ALSA: pcm: Fix UAF in snd_pcm_oss_get_formats()

BugLink: http://bugs.launchpad.net/bugs/1764666

commit 01c0b426 upstream.

snd_pcm_oss_get_formats() has an obvious use-after-free around
snd_mask_test() calls, as spotted by syzbot.  The passed format_mask
argument is a pointer to the hw_params object that is freed before the
loop.  What a surprise that it has been present since the original
code of decades ago...

Reported-by: syzbot+4090700a4f13fccaf648@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

sound/core/oss/pcm_oss.c

@@ -1814,10 +1814,9 @@ static int snd_pcm_oss_get_formats(struct snd_pcm_oss_file *pcm_oss_file)
 		return -ENOMEM;
 	_snd_pcm_hw_params_any(params);
 	err = snd_pcm_hw_refine(substream, params);
-	format_mask = *hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT); 
-	kfree(params);
 	if (err < 0)
-		return err;
+		goto error;
+	format_mask = *hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
 	for (fmt = 0; fmt < 32; ++fmt) {
 		if (snd_mask_test(&format_mask, fmt)) {
 			int f = snd_pcm_oss_format_to(fmt);
@@ -1825,7 +1824,10 @@ static int snd_pcm_oss_get_formats(struct snd_pcm_oss_file *pcm_oss_file)
 				formats |= f;
 		}
 	}
-	return formats;
+
+ error:
+	kfree(params);
+	return err < 0 ? err : formats;
 }
 
 static int snd_pcm_oss_set_format(struct snd_pcm_oss_file *pcm_oss_file, int format)