. Does `tracing_stop_tr` stop the iterators? Does it invalidate them? Let me think...No, that just disables tracing, meaning no new writes will be performed; it won't impact existing iterators.
Okay, so iterators are created when a user opens a `trace` or `trace_pipe`. I need to figure out *when* and *how* these iterators are used, and if the system is doing anything to protect them. I should start by checking `s_start` or `s_next` in `trace.c`. Thatβs where I need to focus my investigation. This could be a nasty bug waiting to happen.
|
| 37/2 |
2026/08/01 00:57 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace.c Name:s_next]
Results: map[SourceCode:2691: static void *s_next(struct seq_file *m, void *v, loff_t *pos)
2692: {
2693: struct trace_iterator *iter = m->private;
2694: int i = (int)*pos;
2695: void *ent;
2696:
2697: WARN_ON_ONCE(iter->leftover);
2698:
2699: (*pos)++;
2700:
2701: /* can't go backwards */
2702: if (iter->idx > i)
2703: return NULL;
2704:
2705: if (iter->idx < 0)
2706: ent = trace_find_next_entry_inc(iter);
2707: else
2708: ent = iter;
2709:
2710: while (ent && iter->idx < i)
2711: ent = trace_find_next_entry_inc(iter);
2712:
2713: iter->pos = *pos;
2714:
2715: return ent;
2716: }
SourceFile:kernel/trace/trace.c]
|
| 38/2 |
2026/08/01 00:57 |
llm |
expert |
0m
Model:
Tokens:
input: 27793
output: 40
thoughts: 672
Thoughts: **Analyzing a Potential Kernel Race Condition and Use-After-Free Vulnerability in the Ring Buffer Subsystem**
Okay, let's break this down. My initial thought was: hold on, `ring_buffer_subbuf_order_set` checks `cpu_buffer->mapped`, but iterators don't set this flag, only mmap does, so there's a potential discrepancy there. The real question is whether there's any synchronization between `ring_buffer_subbuf_order_set` and these iterators.
I needed to revisit the function: I see the mutex protection on `buffer->mutex`, guarding against changes to buffer sizes. The immediate alarm bell is that I *don't* see any checks for active iterators. Now, I thought `tracing_stop_tr` might be enough to protect us, but it seems there's the possibility that `ring_buffer_subbuf_order_set` is called from *elsewhere*. A quick check of the call graph reveals it's also called from `buffer_subbuf_size_write`. So, the question then became: is there a window where an open iterator could coexist with a simultaneous size change?
The answer is yes. You could open a trace file, start reading, and concurrently, write to `buffer_subbuf_size_kb`. But, then again, since `buffer_subbuf_size_kb` requires root (or the `tracing` group), this kind of access is not accessible to unprivileged users. Is it possible to trigger this from a user namespace? No, it looks like `tracefs` can't be mounted there.
So, this appears to be a root-only bug. That narrows the scope somewhat. But is it exploitable? My assessment is that it's a use-after-free scenario involving a `struct buffer_page`. Essentially, `iter->head_page` will point to a freed `struct buffer_page`. Later, when we call `rb_page_size(iter->head_page)`, the kernel attempts to read `iter->head_page->page->commit`. Since the page has been freed, the memory could be reallocated, which could become a significant problem.
If an attacker could control the data reallocating the memory at `iter->head_page`, they could then control `iter->head_page->page`. Now `rb_page_size` will read `page->commit`. If `page` points to an attacker-controlled location, it could lead to arbitrary memory read from `commit`. Hold on. `rb_page_size` actually returns `local_read(&dpage->commit) & ~RB_MISSED_MASK`, so what happens in `rb_advance_iter` next matters.
Looking at `rb_advance_iter`:
```c
if (iter->next_event >= rb_page_size(iter->head_page)) {
/* discarded commits can make the page empty */
if (iter->head_page == cpu_buffer->commit_page)
return;
rb_inc_iter(iter);
return;
}
```
If `rb_page_size` returns a large value, it's possible that `iter->next_event` won't be greater than or equal to this value, meaning the page won't be advanced. It won't call `rb_inc_iter`. So it moves to calling `rb_update_iter_read_stamp(iter, iter->event);` where `iter->event` is calculated based on `iter->head_page` and `iter->next_event`. Okay, let's check `rb_iter_head_event`. I need to figure out the exact implications of that call chain. I can see the potential for memory corruption.
|
| 39/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_iter_head_event]
Results: map[SourceCode:3442: static struct ring_buffer_event *
3443: rb_iter_head_event(struct ring_buffer_iter *iter)
3444: {
3445: struct ring_buffer_event *event;
3446: struct buffer_page *iter_head_page = iter->head_page;
3447: unsigned long commit;
3448: unsigned length;
3449:
3450: if (iter->head != iter->next_event)
3451: return iter->event;
3452:
3453: /*
3454: * When the writer goes across pages, it issues a cmpxchg which
3455: * is a mb(), which will synchronize with the rmb here.
3456: * (see rb_tail_page_update() and __rb_reserve_next())
3457: */
3458: commit = rb_page_size(iter_head_page);
3459: smp_rmb();
3460:
3461: /* An event needs to be at least 8 bytes in size */
3462: if (iter->head > commit - 8)
3463: goto reset;
3464:
3465: event = __rb_page_index(iter_head_page, iter->head);
3466: length = rb_event_length(event);
3467:
3468: /*
3469: * READ_ONCE() doesn't work on functions and we don't want the
3470: * compiler doing any crazy optimizations with length.
3471: */
3472: barrier();
3473:
3474: if ((iter->head + length) > commit || length > iter->event_size)
3475: /* Writer corrupted the read? */
3476: goto reset;
3477:
3478: memcpy(iter->event, event, length);
3479: /*
3480: * If the page stamp is still the same after this rmb() then the
3481: * event was safely copied without the writer entering the page.
3482: */
3483: smp_rmb();
3484:
3485: /* Make sure the page didn't change since we read this */
3486: if (iter->page_stamp != iter_head_page->page->time_stamp ||
3487: commit > rb_page_size(iter_head_page))
3488: goto reset;
3489:
3490: iter->next_event = iter->head + length;
3491: return iter->event;
3492: reset:
3493: /* Reset to the beginning */
3494: iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
3495: iter->head = 0;
3496: iter->next_event = 0;
3497: iter->missed_events = 1;
3498: return NULL;
3499: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 40/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 30204
output: 39
thoughts: 63
Thoughts: **Analyzing the Red-Black Tree Iterator Logic**
Okay, so I'm digging into this red-black tree iterator, and I see this crucial line: `rb_iter_head_event` is copying the event information from `iter_head_page` into `iter->event`. That's the core of how it's getting the data, right? It's like, fetching the event. Then I spot this line: `event = __rb_page_index(iter_head_page, iter->head);` which seems to get an index within the page using `__rb_page_index`. Interesting. I need to understand that `__rb_page_index` function, it's key. Let's see what's happening there to make sure I completely understand the inner workings of this iteration. I need to make sure I understand how events are being accessed from these pages.
|
| 41/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:__rb_page_index]
Results: map[SourceCode:3430: static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
3431: {
3432: return bpage->page->data + index;
3433: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 42/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 30595
output: 43
thoughts: 278
Thoughts: **My Analysis of this Memory Leak Vulnerability**
Okay, so I'm looking at this code and breaking down how this memory leak works. The crux of it seems to be centered around this `event` pointer. Specifically, `event` is pointing to a location within `bpage->page->data` at a calculated offset (`index`). If I understand this correctly, and I *think* I do, the real danger is that if I can control `bpage`, then `bpage->page` can point to *anywhere* in memory.
Then, `memcpy(iter->event, event, length);` is the key operation. It's copying data from that potentially arbitrary memory location (`bpage->page->data + index`) into `iter->event`. And this data is then being handed back to the user through `seq_read`. Bingo. This is an arbitrary memory read. It's definitely an information leak, and I can already see the potential for exploitation here.
Wait a second, let me think this through... `iter->event`... that's a pre-allocated buffer, not a user-controlled address. That's good. But the vulnerability remains, and the core of the problem lies with controlling `bpage`. Can I do that? I have to figure out if it's possible to control where `bpage` is pointing.
Ah, okay, so `bpage` is a `struct buffer_page`, and it looks like it's allocated from `kmalloc-64`. The bug report confirmed this ("belongs to the cache kmalloc-64 of size 64"). That's actually really interesting. `kmalloc-64` is notorious for being easily sprayed and controlled. This gives an attacker a lot of control over the objects within this kmalloc cache, and that's crucial.
So, if I can control `bpage`, I can absolutely control `bpage->page` and make it point to an arbitrary memory address! The code then reads `commit` from that controlled address using `rb_page_size`. Afterwards, `__rb_page_index` calculates an offset and retrieves data from `bpage->page->data + index`. I should check the offset of `data` inside the `struct buffer_data_page` structure. That's the next step, I suppose.
|
| 43/2 |
2026/08/01 00:58 |
tool |
codesearch-struct-layout |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c FieldOffset:<nil> Name:buffer_data_page]
Results: map[Fields:[map[Name:time_stamp OffsetBits:0 SizeBits:64] map[Name:commit OffsetBits:64 SizeBits:64] map[Name:data OffsetBits:128 SizeBits:0]]]
|
| 44/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 31478
output: 38
thoughts: 105
Thoughts: **Analyzing the Memory Corruption Vulnerability**
Okay, so I'm looking at this memory layout. It seems the `data` portion starts at an offset of 16 bytes, or 128 bits, from the base of the structure. I see that the `event` pointer is calculated based on `bpage->page` plus that offset and an `index`. Alright, so the attacker has control over that `bpage->page` value, which is key. They can set it, allowing them to craft an address.
My immediate thought is, if they set `bpage->page` to `target_address - 16 - index`, then `iter->event` will point to a memory location that can be controlled by the attacker. Now, when `memcpy` is called, it will try to copy data *from* `target_address` *to* this attacker controlled pointer. Crucially, the size of this copy is determined by `rb_event_length(event)`. Thatβs the critical piece here, the size determination, because that's where the overflow will potentially occur. So, let me drill down on that function, and how it calculates the length. I need to understand that `rb_event_length` function intimately. That's the gatekeeper.
|
| 45/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_event_length]
Results: map[SourceCode: 205: /*
206: * Return the length of the given event. Will return
207: * the length of the time extend if the event is a
208: * time extend.
209: */
210: static inline unsigned
211: rb_event_length(struct ring_buffer_event *event)
212: {
213: switch (event->type_len) {
214: case RINGBUF_TYPE_PADDING:
215: if (rb_null_event(event))
216: /* undefined */
217: return -1;
218: return event->array[0] + RB_EVNT_HDR_SIZE;
219:
220: case RINGBUF_TYPE_TIME_EXTEND:
221: return RB_LEN_TIME_EXTEND;
222:
223: case RINGBUF_TYPE_TIME_STAMP:
224: return RB_LEN_TIME_STAMP;
225:
226: case RINGBUF_TYPE_DATA:
227: return rb_event_data_length(event);
228: default:
229: WARN_ON_ONCE(1);
230: }
231: /* not hit */
232: return 0;
233: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 46/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 32311
output: 36
thoughts: 111
Thoughts: **Analyzing a Powerful Read Primitive**
Okay, so the attacker has control over the data at `target_address`. That means they can manipulate `event->type_len` and `event->array[0]`, effectively controlling the length of the data being read. This data is then copied into `iter->event`. Then, the `seq_read` function is used to copy this controlled data into userspace. This seems incredibly powerful β it's basically an arbitrary read primitive, a way to read memory from anywhere. The immediate question in my mind is: can I leverage this into arbitrary write, or better yet, code execution?
I need to dig deeper. I see that `bpage` is a `struct buffer_page`, so let's examine the `struct buffer_page` definition. Understanding the structure and potential vulnerabilities of `struct buffer_page` might reveal pathways to escalation from this read primitive. This could be the key to turning this arbitrary read into something much more dangerous.
|
| 47/2 |
2026/08/01 00:58 |
tool |
codesearch-struct-layout |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:buffer_page]
Results: map[Fields:[map[Name:list OffsetBits:0 SizeBits:128] map[Name:write OffsetBits:128 SizeBits:64] map[Name:read OffsetBits:192 SizeBits:32] map[Name:entries OffsetBits:256 SizeBits:64] map[Name:real_end OffsetBits:320 SizeBits:64] map[Name:order OffsetBits:384 SizeBits:32] map[Name:id OffsetBits:416 SizeBits:30] map[Name:range OffsetBits:446 SizeBits:1] map[Name:page OffsetBits:448 SizeBits:64]]]
|
| 48/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 32851
output: 38
thoughts: 225
Thoughts: **Analyzing Potential List-Based Vulnerabilities**
Okay, so I'm looking at this code and immediately my Spidey-sense is tingling β it's got a `list`, specifically a `struct list_head`. My first thought is: if the code frees a `bpage` that's on a list, and an attacker can control that `bpage` after it's freed, then they might be able to achieve an arbitrary write through list manipulation. That's the classic double-free or use-after-free scenario, right?
So, I need to verify: is `bpage` removed from any list *before* it gets freed, or is it used in some list operation *after* it's freed? I'm honed in on the `ring_buffer_subbuf_order_set` function and specifically the section that's freeing the old sub-buffers:
```c
/* Free old sub buffers */
list_for_each_entry_safe(bpage, tmp, &old_pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
```
Okay, good. It looks like `bpage` is indeed removed from the `old_pages` list with `list_del_init()` *before* `free_buffer_page(bpage)` is called. That's a point in the code's favor. But I can't be too hasty.
Now, my mind shifts to `iter->head_page`. This is just a pointer to one of the pages. So is `bpage`. That is the tricky part! Does `rb_advance_iter` or any other iterator function modify `iter->head_page->list`? I need to check `rb_inc_iter`.
|
| 49/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_inc_iter]
Results: map[SourceCode:3517: static void rb_inc_iter(struct ring_buffer_iter *iter)
3518: {
3519: struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3520:
3521: /*
3522: * The iterator could be on the reader page (it starts there).
3523: * But the head could have moved, since the reader was
3524: * found. Check for this case and assign the iterator
3525: * to the head page instead of next.
3526: */
3527: if (iter->head_page == cpu_buffer->reader_page)
3528: iter->head_page = rb_set_head_page(cpu_buffer);
3529: else
3530: rb_inc_page(&iter->head_page);
3531:
3532: if (rb_page_commit(iter->head_page) & RB_MISSED_EVENTS)
3533: iter->missed_events = -1;
3534:
3535: iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
3536: iter->head = 0;
3537: iter->next_event = 0;
3538: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 50/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 33900
output: 38
thoughts: 15
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm an expert in this area and thinking about the implications:
**Thinking About `rb_inc_page` and Its Impact**
Alright, so I'm focusing on `rb_inc_page`. That function is essentially incrementing `iter->head_page`. In my head, I'm immediately mapping this to the context of, most likely, a red-black tree iterator. I'm visualizing the underlying data structure β a red-black tree β and how this iterator traverses it. This means `iter->head_page` is, in all probability, pointing to the current page or a section of memory that contains data within the red-black tree. `rb_inc_page` is, therefore, the function that moves that pointer to the *next* logical page within the iterator's traversal. It's a fundamental operation for walking through the data in a sorted order, typical for a red-black tree. I need to keep in mind, however, the specific implementation details... things such as, how the "next" page is determined, taking into account any potential tree balancing or node-specific data structures. Is it a forward, backward or inorder traversal type of logic? What are the implications if this pointer is pointing to an invalid memory location?
|
| 51/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_inc_page]
Results: map[SourceCode:1385: static inline void rb_inc_page(struct buffer_page **bpage)
1386: {
1387: struct list_head *p = rb_list_head((*bpage)->list.next);
1388:
1389: *bpage = list_entry(p, struct buffer_page, list);
1390: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 52/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 34361
output: 42
thoughts: 250
Thoughts: **My Analysis of the `rb_inc_page` Vulnerability**
Okay, so here's what I'm seeing with this `rb_inc_page` function. It seems that the key lies in how it interacts with the `bpage` structure and, specifically, the `list.next` member. If an attacker can control `bpage`, then they can dictate the value of `bpage->list.next`. That's the first red flag.
The code then uses `list_entry` on `bpage->list.next` to set `iter->head_page`. This means the attacker-controlled `bpage->list.next` effectively becomes the address that `iter->head_page` points to. And that... that's a *huge* deal. We're talking arbitrary memory access here.
The implications are clear: the next time `rb_advance_iter` or `rb_iter_head_event` is called, it's going to operate on this attacker-controlled `iter->head_page`. This is incredibly powerful from an attacker's perspective. It's almost a textbook example of a control-flow hijacking vulnerability.
But hold on, let's not get ahead of ourselves. Does this result in an arbitrary *write* primitive? My initial gut reaction is to say "yes," because with arbitrary read, it can be combined to form an arbitrary write primitive, but I need to be sure. It looks like the iterators themselves don't write to `iter->head_page`, from what I can see. They seem to be designed to be read-only operations. That's a good thing to note, and makes it more straightforward. It would appear that this provides an arbitrary read, not a write.
Let me re-check. I see `iter->head_page` is a `struct buffer_page *`. So the iterator is reading the data at this address. Is it writing? Hmm, not directly, at least not in the immediately obvious functions.
Alright, but wait. There's that `rb_update_iter_read_stamp` function. Could that be a write operation? I should dig into that one. It is likely that this vulnerability is an arbitrary read primitive, but still, this is a very interesting avenue to explore.
|
| 53/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:rb_update_iter_read_stamp]
Results: map[SourceCode:5705: static void
5706: rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
5707: struct ring_buffer_event *event)
5708: {
5709: u64 delta;
5710:
5711: switch (event->type_len) {
5712: case RINGBUF_TYPE_PADDING:
5713: return;
5714:
5715: case RINGBUF_TYPE_TIME_EXTEND:
5716: delta = rb_event_time_stamp(event);
5717: iter->read_stamp += delta;
5718: return;
5719:
5720: case RINGBUF_TYPE_TIME_STAMP:
5721: delta = rb_event_time_stamp(event);
5722: delta = rb_fix_abs_ts(delta, iter->read_stamp);
5723: iter->read_stamp = delta;
5724: return;
5725:
5726: case RINGBUF_TYPE_DATA:
5727: iter->read_stamp += event->time_delta;
5728: return;
5729:
5730: default:
5731: RB_WARN_ON(iter->cpu_buffer, 1);
5732: }
5733: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 54/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 35560
output: 40
thoughts: 92
Thoughts: Okay, let me think this through.
**Analyzing Ring Buffer Iterator Logic**
Right, so this code snippet I'm looking at only seems to be touching `iter->read_stamp`, which is a field within the `ring_buffer_iter` struct. It's not directly writing to `iter->head_page`, which is interesting. My initial thought is to figure out if this has unintended consequences down the line.
The next step is to consider `ring_buffer_iter_advance`. From what I can tell, it simply delegates to `rb_advance_iter`. I need to figure out how this function interacts with `iter->head_page`, because its effect will be propagated.
But, where else could this `iter->head_page` field be used? I need to check every place this field is used in order to have confidence in the system. Let's dig into `ring_buffer_iter_reset`. This seems like a likely place to start looking for interactions with that field.
|
| 55/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:ring_buffer_iter_reset]
Results: map[SourceCode:5604: /**
5605: * ring_buffer_iter_reset - reset an iterator
5606: * @iter: The iterator to reset
5607: *
5608: * Resets the iterator, so that it will start from the beginning
5609: * again.
5610: */
5611: void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
5612: {
5613: struct ring_buffer_per_cpu *cpu_buffer;
5614: unsigned long flags;
5615:
5616: if (!iter)
5617: return;
5618:
5619: cpu_buffer = iter->cpu_buffer;
5620:
5621: raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5622: rb_iter_reset(iter);
5623: raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5624: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 56/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 36225
output: 38
thoughts: 60
Thoughts: Here's my summary, as though I'm thinking through this process:
**Analyzing `rb_iter_reset` and `iter->head_page`**
Okay, so I'm looking at `rb_iter_reset` and trying to understand its potential security implications. It seems pretty straightforward on the surface β it's just setting `iter->head_page` to `cpu_buffer->reader_page`. I'm specifically interested in the possibility of arbitrary writes, and from this initial look, it doesn't seem like there's anything there that jumps out as problematic. No obvious opportunities for writing to arbitrary memory locations. It's just a reset, a pointer assignment.
However, I can't just stop there. I need to be sure. I have to consider the *other* uses of `iter->head_page`. This variable is critical to the ring buffer's operation, so it's a key point of vulnerability if it can be misused. To understand this properly, I'm going to track down every instance `iter->head_page` is used, and the most immediate place to start that analysis is `ring_buffer_read` since that's where the read operations happen. Let's see how that variable is used in the context of reading. This should give me a better understanding of how the pointer is manipulated during read operations, and whether any of those manipulations introduce risks.
|
| 57/2 |
2026/08/01 00:58 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:ring_buffer_read]
Results: map[SourceCode: SourceFile:]
|
| 58/2 |
2026/08/01 00:58 |
llm |
expert |
0m
Model:
Tokens:
input: 36644
output: 38
thoughts: 25
Thoughts: Here's my thought process, as if I were analyzing that code:
**Ring Buffer Function Confusion**
Okay, hold on a second. I'm staring at this code and something doesn't look right. My internal compiler is already kicking in. I'm pretty sure I've never seen a function called `ring_buffer_read` in this context. That's a red flag. Maybe I'm missing something, but that name isn't ringing any bells. It's not standard terminology.
Alright, let me back up and think this through. What's the *intended* function? What's the action here? We're taking data *out* of the ring buffer, right? Okay, so if `ring_buffer_read` isn't the function, what *is*? Does this library or system use a different name for that core operation? Let's see... ah, thatβs it! What about `ring_buffer_consume`? *That* feels right. That name is more common and makes more logical sense. It aligns with the concept of taking elements from the front of a buffer and decreasing its available size. Now *that* sounds like the function I'm expecting to see.
|
| 59/2 |
2026/08/01 00:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c Name:ring_buffer_consume]
Results: map[SourceCode:6312: /**
6313: * ring_buffer_consume - return an event and consume it
6314: * @buffer: The ring buffer to get the next event from
6315: * @cpu: the cpu to read the buffer from
6316: * @ts: a variable to store the timestamp (may be NULL)
6317: * @lost_events: a variable to store if events were lost (may be NULL)
6318: *
6319: * Returns the next event in the ring buffer, and that event is consumed.
6320: * Meaning, that sequential reads will keep returning a different event,
6321: * and eventually empty the ring buffer if the producer is slower.
6322: */
6323: struct ring_buffer_event *
6324: ring_buffer_consume(struct trace_buffer *buffer, int cpu, u64 *ts,
6325: unsigned long *lost_events)
6326: {
6327: struct ring_buffer_per_cpu *cpu_buffer;
6328: struct ring_buffer_event *event = NULL;
6329: unsigned long flags;
6330: bool dolock;
6331:
6332: again:
6333: /* might be called in atomic */
6334: preempt_disable();
6335:
6336: if (!cpumask_test_cpu(cpu, buffer->cpumask))
6337: goto out;
6338:
6339: cpu_buffer = buffer->buffers[cpu];
6340: local_irq_save(flags);
6341: dolock = rb_reader_lock(cpu_buffer);
6342:
6343: event = rb_buffer_peek(cpu_buffer, ts, lost_events);
6344: if (event) {
6345: cpu_buffer->lost_events = 0;
6346: rb_advance_reader(cpu_buffer);
6347: }
6348:
6349: rb_reader_unlock(cpu_buffer, dolock);
6350: local_irq_restore(flags);
6351:
6352: out:
6353: preempt_enable();
6354:
6355: if (event && event->type_len == RINGBUF_TYPE_PADDING)
6356: goto again;
6357:
6358: return event;
6359: }
SourceFile:kernel/trace/ring_buffer.c]
|
| 60/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 37688
output: 56
thoughts: 179
Thoughts: **Analyzing the Arbitrary Read Vulnerability**
Okay, so `ring_buffer_consume` doesn't leverage iterators, which immediately flags a potential issue. This essentially creates an arbitrary read primitive, a classic vulnerability pattern. The question now is: is it exploitable? Absolutely. Arbitrary read is, without a doubt, an information leak. We're talking about bypassing KASLR, potentially grabbing credentials β the whole suite of nasty possibilities.
But I need to take a step back and examine the preconditions. Can an unprivileged user even *trigger* this? I recall we identified `buffer_subbuf_size_kb` as being exclusively writable by root or members of the `tracing` group. That's a crucial mitigating factor; it shields this from most user-level processes.
Alright, what about user namespaces? Could someone leverage that to bypass the privilege requirement? No dice. Tracefs can't be mounted within a user namespace, which effectively blocks that avenue.
So, where else might `ring_buffer_subbuf_order_set` be called? It's time to exhaustively check *all* the callers of that function. We need a complete picture to determine if there's any other access vector.
|
| 61/2 |
2026/08/01 00:59 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/ring_buffer.c IncludeSnippetLines:2 Name:ring_buffer_subbuf_order_set SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:buffer_subbuf_size_write SourceFile:kernel/trace/trace.c SourceLine:8221 SourceSnippet:8219: goto out;
8220:
8221: ret = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, order);
8222: if (ret)
8223: goto out;
] map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:__UNIQUE_ID_addressable_ring_buffer_subbuf_order_set_1268 SourceFile:kernel/trace/ring_buffer.c SourceLine:7470 SourceSnippet:7470: EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:__gendwarfksyms_ptr_ring_buffer_subbuf_order_set SourceFile:kernel/trace/ring_buffer.c SourceLine:7470 SourceSnippet:7470: EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
] map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:__gendwarfksyms_ptr_ring_buffer_subbuf_order_set SourceFile:kernel/trace/ring_buffer.c SourceLine:7470 SourceSnippet:7470: EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
]] TruncatedOutput:false]
|
| 62/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 38642
output: 30
thoughts: 690
Thoughts: **My Assessment of the `buffer_subbuf_size_write` Vulnerability**
Okay, let's break this down. From what I can tell, the `buffer_subbuf_size_write` function is only called by the function itself. And that function is only used for the `buffer_subbuf_size_kb` file within tracefs. That screams "root-only," but let's not jump to conclusions.
The initial concern is the use-after-free potential here. A kernel panic is always a risk with UAF bugs; if freed memory gets unmapped or corrupts other critical structures, we're looking at a crash.
The fact that it's root-only is usually a mitigating factor for security vulnerability classifications, unless it can be somehow triggered from a lower-privileged context. I need to be sure. What about `CAP_TRACING`, but not `CAP_SYS_ADMIN`? I know `CAP_TRACING` gives access to tracefs, and that's an important consideration. Is that capability privileged? Yes, it is. But, I need to check the details.
Let's quickly verify that there aren't any other ways to trigger this. I'll think about `trace_pipe` and `trace_pipe_raw`. Also in tracefs. No other filesystem exposes this.
So, let's summarize the exploitability:
* Exploitable: Yes, it's a use-after-free and leads to arbitrary read
* Denial of Service: Yes, kernel panic is a possibility.
* Accessible From Unprivileged Processes: No.
* Accessible From User Namespaces: No.
* VM Guest Trigger: No.
* VM Host Trigger in The Confidential Computing Context: No.
* Ethernet Network Trigger: No.
* Other Remote Trigger: No.
* Peripheral Trigger: No.
* Malicious Filesystem Trigger: No.
Now, let's get granular and double check access to that file. The code from `init_tracer_tracefs` shows `buffer_subbuf_size_kb` is created with a `0640` permission using `TRACE_MODE_WRITE`. Owner is root, and the group is usually root or `tracing`, so that locks it down. Unprivileged users can't read or write that file. Can unprivileged users open the `trace` file? That's also created with `TRACE_MODE_WRITE` or `TRACE_MODE_READ`, so no, they can't. This bug is utterly inaccessible to unprivileged users.
Finally, just to be thorough, I want to confirm `ring_buffer_subbuf_order_set` can only be called from this particular location. It's exported as `EXPORT_SYMBOL_GPL`, so I'll check if any other parts of the kernel use it, just to be sure. I'll grep for that function.
|
| 63/2 |
2026/08/01 00:59 |
tool |
grepper |
0m
Args: map[Expression:ring_buffer_subbuf_order_set PathPrefix:]
Results: map[Output:include/linux/ring_buffer.h=235=int ring_buffer_subbuf_order_get(struct trace_buffer *buffer);
include/linux/ring_buffer.h:236:int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order);
include/linux/ring_buffer.h-237-int ring_buffer_subbuf_size_get(struct trace_buffer *buffer);
--
kernel/trace/ring_buffer.c=7296=EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_get);
--
kernel/trace/ring_buffer.c-7298-/**
kernel/trace/ring_buffer.c:7299: * ring_buffer_subbuf_order_set - set the size of ring buffer sub page.
kernel/trace/ring_buffer.c-7300- * @buffer: The ring_buffer to set the new page size.
--
kernel/trace/ring_buffer.c-7313- */
kernel/trace/ring_buffer.c:7314:int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order)
kernel/trace/ring_buffer.c-7315-{
--
kernel/trace/ring_buffer.c-7469-}
kernel/trace/ring_buffer.c:7470:EXPORT_SYMBOL_GPL(ring_buffer_subbuf_order_set);
kernel/trace/ring_buffer.c-7471-
--
kernel/trace/trace.c=8191=buffer_subbuf_size_write(struct file *filp, const char __user *ubuf,
--
kernel/trace/trace.c-8220-
kernel/trace/trace.c:8221: ret = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, order);
kernel/trace/trace.c-8222- if (ret)
--
kernel/trace/trace.c-8229-
kernel/trace/trace.c:8230: ret = ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, order);
kernel/trace/trace.c-8231- if (ret) {
kernel/trace/trace.c-8232- /* Put back the old order */
kernel/trace/trace.c:8233: cnt = ring_buffer_subbuf_order_set(tr->array_buffer.buffer, old_order);
kernel/trace/trace.c-8234- if (WARN_ON_ONCE(cnt)) {
--
kernel/trace/trace_snapshot.c=162=int tracing_alloc_snapshot_instance(struct trace_array *tr)
--
kernel/trace/trace_snapshot.c-170- order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer);
kernel/trace/trace_snapshot.c:171: ret = ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, order);
kernel/trace/trace_snapshot.c-172- if (ret < 0)
--
kernel/trace/trace_snapshot.c=187=void free_snapshot(struct trace_array *tr)
--
kernel/trace/trace_snapshot.c-193- */
kernel/trace/trace_snapshot.c:194: ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, 0);
kernel/trace/trace_snapshot.c-195- ring_buffer_resize(tr->snapshot_buffer.buffer, 1, RING_BUFFER_ALL_CPUS);
]
|
| 64/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 40912
output: 40
thoughts: 37
Thoughts: Okay, here's my interpretation of those thoughts, tailored for an expert audience:
**Analyzing Allocation Snapshot Methods**
Right, I'm noting that this process I'm examining, whatever it might be, is invoked from both `tracing_alloc_snapshot_instance` and `free_snapshot`. Interesting. That immediately flags potential interdependencies and a need for careful analysis of how these two functions interact with the core logic. To get a handle on this, my next step is clear β I'm going to dive into `tracing_alloc_snapshot_instance` first. Understanding *its* behavior is likely crucial to understanding the overall snapshot lifecycle and any potential race conditions or inconsistencies that could arise during memory tracking. I need to figure out what that method is doing, where it fits in the sequence. It's the most logical place to start digging to understand how this all fits together.
|
| 65/2 |
2026/08/01 00:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_snapshot.c Name:tracing_alloc_snapshot_instance]
Results: map[SourceCode:2329: static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
2330: {
2331: return 0;
2332: }
SourceFile:kernel/trace/trace.h]
|
| 66/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 41255
output: 40
thoughts: 23
Thoughts: Here's a first-person summary, tailored for an expert audience, based on the provided thought:
**Initial Assessment: The Stub and the Target**
Okay, so I've hit the stub. That immediately tells me I'm likely dealing with the *trace snapshot* functionality. I need to figure out where the code is to understand the context and intent. Right, the obvious place to start digging is `kernel/trace/trace_snapshot.c`. That file is where I'd expect to find the core implementation, initialization, and control logic for taking and managing snapshots of the tracing buffers. Let's see what that yields.
|
| 67/2 |
2026/08/01 00:59 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_snapshot.c Name:tracing_alloc_snapshot_instance]
Results: map[SourceCode:2329: static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
2330: {
2331: return 0;
2332: }
SourceFile:kernel/trace/trace.h]
|
| 68/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 41534
output: 37
thoughts: 17
Thoughts: Here's a summary of my thinking process, rendered in the first person, assuming I'm an expert in the field:
**Debugging My Trace Snapshot Logic**
Okay, hold on a second. I'm just about to dive into this problem, but before I go any further, I need to verify something really crucial. I have a hunch about what might be happening with the trace snapshot, but before I start chasing ghosts, I need to make absolutely sure I'm looking at the right code. The trace snapshot logic is complex, and it's easy to get lost in the details if you're not meticulous. So, just a quick sanity check first: I need to open up `kernel/trace/trace_snapshot.c`. I need to ensure the implementation in there matches what I think I'm seeing behaviorally. Once I have the source code open, I can quickly verify my initial assumption and proceed with debugging. Itβs always best to start with the source of truth, especially when dealing with core kernel functionality. Gotta make sure I'm on the right track before diving deep.
|
| 69/2 |
2026/08/01 00:59 |
tool |
grepper |
0m
Args: map[Expression:int tracing_alloc_snapshot_instance PathPrefix:kernel/trace/trace_snapshot.c]
Results: map[Output:kernel/trace/trace_snapshot.c=137=int resize_buffer_duplicate_size(struct array_buffer *trace_buf,
--
kernel/trace/trace_snapshot.c-161-
kernel/trace/trace_snapshot.c:162:int tracing_alloc_snapshot_instance(struct trace_array *tr)
kernel/trace/trace_snapshot.c-163-{
]
|
| 70/2 |
2026/08/01 00:59 |
llm |
expert |
0m
Model:
Tokens:
input: 41925
output: 37
thoughts: 25
Thoughts: Here's my take on the thought process, as if it were my own:
**Diving into the Tracing Allocator Snapshot**
Alright, time to dig into this `tracing_alloc_snapshot_instance` business. Let's head over to the `kernel/trace/trace_snapshot.c` file. I need to understand exactly how this thing works, how it's implemented in the kernel, and what kind of data it's capturing. I'm hoping to get a handle on the architecture of it. I want to figure out if there's any particular area to start examining given my knowledge of [your field]. Let's see what kind of hooks it's using, and if there are any obvious bottlenecks or potential areas for optimization that jump out at me. I'll be looking for the fundamental mechanisms, the data structures used to store the snapshot information, and how the snapshotting process is triggered and managed. Hopefully, I can grasp the full lifecycle of this thing.
|
| 71/2 |
2026/08/01 00:59 |
tool |
read-file |
0m
Args: map[File:kernel/trace/trace_snapshot.c FirstLine:162 LineCount:30]
Results: map[Contents: 162: int tracing_alloc_snapshot_instance(struct trace_array *tr)
163: {
164: int order;
165: int ret;
166:
167: if (!tr->allocated_snapshot) {
168:
169: /* Make the snapshot buffer have the same order as main buffer */
170: order = ring_buffer_subbuf_order_get(tr->array_buffer.buffer);
171: ret = ring_buffer_subbuf_order_set(tr->snapshot_buffer.buffer, order);
172: if (ret < 0)
173: return ret;
174:
175: /* allocate spare buffer */
176: ret = resize_buffer_duplicate_size(&tr->snapshot_buffer,
177: &tr->array_buffer, RING_BUFFER_ALL_CPUS);
178: if (ret < 0)
179: return ret;
180:
181: tr->allocated_snapshot = true;
182: }
183:
184: return 0;
185: }
186:
187: void free_snapshot(struct trace_array *tr)
188: {
189: /*
190: * We don't free the ring buffer. instead, resize it because
191: * The max_tr ring buffer has some state (e.g. ring->clock) and
]
|
| 72/2 |
2026/08/01 00:59 |
llm |
expert |
1m
Model:
Tokens:
input: 42629
output: 53
thoughts: 24
Thoughts: Here's my take on the thought process, as if it were my own:
**Investigating `tracing_alloc_snapshot_instance`**
Okay, so I'm dealing with `tracing_alloc_snapshot_instance`. The name tells me it's related to tracking memory allocation and likely snapshotting those allocations. The immediate question in my mind is: where the heck is this function actually *being* called from? Knowing the call sites is crucial for understanding the context and purpose of the snapshot instance allocation. I need to trace back from here, see what triggers it, and what other components or functions rely on it. Finding its call sites will dictate how I best investigate its function.
|
| 73/2 |
2026/08/01 01:00 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_snapshot.c IncludeSnippetLines:2 Name:tracing_alloc_snapshot_instance SourceTreePrefix:]
Results: map[References:<nil> TruncatedOutput:false]
|
| 74/2 |
2026/08/01 01:00 |
llm |
expert |
0m
Model:
Tokens:
input: 42867
output: 27
thoughts: 22
Thoughts: Here's my thought process, summarized as you requested:
**Debugging a Missing Component**
Okay, so I'm getting a "not found" error. That's not ideal. My initial hunch is that a critical component is simply missing or not where it's supposed to be. Let's not jump to conclusions about incorrect configurations or complex dependencies just yet. The first, and most straightforward, step is to confirm the presence of this element. The function call I believe is missing is `tracing_alloc_snapshot_instance`. Given the nature of this project I know I can quickly verify its existence through a grep. I'll search the codebase directly. Grep time!
|
| 75/2 |
2026/08/01 01:00 |
tool |
grepper |
0m
Args: map[Expression:tracing_alloc_snapshot_instance PathPrefix:]
Results: map[Output:kernel/trace/trace.c=888=int tracing_alloc_snapshot(void)
--
kernel/trace/trace.c-892-
kernel/trace/trace.c:893: ret = tracing_alloc_snapshot_instance(tr);
kernel/trace/trace.c-894- WARN_ON(ret < 0);
--
kernel/trace/trace.h=2309=void tracing_snapshot_instance(struct trace_array *tr);
kernel/trace/trace.h:2310:int tracing_alloc_snapshot_instance(struct trace_array *tr);
kernel/trace/trace.h-2311-int tracing_arm_snapshot_locked(struct trace_array *tr);
--
kernel/trace/trace.h=2328=static inline void tracing_snapshot_instance(struct trace_array *tr) { }
kernel/trace/trace.h:2329:static inline int tracing_alloc_snapshot_instance(struct trace_array *tr)
kernel/trace/trace.h-2330-{
--
kernel/trace/trace_boot.c=593=trace_boot_enable_tracer(struct trace_array *tr, struct xbc_node *node)
--
kernel/trace/trace_boot.c-606- if (xbc_node_find_value(node, "alloc_snapshot", NULL)) {
kernel/trace/trace_boot.c:607: if (tracing_alloc_snapshot_instance(tr) < 0)
kernel/trace/trace_boot.c-608- pr_err("Failed to allocate snapshot buffer\n");
--
kernel/trace/trace_snapshot.c=137=int resize_buffer_duplicate_size(struct array_buffer *trace_buf,
--
kernel/trace/trace_snapshot.c-161-
kernel/trace/trace_snapshot.c:162:int tracing_alloc_snapshot_instance(struct trace_array *tr)
kernel/trace/trace_snapshot.c-163-{
--
kernel/trace/trace_snapshot.c=201=int tracing_arm_snapshot_locked(struct trace_array *tr)
--
kernel/trace/trace_snapshot.c-215-
kernel/trace/trace_snapshot.c:216: ret = tracing_alloc_snapshot_instance(tr);
kernel/trace/trace_snapshot.c-217- if (ret) {
]
|
| 76/2 |
2026/08/01 01:00 |
llm |
expert |
0m
Model:
Tokens:
input: 43662
output: 25
thoughts: 637
Thoughts: **My Assessment of the Tracefs Use-After-Free Vulnerability**
Okay, let's break this down. My initial assessment is that this looks like a textbook use-after-free, specifically related to `struct buffer_page` within the tracing infrastructure. The attacker, if successful in triggering this bug, could gain a pretty significant arbitrary read primitive. The key is controlling the freed memory and then redirecting `iter->head_page->page` to an arbitrary address. From there, reads within `rb_page_size`, `__rb_page_index`, and the final `memcpy` into `iter->event` become controllable. This data then flows out to userspace through `seq_read`, which is highly problematic.
It's definitely exploitable, giving an attacker arbitrary read access. There's also a significant denial-of-service vector here, as the use-after-free has the potential to crash the kernel.
Now, the crucial part: how accessible is this? Thankfully, it looks like this is *not* something an unprivileged process can just trigger. The vulnerability seems to be rooted in `tracefs` operations, specifically writing to `buffer_subbuf_size_kb` (or other related files) which in turn calls `buffer_subbuf_size_write` that eventually calls the vulnerable code. Those files are locked down. You need root privileges or membership in the `tracing` group to touch those. So, it's not accessible from a standard user account.
The other good news: there's no way to trigger this from within a user namespace, which drastically reduces the attack surface. It's not a VM guest trigger, nor is it related to a confidential computing context or Ethernet, any peripherals, or a malicious filesystem. This all suggests a fairly narrow attack vector, which is good.
Just to be absolutely sure, I'm checking if there is any other call to `buffer_subbuf_size_write` other than `buffer_subbuf_size_kb`. No. It's also worth checking for other methods to trigger `ring_buffer_subbuf_order_set`. This function is critical because it's called from functions that eventually call the vulnerable code. After a deeper dive, it looks like the entry points are `tracing_alloc_snapshot_instance` and `free_snapshot`. These calls lead back through `tracing_snapshot` to various `tracefs` operations as well, which are all restricted. Therefore, I can confirm, it looks to be strictly root-only.
Finally, just to be thorough I need to check the eBPF angle. I have to make sure that some eBPF helper doesn't offer a backdoor to trigger this. I know that `bpf_trace_printk` doesn't change the buffer size or allocate snapshots, but let me double check the `bpf_snapshot` helper, just to be sure... I see nothing that lets eBPF bypass the root restriction. So I think it's all good.
|
| 77/2 |
2026/08/01 01:01 |
tool |
grepper |
0m
Args: map[Expression:bpf_.*snapshot PathPrefix:]
Results: map[Output:include/uapi/linux/bpf.h=1527=union bpf_attr {
--
include/uapi/linux/bpf.h-5425- *
include/uapi/linux/bpf.h:5426: * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
include/uapi/linux/bpf.h-5427- * Description
--
kernel/bpf/fixups.c=1481=int bpf_do_misc_fixups(struct bpf_verifier_env *env)
--
kernel/bpf/fixups.c-2256-
kernel/bpf/fixups.c:2257: /* Implement bpf_get_branch_snapshot inline. */
kernel/bpf/fixups.c-2258- if (IS_ENABLED(CONFIG_PERF_EVENTS) &&
--
kernel/bpf/fixups.c-2261- /* We are dealing with the following func protos:
kernel/bpf/fixups.c:2262: * u64 bpf_get_branch_snapshot(void *buf, u32 size, u64 flags);
kernel/bpf/fixups.c-2263- * int perf_snapshot_branch_stack(struct perf_branch_entry *entries, u32 cnt);
--
kernel/bpf/helpers.c=2063=const struct bpf_func_proto bpf_get_task_stack_proto __weak;
kernel/bpf/helpers.c:2064:const struct bpf_func_proto bpf_get_branch_snapshot_proto __weak;
kernel/bpf/helpers.c-2065-
--
kernel/bpf/helpers.c=2067=bpf_base_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
--
kernel/bpf/helpers.c-2237- case BPF_FUNC_get_branch_snapshot:
kernel/bpf/helpers.c:2238: return &bpf_get_branch_snapshot_proto;
kernel/bpf/helpers.c-2239- case BPF_FUNC_find_vma:
--
kernel/bpf/task_iter.c=914=bpf_iter_task_vma_find_next(struct bpf_iter_task_vma_kern_data *data)
--
kernel/bpf/task_iter.c-949-
kernel/bpf/task_iter.c:950:static void bpf_iter_task_vma_snapshot_reset(struct vm_area_struct *snap)
kernel/bpf/task_iter.c-951-{
--
kernel/bpf/task_iter.c=958=__bpf_kfunc struct vm_area_struct *bpf_iter_task_vma_next(struct bpf_iter_task_vma *it)
--
kernel/bpf/task_iter.c-967-
kernel/bpf/task_iter.c:968: bpf_iter_task_vma_snapshot_reset(snap);
kernel/bpf/task_iter.c-969-
--
kernel/bpf/task_iter.c=991=__bpf_kfunc void bpf_iter_task_vma_destroy(struct bpf_iter_task_vma *it)
--
kernel/bpf/task_iter.c-995- if (kit->data) {
kernel/bpf/task_iter.c:996: bpf_iter_task_vma_snapshot_reset(&kit->data->snapshot);
kernel/bpf/task_iter.c-997- put_task_struct(kit->data->task);
--
kernel/trace/bpf_trace.c=1193=static const struct bpf_func_proto bpf_get_attach_cookie_proto_tracing = {
--
kernel/trace/bpf_trace.c-1199-
kernel/trace/bpf_trace.c:1200:BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
kernel/trace/bpf_trace.c-1201-{
--
kernel/trace/bpf_trace.c-1215-
kernel/trace/bpf_trace.c:1216:const struct bpf_func_proto bpf_get_branch_snapshot_proto = {
kernel/trace/bpf_trace.c:1217: .func = bpf_get_branch_snapshot,
kernel/trace/bpf_trace.c-1218- .gpl_only = true,
--
tools/include/uapi/linux/bpf.h=1527=union bpf_attr {
--
tools/include/uapi/linux/bpf.h-5425- *
tools/include/uapi/linux/bpf.h:5426: * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
tools/include/uapi/linux/bpf.h-5427- * Description
--
tools/testing/selftests/bpf/progs/get_branch_snapshot.c=24=int BPF_PROG(test1, int n, int ret)
--
tools/testing/selftests/bpf/progs/get_branch_snapshot.c-27-
tools/testing/selftests/bpf/progs/get_branch_snapshot.c:28: total_entries = bpf_get_branch_snapshot(entries, sizeof(entries), 0);
tools/testing/selftests/bpf/progs/get_branch_snapshot.c-29- total_entries /= sizeof(struct perf_branch_entry);
]
|
| 78/2 |
2026/08/01 01:01 |
llm |
expert |
0m
Model:
Tokens:
input: 46445
output: 66
thoughts: 437
Thoughts: **My Assessment of the Tracefs Bug**
Okay, so I've been digging into this tracefs issue. First off, `bpf_get_branch_snapshot` is a dead end β that's for perf branch stack, not ftrace snapshots. Can't trigger this via eBPF. I then thought about `trace_boot_enable_tracer`, but that's only called during boot if `alloc_snapshot` is specified in the boot command line, and it requires root to modify boot parameters. Looks like this bug is *strictly* a root-only problem.
But the good news, if you can call it that, is that it *is* exploitable β it's an arbitrary read vulnerability. It could also lead to a denial of service. The important part is that it is *not* accessible from unprivileged processes or within user namespaces. It's also not triggered remotely or by network interactions, peripherals, or malicious filesystems.
I went back and checked if any other path might hit `buffer_subbuf_size_write`, like maybe a script as root, but which gets input from an unprivileged user. No, that's not our threat model; we're evaluating the core kernel.
So here's the final verdict:
* **Exploitable: Yes.** This is a use-after-free situation with `struct buffer_page`. An attacker who can write to `buffer_subbuf_size_kb` can control `iter->head_page->page`. Then, when `rb_page_size` and `__rb_page_index` are called, they read from that attacker-controlled address. The `memcpy` then copies that controlled data to `iter->event`, which gets leaked to userspace via `seq_read`. This provides a very powerful arbitrary read primitive.
* **Denial of Service: Yes.** The use-after-free *can* cause a kernel panic, which is a DoS.
* **Unprivileged: No.** It requires writing to `buffer_subbuf_size_kb` in tracefs, so that's restricted to root or users in the `tracing` group.
* **UserNamespace: No.** Tracefs isn't mountable inside user namespaces.
* **Trigger Types:** Not triggered by any VMGuest, VMHost, Network, Remote, Peripheral, or File System events.
|
| 79/2 |
2026/08/01 01:01 |
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 |
2026/08/01 01:01 |
llm |
expert |
0m
Model:
Tokens:
input: 47524
output: 501
thoughts: 382
Thoughts: **Final Response Generation**
Okay, the analysis is complete, and it's time to craft the definitive response. Based on the investigation, I've got a solid understanding of the issue.
The core problem, as I see it, centers around a classic use-after-free vulnerability within the ring buffer iterator code. Specifically, the race condition between an active iterator (reading from, say, the `trace` or `trace_pipe` files) and a concurrent modification of the sub-buffer size (achieved by writing to `buffer_subbuf_size_kb`) is the crux of the issue.
The function `ring_buffer_subbuf_order_set` handles sub-buffer size changes by allocating new pages, performing a swap, and deallocating the old pages. However, and this is the critical oversight, it *doesn't* update the `head_page` pointers for any iterators that are actively traversing the buffer. Consequently, an iterator ends up pointing to a `struct buffer_page` that has been freed.
When that iterator proceeds, accessing the freed `buffer_page` results in reading garbage values when the size is needed, resulting in a potential crash. If an attacker can then reallocate this freed memory (e.g., using a `kmalloc-64` spray) and control its contents, they can manipulate the `iter->head_page->page` pointer to point to any arbitrary memory address. The kernel would then happily read from this controlled address and copy the data to `iter->event`. This effectively gives the attacker a potent arbitrary read primitive, a dangerous information leak that can be exploited to bypass KASLR or read sensitive data. It also carries the risk of a kernel panic, resulting in a denial-of-service condition.
However, I'm noting that the vulnerability's impact is, in some ways, restricted. Because triggering the bug involves modifying files like `buffer_subbuf_size_kb`, it's not directly accessible to unprivileged users. Those files are locked down with mode `0640` and require either root privileges or membership in the `tracing` group to write to. Moreover, the restriction on tracefs makes exploitation even harder, since it can't be mounted inside a user namespace. The kernel developers did a good job of adding those restrictions.
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Results: map[Explanation:**Exploitable:** Yes
**Denial Of Service:** Yes
**Accessible From Unprivileged Processes:** No
**Accessible From User Namespaces:** No
**VM Guest Trigger:** No
**VM Host Trigger in The Confidential Computing Context:** No
**Ethernet Network Trigger:** No
**Other Remote Trigger:** No
**Peripheral Trigger:** No
**Malicious Filesystem Trigger:** No
**Reasoning:**
The bug is a use-after-free in the ftrace ring buffer iterator code. It occurs
when an active iterator (e.g., a process reading from the `trace` or
`trace_pipe` files) races with a change to the sub-buffer size (e.g., writing to
`buffer_subbuf_size_kb`). The `ring_buffer_subbuf_order_set` function allocates
new pages, swaps them in, and frees the old pages, but it fails to update the
`head_page` pointer of any active iterators. As a result, the iterator continues
to use a freed `struct buffer_page`.
This is exploitable because the freed `struct buffer_page` is allocated from the
`kmalloc-64` cache, which is easy to spray and control. If an attacker
reallocates this memory and controls its contents, they can point
`iter->head_page->page` to an arbitrary memory address. When the iterator
advances, `rb_page_size` and `__rb_page_index` will read from this
attacker-controlled address, and `memcpy` will copy the data to `iter->event`,
which is subsequently returned to userspace via `seq_read`. This provides a
powerful arbitrary read primitive (information leak), which can be used to
bypass KASLR or read sensitive kernel memory. The use-after-free can also easily
lead to a kernel panic, causing a denial of service.
However, the bug is strictly restricted to privileged users. Triggering it
requires writing to `buffer_subbuf_size_kb` (or other tracefs files that
allocate/free snapshot buffers). These files are created with `TRACE_MODE_WRITE`
(mode `0640`) and are only writable by `root` (or users in the `tracing` group).
Furthermore, `tracefs` cannot be mounted inside a user namespace, meaning the
bug cannot be reached by an unprivileged user even within a container.]
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