[PATCH] sound: ua101: fix division by zero at probe

[SeungJu Cheon <suunj1331@gmail.com>]

Add a missing sanity check for bNrChannels in detect_usb_format()
to prevent a division by zero in playback_urb_complete() and
capture_urb_complete().

USB core does not validate class-specific descriptor fields such
as bNrChannels, so drivers must verify them before use. If a
device provides bNrChannels = 0, frame_bytes becomes zero and is
later used as a divisor in the URB completion handlers, leading
to a kernel crash.

Fixes: 63978ab3e3e9 ("sound: add Edirol UA-101 support")
Cc: stable@vger.kernel.org
Signed-off-by: SeungJu Cheon <suunj1331@gmail.com>
---
Testing:
- dummy_hcd + raw_gadget emulating a UA-101 with bNrChannels=0.

 sound/usb/misc/ua101.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/usb/misc/ua101.c b/sound/usb/misc/ua101.c
index 49b3dd8d827d..d129b42eb979 100644
--- a/sound/usb/misc/ua101.c
+++ b/sound/usb/misc/ua101.c
@@ -974,6 +974,13 @@ static int detect_usb_format(struct ua101 *ua)
 
 	ua->capture.channels = fmt_capture->bNrChannels;
 	ua->playback.channels = fmt_playback->bNrChannels;
+	if (!ua->capture.channels || !ua->playback.channels) {
+		dev_err(&ua->dev->dev,
+			"invalid channel count: capture %u, playback %u\n",
+			ua->capture.channels, ua->playback.channels);
+		return -EINVAL;
+	}
+
 	ua->capture.frame_bytes =
 		fmt_capture->bSubframeSize * ua->capture.channels;
 	ua->playback.frame_bytes =
-- 
2.52.0