AZL-98171

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

ALSA: pcm: wake linked drain waiters on unlink

sndpcmdrain() on a linked stream parks an on-stack wait entry on the drained peer's runtime->sleep, and after scheduletimeout() removes it only if that peer is still found in the caller's group. If group membership changes during the wait and the sleep ends by signal or timeout (so autoremovewakefunction() does not run), finishwait() is skipped and sndpcmdrain() returns with the entry still queued on that stream's sleep list; a later wake_up() then walks a freed stack frame. This is reachable by unlinking either the drained or the draining stream.

Unlike the close path (sndpcmdrop() -> sndpcmpoststop()), sndpcm_unlink() never wakes the sleep queues. Wake every group member under the group lock before the membership change, so a linked drainer is released and drops its entry while the streams are still grouped.

The window was opened when sndpcmlinkrwsem stopped being held across the wait and the removal became conditional on group membership (see Fixes). The later switch to finishwait() kept that conditional removal, so the signal/timeout case remained.