ALSA: aloop: Fix access to not-yet-ready substream via cable (8e6b1a72) · Commits · 戴 / test

In loopback_open() and loopback_close(), we assign and release the substream object to the corresponding cable in a racy way. It's neither locked nor done in the right position. The open callback assigns the substream before its preparation finishes, hence the other side of the cable may pick it up, which may lead to the invalid memory access. This patch addresses these: move the assignment to the end of the open callback, and wrap with cable->lock for avoiding concurrent accesses. Cc: <stable@vger.kernel.org> Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/drivers/aloop.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -666,7 +666,9 @@ static void free_cable(struct snd_pcm_substream *substream)
		return;
		if (cable->streams[!substream->stream]) {
		/* other stream is still alive */
		spin_lock_irq(&cable->lock);
		cable->streams[substream->stream] = NULL;
		spin_unlock_irq(&cable->lock);
		} else {
		/* free the cable */
		loopback->cables[substream->number][dev] = NULL;
		@@ -705,7 +707,6 @@ static int loopback_open(struct snd_pcm_substream *substream)
		loopback->cables[substream->number][dev] = cable;
		}
		dpcm->cable = cable;
		cable->streams[substream->stream] = dpcm;

		snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);

		@@ -737,6 +738,11 @@ static int loopback_open(struct snd_pcm_substream *substream)
		runtime->hw = loopback_pcm_hardware;
		else
		runtime->hw = cable->hw;

		spin_lock_irq(&cable->lock);
		cable->streams[substream->stream] = dpcm;
		spin_unlock_irq(&cable->lock);

		unlock:
		if (err < 0) {
		free_cable(substream);

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