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Commit 08d1807f authored by Takashi Iwai's avatar Takashi Iwai Committed by Greg Kroah-Hartman
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ALSA: pcm: Fix races among concurrent read/write and buffer changes 



commit dca947d4d26dbf925a64a6cfb2ddbc035e831a3d upstream.

In the current PCM design, the read/write syscalls (as well as the
equivalent ioctls) are allowed before the PCM stream is running, that
is, at PCM PREPARED state.  Meanwhile, we also allow to re-issue
hw_params and hw_free ioctl calls at the PREPARED state that may
change or free the buffers, too.  The problem is that there is no
protection against those mix-ups.

This patch applies the previously introduced runtime->buffer_mutex to
the read/write operations so that the concurrent hw_params or hw_free
call can no longer interfere during the operation.  The mutex is
unlocked before scheduling, so we don't take it too long.

Cc: <stable@vger.kernel.org>
Reviewed-by: default avatarJaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220322170720.3529-3-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
Signed-off-by: default avatarOvidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fbeb4926

sound/core/pcm_lib.c

+4 −0
Original line number Diff line number Diff line
@@ -1861,9 +1861,11 @@ static int wait_for_avail(struct snd_pcm_substream *substream, 
		if (avail >= runtime->twake)

			break;

		snd_pcm_stream_unlock_irq(substream);

		mutex_unlock(&runtime->buffer_mutex);



		tout = schedule_timeout(wait_time);



		mutex_lock(&runtime->buffer_mutex);

		snd_pcm_stream_lock_irq(substream);

		set_current_state(TASK_INTERRUPTIBLE);

		switch (runtime->status->state) {
@@ -2157,6 +2159,7 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream, 


	nonblock = !!(substream->f_flags & O_NONBLOCK);



	mutex_lock(&runtime->buffer_mutex);

	snd_pcm_stream_lock_irq(substream);

	err = pcm_accessible_state(runtime);

	if (err < 0)
@@ -2244,6 +2247,7 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream, 
	if (xfer > 0 && err >= 0)

		snd_pcm_update_state(substream, runtime);

	snd_pcm_stream_unlock_irq(substream);

	mutex_unlock(&runtime->buffer_mutex);

	return xfer > 0 ? (snd_pcm_sframes_t)xfer : err;

}

EXPORT_SYMBOL(__snd_pcm_lib_xfer);