CVE-2026-43437

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.