media: uvcvideo: Fix allocation for small frame sizes

If a frame has size of less or equal than one packet size
uvc_alloc_urb_buffers() is unable to allocate memory for it due to a
off-by-one error.

Fix the off-by-one-error and now that we are at it, make sure that
stream->urb_size has always a valid value when we return from the
function, even when an error happens.

Fixes: efdc8a9 ("V4L/DVB (10295): uvcvideo: Retry URB buffers allocation when the system is low on memory.")
Reported-by: Itay Chamiel <[email protected]>
Closes: https://lore.kernel.org/linux-media/CANiDSCsSoZf2LsCCoWAUbCg6tJT-ypXR1B85aa6rAdMVYr2iBQ@mail.gmail.com/T/#t
Co-developed-by: Itay Chamiel <[email protected]>
Signed-off-by: Itay Chamiel <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
Reviewed-by: Laurent Pinchart <[email protected]>
Tested-by: Itay Chamiel <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Laurent Pinchart <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>

Author: ribalda

drivers/media/usb/uvc/uvc_video.c

@@ -1812,7 +1812,7 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
 		npackets = UVC_MAX_PACKETS;
 
 	/* Retry allocations until one succeed. */
-	for (; npackets > 1; npackets /= 2) {
+	for (; npackets > 0; npackets /= 2) {
 		stream->urb_size = psize * npackets;
 
 		for (i = 0; i < UVC_URBS; ++i) {
@@ -1837,6 +1837,7 @@ static int uvc_alloc_urb_buffers(struct uvc_streaming *stream,
 	uvc_dbg(stream->dev, VIDEO,
 		"Failed to allocate URB buffers (%u bytes per packet)\n",
 		psize);
+	stream->urb_size = 0;
 	return 0;
 }