Commit df393c57 authored by Takashi Iwai's avatar Takashi Iwai Committed by Kamal Mostafa

ALSA: timer: Fix race between stop and interrupt

commit ed8b1d6d upstream.

A slave timer element also unlinks at snd_timer_stop() but it takes
only slave_active_lock.  When a slave is assigned to a master,
however, this may become a race against the master's interrupt
handling, eventually resulting in a list corruption.  The actual bug
could be seen with a syzkaller fuzzer test case in BugLink below.

As a fix, we need to take timeri->timer->lock when timer isn't NULL,
i.e. assigned to a master, while the assignment to a master itself is
protected by slave_active_lock.

BugLink: http://lkml.kernel.org/r/CACT4Y+Y_Bm+7epAb=8Wi=AaWd+DYS7qawX52qxdCfOfY49vozQ@mail.gmail.comSigned-off-by: default avatarTakashi Iwai <tiwai@suse.de>
[ kamal: backport to 3.13-stable: context ]
Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
parent f8093c3b
......@@ -511,9 +511,13 @@ static int _snd_timer_stop(struct snd_timer_instance * timeri,
spin_unlock_irqrestore(&slave_active_lock, flags);
return -EBUSY;
}
if (timeri->timer)
spin_lock(&timeri->timer->lock);
timeri->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
list_del_init(&timeri->ack_list);
list_del_init(&timeri->active_list);
if (timeri->timer)
spin_unlock(&timeri->timer->lock);
spin_unlock_irqrestore(&slave_active_lock, flags);
}
goto __end;
......
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