Bug 2468150 (CVE-2026-43437)

Summary: CVE-2026-43437 kernel: ALSA: pcm: fix use-after-free on linked stream runtime in snd_pcm_drain()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's ALSA (Advanced Linux Sound Architecture) PCM (Pulse Code Modulation) subsystem. A local attacker could exploit a use-after-free vulnerability by triggering a race condition when closing a linked audio stream. This could lead to system instability, denial of service, or potentially privilege escalation by allowing access to freed memory.
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Description OSIDB Bzimport 2026-05-08 15:01:45 UTC 
In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: fix use-after-free on linked stream runtime in snd_pcm_drain()

In the drain loop, the local variable 'runtime' is reassigned to a
linked stream's runtime (runtime = s->runtime at line 2157).  After
releasing the stream lock at line 2169, the code accesses
runtime->no_period_wakeup, runtime->rate, and runtime->buffer_size
(lines 2170-2178) — all referencing the linked stream's runtime without
any lock or refcount protecting its lifetime.

A concurrent close() on the linked stream's fd triggers
snd_pcm_release_substream() → snd_pcm_drop() → pcm_release_private()
→ snd_pcm_unlink() → snd_pcm_detach_substream() → kfree(runtime).
No synchronization prevents kfree(runtime) from completing while the
drain path dereferences the stale pointer.

Fix by caching the needed runtime fields (no_period_wakeup, rate,
buffer_size) into local variables while still holding the stream lock,
and using the cached values after the lock is released.
Comment 1 Keith Grant 2026-05-08 23:54:44 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050853-CVE-2026-43437-be27@gregkh/T