CVE-2026-89979: ALSA: pcm: Fix race between non-atomic ops and trigger-start

CVE-2026-89979: ALSA: pcm: Fix race between non-atomic ops and trigger-start

[Greg Kroah-Hartman]

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

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

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

ALSA: pcm: Fix race between non-atomic ops and trigger-start

We protect the races of the concurrent state transitions between
atomic PCM ops, but the checks between the non-atomic ops (hw_params,
hw_free and prepare) and the atomic ops aren't perfect; there is a
check of the conflicting PCM state at the beginning of hw_params & co,
but the atomic PCM ops can be still issued during the non-atomic PCM
operations.  An example such scenario is that a thread A re-issues the
PREPARE or HW_PARAMS for the already prepared stream, while another
thread B triggers the PCM start in the middle of the prepare
operation.  Although this usually doesn't lead to much serious issues,
it can give some inconsistency as reported by syzkaller (such as
ODEBUG warning).

There are various atomic PCM ops, and basically the only problem is
the PCM start as it operates from the PREPARED state.  Other trigger
commands (stop, etc) are for the running or the other special state,
hence they are filtered as pre-condition.

This patch is for preventing the PCM trigger-start during the non-
atomic operations in order to address the problems above.
Fortunately, the hw_params, hw_free and prepare operations call
snd_pcm_buffer_access_lock(), and this can be used for checking the
concurrent operations at the PCM trigger -- which sets the
runtime->buffer_accessing to a negative (if possible), so the PCM
trigger just needs to check the runtime->buffer_accessing value; if
it's negative, it means the concurrent non-atomic PCM ops is running.

The Linux kernel CVE team has assigned CVE-2026-89979 to this issue.


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

	Fixed in 5.10.270 with commit b1d12144557fceed5de6e22e2c2e30a40ed37702
	Fixed in 5.15.221 with commit b2edc017f94c08bdd0b046a586e43ac771a2f942
	Fixed in 6.1.188 with commit b599e7f16441386754ec083fa62a549bccb02fca
	Fixed in 6.6.157 with commit ad29779736cfd6f5595f0cab300dd7611418e363
	Fixed in 6.12.110 with commit 5abeb4f9f2023f001d693b4e5e1ebbf25e25d0eb
	Fixed in 6.18.51 with commit 7ad2ea7c10044b08ecf7b04376916faf12e17a99
	Fixed in 7.2.5 with commit 50afadf1ea66597116eb14e73c24da7ae99b759f
	Fixed in 7.3-rc2 with commit acac7b5e07349a9d10d78873afb4b93cd1dc721f

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-2026-89979
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:
	sound/core/pcm_native.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/b1d12144557fceed5de6e22e2c2e30a40ed37702
	https://git.kernel.org/stable/c/b2edc017f94c08bdd0b046a586e43ac771a2f942
	https://git.kernel.org/stable/c/b599e7f16441386754ec083fa62a549bccb02fca
	https://git.kernel.org/stable/c/ad29779736cfd6f5595f0cab300dd7611418e363
	https://git.kernel.org/stable/c/5abeb4f9f2023f001d693b4e5e1ebbf25e25d0eb
	https://git.kernel.org/stable/c/7ad2ea7c10044b08ecf7b04376916faf12e17a99
	https://git.kernel.org/stable/c/50afadf1ea66597116eb14e73c24da7ae99b759f
	https://git.kernel.org/stable/c/acac7b5e07349a9d10d78873afb4b93cd1dc721f