ALSA: pcm: Zero-clear reserved fields of PCM status ioctl in compat mode

commit 317168d0 upstream.

In compat mode, we copy each field of snd_pcm_status struct but don't
touch the reserved fields, and this leaves uninitialized values
there.  Meanwhile the native ioctl does zero-clear the whole
structure, so we should follow the same rule in compat mode, too.
Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

sound/core/pcm_compat.c

@@ -206,6 +206,8 @@ static int snd_pcm_status_user_compat(struct snd_pcm_substream *substream,
 	if (err < 0)
 		return err;
 
+	if (clear_user(src, sizeof(*src)))
+		return -EFAULT;
 	if (put_user(status.state, &src->state) ||
 	    compat_put_timespec(&status.trigger_tstamp, &src->trigger_tstamp) ||
 	    compat_put_timespec(&status.tstamp, &src->tstamp) ||