ipv4: fix ip_send_skb()

ip_send_skb() can send orphaned skb, so we must pass the net pointer to
avoid possible NULL dereference in error path.

Bug added by commit 3a7c384ffd57 (ipv4: tcp: unicast_sock should not
land outside of TCP stack)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ec410e0..147ccc3 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1366,9 +1366,8 @@
 	return skb;
 }
 
-int ip_send_skb(struct sk_buff *skb)
+int ip_send_skb(struct net *net, struct sk_buff *skb)
 {
-	struct net *net = sock_net(skb->sk);
 	int err;
 
 	err = ip_local_out(skb);
@@ -1391,7 +1390,7 @@
 		return 0;
 
 	/* Netfilter gets whole the not fragmented skb. */
-	return ip_send_skb(skb);
+	return ip_send_skb(sock_net(sk), skb);
 }
 
 /*