ALSA: usb-audio: Stop parsing channels bits when all channels are found.

If a usb audio device sets more bits than the amount of channels
it could write outside of the map array.

Signed-off-by: Johan Carlsson <johan.carlsson@teenage.engineering>
Fixes: 04324cc ("ALSA: usb-audio: add channel map support")
Message-ID: <20240313081509.9801-1-johan.carlsson@teenage.engineering>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Author: Johan Carlsson

sound/usb/stream.c

@@ -300,9 +300,12 @@ static struct snd_pcm_chmap_elem *convert_chmap(int channels, unsigned int bits,
 	c = 0;
 
 	if (bits) {
-		for (; bits && *maps; maps++, bits >>= 1)
+		for (; bits && *maps; maps++, bits >>= 1) {
 			if (bits & 1)
 				chmap->map[c++] = *maps;
+			if (c == chmap->channels)
+				break;
+		}
 	} else {
 		/* If we're missing wChannelConfig, then guess something
 		    to make sure the channel map is not skipped entirely */