[PATCH 4.9 57/83] ALSA: usb-audio: Fix an OOB bug in parse_audio_mixer_unit

From: Greg Kroah-Hartman
Date: Wed Sep 04 2019 - 14:01:03 EST

From: Hui Peng <benquike@xxxxxxxxx>

commit daac07156b330b18eb5071aec4b3ddca1c377f2c upstream.

The `uac_mixer_unit_descriptor` shown as below is read from the
device side. In `parse_audio_mixer_unit`, `baSourceID` field is
accessed from index 0 to `bNrInPins` - 1, the current implementation
assumes that descriptor is always valid (the length of descriptor
is no shorter than 5 + `bNrInPins`). If a descriptor read from
the device side is invalid, it may trigger out-of-bound memory

struct uac_mixer_unit_descriptor {
__u8 bLength;
__u8 bDescriptorType;
__u8 bDescriptorSubtype;
__u8 bUnitID;
__u8 bNrInPins;
__u8 baSourceID[];

This patch fixes the bug by add a sanity check on the length of
the descriptor.

Reported-by: Hui Peng <benquike@xxxxxxxxx>
Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

sound/usb/mixer.c | 1 +
1 file changed, 1 insertion(+)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1713,6 +1713,7 @@ static int parse_audio_mixer_unit(struct
int pin, ich, err;

if (desc->bLength < 11 || !(input_pins = desc->bNrInPins) ||
+ desc->bLength < sizeof(*desc) + desc->bNrInPins ||
!(num_outs = uac_mixer_unit_bNrChannels(desc))) {
"invalid MIXER UNIT descriptor %d\n",