CVE-2026-43437

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

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

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->noperiodwakeup, 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 sndpcmreleasesubstream() → sndpcmdrop() → pcmreleaseprivate() → sndpcmunlink() → sndpcmdetachsubstream() → kfree(runtime). No synchronization prevents kfree(runtime) from completing while the drain path dereferences the stale pointer.

Fix by caching the needed runtime fields (noperiodwakeup, rate, buffer_size) into local variables while still holding the stream lock, and using the cached values after the lock is released.