ALSA: usb-audio: Fix potential out-of-bound access at parsing SU

The usb-audio driver may trigger an out-of-bound access at parsing a
malformed selector unit, as it checks the header length only after
evaluating bNrInPins field, which can be already above the given
length.  Fix it by adding the length check beforehand.

Fixes: 99fc86450c43 ("ALSA: usb-mixer: parse descriptors with structs")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index b8ce651e392c4d43f732dad3c15865bb2ea812b6..61b348383de88fa282028a78603567fa513589b7 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2098,7 +2098,8 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid,
        const struct usbmix_name_map *map;
        char **namelist;
 
-       if (!desc->bNrInPins || desc->bLength < 5 + desc->bNrInPins) {
+       if (desc->bLength < 5 || !desc->bNrInPins ||
+           desc->bLength < 5 + desc->bNrInPins) {
                usb_audio_err(state->chip,
                        "invalid SELECTOR UNIT descriptor %d\n", unitid);
                return -EINVAL;