xsk: frame could be completed more than once in SKB path

Fixed a bug in which a frame could be completed more than once
when an error was returned from dev_direct_xmit(). The code
erroneously retried sending the message leading to multiple
calls to the SKB destructor and therefore multiple completions
of the same buffer to user space.

The error code in this case has been changed from EAGAIN to EBUSY
in order to tell user space that the sending of the packet failed
and the buffer has been return to user space through the completion
queue.

Fixes: 35fcde7f8deb ("xsk: support for Tx")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Reported-by: Pavel Odintsov <pavel@fastnetmon.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 59fb7d3c36a34089095a81a979ecf64b8b152e7f..15aca73805fcc61b91740dc0b7c71e49929e5f78 100644 (file)
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -268,15 +268,15 @@ static int xsk_generic_xmit(struct sock *sk, struct msghdr *m,
                skb->destructor = xsk_destruct_skb;
 
                err = dev_direct_xmit(skb, xs->queue_id);
+               xskq_discard_desc(xs->tx);
                /* Ignore NET_XMIT_CN as packet might have been sent */
                if (err == NET_XMIT_DROP || err == NETDEV_TX_BUSY) {
-                       err = -EAGAIN;
-                       /* SKB consumed by dev_direct_xmit() */
+                       /* SKB completed but not sent */
+                       err = -EBUSY;
                        goto out;
                }
 
                sent_frame = true;
-               xskq_discard_desc(xs->tx);
        }
 
 out: