CVE-2024-38600

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

ALSA: Fix deadlocks with kctl removals at disconnection

In sndcarddisconnect(), we set card->shutdown flag at the beginning, call callbacks and do sync for card->powerrefsleep waiters at the end. The callback may delete a kctl element, and this can lead to a deadlock when the device was in the suspended state. Namely:

• A process waits for the power up at sndpowerrefandwait() in sndctlinfo() or read/write() inside card->controls_rwsem.

• The system gets disconnected meanwhile, and the driver tries to delete a kctl via sndctlremove*(); it tries to take card->controls_rwsem again, but this is already locked by the above. Since the sleeper isn't woken up, this deadlocks.

An easy fix is to wake up sleepers before processing the driver disconnect callbacks but right after setting the card->shutdown flag. Then all sleepers will abort immediately, and the code flows again.

So, basically this patch moves the waitevent() call at the right timing. While we're at it, just to be sure, call waiteventall() instead of waitevent(), although we don't use exclusive events on this queue for now.