[PATCH 3.2 55/79] ALSA: usb-audio: Add sanity checks to FE parser

[Ben Hutchings]

3.2.99-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit d937cd6790a2bef2d07b500487646bd794c039bb upstream.

When the usb-audio descriptor contains the malformed feature unit
description with a too short length, the driver may access
out-of-bounds.  Add a sanity check of the header size at the beginning
of parse_audio_feature_unit().

Fixes: 23caaf19b11e ("ALSA: usb-mixer: Add support for Audio Class v2.0")
Reported-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
[bwh: Backported to 3.2: use snd_printk() for logging]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 sound/usb/mixer.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1255,6 +1255,12 @@ static int parse_audio_feature_unit(stru
 	__u8 *bmaControls;
 
 	if (state->mixer->protocol == UAC_VERSION_1) {
+		if (hdr->bLength < 7) {
+			snd_printk(KERN_ERR
+				   "usbaudio: unit %u: invalid UAC_FEATURE_UNIT descriptor\n",
+				   unitid);
+			return -EINVAL;
+		}
 		csize = hdr->bControlSize;
 		if (!csize) {
 			snd_printdd(KERN_ERR "usbaudio: unit %u: "
@@ -1271,6 +1277,12 @@ static int parse_audio_feature_unit(stru
 		}
 	} else {
 		struct uac2_feature_unit_descriptor *ftr = _ftr;
+		if (hdr->bLength < 6) {
+			snd_printk(KERN_ERR
+				   "usbaudio: unit %u: invalid UAC_FEATURE_UNIT descriptor\n",
+				   unitid);
+			return -EINVAL;
+		}
 		csize = 4;
 		channels = (hdr->bLength - 6) / 4 - 1;
 		bmaControls = ftr->bmaControls;