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    Subject[PATCH 3.14 49/76] ALSA: timer: Fix race between stop and interrupt
    Date
    3.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Takashi Iwai <tiwai@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+DYS7qawX52qxdCfOfY49vozQ@mail.gmail.com
    Signed-off-by: Takashi Iwai <tiwai@suse.de>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    sound/core/timer.c | 4 ++++
    1 file changed, 4 insertions(+)

    --- a/sound/core/timer.c
    +++ b/sound/core/timer.c
    @@ -508,9 +508,13 @@ 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;
    }

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