ALSA: usb-audio: fix invalid length check for RME and other UAC 2 devices

Commit 23caaf19b11e (ALSA: usb-mixer: Add support for Audio Class v2.0)
forgot to adjust the length check for UAC 2.0 feature unit descriptors.
This would make the code abort on encountering a feature unit without
per-channel controls, and thus prevented the driver to work with any
device having such a unit, such as the RME Babyface or Fireface UCX.

Reported-by: Florian Hanisch <fhanisch@uni-potsdam.de>
Tested-by: Matthew Robbetts <wingfeathera@gmail.com>
Tested-by: Michael Beer <beerml@sigma6audio.de>
Cc: Daniel Mack <daniel@caiaq.de>
Cc: 2.6.35+ <stable@vger.kernel.org>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 12 insertions, 5 deletions

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ed4d89c8b52a..e90daf8cdaa8 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1331,16 +1331,23 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid, void
                 }
                 channels = (hdr->bLength - 7) / csize - 1;
                 bmaControls = hdr->bmaControls;
+                if (hdr->bLength < 7 + csize) {
+                        snd_printk(KERN_ERR "usbaudio: unit %u: "
+                                   "invalid UAC_FEATURE_UNIT descriptor\n",
+                                   unitid);
+                        return -EINVAL;
+                }
         } else {
                 struct uac2_feature_unit_descriptor *ftr = _ftr;
                 csize = 4;
                 channels = (hdr->bLength - 6) / 4 - 1;
                 bmaControls = ftr->bmaControls;
-        }
-
-        if (hdr->bLength < 7 || !csize || hdr->bLength < 7 + csize) {
-                snd_printk(KERN_ERR "usbaudio: unit %u: invalid UAC_FEATURE_UNIT descriptor\n", unitid);
-                return -EINVAL;
+                if (hdr->bLength < 6 + csize) {
+                        snd_printk(KERN_ERR "usbaudio: unit %u: "
+                                   "invalid UAC_FEATURE_UNIT descriptor\n",
+                                   unitid);
+                        return -EINVAL;
+                }
         }
 
         /* parse the source unit */