[alsa-devel] [PATCH] ALSA: pcm: Fix memory leak at closing a stream without hw_free

[Pierre-Louis Bossart]

On 1/29/20 1:59 PM, Takashi Iwai wrote:
> ALSA PCM core recently introduced a new managed PCM buffer allocation
> mode that does allocate / free automatically at hw_params and
> hw_free.  However, it overlooked the code path directly calling
> hw_free PCM ops at releasing the PCM substream, and it may result in a
> memory leak as spotted by syzkaller when no buffer preallocation is
> used (e.g. vmalloc buffer).
> 
> This patch papers over it with a slight refactoring.  The hw_free ops
> call and relevant tasks are unified in a new helper function, and call
> it from both places.
> 
> Fixes: 0dba808eae26 ("ALSA: pcm: Introduce managed buffer allocation mode")
> Reported-by: syzbot+30edd0f34bfcdc548ac4 at syzkaller.appspotmail.com
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>

Takashi, this patch introduces a regression for our SoundWire work - 
credits to Bard Liao for reporting this the first.

We see the hw_free() being called twice and as a result the SoundWire 
stream state becomes inconsistent, with some memory becoming corrupted:

[  107.864109] sof-audio-pci 0000:00:1f.3: pcm: free stream 0 dir 0
[  107.864324] sof-audio-pci 0000:00:1f.3: ipc tx: 0x80010000: 
GLB_DAI_MSG: CONFIG
[  107.864507] sof-audio-pci 0000:00:1f.3: ipc tx succeeded: 0x80010000: 
GLB_DAI_MSG: CONFIG
[  107.864615] sof-audio-pci 0000:00:1f.3: pcm: free stream 0 dir 0
[  107.864627] sdw_deprepare_stream: \xc0Pjf\xe0\xa3\xff\xff: 
inconsistent state state 6
[  107.864640] int-sdw int-sdw.0: sdw_deprepare_stream: failed -22

we detected this while merging your latest code as part of our weekly 
rebase, then realized the error was already present in v5.6-rc1 and 
continued to narrow the scope to sound-fix-5.6-rc1 and this specific patch.

I can't claim to fully understand the code in this patch, but I am not 
sure why hw_free() ends up being unconditionally called at [1] below

> ---
>   sound/core/pcm_native.c | 24 +++++++++++++++---------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index bb23f5066654..4ac42ee1238c 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -786,10 +786,22 @@ static int snd_pcm_hw_params_user(struct snd_pcm_substream *substream,
>   	return err;
>   }
>   
> +static int do_hw_free(struct snd_pcm_substream *substream)
> +{
> +	int result = 0;
> +
> +	snd_pcm_sync_stop(substream);
> +	if (substream->ops->hw_free)
> +		result = substream->ops->hw_free(substream);
> +	if (substream->managed_buffer_alloc)
> +		snd_pcm_lib_free_pages(substream);
> +	return result;
> +}
> +
>   static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
>   {
>   	struct snd_pcm_runtime *runtime;
> -	int result = 0;
> +	int result;
>   
>   	if (PCM_RUNTIME_CHECK(substream))
>   		return -ENXIO;
> @@ -806,11 +818,7 @@ static int snd_pcm_hw_free(struct snd_pcm_substream *substream)
>   	snd_pcm_stream_unlock_irq(substream);
>   	if (atomic_read(&substream->mmap_count))
>   		return -EBADFD;
> -	snd_pcm_sync_stop(substream);
> -	if (substream->ops->hw_free)
> -		result = substream->ops->hw_free(substream);
> -	if (substream->managed_buffer_alloc)
> -		snd_pcm_lib_free_pages(substream);
> +	result = do_hw_free(substream);
>   	snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
>   	pm_qos_remove_request(&substream->latency_pm_qos_req);
>   	return result;
> @@ -2529,9 +2537,7 @@ void snd_pcm_release_substream(struct snd_pcm_substream *substream)
>   
>   	snd_pcm_drop(substream);
>   	if (substream->hw_opened) {
> -		if (substream->ops->hw_free &&
> -		    substream->runtime->status->state != SNDRV_PCM_STATE_OPEN)
> -			substream->ops->hw_free(substream);
> +		do_hw_free(substream);

[1] don't we need to only do the hw_free() when	

substream->runtime->status->state != SNDRV_PCM_STATE_OPEN

e.g. with the following patch?

Or is the expectation that the hw_free() callback be implemented so that 
only the first call has an effect?

Thanks
-Pierre

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 336406bcb59e..051a1f234975 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -787,12 +787,12 @@ static int snd_pcm_hw_params_user(struct 
snd_pcm_substream *substream,
         return err;
  }

-static int do_hw_free(struct snd_pcm_substream *substream)
+static int do_hw_free(struct snd_pcm_substream *substream, bool cond_free)
  {
         int result = 0;

         snd_pcm_sync_stop(substream);
-       if (substream->ops->hw_free)
+       if (cond_free && substream->ops->hw_free)
                 result = substream->ops->hw_free(substream);
         if (substream->managed_buffer_alloc)
                 snd_pcm_lib_free_pages(substream);
@@ -819,7 +819,7 @@ static int snd_pcm_hw_free(struct snd_pcm_substream 
*substream)
         snd_pcm_stream_unlock_irq(substream);
         if (atomic_read(&substream->mmap_count))
                 return -EBADFD;
-       result = do_hw_free(substream);
+       result = do_hw_free(substream, true);
         snd_pcm_set_state(substream, SNDRV_PCM_STATE_OPEN);
         pm_qos_remove_request(&substream->latency_pm_qos_req);
         return result;
@@ -2594,7 +2594,9 @@ void snd_pcm_release_substream(struct 
snd_pcm_substream *substream)

         snd_pcm_drop(substream);
         if (substream->hw_opened) {
-               do_hw_free(substream);
+               do_hw_free(substream,
+                          substream->runtime->status->state !=
+                          SNDRV_PCM_STATE_OPEN);
                 substream->ops->close(substream);
                 substream->hw_opened = 0;
         }