ALSA: pcm: Fix races among concurrent read/write and buffer changes

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: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220322170720.3529-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index f2090025236b92395daa26ba3b2d83b2245e42c7..a40a35e51fad7c842af674923e52aad9ce127f70 100644 (file)
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1906,9 +1906,11 @@ 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) {
@@ -2219,6 +2221,7 @@ 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)
@@ -2310,6 +2313,7 @@ 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);