On Wed, Jan 13, 2016 at 8:05 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Wed, 13 Jan 2016 19:34:36 +0100,
> Dmitry Vyukov wrote:
>>
>> On Wed, Jan 13, 2016 at 5:53 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
>> > This and your other relevant reports seem pointing the race of timer
>> > ioctls. Although snd_timer_close() itself calls snd_timer_stop(),
>> > there is no other protection against the concurrent execution.
>> >
>> > If my guess is correct, a simplistic fix like below should work. It
>> > basically serializes the timer ioctl by using a new mutex (and
>> > replacing the old tread_sem mutex). They are no longtime blocking
>> > calls, so this shouldn't be a big problem. But certainly there can be
>> > a less intrusive way to paper over this if this really matters.
>> >
>> > In this case for timer.c, I'd leave the final decision rather to
>> > Jaroslav. Jaroslav, what do you think?
>>
>>
>> After applying this patch I still see the following WARNINGS:
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 2 PID: 30398 at lib/list_debug.c:53 __list_del_entry+0x10b/0x1e0()
>> list_del corruption, ffff880032d933b0->next is LIST_POISON1 (dead000000000100)
>> Modules linked in:
>> CPU: 2 PID: 30398 Comm: syz-executor Not tainted 4.4.0+ #241
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> 00000000ffffffff ffff8800627778d8 ffffffff82926eed ffff880062777948
>> ffff880061c2af80 ffffffff8660b640 ffff880062777918 ffffffff81350c89
>> ffffffff8298e77b ffffed000c4eef25 ffffffff8660b640 0000000000000035
>> Call Trace:
>> [< inline >] __dump_stack lib/dump_stack.c:15
>> [<ffffffff82926eed>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>> [<ffffffff81350c89>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:483
>> [<ffffffff81350d99>] warn_slowpath_fmt+0xa9/0xd0 kernel/panic.c:495
>> [<ffffffff8298e77b>] __list_del_entry+0x10b/0x1e0 lib/list_debug.c:51
>> [< inline >] list_del_init include/linux/list.h:145
>> [<ffffffff84ebd199>] _snd_timer_stop+0x119/0x450 sound/core/timer.c:501
>
> This is
>
> list_del_init(&timeri->active_list);
>
> right? Possibly the following oneliner covers it?
Yes, that is this line.
Yes, these two patches fix use-after-frees and GPFs.
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
The only one that still happens is "sound: spinlock lockup in
sound/core/timer.c".
> thanks,
>
> Takashi
>
> ---
> diff --git a/sound/core/timer.c b/sound/core/timer.c
> index b03a9e489286..3810ee8f1205 100644
> --- a/sound/core/timer.c
> +++ b/sound/core/timer.c
> @@ -694,7 +694,7 @@ void snd_timer_interrupt(struct snd_timer * timer, unsigned long ticks_left)
> } else {
> ti->flags &= ~SNDRV_TIMER_IFLG_RUNNING;
> if (--timer->running)
> - list_del(&ti->active_list);
> + list_del_init(&ti->active_list);
> }
> if ((timer->hw.flags & SNDRV_TIMER_HW_TASKLET) ||
> (ti->flags & SNDRV_TIMER_IFLG_FAST))
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
