On Sun, 14 Feb 2016 20:25:55 +0100,
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
>
> The patch below does not apply to the 4.4-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
There is a prerequisite change by the commit
c3b1681375dc6e71d89a3ae00cc3ce9e775a8917
ALSA: timer: Code cleanup
Could you cherry-pick it beforehand?
thanks,
Takashi
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> >From ed8b1d6d2c741ab26d60d499d7fbb7ac801f0f51 Mon Sep 17 00:00:00 2001
> From: Takashi Iwai <tiwai@xxxxxxx>
> Date: Tue, 9 Feb 2016 12:02:32 +0100
> Subject: [PATCH] ALSA: timer: Fix race between stop and interrupt
>
> 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@xxxxxxxxxxxxxx
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
>
> diff --git a/sound/core/timer.c b/sound/core/timer.c
> index dea932ac6165..a0405b0078c6 100644
> --- a/sound/core/timer.c
> +++ b/sound/core/timer.c
> @@ -518,9 +518,13 @@ static int _snd_timer_stop(struct snd_timer_instance *timeri, int event)
> 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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