Commit b2483716 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: pcm: Fix potential deadlock in OSS emulation 

There are potential deadlocks in PCM OSS emulation code while
accessing read/write and mmap concurrently.  This comes from the
infamous mmap_sem usage in copy_from/to_user().  Namely,

   snd_pcm_oss_write() ->
     &runtime->oss.params_lock ->
        copy_to_user() ->
          &mm->mmap_sem
  mmap() ->
    &mm->mmap_sem ->
      snd_pcm_oss_mmap() ->
        &runtime->oss.params_lock

Since we can't avoid taking params_lock from mmap code path, use
trylock variant and aborts with -EAGAIN as a workaround of this AB/BA
deadlock.

BugLink: http://lkml.kernel.org/r/CACT4Y+bVrBKDG0G2_AcUgUQa+X91VKTeS4v+wN7BSHwHtqn3kQ@mail.gmail.com


Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent cc85f7a6

sound/core/oss/pcm_oss.c

+15 −6
Original line number Diff line number Diff line
@@ -835,7 +835,8 @@ static int choose_rate(struct snd_pcm_substream *substream, 
	return snd_pcm_hw_param_near(substream, params, SNDRV_PCM_HW_PARAM_RATE, best_rate, NULL);

}



static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream)

static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream,

				     bool trylock)

{

	struct snd_pcm_runtime *runtime = substream->runtime;

	struct snd_pcm_hw_params *params, *sparams;
@@ -849,7 +850,10 @@ static int snd_pcm_oss_change_params(struct snd_pcm_substream *substream) 
	struct snd_mask sformat_mask;

	struct snd_mask mask;



	if (mutex_lock_interruptible(&runtime->oss.params_lock))

	if (trylock) {

		if (!(mutex_trylock(&runtime->oss.params_lock)))

			return -EAGAIN;

	} else if (mutex_lock_interruptible(&runtime->oss.params_lock))

		return -EINTR;

	sw_params = kzalloc(sizeof(*sw_params), GFP_KERNEL);

	params = kmalloc(sizeof(*params), GFP_KERNEL);
@@ -1092,7 +1096,7 @@ static int snd_pcm_oss_get_active_substream(struct snd_pcm_oss_file *pcm_oss_fil 
		if (asubstream == NULL)

			asubstream = substream;

		if (substream->runtime->oss.params) {

			err = snd_pcm_oss_change_params(substream);

			err = snd_pcm_oss_change_params(substream, false);

			if (err < 0)

				return err;

		}
@@ -1132,7 +1136,7 @@ static int snd_pcm_oss_make_ready(struct snd_pcm_substream *substream) 
		return 0;

	runtime = substream->runtime;

	if (runtime->oss.params) {

		err = snd_pcm_oss_change_params(substream);

		err = snd_pcm_oss_change_params(substream, false);

		if (err < 0)

			return err;

	}
@@ -2163,7 +2167,7 @@ static int snd_pcm_oss_get_space(struct snd_pcm_oss_file *pcm_oss_file, int stre 
	runtime = substream->runtime;



	if (runtime->oss.params &&

	    (err = snd_pcm_oss_change_params(substream)) < 0)

	    (err = snd_pcm_oss_change_params(substream, false)) < 0)

		return err;



	info.fragsize = runtime->oss.period_bytes;
@@ -2804,7 +2808,12 @@ static int snd_pcm_oss_mmap(struct file *file, struct vm_area_struct *area) 
		return -EIO;

	

	if (runtime->oss.params) {

		if ((err = snd_pcm_oss_change_params(substream)) < 0)

		/* use mutex_trylock() for params_lock for avoiding a deadlock

		 * between mmap_sem and params_lock taken by

		 * copy_from/to_user() in snd_pcm_oss_write/read()

		 */

		err = snd_pcm_oss_change_params(substream, true);

		if (err < 0)

			return err;

	}

#ifdef CONFIG_SND_PCM_OSS_PLUGINS

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