sock: free skb in skb_complete_tx_timestamp on error

BugLink: http://bugs.launchpad.net/bugs/1745069

[ Upstream commit 35b99dff ]

skb_complete_tx_timestamp must ingest the skb it is passed. Call
kfree_skb if the skb cannot be enqueued.

Fixes: b245be1f ("net-timestamp: no-payload only sysctl")
Fixes: 9ac25fc0 ("net: fix socket refcounting in skb_complete_tx_timestamp()")
Reported-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

net/core/skbuff.c

@@ -3747,7 +3747,7 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
 	struct sock *sk = skb->sk;
 
 	if (!skb_may_tx_timestamp(sk, false))
-		return;
+		goto err;
 
 	/* Take a reference to prevent skb_orphan() from freeing the socket,
 	 * but only if the socket refcount is not zero.
@@ -3756,7 +3756,11 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
 		*skb_hwtstamps(skb) = *hwtstamps;
 		__skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND);
 		sock_put(sk);
+		return;
 	}
+
+err:
+	kfree_skb(skb);
 }
 EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);