ALSA: pcm: Fix memory leak at closing a stream without hw_free

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: 0dba808e ("ALSA: pcm: Introduce managed buffer allocation mode")
Reported-by: syzbot+30edd0f34bfcdc548ac4@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200129195907.12197-1-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

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);
 		substream->ops->close(substream);
 		substream->hw_opened = 0;
 	}