ALSA: usb-audio: Fix an OOB bug in parse_audio_mixer_unit

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
access.

```
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@gmail.com>
Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Hui Peng <benquike@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index edff302cac23cd6136b11b24d7b561a420b238e2..e24572fd6e30aa069289d74fc968c4ae61d2a807 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1647,6 +1647,7 @@ static int parse_audio_mixer_unit(struct mixer_build *state, int unitid,
        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))) {
                usb_audio_err(state->chip,
                              "invalid MIXER UNIT descriptor %d\n",