linux-kernel - Re: snd_seq_timer_open() NULL pointer dereference

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Date:	Fri, 8 Mar 2013 20:59:11 +0200
From:	Tommi Rantala <tt.rantala@...il.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: snd_seq_timer_open() NULL pointer dereference

2013/3/8 Takashi Iwai <tiwai@...e.de>:
> At Thu, 7 Mar 2013 21:59:32 +0200,
> Tommi Rantala wrote:
>>
>> Hello,
>>
>> I'm hitting this while fuzzing the kernel with Trinity:
>
> The patch below fixes a clear bug in the code path.
> Could you check whether it'll fit?
>
>
> thanks,
>
> Takashi
>
> ---
> From: Takashi Iwai <tiwai@...e.de>
> Subject: [PATCH] ALSA: seq: Fix missing error handling in snd_seq_timer_open()
>
> snd_seq_timer_open() didn't catch the whole error path but let through
> if the timer id is a slave.  This may lead to Oops by accessing the
> uninitialized pointer.
>
> Signed-off-by: Takashi Iwai <tiwai@...e.de>

Confirmed, this fixes the bug. Thanks!

Reported-and-tested-by: Tommi Rantala <tt.rantala@...il.com>

> ---
>  sound/core/seq/seq_timer.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
> index 160b1bd..24d44b2 100644
> --- a/sound/core/seq/seq_timer.c
> +++ b/sound/core/seq/seq_timer.c
> @@ -290,10 +290,10 @@ int snd_seq_timer_open(struct snd_seq_queue *q)
>                         tid.device = SNDRV_TIMER_GLOBAL_SYSTEM;
>                         err = snd_timer_open(&t, str, &tid, q->queue);
>                 }
> -               if (err < 0) {
> -                       snd_printk(KERN_ERR "seq fatal error: cannot create timer (%i)\n", err);
> -                       return err;
> -               }
> +       }
> +       if (err < 0) {
> +               snd_printk(KERN_ERR "seq fatal error: cannot create timer (%i)\n", err);
> +               return err;
>         }
>         t->callback = snd_seq_timer_interrupt;
>         t->callback_data = q;
> --
> 1.8.1.4
>
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