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

[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@uniontech.com>
---
 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

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

[Petko Manolov]

On 26-04-21 19:10:25, Morduan Zang wrote:
> 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.

Another approach would be to use skb_copy_from_linear_data() to a static buffer
and free the skb right away.  Take a look at pegasus_start_xmit() in
drivers/net/usb/pegasus.c.  This comes at the cost of yet another memcpy,
though.

The above is not to say i don't like your current approach, just FYI.


		Petko

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

[Andrew Lunn]

On Tue, Apr 21, 2026 at 07:10:25PM +0800, Morduan Zang wrote:
> 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@uniontech.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew