Commit df7a2d0a authored by Takashi Iwai's avatar Takashi Iwai Committed by Ben Hutchings

ALSA: seq: Fix race during FIFO resize

commit 2d7d5400 upstream.

When a new event is queued while processing to resize the FIFO in
snd_seq_fifo_clear(), it may lead to a use-after-free, as the old pool
that is being queued gets removed.  For avoiding this race, we need to
close the pool to be deleted and sync its usage before actually
deleting it.

The issue was spotted by syzkaller.
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 274b827b
......@@ -267,6 +267,10 @@ int snd_seq_fifo_resize(struct snd_seq_fifo *f, int poolsize)
/* NOTE: overflow flag is not cleared */
spin_unlock_irqrestore(&f->lock, flags);
/* close the old pool and wait until all users are gone */
snd_seq_pool_mark_closing(oldpool);
snd_use_lock_sync(&f->use_lock);
/* release cells in old pool */
for (cell = oldhead; cell; cell = next) {
next = cell->next;
......
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