| 0/0 |
2026/08/12 02:10 |
flow |
assessment-security |
28m
Results: map[DenialOfService:true Explanation:**Analysis of the Bug**
The bug report indicates a hung task (`INFO: task syz.0.17:6034 blocked for more
than 143 seconds`) where a process is blocked in `__mutex_lock` while trying to
acquire the `event_mutex` in `__ftrace_set_clr_event`.
Looking at the provided reproducer, the program performs the following actions:
1. Mounts `tracefs`.
2. Opens the `./trace/set_event` file.
3. Writes `*:` to it.
Writing `*:` to the `set_event` file is a command to the ftrace subsystem to
enable **all** available trace events in the kernel. The kernel processes this
by iterating over every registered trace event and enabling them one by one.
Enabling a trace event involves modifying static keys (code patching) and
performing RCU synchronizations (`tracepoint_add_func` -> `tp_rcu_cond_sync`).
When this is done for thousands of trace events sequentially, the operation
takes a significant amount of time (often well over 120 seconds).
Crucially, the entire loop in `__ftrace_set_clr_event` is protected by the
global `event_mutex`. If syzkaller runs multiple instances of this reproducer
concurrently, one instance will acquire the `event_mutex` and begin the slow
process of enabling all events. The other instances will attempt to acquire the
same mutex and block. Because the first instance takes longer than the hung task
timeout (typically 120 seconds) to finish, the blocked instances trigger the
kernel's hung task watchdog, resulting in the reported splat.
**Security Impact Assessment**
* **Exploitable:** No. This is not a memory corruption, use-after-free, or
information leak. It is purely a lock contention issue caused by an
intentionally slow administrative operation.
* **Denial of Service:** Yes. It causes tasks to hang for long periods, and any
other subsystem attempting to acquire `event_mutex` (e.g., `perf_event_open` for
tracepoints, `user_events`) will also be blocked.
* **Accessible From Unprivileged Processes:** No. The `set_event` file is
located within `tracefs`. By default, files in `tracefs` are owned by
`root:root` and `set_event` is created with `0640` (`TRACE_MODE_WRITE`)
permissions. Therefore, unprivileged users cannot write to it.
* **Accessible From User Namespaces:** No. The `tracefs` filesystem does not
have the `FS_USERNS_MOUNT` flag, meaning it cannot be mounted from within an
unprivileged user namespace. It requires `CAP_SYS_ADMIN` in the initial user
namespace.
**Conclusion**
This is a known behavior of the tracing subsystem where enabling all events is
an extremely heavy operation. Because it strictly requires root privileges in
the initial namespace to mount `tracefs` and write to the `set_event` file, it
does not cross any security boundaries and is not considered a security
vulnerability. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/08/12 02:10 |
action |
syz-repro-to-c-repro |
0m
Results: map[SimplifiedCRepro:// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 00} (length 0x8)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000000, "./trace\000", 8);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000000ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 00} (length 0x8)
// }
// type: ptr[in, buffer] {
// buffer: {74 72 61 63 65 66 73 00} (length 0x8)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000000000, "./trace\000", 8);
memcpy((void*)0x200000000100, "tracefs\000", 8);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x200000000000ul, /*type=*/0x200000000100ul, /*flags=*/0ul, /*data=*/0ul);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 2f 73 65 74 5f 65 76 65 6e 74 00} (length 0x12)
// }
// flags: open_flags = 0x2 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000200, "./trace/set_event\000", 18);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000200ul, /*flags=O_RDWR*/2, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {2a 3a} (length 0x2)
// }
// count: len = 0x2 (8 bytes)
// ]
memcpy((void*)0x200000000040, "*:", 2);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x200000000040ul, /*count=*/2ul);
return 0;
}
]
|
| 2/1 |
2026/08/12 02:10 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/1a0aec36943dd0206494f9376d07cfbf81ffc6ec]
|
| 3/1 |
2026/08/12 02:11 |
action |
kernel-builder |
15m
Results: map[KernelObj:/app/workdir/cache/build/08334821d8d80cb6f47ee2b4101b354a0ad47823]
|
| 4/1 |
2026/08/12 02:27 |
action |
codesearch-prepare |
10m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/08/12 02:37 |
agent |
expert |
1m
Model:
Results: map[DenialOfService:true Exploitable:false 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:
INFO: task syz.0.17:6034 blocked for more than 143 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17 state:D stack:27496 pid:6034 tgid:6033 ppid:5744 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0x164/0x2b0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0x7bf/0x1550 kernel/locking/mutex.c:821
__ftrace_set_clr_event kernel/trace/trace_events.c:1409 [inline]
ftrace_set_clr_event+0x3ba/0x5c0 kernel/trace/trace_events.c:1460
ftrace_event_write+0x1fe/0x2b0 kernel/trace/trace_events.c:1548
vfs_write+0x296/0xba0 fs/read_write.c:685
ksys_write+0x150/0x270 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fc695d9e0d9
RSP: 002b:00007fc696c90028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fc696025fa0 RCX: 00007fc695d9e0d9
RDX: 0000000000000002 RSI: 0000200000000040 RDI: 0000000000000003
RBP: 00007fc695e35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc696026038 R14: 00007fc696025fa0 R15: 00007ffd5a54d898
</TASK>
Showing all locks held in the system:
3 locks held by kworker/u8:0/12:
4 locks held by kworker/1:0/24:
#0: ffff88801b02b140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline]
#0: ffff88801b02b140 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405
#1: ffffc900001e7c40 (reg_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline]
#1: ffffc900001e7c40 (reg_work){+.+.}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405
#2: ffffffff90027f40 (rtnl_mutex){+.+.}-{4:4}, at: reg_todo+0x1c/0xa40 net/wireless/reg.c:3205
#3: ffff88806a4807a0 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: class_wiphy_constructor include/net/cfg80211.h:6884 [inline]
#3: ffff88806a4807a0 (&rdev->wiphy.mtx){+.+.}-{4:4}, at: reg_process_self_managed_hints+0x8d/0x160 net/wireless/reg.c:3195
1 lock held by khungtaskd/32:
It is reproducible with the followint program.
Keep in mind that it may lack the precise threading, sandboxing, and some arguments of a working reproducer.
But it should give an idea of the involved syscalls.
// autogenerated by syzkaller (https://github.com/google/syzkaller)
#define _GNU_SOURCE
#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
uint64_t r[1] = {0xffffffffffffffff};
int main(void)
{
syscall(__NR_mmap, /*addr=*/0x1ffffffff000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200000000000ul, /*len=*/0x1000000, /*prot=PROT_WRITE|PROT_READ|PROT_EXEC*/7ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
syscall(__NR_mmap, /*addr=*/0x200001000000ul, /*len=*/0x1000, /*prot=*/0ul, /*flags=MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE*/0x32ul, /*fd=*/(intptr_t)-1, /*offset=*/0ul);
const char* reason;
(void)reason;
intptr_t res = 0;
if (write(1, "executing program\n", sizeof("executing program\n") - 1)) {}
// mkdirat arguments: [
// fd: fd_dir (resource)
// path: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 00} (length 0x8)
// }
// mode: open_mode = 0x1ff (8 bytes)
// ]
memcpy((void*)0x200000000000, "./trace\000", 8);
syscall(__NR_mkdirat, /*fd=*/0xffffff9c, /*path=*/0x200000000000ul, /*mode=S_IXOTH|S_IWOTH|S_IROTH|S_IXGRP|S_IWGRP|S_IRGRP|S_IXUSR|S_IWUSR|0x100*/0x1fful);
// mount arguments: [
// src: nil
// dst: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 00} (length 0x8)
// }
// type: ptr[in, buffer] {
// buffer: {74 72 61 63 65 66 73 00} (length 0x8)
// }
// flags: mount_flags = 0x0 (8 bytes)
// data: nil
// ]
memcpy((void*)0x200000000000, "./trace\000", 8);
memcpy((void*)0x200000000100, "tracefs\000", 8);
syscall(__NR_mount, /*src=*/0ul, /*dst=*/0x200000000000ul, /*type=*/0x200000000100ul, /*flags=*/0ul, /*data=*/0ul);
// openat arguments: [
// fd: fd_dir (resource)
// file: ptr[in, buffer] {
// buffer: {2e 2f 74 72 61 63 65 2f 73 65 74 5f 65 76 65 6e 74 00} (length 0x12)
// }
// flags: open_flags = 0x2 (4 bytes)
// mode: open_mode = 0x0 (2 bytes)
// ]
// returns fd
memcpy((void*)0x200000000200, "./trace/set_event\000", 18);
res = syscall(__NR_openat, /*fd=*/0xffffff9c, /*file=*/0x200000000200ul, /*flags=O_RDWR*/2, /*mode=*/0);
if (res != -1)
r[0] = res;
// write arguments: [
// fd: fd (resource)
// buf: ptr[in, buffer] {
// buffer: {2a 3a} (length 0x2)
// }
// count: len = 0x2 (8 bytes)
// ]
memcpy((void*)0x200000000040, "*:", 2);
syscall(__NR_write, /*fd=*/r[0], /*buf=*/0x200000000040ul, /*count=*/2ul);
return 0;
}
Reply: **Analysis of the Bug**
The bug report indicates a hung task (`INFO: task syz.0.17:6034 blocked for more than 143 seconds`) where a process is blocked in `__mutex_lock` while trying to acquire the `event_mutex` in `__ftrace_set_clr_event`.
Looking at the provided reproducer, the program performs the following actions:
1. Mounts `tracefs`.
2. Opens the `./trace/set_event` file.
3. Writes `*:` to it.
Writing `*:` to the `set_event` file is a command to the ftrace subsystem to enable **all** available trace events in the kernel. The kernel processes this by iterating over every registered trace event and enabling them one by one. Enabling a trace event involves modifying static keys (code patching) and performing RCU synchronizations (`tracepoint_add_func` -> `tp_rcu_cond_sync`). When this is done for thousands of trace events sequentially, the operation takes a significant amount of time (often well over 120 seconds).
Crucially, the entire loop in `__ftrace_set_clr_event` is protected by the global `event_mutex`. If syzkaller runs multiple instances of this reproducer concurrently, one instance will acquire the `event_mutex` and begin the slow process of enabling all events. The other instances will attempt to acquire the same mutex and block. Because the first instance takes longer than the hung task timeout (typically 120 seconds) to finish, the blocked instances trigger the kernel's hung task watchdog, resulting in the reported splat.
**Security Impact Assessment**
* **Exploitable:** No. This is not a memory corruption, use-after-free, or information leak. It is purely a lock contention issue caused by an intentionally slow administrative operation.
* **Denial of Service:** Yes. It causes tasks to hang for long periods, and any other subsystem attempting to acquire `event_mutex` (e.g., `perf_event_open` for tracepoints, `user_events`) will also be blocked.
* **Accessible From Unprivileged Processes:** No. The `set_event` file is located within `tracefs`. By default, files in `tracefs` are owned by `root:root` and `set_event` is created with `0640` (`TRACE_MODE_WRITE`) permissions. Therefore, unprivileged users cannot write to it.
* **Accessible From User Namespaces:** No. The `tracefs` filesystem does not have the `FS_USERNS_MOUNT` flag, meaning it cannot be mounted from within an unprivileged user namespace. It requires `CAP_SYS_ADMIN` in the initial user namespace.
**Conclusion**
This is a known behavior of the tracing subsystem where enabling all events is an extremely heavy operation. Because it strictly requires root privileges in the initial namespace to mount `tracefs` and write to the `set_event` file, it does not cross any security boundaries and is not considered a security vulnerability.
|
| 6/2 |
2026/08/12 02:37 |
llm |
expert |
0m
Model:
Tokens:
input: 8526
output: 32
thoughts: 190
Thoughts: **Analyzing a Hung Task Report**
Okay, so I'm looking at this hung task report. It's saying task `syz.0.17:6034` has been blocked for over 143 seconds. That's a red flag. Let's trace back the call stack to see where it's stuck. The call trace points to `__schedule`, then `schedule`, all the way down to `do_syscall_64`. From this, I can see it's calling `vfs_write`, which probably means it's writing to a file. That's interesting.
The reproducer description is crucial now. It mounts `tracefs` and writes `*:` to `./trace/set_event`. Ah, that's what's happening. `*:` enables all trace events. I know from experience that enabling *all* trace events, especially on a busy system, can be incredibly resource-intensive. It can cause significant delays, potentially locking up the system completely or causing tasks to block while waiting for a mutex. Given that `ftrace_set_clr_event` is in the call stack, I'm going to look closer at that function. I need to understand how the system's events get set and cleared by using that specific trigger.
|
| 7/2 |
2026/08/12 02:37 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile: Name:ftrace_set_clr_event]
Results: map[SourceCode:1416: int ftrace_set_clr_event(struct trace_array *tr, char *buf, int set)
1417: {
1418: char *event = NULL, *sub = NULL, *match, *mod;
1419: int ret;
1420:
1421: if (!tr)
1422: return -ENOENT;
1423:
1424: /* Modules events can be appended with :mod:<module> */
1425: mod = strstr(buf, ":mod:");
1426: if (mod) {
1427: *mod = '\0';
1428: /* move to the module name */
1429: mod += 5;
1430: }
1431:
1432: /*
1433: * The buf format can be <subsystem>:<event-name>
1434: * *:<event-name> means any event by that name.
1435: * :<event-name> is the same.
1436: *
1437: * <subsystem>:* means all events in that subsystem
1438: * <subsystem>: means the same.
1439: *
1440: * <name> (no ':') means all events in a subsystem with
1441: * the name <name> or any event that matches <name>
1442: */
1443:
1444: match = strsep(&buf, ":");
1445: if (buf) {
1446: sub = match;
1447: event = buf;
1448: match = NULL;
1449:
1450: if (!strlen(sub) || strcmp(sub, "*") == 0)
1451: sub = NULL;
1452: if (!strlen(event) || strcmp(event, "*") == 0)
1453: event = NULL;
1454: } else if (mod) {
1455: /* Allow wildcard for no length or star */
1456: if (!strlen(match) || strcmp(match, "*") == 0)
1457: match = NULL;
1458: }
1459:
1460: ret = __ftrace_set_clr_event(tr, match, sub, event, set, mod);
1461:
1462: /* Put back the colon to allow this to be called again */
1463: if (buf)
1464: *(buf - 1) = ':';
1465:
1466: return ret;
1467: }
SourceFile:kernel/trace/trace_events.c]
|
| 8/2 |
2026/08/12 02:37 |
llm |
expert |
0m
Model:
Tokens:
input: 9780
output: 42
thoughts: 29
Thoughts: Here's a summary of my thought process, as requested:
**Deconstructing the Function Call**
Alright, the code's calling `__ftrace_set_clr_event`. Immediately, that sparks my interest. This function name strongly suggests we're dealing with setting or clearing something related to ftrace events. The double underscore prefix is a good indicator that it's an internal function, probably not meant for direct user interaction. Now, the next logical step is to dive right into the definition of `__ftrace_set_clr_event`. I need to understand exactly what parameters it takes, what it does with them, and how it interacts with the ftrace infrastructure. I'm especially keen to see how it handles the "set" and "clear" aspects of the function name. Is it a single function with conditional logic, or is it two distinct paths, perhaps using bitflags to determine behavior? Digging into its implementation will illuminate the core mechanism.
|
| 9/2 |
2026/08/12 02:37 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:__ftrace_set_clr_event]
Results: map[SourceCode:1400: static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
1401: const char *sub, const char *event, int set,
1402: const char *mod)
1403: {
1404: int ret;
1405:
1406: if (trace_array_is_readonly(tr))
1407: return -EACCES;
1408:
1409: mutex_lock(&event_mutex);
1410: ret = __ftrace_set_clr_event_nolock(tr, match, sub, event, set, mod);
1411: mutex_unlock(&event_mutex);
1412:
1413: return ret;
1414: }
SourceFile:kernel/trace/trace_events.c]
|
| 10/2 |
2026/08/12 02:37 |
llm |
expert |
0m
Model:
Tokens:
input: 10303
output: 45
thoughts: 641
Thoughts: **Debugging a Tracing Event Hang**
Okay, so I'm looking at this trace and it seems like something is hanging while trying to acquire `event_mutex`. The hung task is stuck in `__mutex_lock_common` and from the call stack it looks like it's coming from `__ftrace_set_clr_event`. So, the problem is definitely around getting that mutex.
Now, who's holding it? Let's check the lock report. Hmm... it shows other locks being held: things related to workqueues (`wq_completion`, `reg_work`) and networking (`rtnl_mutex`, `rdev->wiphy.mtx`) by various `kworker` threads and `khungtaskd`. But wait a minute, the report doesn't actually tell me who *has* `event_mutex`! That's not helpful at all.
This makes me think. If I write `*:` to `set_event`, which is supposed to enable all events, could that be the problem? Does it take a long time to enable *all* events, or is there a bigger issue? Is it simply a huge amount of overhead to do so? Perhaps there is a potential deadlock!
Let's see. If I write `*:` to `set_event` and it goes through `__ftrace_set_clr_event`, then it calls `__ftrace_set_clr_event_nolock` with `sub = NULL` and `event = NULL`. I need to figure out what's going on *within* `__ftrace_set_clr_event_nolock`. That function must be the key here.
|
| 11/2 |
2026/08/12 02:37 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:__ftrace_set_clr_event_nolock]
Results: map[SourceCode:1321: /*
1322: * __ftrace_set_clr_event(NULL, NULL, NULL, set) will set/unset all events.
1323: */
1324: static int
1325: __ftrace_set_clr_event_nolock(struct trace_array *tr, const char *match,
1326: const char *sub, const char *event, int set,
1327: const char *mod)
1328: {
1329: struct trace_event_file *file;
1330: struct trace_event_call *call;
1331: char *module __free(kfree) = NULL;
1332: const char *name;
1333: int ret = -EINVAL;
1334: int eret = 0;
1335:
1336: if (mod) {
1337: char *p;
1338:
1339: module = kstrdup(mod, GFP_KERNEL);
1340: if (!module)
1341: return -ENOMEM;
1342:
1343: /* Replace all '-' with '_' as that's what modules do */
1344: for (p = strchr(module, '-'); p; p = strchr(p + 1, '-'))
1345: *p = '_';
1346: }
1347:
1348: list_for_each_entry(file, &tr->events, list) {
1349:
1350: call = file->event_call;
1351:
1352: /* If a module is specified, skip events that are not that module */
1353: if (module &&
1354: ((call->flags & TRACE_EVENT_FL_DYNAMIC) ||
1355: !call->module || strcmp(module_name(call->module), module)))
1356: continue;
1357:
1358: name = trace_event_name(call);
1359:
1360: if (!name || !call->class || !call->class->reg)
1361: continue;
1362:
1363: if (call->flags & TRACE_EVENT_FL_IGNORE_ENABLE)
1364: continue;
1365:
1366: if (match &&
1367: strcmp(match, name) != 0 &&
1368: strcmp(match, call->class->system) != 0)
1369: continue;
1370:
1371: if (sub && strcmp(sub, call->class->system) != 0)
1372: continue;
1373:
1374: if (event && strcmp(event, name) != 0)
1375: continue;
1376:
1377: ret = ftrace_event_enable_disable(file, set);
1378:
1379: /*
1380: * Save the first error and return that. Some events
1381: * may still have been enabled, but let the user
1382: * know that something went wrong.
1383: */
1384: if (ret && !eret)
1385: eret = ret;
1386:
1387: ret = eret;
1388: }
1389:
1390: /*
1391: * If this is a module setting and nothing was found,
1392: * check if the module was loaded. If it wasn't cache it.
1393: */
1394: if (module && ret == -EINVAL && !eret)
1395: ret = cache_mod(tr, module, set, match, sub, event);
1396:
1397: return ret;
1398: }
SourceFile:kernel/trace/trace_events.c]
|
| 12/2 |
2026/08/12 02:37 |
llm |
expert |
0m
Model:
Tokens:
input: 12449
output: 41
thoughts: 616
Thoughts: **Analyzing the Trace Event Enabling Issue**
Okay, so I'm looking at this trace event enabling process, and it seems like it's iterating through events, calling `ftrace_event_enable_disable` for each one. The crucial part here is when it writes `*:` to the `set_event` file β that's a wildcard, meaning it's trying to enable *all* events. I know that enabling all events can be slow, but I'm seeing a much bigger problem here.
The hang is happening inside `__mutex_lock_common`, specifically within `__ftrace_set_clr_event`. That means something is blocking on `event_mutex`. It's likely another task is holding the mutex for an extended period, or possibly a deadlock situation. But, `__ftrace_set_clr_event` *acquires* the mutex, so it can't be holding it itself.
Let me check the reproducer to see if it's spawning multiple threads. Nope, it's single-threaded. That's odd.
Wait a second⦠I see the reproducer code is mounting tracefs, opening `set_event`, and writing `*:`. A single-threaded reproducer shouldn't be blocked on the mutex if it's the *only* thing writing to it.
Ah! The lightbulb goes on. This is Syzkaller! It's running the same reproducer multiple times concurrently. So, if multiple instances are all trying to write `*:` to `set_event` at the same time, one wins the mutex and gets to enable all events, which takes a potentially *very* long time. Meanwhile, the other instances are stuck, blocking on `event_mutex`. That explains why the task blocked for more than 143 seconds.
But is enabling all events really taking *that* long? I should probably check what `ftrace_event_enable_disable` is actually doing behind the scenes.
|
| 13/2 |
2026/08/12 02:37 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:ftrace_event_enable_disable]
Results: map[SourceCode: 904: static int ftrace_event_enable_disable(struct trace_event_file *file,
905: int enable)
906: {
907: return __ftrace_event_enable_disable(file, enable, 0);
908: }
SourceFile:kernel/trace/trace_events.c]
|
| 14/2 |
2026/08/12 02:37 |
llm |
expert |
0m
Model:
Tokens:
input: 13640
output: 42
thoughts: 15
Thoughts: Here's a summary of my thought process, as requested:
**Diving into `__ftrace_event_enable_disable`**
Okay, time to get my hands dirty. Let's start by digging into `__ftrace_event_enable_disable`. This function is likely the linchpin for controlling Ftrace event tracing at its most fundamental level. I'm assuming it handles enabling and disabling specific events, and probably interacts directly with the underlying tracing infrastructure. I need to understand its behavior thoroughly to assess any implications for performance overhead, potential bottlenecks, and how it handles concurrency. I'll need to look at how it interacts with the event table, locking mechanisms, and the actual enabling/disabling of the underlying hardware or software probes. I bet there are some interesting subtleties with the RCU usage in that function. My first step is to trace through the code, looking for the important bits, and then I'll formulate test cases to see how it operates in practice.
|
| 15/2 |
2026/08/12 02:38 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:__ftrace_event_enable_disable]
Results: map[SourceCode: 784: static int __ftrace_event_enable_disable(struct trace_event_file *file,
785: int enable, int soft_disable)
786: {
787: struct trace_event_call *call = file->event_call;
788: struct trace_array *tr = file->tr;
789: bool soft_mode = atomic_read(&file->sm_ref) != 0;
790: int ret = 0;
791: int disable;
792:
793: switch (enable) {
794: case 0:
795: /*
796: * When soft_disable is set and enable is cleared, the sm_ref
797: * reference counter is decremented. If it reaches 0, we want
798: * to clear the SOFT_DISABLED flag but leave the event in the
799: * state that it was. That is, if the event was enabled and
800: * SOFT_DISABLED isn't set, then do nothing. But if SOFT_DISABLED
801: * is set we do not want the event to be enabled before we
802: * clear the bit.
803: *
804: * When soft_disable is not set but the soft_mode is,
805: * we do nothing. Do not disable the tracepoint, otherwise
806: * "soft enable"s (clearing the SOFT_DISABLED bit) won't work.
807: */
808: if (soft_disable) {
809: if (atomic_dec_return(&file->sm_ref) > 0)
810: break;
811: disable = file->flags & EVENT_FILE_FL_SOFT_DISABLED;
812: soft_mode = false;
813: /* Disable use of trace_buffered_event */
814: trace_buffered_event_disable();
815: } else
816: disable = !soft_mode;
817:
818: if (disable && (file->flags & EVENT_FILE_FL_ENABLED)) {
819: clear_bit(EVENT_FILE_FL_ENABLED_BIT, &file->flags);
820: if (file->flags & EVENT_FILE_FL_RECORDED_CMD) {
821: tracing_stop_cmdline_record();
822: clear_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
823: }
824:
825: if (file->flags & EVENT_FILE_FL_RECORDED_TGID) {
826: tracing_stop_tgid_record();
827: clear_bit(EVENT_FILE_FL_RECORDED_TGID_BIT, &file->flags);
828: }
829:
830: ret = call->class->reg(call, TRACE_REG_UNREGISTER, file);
831:
832: WARN_ON_ONCE(ret);
833: }
834: /* If in soft mode, just set the SOFT_DISABLE_BIT, else clear it */
835: if (soft_mode)
836: set_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
837: else
838: clear_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
839: break;
840: case 1:
841: /*
842: * When soft_disable is set and enable is set, we want to
843: * register the tracepoint for the event, but leave the event
844: * as is. That means, if the event was already enabled, we do
845: * nothing. If the event is disabled, we set SOFT_DISABLED
846: * before enabling the event tracepoint, so it still seems
847: * to be disabled.
848: */
849: if (!soft_disable)
850: clear_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
851: else {
852: if (atomic_inc_return(&file->sm_ref) > 1)
853: break;
854: /* Enable use of trace_buffered_event */
855: trace_buffered_event_enable();
856: }
857:
858: if (!(file->flags & EVENT_FILE_FL_ENABLED)) {
859: bool cmd = false, tgid = false;
860:
861: /* Keep the event disabled, when going to soft mode. */
862: if (soft_disable)
863: set_bit(EVENT_FILE_FL_SOFT_DISABLED_BIT, &file->flags);
864:
865: if (tr->trace_flags & TRACE_ITER(RECORD_CMD)) {
866: cmd = true;
867: tracing_start_cmdline_record();
868: set_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
869: }
870:
871: if (tr->trace_flags & TRACE_ITER(RECORD_TGID)) {
872: tgid = true;
873: tracing_start_tgid_record();
874: set_bit(EVENT_FILE_FL_RECORDED_TGID_BIT, &file->flags);
875: }
876:
877: ret = call->class->reg(call, TRACE_REG_REGISTER, file);
878: if (ret) {
879: if (cmd)
880: tracing_stop_cmdline_record();
881: if (tgid)
882: tracing_stop_tgid_record();
883: pr_info("event trace: Could not enable event "
884: "%s\n", trace_event_name(call));
885: break;
886: }
887: set_bit(EVENT_FILE_FL_ENABLED_BIT, &file->flags);
888:
889: /* WAS_ENABLED gets set but never cleared. */
890: set_bit(EVENT_FILE_FL_WAS_ENABLED_BIT, &file->flags);
891: }
892: break;
893: }
894:
895: return ret;
896: }
SourceFile:kernel/trace/trace_events.c]
|
| 16/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 15745
output: 39
thoughts: 93
Thoughts: **Investigating Potential Tracepoint Registration Bottleneck**
Okay, so I see this code calling `call->class->reg(call, TRACE_REG_REGISTER, file)`. That's the registration of a tracepoint. Hmm, well, I know that if we're dealing with a large number of tracepoints, this registration process can become a performance bottleneck. But 143 seconds? That seems excessive, even for a significant number of tracepoints. I need to get to the root of this.
I'm thinking this likely involves some kind of RCU synchronization or a similar mechanism, especially if there are thousands of tracepoints involved, and that is what is causing the bottleneck. I need to dive deeper into the code. Let me check the `tracepoint_add_func` function or something similar within the tracing framework. I'm sure that will give me some insight. Time to go digging.
|
| 17/2 |
2026/08/12 02:38 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:tracepoint_add_func]
Results: map[SourceCode: 283: /*
284: * Add the probe function to a tracepoint.
285: */
286: static int tracepoint_add_func(struct tracepoint *tp,
287: struct tracepoint_func *func, int prio,
288: bool warn)
289: {
290: struct tracepoint_func *old, *tp_funcs;
291: int ret;
292:
293: if (tp->ext && tp->ext->regfunc && !static_key_enabled(&tp->key)) {
294: ret = tp->ext->regfunc();
295: if (ret < 0)
296: return ret;
297: }
298:
299: tp_funcs = rcu_dereference_protected(tp->funcs,
300: lockdep_is_held(&tracepoints_mutex));
301: old = func_add(&tp_funcs, func, prio);
302: if (IS_ERR(old)) {
303: if (tp->ext && tp->ext->unregfunc && !static_key_enabled(&tp->key))
304: tp->ext->unregfunc();
305: WARN_ON_ONCE(warn && PTR_ERR(old) != -ENOMEM);
306: return PTR_ERR(old);
307: }
308:
309: /*
310: * rcu_assign_pointer has as smp_store_release() which makes sure
311: * that the new probe callbacks array is consistent before setting
312: * a pointer to it. This array is referenced by __DO_TRACE from
313: * include/linux/tracepoint.h using rcu_dereference_sched().
314: */
315: switch (nr_func_state(tp_funcs)) {
316: case TP_FUNC_1: /* 0->1 */
317: /*
318: * Make sure new static func never uses old data after a
319: * 1->0->1 transition sequence.
320: */
321: tp_rcu_cond_sync(TP_TRANSITION_SYNC_1_0_1);
322: /* Set static call to first function */
323: tracepoint_update_call(tp, tp_funcs);
324: /* Both iterator and static call handle NULL tp->funcs */
325: rcu_assign_pointer(tp->funcs, tp_funcs);
326: static_branch_enable(&tp->key);
327: break;
328: case TP_FUNC_2: /* 1->2 */
329: /* Set iterator static call */
330: tracepoint_update_call(tp, tp_funcs);
331: /*
332: * Iterator callback installed before updating tp->funcs.
333: * Requires ordering between RCU assign/dereference and
334: * static call update/call.
335: */
336: fallthrough;
337: case TP_FUNC_N: /* N->N+1 (N>1) */
338: rcu_assign_pointer(tp->funcs, tp_funcs);
339: /*
340: * Make sure static func never uses incorrect data after a
341: * N->...->2->1 (N>1) transition sequence.
342: */
343: if (tp_funcs[0].data != old[0].data)
344: tp_rcu_get_state(TP_TRANSITION_SYNC_N_2_1);
345: break;
346: default:
347: WARN_ON_ONCE(1);
348: break;
349: }
350:
351: release_probes(tp, old);
352: return 0;
353: }
SourceFile:kernel/tracepoint.c]
|
| 18/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 17213
output: 37
thoughts: 325
Thoughts: **Analyzing Tracepoint Enablement Performance**
Okay, so I'm looking at this tracepoint enablement process, and I'm realizing that `static_branch_enable` could be a real bottleneck, especially since it involves modifying code and might block waiting for RCU synchronization. Then there's `tp_rcu_cond_sync`, which also might have to wait for RCU. The problem really escalates when you consider enabling thousands of tracepoints. That translates to thousands of `static_branch_enable` calls and subsequent RCU syncs. Suddenly, 143 seconds doesn't seem unreasonable, and the delay could easily be much worse.
Is this actually a bug? Well, it seems it's a known issue, that enabling a large number of trace events causes extended delays and can even result in hung task warnings. That matches the observations. But I need to determine if there's any security exposure.
Looking at the reproducer, it shows the use of `tracefs`. And it looks like the reproducer mounts `tracefs`, and that requires `CAP_SYS_ADMIN` in the initial user namespace. But wait, can tracefs even be mounted in a user namespace? This warrants further investigation to understand the security implications.
|
| 19/2 |
2026/08/12 02:38 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/tracefs/inode.c Name:trace_fs_type]
Results: map[SourceCode: 517: static struct file_system_type trace_fs_type = {
518: .owner = THIS_MODULE,
519: .name = "tracefs",
520: .init_fs_context = tracefs_init_fs_context,
521: .parameters = tracefs_param_specs,
522: .kill_sb = kill_anon_super,
523: };
SourceFile:fs/tracefs/inode.c]
|
| 20/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 17987
output: 42
thoughts: 64
Thoughts: Okay, let me think this through.
**Analyzing the Tracefs Mounting Scenario**
Right, so this thing doesn't have the `FS_USERNS_MOUNT` flag set. That means, as far as I understand it, I can't directly mount this within a user namespace. Okay, that's a hurdle, but not necessarily a showstopper. Hold on a second, though... what about the common case? Isn't `tracefs` usually already mounted by root, typically at the standard `/sys/kernel/tracing` location? If it is already mounted, my perspective changes. It would mean I don't need to _create_ the mount.
The critical question now becomes: can an unprivileged user actually *write* to the `set_event` file in that pre-existing, root-mounted `tracefs`? That's the key. If I can't write, the scenario is still dead in the water. But if I *can* write, even a limited set of events, then I might be able to achieve my objective. I need to test that quickly. That's the next step.
|
| 21/2 |
2026/08/12 02:38 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/trace/trace_events.c Name:ftrace_set_event_fops]
Results: map[SourceCode:2645: static const struct file_operations ftrace_set_event_fops = {
2646: .open = ftrace_event_set_open,
2647: .read = seq_read,
2648: .write = ftrace_event_write,
2649: .llseek = seq_lseek,
2650: .release = ftrace_event_release,
2651: };
SourceFile:kernel/trace/trace_events.c]
|
| 22/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 18481
output: 55
thoughts: 12
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Assessing `set_event` Permissions**
Alright, before I proceed any further, I need to meticulously verify the permissions associated with the `set_event` function or object. It's a fundamental step I always take, especially when dealing with any system that could be security-sensitive. My primary concern is ensuring that this function operates within the correct boundaries, that no overly permissive access has been granted, and that it adheres to the principle of least privilege. I'm thinking about the potential impact of improper permissions; any misconfiguration could lead to unintended consequences, data breaches, or, at worst, system compromise. I will carefully examine the access control lists (ACLs), role-based access control (RBAC) configurations, or whatever authorization mechanism is in place. I will be looking for any indications of excessive privileges. The goal is to identify and address any potential security vulnerabilities before they can be exploited. This will include not only examining the `set_event` function itself, but the contexts in which it's executed. Essentially, I'm checking to make sure everything's locked down before I continue. This is just standard operating procedure, nothing to get excited about.
|
| 23/2 |
2026/08/12 02:38 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:2 Name:ftrace_set_event_fops SourceTreePrefix:]
Results: map[References:<nil> TruncatedOutput:false]
|
| 24/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 18826
output: 35
thoughts: 13
Thoughts: Here's my thought process, summarized as you requested:
**Investigating Event Creation**
Okay, hold on a second. Before I dive too deep into this problem, I should take a step back and make sure I'm not missing something fundamental. My initial instinct is to focus on the specific issue at hand, but experience tells me it's often more efficient to check for the most basic building blocks first. Let me perform a quick search for how a `set_event` is created in this context. I need to understand the lifecycle. Perhaps there's a simple, overlooked detail in the event creation process that's causing this. Starting from the foundation will eliminate a whole class of potential errors right away. I need to see how the event is *supposed* to be initialized. A quick search should illuminate the proper setup.
|
| 25/2 |
2026/08/12 02:38 |
tool |
grepper |
0m
Args: map[Expression:trace_create_file.*"set_event" PathPrefix:kernel/trace/]
Results: map[Output: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);
]
|
| 26/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 19198
output: 38
thoughts: 14
Thoughts: Here's my understanding of the thought process, presented as a personal summary:
**File Permissions and Trace Mode**
Okay, so I'm looking at this `TRACE_MODE_WRITE` value, and it's set to `0644`. Right away, that tells me something about the security and access control involved. In this context, I'm assuming we're dealing with file permissions, which is classic.
`0644` translates to read and write permissions for the owner, and read-only permissions for the group and others. That's pretty standard for a lot of configuration files or logs, I'd say. I'm wondering what data this trace mode is writing into the files. Because if it's sensitive information, this setting could introduce a vulnerability. If not, it can be adjusted as required to accommodate the context.
I need to quickly remember the context this is happening in, to decide whether this is appropriate.
|
| 27/2 |
2026/08/12 02:38 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:kernel/trace/trace_events.c Name:TRACE_MODE_WRITE]
Results: map[SourceCode: SourceFile:]
|
| 28/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 19473
output: 31
thoughts: 12
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the Trace Mode**
Alright, let's dive in. My immediate instinct is to pinpoint where this `TRACE_MODE_WRITE` is defined and used. A quick `grep` should do the trick. I need to understand the scope and implications of this particular trace mode, specifically the "write" aspect. This likely means we're dealing with logging or data output related to tracing. Knowing where it's activated will tell me what systems are involved. I'll be looking for source code files, configuration files, and maybe even scripts that reference this constant. The goal is to get a handle on what events or data are being traced when `TRACE_MODE_WRITE` is enabled. Once I've found those locations, I'll be able to quickly determine how to manipulate, and better control it.
|
| 29/2 |
2026/08/12 02:38 |
tool |
grepper |
0m
Args: map[Expression:define TRACE_MODE_WRITE PathPrefix:kernel/trace/]
Results: map[Output: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
]
|
| 30/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 19776
output: 54
thoughts: 178
Thoughts: **Analyzing Tracefs Permissions and Accessibility**
Okay, so looking at this `0640` permission set for files like `set_event` in `tracefs`, I'm processing that: root has full control, the group can read, but everyone else is locked out. This means an unprivileged user can't just go writing to it.
My first thought is, "Well, hang on, syzkaller runs as root in its VM, right?" So, logically, syzkaller *can* mount `tracefs`, it can open and write to `set_event`. But, the real question is, can a non-root user somehow trigger this?
Let's break that down, because a direct route seems unlikely. My knowledge tells me that tracefs requires root to mount it. Even if mounted, the permissions are clearly designed to prevent unprivileged users from fiddling with the contents, like that `0640` on files. The ownership is usually root:root, so the group access wouldn't help.
Alright, so the default permissions on `tracefs` are a dead end for an unprivileged user.
But I still need to be sure. I'm going to quickly check if there is some other way to get to that `ftrace_set_clr_event`.
|
| 31/2 |
2026/08/12 02:38 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:kernel/trace/trace_events.c IncludeSnippetLines:2 Name:ftrace_set_clr_event SourceTreePrefix:]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__early_set_events SourceFile:kernel/trace/trace_events.c SourceLine:4705 SourceSnippet:4703: if (*token) {
4704: if (enable) {
4705: if (ftrace_set_clr_event(tr, token, 1))
4706: pr_warn("Failed to enable trace event: %s\n", token);
4707: } else {
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:__early_set_events SourceFile:kernel/trace/trace_events.c SourceLine:4708 SourceSnippet:4706: pr_warn("Failed to enable trace event: %s\n", token);
4707: } else {
4708: ftrace_set_clr_event(tr, token, 0);
4709: }
4710: }
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:ftrace_event_write SourceFile:kernel/trace/trace_events.c SourceLine:1548 SourceSnippet:1546: set = 0;
1547:
1548: ret = ftrace_set_clr_event(tr, parser.buffer + !set, set);
1549: if (ret)
1550: goto out_put;
]] TruncatedOutput:false]
|
| 32/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 20709
output: 32
thoughts: 1721
Thoughts: **My Analysis of the Hung Task Vulnerability**
Okay, so here's what I've got. The root of the problem is this `__early_set_events` call during boot, which, along with `ftrace_event_write`, lets us write to `set_event` and therefore to tracefs. Since tracefs is the only way to get in here, this isn't an issue unless you have root.
My first thought was, "Could we maybe hit this via perf?" Perf *can* enable tracepoints, so maybe a user could trigger a hang that way. But then I remembered `perf_event_paranoid`. Typically, that's set to 2, which blocks unprivileged users from using tracepoints. However, if it's set to 0 or 1...well, theoretically, yes, an unprivileged user *could* enable tracepoints through `perf_event_open`, but it requires opening each tracepoint individually. Even if that worked, it would take a really long time, and I bet it would be interrupted by signals anyway, so it would avoid the mutex issues. The slow operation holding the mutex for the entire duration is only triggered via the `set_event` write.
The real problem lies in writing `*:` to `set_event`. This holds the `event_mutex` for the full duration of a loop over *all* trace events. That's the slow operation causing the hang.
So, *this* bug is a Denial of Service. It's a hung task.
Is it exploitable? No, it's just a hung task due to a slow operation holding a mutex.
Is it accessible from unprivileged processes? No, `tracefs` is root-only.
Is it accessible from user namespaces? No, `tracefs` is not mountable in user namespaces. I checked the `trace_fs_type` struct, it doesn't have the `FS_USERNS_MOUNT` flag. I also checked that there isn't another way to mount it.
I also double-checked that unprivileged users cannot write to `set_event`. `TRACE_MODE_WRITE` is `0640`, meaning root or group can write to it, and by default, tracefs files are owned by root:root.
I also double-checked there is no other path in the code to trigger `ftrace_set_clr_event`.
The report also mentions other locks held, but those are just normal system state. The hung task is `syz.0.17`, which is the reproducer. It's blocked on `__mutex_lock_common` within `__ftrace_set_clr_event`. This confirms that another task is indeed holding `event_mutex`. Since syzkaller is running multiple instances of the reproducer concurrently, one instance is doing the slow enable-all-events operation (and therefore holds the `event_mutex`), while the other is blocked on `event_mutex` waiting for the first one to finish. The one holding the mutex takes longer than 143 seconds, and the one waiting is then reported as hung. Classic syzkaller, concurrent execution of a slow operation, leading to a hung task.
Okay, so what about security impact?
Since you need root to write to `set_event`, it's *not* a standard security vulnerability. Root can cause a DoS (in many ways), so this isn't really new. So, here's my breakdown:
* **Exploitable:** False (it's a hang)
* **DenialOfService:** True (because it *does* cause a hung task), even though it needs root, and usually if it requires root it is not an issue.
* **Accessible From Unprivileged Processes:** False (requires root)
* **Accessible From User Namespaces:** False (cannot mount in user namespaces)
* **VM Guest Trigger:** False
* **VM Host Trigger in The Confidential Computing Context:** False
* **Ethernet Network Trigger:** False
* **Other Remote Trigger:** False
* **Peripheral Trigger:** False
* **Malicious Filesystem Trigger:** False
I'll double-check `tracefs` can *still* not be mounted in a user namespace in modern kernels, just to be sure.
|
| 33/2 |
2026/08/12 02:38 |
tool |
grepper |
0m
Error:
Args: map[Expression:FS_USERNS_MOUNT PathPrefix:fs/tracefs/]
Results:
|
| 34/2 |
2026/08/12 02:38 |
llm |
expert |
0m
Model:
Tokens:
input: 23410
output: 33
thoughts: 50
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating a Potential Race Condition**
Alright, that's not going to work. Trying to directly write to `set_event` from where I was isn't feasible, and I need to be sure. Let's make absolutely sure there aren't any other code paths, any sneaky alternatives, that could somehow be used to call that function.
Nope, nothing.
Okay, so if I can't directly trigger `set_event`, the only other path is indirectly. I need to now scrutinize `event_mutex` with laser focus. Is there *anything* else holding that mutex that could be influenced or triggered by an unprivileged user? This is where the vulnerability would likely lie. I need to follow the mutex usage thoroughly.
|
| 35/2 |
2026/08/12 02:39 |
tool |
grepper |
0m
Args: map[Expression:mutex_lock\(&event_mutex\) PathPrefix:kernel/trace/]
Results: map[Output:kernel/trace/trace.c=4074=int trace_set_options(struct trace_array *tr, char *option)
--
kernel/trace/trace.c-4089-
kernel/trace/trace.c:4090: mutex_lock(&event_mutex);
kernel/trace/trace.c-4091- mutex_lock(&trace_types_lock);
--
kernel/trace/trace.c=7811=trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
--
kernel/trace/trace.c-7828-
kernel/trace/trace.c:7829: mutex_lock(&event_mutex);
kernel/trace/trace.c-7830- mutex_lock(&trace_types_lock);
--
kernel/trace/trace_boot.c=463=trace_boot_init_one_event(struct trace_array *tr, struct xbc_node *gnode,
--
kernel/trace/trace_boot.c-480-
kernel/trace/trace_boot.c:481: mutex_lock(&event_mutex);
kernel/trace/trace_boot.c-482- file = find_event_file(tr, group, event);
--
kernel/trace/trace_dynevent.c=72=int dyn_event_release(const char *raw_command, struct dyn_event_operations *type)
--
kernel/trace/trace_dynevent.c-101-
kernel/trace/trace_dynevent.c:102: mutex_lock(&event_mutex);
kernel/trace/trace_dynevent.c-103- for_each_dyn_event_safe(pos, n) {
--
kernel/trace/trace_dynevent.c=164=void *dyn_event_seq_start(struct seq_file *m, loff_t *pos)
kernel/trace/trace_dynevent.c-165-{
kernel/trace/trace_dynevent.c:166: mutex_lock(&event_mutex);
kernel/trace/trace_dynevent.c-167- return seq_list_start(&dyn_event_list, *pos);
--
kernel/trace/trace_dynevent.c=208=int dyn_events_release_all(struct dyn_event_operations *type)
--
kernel/trace/trace_dynevent.c-212-
kernel/trace/trace_dynevent.c:213: mutex_lock(&event_mutex);
kernel/trace/trace_dynevent.c-214- for_each_dyn_event(ev) {
--
kernel/trace/trace_event_perf.c=215=int perf_trace_init(struct perf_event *p_event)
--
kernel/trace/trace_event_perf.c-220-
kernel/trace/trace_event_perf.c:221: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-222- list_for_each_entry(tp_event, &ftrace_events, list) {
--
kernel/trace/trace_event_perf.c=237=void perf_trace_destroy(struct perf_event *p_event)
kernel/trace/trace_event_perf.c-238-{
kernel/trace/trace_event_perf.c:239: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-240- perf_trace_event_close(p_event);
--
kernel/trace/trace_event_perf.c=247=int perf_kprobe_init(struct perf_event *p_event, bool is_retprobe)
--
kernel/trace/trace_event_perf.c-274-
kernel/trace/trace_event_perf.c:275: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-276- ret = perf_trace_event_init(tp_event, p_event);
--
kernel/trace/trace_event_perf.c=285=void perf_kprobe_destroy(struct perf_event *p_event)
kernel/trace/trace_event_perf.c-286-{
kernel/trace/trace_event_perf.c:287: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-288- perf_trace_event_close(p_event);
--
kernel/trace/trace_event_perf.c=298=int perf_uprobe_init(struct perf_event *p_event,
--
kernel/trace/trace_event_perf.c-330- */
kernel/trace/trace_event_perf.c:331: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-332- ret = perf_trace_event_init(tp_event, p_event);
--
kernel/trace/trace_event_perf.c=341=void perf_uprobe_destroy(struct perf_event *p_event)
kernel/trace/trace_event_perf.c-342-{
kernel/trace/trace_event_perf.c:343: mutex_lock(&event_mutex);
kernel/trace/trace_event_perf.c-344- perf_trace_event_close(p_event);
--
kernel/trace/trace_events.c=1024=static void ftrace_clear_events(struct trace_array *tr)
--
kernel/trace/trace_events.c-1027-
kernel/trace/trace_events.c:1028: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1029- list_for_each_entry(file, &tr->events, list) {
--
kernel/trace/trace_events.c=1219=static void ftrace_clear_event_pids(struct trace_array *tr, int type)
kernel/trace/trace_events.c-1220-{
kernel/trace/trace_events.c:1221: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1222- __ftrace_clear_event_pids(tr, type);
--
kernel/trace/trace_events.c=1268=static void put_system(struct trace_subsystem_dir *dir)
kernel/trace/trace_events.c-1269-{
kernel/trace/trace_events.c:1270: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1271- __put_system_dir(dir);
--
kernel/trace/trace_events.c=1400=static int __ftrace_set_clr_event(struct trace_array *tr, const char *match,
--
kernel/trace/trace_events.c-1408-
kernel/trace/trace_events.c:1409: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1410- ret = __ftrace_set_clr_event_nolock(tr, match, sub, event, set, mod);
--
kernel/trace/trace_events.c=1584=static void *t_start(struct seq_file *m, loff_t *pos)
--
kernel/trace/trace_events.c-1589-
kernel/trace/trace_events.c:1590: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1591-
--
kernel/trace/trace_events.c=1652=static void *s_start(struct seq_file *m, loff_t *pos)
--
kernel/trace/trace_events.c-1658- iter = kzalloc_obj(*iter);
kernel/trace/trace_events.c:1659: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1660- if (!iter)
--
kernel/trace/trace_events.c=1832=static void *__start(struct seq_file *m, loff_t *pos, int type)
--
kernel/trace/trace_events.c-1843- */
kernel/trace/trace_events.c:1844: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1845- rcu_read_lock_sched();
--
kernel/trace/trace_events.c=1878=event_enable_read(struct file *filp, char __user *ubuf, size_t cnt,
--
kernel/trace/trace_events.c-1884-
kernel/trace/trace_events.c:1885: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-1886- file = event_file_file(filp);
--
kernel/trace/trace_events.c=2141=static void *f_start(struct seq_file *m, loff_t *pos)
--
kernel/trace/trace_events.c-2147- /* ->stop() is called even if ->start() fails */
kernel/trace/trace_events.c:2148: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-2149- file = event_file_file(m->private);
--
kernel/trace/trace_events.c=2206=event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
--
kernel/trace/trace_events.c-2222-
kernel/trace/trace_events.c:2223: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-2224- file = event_file_file(filp);
--
kernel/trace/trace_events.c=2239=event_filter_write(struct file *filp, const char __user *ubuf, size_t cnt,
--
kernel/trace/trace_events.c-2252-
kernel/trace/trace_events.c:2253: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-2254- file = event_file_file(filp);
--
kernel/trace/trace_events.c=2270=static int subsystem_open(struct inode *inode, struct file *filp)
--
kernel/trace/trace_events.c-2280- /* Make sure the system still exists */
kernel/trace/trace_events.c:2281: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-2282- mutex_lock(&trace_types_lock);
--
kernel/trace/trace_events.c=3748=static void trace_early_triggers(struct trace_event_file *file, const char *name)
--
kernel/trace/trace_events.c-3755- continue;
kernel/trace/trace_events.c:3756: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-3757- ret = trigger_process_regex(file, bootup_triggers[i].trigger);
--
kernel/trace/trace_events.c=3976=static int trace_module_notify(struct notifier_block *self,
--
kernel/trace/trace_events.c-3980-
kernel/trace/trace_events.c:3981: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-3982- mutex_lock(&trace_types_lock);
--
kernel/trace/trace_events.c=4123=void trace_put_event_file(struct trace_event_file *file)
kernel/trace/trace_events.c-4124-{
kernel/trace/trace_events.c:4125: mutex_lock(&event_mutex);
kernel/trace/trace_events.c-4126- trace_event_put_ref(file->event_call);
--
kernel/trace/trace_events_filter.c=1270=void print_subsystem_event_filter(struct event_subsystem *system,
--
kernel/trace/trace_events_filter.c-1274-
kernel/trace/trace_events_filter.c:1275: mutex_lock(&event_mutex);
kernel/trace/trace_events_filter.c-1276- filter = system->filter;
--
kernel/trace/trace_events_filter.c=2859=static __init int ftrace_test_event_filter(void)
--
kernel/trace/trace_events_filter.c-2880- /* Needed to dereference filter->prog */
kernel/trace/trace_events_filter.c:2881: mutex_lock(&event_mutex);
kernel/trace/trace_events_filter.c-2882- /*
--
kernel/trace/trace_events_inject.c=284=event_inject_write(struct file *filp, const char __user *ubuf, size_t cnt,
--
kernel/trace/trace_events_inject.c-300-
kernel/trace/trace_events_inject.c:301: mutex_lock(&event_mutex);
kernel/trace/trace_events_inject.c-302- file = event_file_file(filp);
--
kernel/trace/trace_events_synth.c=1366=static int __create_synth_event(const char *name, const char *raw_fields)
--
kernel/trace/trace_events_synth.c-1390-
kernel/trace/trace_events_synth.c:1391: mutex_lock(&event_mutex);
kernel/trace/trace_events_synth.c-1392-
--
kernel/trace/trace_events_synth.c=1584=int synth_event_delete(const char *event_name)
--
kernel/trace/trace_events_synth.c-1589-
kernel/trace/trace_events_synth.c:1590: mutex_lock(&event_mutex);
kernel/trace/trace_events_synth.c-1591- se = find_synth_event(event_name);
--
kernel/trace/trace_events_trigger.c=282=static void *trigger_start(struct seq_file *m, loff_t *pos)
--
kernel/trace/trace_events_trigger.c-286- /* ->stop() is called even if ->start() fails */
kernel/trace/trace_events_trigger.c:287: mutex_lock(&event_mutex);
kernel/trace/trace_events_trigger.c-288- event_file = event_file_file(m->private);
--
kernel/trace/trace_events_user.c=241=static void delayed_destroy_user_event(struct work_struct *work)
--
kernel/trace/trace_events_user.c-245-
kernel/trace/trace_events_user.c:246: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-247-
--
kernel/trace/trace_events_user.c=468=static void user_event_enabler_fault_fixup(struct work_struct *work)
--
kernel/trace/trace_events_user.c-487- /* Prevent state changes from racing */
kernel/trace/trace_events_user.c:488: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-489-
--
kernel/trace/trace_events_user.c=906=static struct user_event_enabler
--
kernel/trace/trace_events_user.c-935- /* Prevents state changes from racing with new enablers */
kernel/trace/trace_events_user.c:936: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-937-
--
kernel/trace/trace_events_user.c=2086=static int user_event_parse(struct user_event_group *group, char *name,
--
kernel/trace/trace_events_user.c-2110- /* Prevent dyn_event from racing */
kernel/trace/trace_events_user.c:2111: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2112- user = find_user_event(group, name, argc, (const char **)argv,
--
kernel/trace/trace_events_user.c-2179-
kernel/trace/trace_events_user.c:2180: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2181-
--
kernel/trace/trace_events_user.c=2553=static long user_events_ioctl_del(struct user_event_file_info *info,
--
kernel/trace/trace_events_user.c-2565- /* event_mutex prevents dyn_event from racing */
kernel/trace/trace_events_user.c:2566: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2567- ret = delete_user_event(info->group, name);
--
kernel/trace/trace_events_user.c=2601=static int user_event_mm_clear_bit(struct user_event_mm *user_mm,
--
kernel/trace/trace_events_user.c-2613- /* Prevents state changes from racing with new enablers */
kernel/trace/trace_events_user.c:2614: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2615-
--
kernel/trace/trace_events_user.c=2635=static long user_events_ioctl_unreg(unsigned long uarg)
--
kernel/trace/trace_events_user.c-2661- */
kernel/trace/trace_events_user.c:2662: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2663-
--
kernel/trace/trace_events_user.c=2900=static int set_max_user_events_sysctl(const struct ctl_table *table, int write,
--
kernel/trace/trace_events_user.c-2904-
kernel/trace/trace_events_user.c:2905: mutex_lock(&event_mutex);
kernel/trace/trace_events_user.c-2906-
--
kernel/trace/trace_fprobe.c=1109=static int __tprobe_event_module_cb(struct notifier_block *self,
--
kernel/trace/trace_fprobe.c-1118-
kernel/trace/trace_fprobe.c:1119: mutex_lock(&event_mutex);
kernel/trace/trace_fprobe.c-1120- for_each_trace_fprobe(tf, pos) {
]
|
| 36/2 |
2026/08/12 02:39 |
llm |
expert |
0m
Model:
Tokens:
input: 28511
output: 66
thoughts: 828
Thoughts: **Analyzing the Impact of the `event_mutex` Issue**
Okay, let's break this down. My initial concern was whether unprivileged users could somehow leverage `user_events` or `perf_event_open` to hold the `event_mutex` and cause problems. I see that `user_events` is off-limits because it's exposed through tracefs, which unprivileged users can't directly access. `perf_event_open` uses the mutex, too, but I need to figure out how exploitable this is.
If `perf_event_paranoid` is set appropriately, an unprivileged user *could* open a tracepoint using `perf_event_open`. But the important thing is that `perf_event_open` only opens one at a time. So, it would acquire the mutex, do something relatively quick, and release it. It's not a sustained hold.
The potential race condition, however, is intriguing. Could a concurrent `perf_event_open` call block on the mutex while root is doing a lengthy operation on `set_event`, locking the mutex for a long period? Yes, that's the scenario, and I think that's it. It's a "hung task" on the unprivileged side, but it's the root process that is doing the slow part. However, an unprivileged user can't *cause* the 143-second lock. They can only get blocked by it.
So, the core issue is only triggerable by root, the scenario I analyzed. The provided reproducer confirms this.
Therefore, the exploitability is False, and the denial of service aspect, though impactful, requires root privileges to trigger. Unprivileged users can only be indirectly affected. So, Unprivileged is False and DenialOfService is True. UserNamespace is False, it's not a VM trigger, network, remote, peripheral or filesystem triggered.
A hung task doesn't *necessarily* crash the system, unless `kernel.hung_task_panic` is set. It's a denial of service because the task is blocked for a significant amount of time, and anything else using the same mutex is blocked, too, though it requires root. I will set the DenialOfService to True and Unprivileged to False.
Time to set the results.
|
| 37/2 |
2026/08/12 02:39 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:false VMGuestTrigger:false VMHostTrigger:false]
|
| 38/2 |
2026/08/12 02:39 |
llm |
expert |
0m
Model:
Tokens:
input: 29962
output: 662
thoughts: 273
Thoughts: **Final Thoughts on the Hung Task Bug**
Okay, the analysis is complete, and the outcome is clear. Now it's time to craft the final response, succinctly summarizing what I've discovered.
Essentially, we're looking at a hung task situation. Itβs triggered by a specific, albeit broad, action within the `tracefs` filesystem: writing `*:` to the `set_event` file. This command effectively attempts to enable *every* single trace event available in the system. The root of the problem? Enabling thousands of events sequentially is, well, slow. It's an inherently time-consuming process due to the underlying synchronization mechanisms, specifically the RCU synchronizations and the static branch updates that need to occur for each individual event. Critically, the entire operation is serialized by holding the `event_mutex`.
The crux of the matter is that when multiple threads or processes attempt to enable all events concurrently, one process will inevitably grab that `event_mutex` and hold it for an extended period. This leads to other processes, wanting the mutex, blocking for far too longβdefinitely exceeding the kernel's hung task watchdog timeout of 120 seconds. And boom, the watchdog triggers a hung task report.
Now, a couple of key mitigating factors: `tracefs` can *only* be mounted in the initial user namespace, and the `set_event` file itself is restricted to root access, with permissions set to `0640`. That limits this bug's reach significantly. It can *only* be triggered by a privileged user β root β it is not accessible to unprivileged users or within user namespaces.
Considering that the issue requires root privileges to trigger, it does not constitute a security vulnerability. This bug won't allow memory corruption or privilege escalation, and therefore, it's not exploitable in the conventional sense. The only real-world consequence is a temporary denial of service; any process that tries to acquire `event_mutex` will have a hung task, but again, that is only possible with root access.
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Results: map[Explanation:**Analysis of the Bug**
The bug report indicates a hung task (`INFO: task syz.0.17:6034 blocked for more
than 143 seconds`) where a process is blocked in `__mutex_lock` while trying to
acquire the `event_mutex` in `__ftrace_set_clr_event`.
Looking at the provided reproducer, the program performs the following actions:
1. Mounts `tracefs`.
2. Opens the `./trace/set_event` file.
3. Writes `*:` to it.
Writing `*:` to the `set_event` file is a command to the ftrace subsystem to
enable **all** available trace events in the kernel. The kernel processes this
by iterating over every registered trace event and enabling them one by one.
Enabling a trace event involves modifying static keys (code patching) and
performing RCU synchronizations (`tracepoint_add_func` -> `tp_rcu_cond_sync`).
When this is done for thousands of trace events sequentially, the operation
takes a significant amount of time (often well over 120 seconds).
Crucially, the entire loop in `__ftrace_set_clr_event` is protected by the
global `event_mutex`. If syzkaller runs multiple instances of this reproducer
concurrently, one instance will acquire the `event_mutex` and begin the slow
process of enabling all events. The other instances will attempt to acquire the
same mutex and block. Because the first instance takes longer than the hung task
timeout (typically 120 seconds) to finish, the blocked instances trigger the
kernel's hung task watchdog, resulting in the reported splat.
**Security Impact Assessment**
* **Exploitable:** No. This is not a memory corruption, use-after-free, or
information leak. It is purely a lock contention issue caused by an
intentionally slow administrative operation.
* **Denial of Service:** Yes. It causes tasks to hang for long periods, and any
other subsystem attempting to acquire `event_mutex` (e.g., `perf_event_open` for
tracepoints, `user_events`) will also be blocked.
* **Accessible From Unprivileged Processes:** No. The `set_event` file is
located within `tracefs`. By default, files in `tracefs` are owned by
`root:root` and `set_event` is created with `0640` (`TRACE_MODE_WRITE`)
permissions. Therefore, unprivileged users cannot write to it.
* **Accessible From User Namespaces:** No. The `tracefs` filesystem does not
have the `FS_USERNS_MOUNT` flag, meaning it cannot be mounted from within an
unprivileged user namespace. It requires `CAP_SYS_ADMIN` in the initial user
namespace.
**Conclusion**
This is a known behavior of the tracing subsystem where enabling all events is
an extremely heavy operation. Because it strictly requires root privileges in
the initial namespace to mount `tracefs` and write to the `set_event` file, it
does not cross any security boundaries and is not considered a security
vulnerability.]
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