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SubjectRe: [PATCH] ALSA: core: Fix possible null-pointer dereferences in snd_timer_proc_read()
On Wed, 24 Jul 2019 14:13:27 +0200,
Jia-Ju Bai wrote:
>
> In snd_timer_proc_read(), there is an if statement on line 1204 to check
> whether timer->card is NULL:
> if (timer->card && timer->card->shutdown)
>
> When timer->card is NULL, it is used on lines 1212 and 1215:
> timer->card->number
>
> Thus, possible null-pointer dereferences may occur.
>
> To fix these bugs, timer->card is checked before being used.

Both cases can (should) never happen. The SNDRV_TIMER_CLASS_CARD is
always associated with a timer with a card object. Ditto for
SNDRV_TIMER_CLASS_PCM, where a PCM is always tied with a card.

So, if any, this should be a WARN_ON(). But I doubt it being any
useful.


thanks,

Takashi

>
> These bugs are found by a static analysis tool STCheck written by us.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
> sound/core/timer.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/sound/core/timer.c b/sound/core/timer.c
> index 5c9fbf3f4340..967d06a3cdec 100644
> --- a/sound/core/timer.c
> +++ b/sound/core/timer.c
> @@ -1208,11 +1208,13 @@ static void snd_timer_proc_read(struct snd_info_entry *entry,
> snd_iprintf(buffer, "G%i: ", timer->tmr_device);
> break;
> case SNDRV_TIMER_CLASS_CARD:
> - snd_iprintf(buffer, "C%i-%i: ",
> - timer->card->number, timer->tmr_device);
> + snd_iprintf(buffer, "C%i-%i: ",
> + timer->card ? timer->card->number : -1,
> + timer->tmr_device);
> break;
> case SNDRV_TIMER_CLASS_PCM:
> - snd_iprintf(buffer, "P%i-%i-%i: ", timer->card->number,
> + snd_iprintf(buffer, "P%i-%i-%i: ",
> + timer->card ? timer->card->number : -1,
> timer->tmr_device, timer->tmr_subdevice);
> break;
> default:
> --
> 2.17.0
>
>

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