linux-kernel - [PATCH 3.2 57/79] ALSA: usb-audio: Fix potential zero-division at parsing FU

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Message-ID: <lsq.1518322806.943407157@decadent.org.uk>
Date:   Sun, 11 Feb 2018 04:20:06 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Takashi Iwai" <tiwai@...e.de>
Subject: [PATCH 3.2 57/79] ALSA: usb-audio: Fix potential zero-division at
 parsing FU

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

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

From: Takashi Iwai <tiwai@...e.de>

commit 8428a8ebde2db1e988e41a58497a28beb7ce1705 upstream.

parse_audio_feature_unit() contains a code dividing potentially with
zero when a malformed FU descriptor is passed.  Although there is
already a sanity check, it checks only the value zero, hence it can
still lead to a zero-division when a value 1 is passed there.

Fix it by correcting the sanity check (and the error message
thereof).

Fixes: 23caaf19b11e ("ALSA: usb-mixer: Add support for Audio Class v2.0")
Signed-off-by: Takashi Iwai <tiwai@...e.de>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 sound/usb/mixer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1262,9 +1262,9 @@ static int parse_audio_feature_unit(stru
 			return -EINVAL;
 		}
 		csize = hdr->bControlSize;
-		if (!csize) {
+		if (csize <= 1) {
 			snd_printdd(KERN_ERR "usbaudio: unit %u: "
-				    "invalid bControlSize == 0\n", unitid);
+				    "invalid bControlSize <= 1\n", unitid);
 			return -EINVAL;
 		}
 		channels = (hdr->bLength - 7) / csize - 1;