CVE-2025-37747 in Linux
Summary
by MITRE • 05/01/2025
In the Linux kernel, the following vulnerability has been resolved:
perf: Fix hang while freeing sigtrap event
Perf can hang while freeing a sigtrap event if a related deferred signal hadn't managed to be sent before the file got closed:
perf_event_overflow() task_work_add(perf_pending_task)
fput() task_work_add(____fput())
task_work_run() ____fput() perf_release() perf_event_release_kernel() _free_event() perf_pending_task_sync() task_work_cancel() -> FAILED rcuwait_wait_event()
Once task_work_run() is running, the list of pending callbacks is removed from the task_struct and from this point on task_work_cancel() can't remove any pending and not yet started work items, hence the task_work_cancel() failure and the hang on rcuwait_wait_event().
Task work could be changed to remove one work at a time, so a work running on the current task can always cancel a pending one, however the wait / wake design is still subject to inverted dependencies when remote targets are involved, as pictured by Oleg:
T1 T2
fd = perf_event_open(pid => T2->pid); fd = perf_event_open(pid => T1->pid); close(fd) close(fd) <IRQ> <IRQ> perf_event_overflow() perf_event_overflow() task_work_add(perf_pending_task) task_work_add(perf_pending_task) </IRQ> </IRQ> fput() fput() task_work_add(____fput()) task_work_add(____fput())
task_work_run() task_work_run() ____fput() ____fput() perf_release() perf_release() perf_event_release_kernel() perf_event_release_kernel() _free_event() _free_event() perf_pending_task_sync() perf_pending_task_sync() rcuwait_wait_event() rcuwait_wait_event()
Therefore the only option left is to acquire the event reference count upon queueing the perf task work and release it from the task work, just like it was done before 3a5465418f5f ("perf: Fix event leak upon exec and file release") but without the leaks it fixed.
Some adjustments are necessary to make it work:
* A child event might dereference its parent upon freeing. Care must be taken to release the parent last.
* Some places assuming the event doesn't have any reference held and therefore can be freed right away must instead put the reference and let the reference counting to its job.
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Analysis
by VulDB Data Team • 03/15/2026
The vulnerability described in CVE-2025-37747 resides within the Linux kernel's performance monitoring subsystem, specifically affecting the perf event handling mechanism during the cleanup process of signal trap events. This issue manifests as a potential deadlock or hang condition that occurs when attempting to free a sigtrap event while a related deferred signal has not yet been dispatched. The root cause lies in the interaction between task work execution and event reference counting, creating a scenario where the system becomes unresponsive due to circular dependency issues during resource deallocation.
The technical flaw stems from the improper handling of task work callbacks and reference counting within the perf subsystem. When perf_event_overflow() is invoked, it schedules perf_pending_task work via task_work_add(), which later gets executed during task_work_run(). However, if a file descriptor is closed before the deferred signal can be sent, the cleanup process encounters a critical failure during perf_pending_task_sync() where task_work_cancel() fails. This failure occurs because once task_work_run() begins executing, the list of pending callbacks is removed from the task_struct, preventing further cancellation attempts and resulting in an indefinite hang on rcuwait_wait_event(). The vulnerability is classified under CWE-362, which deals with concurrent execution using shared data, and aligns with ATT&CK technique T1486 for data manipulation and T1059 for command and scripting interpreter.
The operational impact of this vulnerability is significant as it can lead to system hangs or unresponsiveness, particularly in environments where performance monitoring is actively used. The hang occurs during the file closing operation when perf events are being torn down, potentially affecting system stability and responsiveness. An attacker could exploit this by creating conditions that trigger the specific race scenario, leading to denial of service through system resource exhaustion or complete system freeze. The vulnerability affects systems using the Linux kernel's perf subsystem and can be particularly problematic in high-performance computing environments or systems with intensive monitoring requirements.
Mitigation strategies should focus on implementing proper reference counting mechanisms during task work scheduling. The solution involves acquiring the event reference count when queuing perf task work and releasing it from the task work context, similar to previous fixes but without reintroducing the memory leaks that were previously addressed. This approach ensures that events remain valid during cleanup operations and prevents premature deallocation. System administrators should ensure kernel updates are applied promptly, as this fix requires modifications to the core perf subsystem. Additionally, monitoring for performance monitoring subsystem anomalies and implementing proper resource cleanup procedures can help detect potential exploitation attempts, though the primary defense lies in the kernel-level fix that properly handles reference counting during concurrent task work execution.