[PATCH 3.16 125/136] ALSA: usb-audio: Fix missing error check at mixer resolution test

[Ben Hutchings]

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 167beb1756791e0806365a3f86a0da10d7a327ee upstream.

A check of the return value from get_cur_mix_raw() is missing at the
resolution test code in get_min_max_with_quirks(), which may leave the
variable untouched, leading to a random uninitialized value, as
detected by syzkaller fuzzer.

Add the missing return error check for fixing that.

Reported-and-tested-by: syzbot+abe1ab7afc62c6bb6377@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20191109181658.30368-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 sound/usb/mixer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1014,7 +1014,8 @@ static int get_min_max_with_quirks(struc
 		if (cval->min + cval->res < cval->max) {
 			int last_valid_res = cval->res;
 			int saved, test, check;
-			get_cur_mix_raw(cval, minchn, &saved);
+			if (get_cur_mix_raw(cval, minchn, &saved) < 0)
+				goto no_res_check;
 			for (;;) {
 				test = saved;
 				if (test < cval->max)
@@ -1034,6 +1035,7 @@ static int get_min_max_with_quirks(struc
 			set_cur_mix_value(cval, minchn, 0, saved);
 		}
 
+no_res_check:
 		cval->initialized = 1;
 	}