Commit message: can: usb_8dev: usb_8dev_start_xmit(): fix double dev_kfree_skb() in error path

There is no need to call dev_kfree_skb() when usb_submit_urb() fails
because can_put_echo_skb() deletes original skb and
can_free_echo_skb() deletes the cloned skb.

Fixes: 0024d8ad1639 ("can: usb_8dev: Add support for USB2CAN interface from 8 devices")
Link: https://lore.kernel.org/all/20220311080614.45229-1-hbh25y@gmail.com
Cc: stable@vger.kernel.org
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
CVE: CVE-2022-28388
CWE: CWE-415
Vulnerability description: usb_8dev_start_xmit in drivers/net/can/usb/usb_8dev.c in the Linux kernel through 5.17.1 has a double free.

Project: linux
File: usb_8dev.c

static netdev_tx_t usb_8dev_start_xmit(struct sk_buff *skb,
				      struct net_device *netdev)
{
	struct usb_8dev_priv *priv = netdev_priv(netdev);
	struct net_device_stats *stats = &netdev->stats;
	struct can_frame *cf = (struct can_frame *) skb->data;
	struct usb_8dev_tx_msg *msg;
	struct urb *urb;
	struct usb_8dev_tx_urb_context *context = NULL;
	u8 *buf;
	int i, err;
	size_t size = sizeof(struct usb_8dev_tx_msg);

	if (can_dropped_invalid_skb(netdev, skb))
		return NETDEV_TX_OK;

	/* create a URB, and a buffer for it, and copy the data to the URB */
	urb = usb_alloc_urb(0, GFP_ATOMIC);
	if (!urb)
		goto nomem;

	buf = usb_alloc_coherent(priv->udev, size, GFP_ATOMIC,
				 &urb->transfer_dma);
	if (!buf) {
		netdev_err(netdev, "No memory left for USB buffer\n");
		goto nomembuf;
	}

	memset(buf, 0, size);

	msg = (struct usb_8dev_tx_msg *)buf;
	msg->begin = USB_8DEV_DATA_START;
	msg->flags = 0x00;

	if (cf->can_id & CAN_RTR_FLAG)
		msg->flags |= USB_8DEV_RTR;

	if (cf->can_id & CAN_EFF_FLAG)
		msg->flags |= USB_8DEV_EXTID;

	msg->id = cpu_to_be32(cf->can_id & CAN_ERR_MASK);
	msg->dlc = can_get_cc_dlc(cf, priv->can.ctrlmode);
	memcpy(msg->data, cf->data, cf->len);
	msg->end = USB_8DEV_DATA_END;

	for (i = 0; i < MAX_TX_URBS; i++) {
		if (priv->tx_contexts[i].echo_index == MAX_TX_URBS) {
			context = &priv->tx_contexts[i];
			break;
		}
	}

	/* May never happen! When this happens we'd more URBs in flight as
	 * allowed (MAX_TX_URBS).
	 */
	if (!context)
		goto nofreecontext;

	context->priv = priv;
	context->echo_index = i;

	usb_fill_bulk_urb(urb, priv->udev,
			  usb_sndbulkpipe(priv->udev, USB_8DEV_ENDP_DATA_TX),
			  buf, size, usb_8dev_write_bulk_callback, context);
	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
	usb_anchor_urb(urb, &priv->tx_submitted);

	can_put_echo_skb(skb, netdev, context->echo_index, 0);

	atomic_inc(&priv->active_tx_urbs);

	err = usb_submit_urb(urb, GFP_ATOMIC);
	if (unlikely(err))
		goto failed;
	else if (atomic_read(&priv->active_tx_urbs) >= MAX_TX_URBS)
		/* Slow down tx path */
		netif_stop_queue(netdev);

	/* Release our reference to this URB, the USB core will eventually free
	 * it entirely.
	 */
	usb_free_urb(urb);

	return NETDEV_TX_OK;

nofreecontext:
	usb_free_coherent(priv->udev, size, buf, urb->transfer_dma);
	usb_free_urb(urb);

	netdev_warn(netdev, "couldn't find free context");

	return NETDEV_TX_BUSY;

failed:
	can_free_echo_skb(netdev, context->echo_index, NULL);

	usb_unanchor_urb(urb);
	usb_free_coherent(priv->udev, size, buf, urb->transfer_dma);

	atomic_dec(&priv->active_tx_urbs);

	if (err == -ENODEV)
		netif_device_detach(netdev);
	else
		netdev_warn(netdev, "failed tx_urb %d\n", err);

nomembuf:
	usb_free_urb(urb);

nomem:
	dev_kfree_skb(skb);
	stats->tx_dropped++;

	return NETDEV_TX_OK;
}