ALSA: usb: Fix UBSAN warning in parse_audio_unit()

A malformed USB descriptor may pass the lengthy mixer description with
a lot of channels, and this may overflow the 32bit integer shift
size, as caught by syzbot UBSAN test.  Although this won't cause any
real trouble, it's better to address.

This patch introduces a sanity check of the number of channels to bail
out the parsing when too many channels are found.

Reported-by: syzbot+78d5b129a762182225aa@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/0000000000000adac5061d3c7355@google.com
Link: https://patch.msgid.link/20240715123619.26612-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 409fc11646948e40ec6b03be6840c150c04db8b7..fd6b94b3b638650e9f0a1cc5357fd553c90cdf10 100644 (file)
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -2014,6 +2014,13 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid,
                bmaControls = ftr->bmaControls;
        }
 
+       if (channels > 32) {
+               usb_audio_info(state->chip,
+                              "usbmixer: too many channels (%d) in unit %d\n",
+                              channels, unitid);
+               return -EINVAL;
+       }
+
        /* parse the source unit */
        err = parse_audio_unit(state, hdr->bSourceID);
        if (err < 0)