usbip: fix stub_rx: get_pipe() to validate endpoint number

get_pipe() routine doesn't validate the input endpoint number
and uses to reference ep_in and ep_out arrays. Invalid endpoint
number can trigger BUG(). Range check the epnum and returning
error instead of calling BUG().

Change caller stub_recv_cmd_submit() to handle the get_pipe()
error return.
Reported-by: Secunia Research <vuln@secunia.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/stub_rx.c

@@ -328,15 +328,15 @@ static int get_pipe(struct stub_device *sdev, int epnum, int dir)
 	struct usb_host_endpoint *ep;
 	struct usb_endpoint_descriptor *epd = NULL;
 
+	if (epnum < 0 || epnum > 15)
+		goto err_ret;
+
 	if (dir == USBIP_DIR_IN)
 		ep = udev->ep_in[epnum & 0x7f];
 	else
 		ep = udev->ep_out[epnum & 0x7f];
-	if (!ep) {
-		dev_err(&sdev->udev->dev, "no such endpoint?, %d\n",
-			epnum);
-		BUG();
-	}
+	if (!ep)
+		goto err_ret;
 
 	epd = &ep->desc;
 	if (usb_endpoint_xfer_control(epd)) {
@@ -367,9 +367,10 @@ static int get_pipe(struct stub_device *sdev, int epnum, int dir)
 			return usb_rcvisocpipe(udev, epnum);
 	}
 
+err_ret:
 	/* NOT REACHED */
-	dev_err(&sdev->udev->dev, "get pipe, epnum %d\n", epnum);
-	return 0;
+	dev_err(&sdev->udev->dev, "get pipe() invalid epnum %d\n", epnum);
+	return -1;
 }
 
 static void masking_bogus_flags(struct urb *urb)
@@ -435,6 +436,9 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
 	struct usb_device *udev = sdev->udev;
 	int pipe = get_pipe(sdev, pdu->base.ep, pdu->base.direction);
 
+	if (pipe == -1)
+		return;
+
 	priv = stub_priv_alloc(sdev, pdu);
 	if (!priv)
 		return;