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ALSA: sh: aica: reorder cleanup operations to avoid UAF bugs 

The dreamcastcard->timer could schedule the spu_dma_work and the
spu_dma_work could also arm the dreamcastcard->timer.

When the snd_pcm_substream is closing, the aica_channel will be
deallocated. But it could still be dereferenced in the worker
thread. The reason is that del_timer() will return directly
regardless of whether the timer handler is running or not and
the worker could be rescheduled in the timer handler. As a result,
the UAF bug will happen. The racy situation is shown below:

      (Thread 1)                 |      (Thread 2)
snd_aicapcm_pcm_close()          |
 ...                             |  run_spu_dma() //worker
                                 |    mod_timer()
  flush_work()                   |
  del_timer()                    |  aica_period_elapsed() //timer
  kfree(dreamcastcard->channel)  |    schedule_work()
                                 |  run_spu_dma() //worker
  ...                            |    dreamcastcard->channel-> //USE

In order to mitigate this bug and other possible corner cases,
call mod_timer() conditionally in run_spu_dma(), then implement
PCM sync_stop op to cancel both the timer and worker. The sync_stop
op will be called from PCM core appropriately when needed.

Fixes: 198de43d75 ("[ALSA] Add ALSA support for the SEGA Dreamcast PCM device")
Suggested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Message-ID: <20240326094238.95442-1-duoming@zju.edu.cn>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Duoming Zhou 2024-03-26 17:42:38 +08:00 committed by Takashi Iwai
parent cafe9c6a72
commit 051e0840ff
1 changed files with 14 additions and 3 deletions
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15
sound/sh/aica.c
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@ -278,6 +278,7 @@ static void run_spu_dma(struct work_struct *work)
dreamcastcard->clicks++;
if (unlikely(dreamcastcard->clicks >= AICA_PERIOD_NUMBER))
dreamcastcard->clicks %= AICA_PERIOD_NUMBER;
if (snd_pcm_running(dreamcastcard->substream))
mod_timer(&dreamcastcard->timer, jiffies + 1);
}
}
@ -290,6 +291,8 @@ static void aica_period_elapsed(struct timer_list *t)
/*timer function - so cannot sleep */
int play_period;
struct snd_pcm_runtime *runtime;
if (!snd_pcm_running(substream))
return;
runtime = substream->runtime;
dreamcastcard = substream->pcm->private_data;
/* Have we played out an additional period? */
@ -350,12 +353,19 @@ static int snd_aicapcm_pcm_open(struct snd_pcm_substream
return 0;
}
static int snd_aicapcm_pcm_sync_stop(struct snd_pcm_substream *substream)
{
struct snd_card_aica *dreamcastcard = substream->pcm->private_data;
del_timer_sync(&dreamcastcard->timer);
cancel_work_sync(&dreamcastcard->spu_dma_work);
return 0;
}
static int snd_aicapcm_pcm_close(struct snd_pcm_substream
*substream)
{
struct snd_card_aica *dreamcastcard = substream->pcm->private_data;
flush_work(&(dreamcastcard->spu_dma_work));
del_timer(&dreamcastcard->timer);
dreamcastcard->substream = NULL;
kfree(dreamcastcard->channel);
spu_disable();
@ -401,6 +411,7 @@ static const struct snd_pcm_ops snd_aicapcm_playback_ops = {
.prepare = snd_aicapcm_pcm_prepare,
.trigger = snd_aicapcm_pcm_trigger,
.pointer = snd_aicapcm_pcm_pointer,
.sync_stop = snd_aicapcm_pcm_sync_stop,
};
/* TO DO: set up to handle more than one pcm instance */