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>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index ed4d89c8b52a52e6425ce5c992cc5d324b339d35..e90daf8cdaa8726f8311092636461a9fee10b187 100644 (file)
--- 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 */