[PATCH 5.17 12/39] ALSA: pcm: Fix races among concurrent read/write and buffer changes

Greg Kroah-Hartman
2022-03-25T15:34:19Z

From: Takashi Iwai <tiwai@suse.de>

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: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/core/pcm_lib.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1906,9 +1906,11 @@ static int wait_for_avail(struct snd_pcm
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(str

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(str
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);