[PATCH] net: usb: rtl8150: free skb on usb_submit_urb() failure in xmit

[Morduan Zang]

When rtl8150_start_xmit() fails to submit the tx URB, the URB is never
handed to the USB core and write_bulk_callback() will not run.  The
driver returns NETDEV_TX_OK, which tells the networking stack that the
skb has been consumed, but nothing actually frees the skb on this
error path:

  dev->tx_skb = skb;
  ...
  if ((res = usb_submit_urb(dev->tx_urb, GFP_ATOMIC))) {
          ...
          /* no kfree_skb here */
  }
  return NETDEV_TX_OK;

This leaks the skb on every submit failure and also leaves dev->tx_skb
pointing at memory that the driver itself may later free, which is
fragile.

Free the skb with dev_kfree_skb_any() in the error path and clear
dev->tx_skb so no stale pointer is left behind.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Morduan Zang <zhangdandan@xxxxxxxxxxxxx>
---
 drivers/net/usb/rtl8150.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/usb/rtl8150.c b/drivers/net/usb/rtl8150.c
index a0f790a368ba..d358b6d41a53 100644
--- a/drivers/net/usb/rtl8150.c
+++ b/drivers/net/usb/rtl8150.c
@@ -716,6 +716,13 @@ static netdev_tx_t rtl8150_start_xmit(struct sk_buff *skb,
 			netdev->stats.tx_errors++;
 			netif_start_queue(netdev);
 		}
+		/*
+		 * The URB was not submitted, so write_bulk_callback() will
+		 * never run to free dev->tx_skb.  Drop the skb here and
+		 * clear tx_skb to avoid leaving a stale pointer.
+		 */
+		dev->tx_skb = NULL;
+		dev_kfree_skb_any(skb);
 	} else {
 		netdev->stats.tx_packets++;
 		netdev->stats.tx_bytes += skb_len;
-- 
2.50.1