usb: wusbcore: allow wa_xfer_destroy to clean up partially constructed xfers

If __wa_xfer_setup fails, it can leave a partially constructed wa_xfer
object.  The error handling code eventually calls wa_xfer_destroy which
does not check for NULL before dereferencing xfer->seg which could cause
a kernel panic.  This change also makes sure to free xfer->seg which was
being leaked for all transfers before this change.
Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/wusbcore/wa-xfer.c

@@ -178,9 +178,15 @@ static void wa_xfer_destroy(struct kref *_xfer)
 	if (xfer->seg) {
 		unsigned cnt;
 		for (cnt = 0; cnt < xfer->segs; cnt++) {
-			usb_free_urb(xfer->seg[cnt]->dto_urb);
-			usb_free_urb(&xfer->seg[cnt]->tr_urb);
+			if (xfer->seg[cnt]) {
+				if (xfer->seg[cnt]->dto_urb) {
+					kfree(xfer->seg[cnt]->dto_urb->sg);
+					usb_free_urb(xfer->seg[cnt]->dto_urb);
+				}
+				usb_free_urb(&xfer->seg[cnt]->tr_urb);
+			}
 		}
+		kfree(xfer->seg);
 	}
 	kfree(xfer);
 }