4.4-stable review patch. If anyone has any objections, please let me know.
------------------ From: Takashi Iwai <ti...@suse.de> commit ed8b1d6d2c741ab26d60d499d7fbb7ac801f0f51 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+dys7qawx52qxdcfofy49v...@mail.gmail.com Signed-off-by: Takashi Iwai <ti...@suse.de> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- sound/core/timer.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -518,9 +518,13 @@ static int _snd_timer_stop(struct snd_ti 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; }
