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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Takashi Iwai <tiwai@suse.de>
Subject: [PATCH 4.20 19/65] ALSA: usb-audio: Avoid access before bLength check in build_audio_procunit()
Date:   Fri, 11 Jan 2019 15:15:05 +0100
Message-Id: <20190111131059.079395634@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

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

From: Takashi Iwai <tiwai@suse.de>

commit f4351a199cc120ff9d59e06d02e8657d08e6cc46 upstream.

The parser for the processing unit reads bNrInPins field before the
bLength sanity check, which may lead to an out-of-bound access when a
malformed descriptor is given.  Fix it by assignment after the bLength
check.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 sound/usb/mixer.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2314,7 +2314,7 @@ static int build_audio_procunit(struct m
 				char *name)
 {
 	struct uac_processing_unit_descriptor *desc = raw_desc;
-	int num_ins = desc->bNrInPins;
+	int num_ins;
 	struct usb_mixer_elem_info *cval;
 	struct snd_kcontrol *kctl;
 	int i, err, nameid, type, len;
@@ -2329,7 +2329,13 @@ static int build_audio_procunit(struct m
 		0, NULL, default_value_info
 	};
 
-	if (desc->bLength < 13 || desc->bLength < 13 + num_ins ||
+	if (desc->bLength < 13) {
+		usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid);
+		return -EINVAL;
+	}
+
+	num_ins = desc->bNrInPins;
+	if (desc->bLength < 13 + num_ins ||
 	    desc->bLength < num_ins + uac_processing_unit_bControlSize(desc, state->mixer->protocol)) {
 		usb_audio_err(state->chip, "invalid %s descriptor (id %d)\n", name, unitid);
 		return -EINVAL;