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authorTakashi Iwai <tiwai@suse.de>2016-01-14 16:30:58 +0100
committerTakashi Iwai <tiwai@suse.de>2016-01-15 15:50:34 +0100
commitb5a663aa426f4884c71cd8580adae73f33570f0d (patch)
tree87f6d8a3994ca42949130ddb53cb51603fea704f /fs/nfs
parentcf52103a218744f3fd18111325c28e95aa9cd226 (diff)
ALSA: timer: Harden slave timer list handling
A slave timer instance might be still accessible in a racy way while operating the master instance as it lacks of locking. Since the master operation is mostly protected with timer->lock, we should cope with it while changing the slave instance, too. Also, some linked lists (active_list and ack_list) of slave instances aren't unlinked immediately at stopping or closing, and this may lead to unexpected accesses. This patch tries to address these issues. It adds spin lock of timer->lock (either from master or slave, which is equivalent) in a few places. For avoiding a deadlock, we ensure that the global slave_active_lock is always locked at first before each timer lock. Also, ack and active_list of slave instances are properly unlinked at snd_timer_stop() and snd_timer_close(). Last but not least, remove the superfluous call of _snd_timer_stop() at removing slave links. This is a noop, and calling it may confuse readers wrt locking. Further cleanup will follow in a later patch. Actually we've got reports of use-after-free by syzkaller fuzzer, and this hopefully fixes these issues. Reported-by: Dmitry Vyukov <dvyukov@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
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