sock: free skb in skb_complete_tx_timestamp on error

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

Fixes: b245be1f4db1 ("net-timestamp: no-payload only sysctl")
Fixes: 9ac25fc06375 ("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>

net/core/skbuff.c

@@ -4293,7 +4293,7 @@ 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.
@@ -4302,7 +4302,11 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
 		*skb_hwtstamps(skb) = *hwtstamps;
 		__skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND, false);
 		sock_put(sk);
+		return;
 	}
+
+err:
+	kfree_skb(skb);
 }
 EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);