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linux/sound/core/timer.c
Takashi Iwai 15291b561d ALSA: timer: Don't take register_mutex with copy_from/to_user() 
[ Upstream commit 3424c8f53b ]

The infamous mmap_lock taken in copy_from/to_user() can be often
problematic when it's called inside another mutex, as they might lead
to deadlocks.

In the case of ALSA timer code, the bad pattern is with
guard(mutex)(&register_mutex) that covers copy_from/to_user() -- which
was mistakenly introduced at converting to guard(), and it had been
carefully worked around in the past.

This patch fixes those pieces simply by moving copy_from/to_user() out
of the register mutex lock again.

Fixes: 3923de04c8 ("ALSA: pcm: oss: Use guard() for setup")
Reported-by: syzbot+2b96f44164236dda0f3b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/67dd86c8.050a0220.25ae54.0059.GAE@google.com
Link: https://patch.msgid.link/20250321172653.14310-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2025-04-10 14:39:13 +02:00

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