USB: devio: Don't corrupt user memory

The user buffer has "uurb->buffer_length" bytes.  If the kernel has more
information than that, we should truncate it instead of writing past
the end of the user's buffer.  I added a WARN_ONCE() to help the user
debug the issue.

Reported-by: Alan Stern <[email protected]>
Cc: stable <[email protected]>
Signed-off-by: Dan Carpenter <[email protected]>
Acked-by: Alan Stern <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Dan Carpenter

drivers/usb/core/devio.c

@@ -1576,7 +1576,11 @@ static int proc_do_submiturb(struct usb_dev_state *ps, struct usbdevfs_urb *uurb
 			totlen += isopkt[u].length;
 		}
 		u *= sizeof(struct usb_iso_packet_descriptor);
-		uurb->buffer_length = totlen;
+		if (totlen <= uurb->buffer_length)
+			uurb->buffer_length = totlen;
+		else
+			WARN_ONCE(1, "uurb->buffer_length is too short %d vs %d",
+				  totlen, uurb->buffer_length);
 		break;
 
 	default: