linux-cve-announce - CVE-2025-40327: perf/core: Fix system hang caused by cpu-clock usage

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Message-ID: <2025120908-CVE-2025-40327-e82c@gregkh>
Date: Tue,  9 Dec 2025 13:10:09 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40327: perf/core: Fix system hang caused by cpu-clock usage

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

perf/core: Fix system hang caused by cpu-clock usage

cpu-clock usage by the async-profiler tool can trigger a system hang,
which got bisected back to the following commit by Octavia Togami:

  18dbcbfabfff ("perf: Fix the POLL_HUP delivery breakage") causes this issue

The root cause of the hang is that cpu-clock is a special type of SW
event which relies on hrtimers. The __perf_event_overflow() callback
is invoked from the hrtimer handler for cpu-clock events, and
__perf_event_overflow() tries to call cpu_clock_event_stop()
to stop the event, which calls htimer_cancel() to cancel the hrtimer.

But that's a recursion into the hrtimer code from a hrtimer handler,
which (unsurprisingly) deadlocks.

To fix this bug, use hrtimer_try_to_cancel() instead, and set
the PERF_HES_STOPPED flag, which causes perf_swevent_hrtimer()
to stop the event once it sees the PERF_HES_STOPPED flag.

[ mingo: Fixed the comments and improved the changelog. ]

The Linux kernel CVE team has assigned CVE-2025-40327 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit 18dbcbfabfffc4a5d3ea10290c5ad27f22b0d240 and fixed in 6.17.8 with commit 6b8c512811644cf2f5eaf6f44e928683c54127f0
	Issue introduced in 6.17 with commit 18dbcbfabfffc4a5d3ea10290c5ad27f22b0d240 and fixed in 6.18 with commit eb3182ef0405ff2f6668fd3e5ff9883f60ce8801
	Issue introduced in 6.16.8 with commit b2de0c9ce8e542b5cb4cd3944620d9dd1ea1f0ac

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-40327
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	kernel/events/core.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/6b8c512811644cf2f5eaf6f44e928683c54127f0
	https://git.kernel.org/stable/c/eb3182ef0405ff2f6668fd3e5ff9883f60ce8801