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 3a7c384ffd (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>

include/net/ip.h

@@ -120,7 +120,7 @@ extern struct sk_buff  *__ip_make_skb(struct sock *sk,
 				      struct flowi4 *fl4,
 				      struct sk_buff_head *queue,
 				      struct inet_cork *cork);
-extern int		ip_send_skb(struct sk_buff *skb);
+extern int		ip_send_skb(struct net *net, struct sk_buff *skb);
 extern int		ip_push_pending_frames(struct sock *sk, struct flowi4 *fl4);
 extern void		ip_flush_pending_frames(struct sock *sk);
 extern struct sk_buff  *ip_make_skb(struct sock *sk,

net/ipv4/ip_output.c

@@ -1366,9 +1366,8 @@ out:
 	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 @@ int ip_push_pending_frames(struct sock *sk, struct flowi4 *fl4)
 		return 0;
 
 	/* Netfilter gets whole the not fragmented skb. */
-	return ip_send_skb(skb);
+	return ip_send_skb(sock_net(sk), skb);
 }
 
 /*

net/ipv4/udp.c

@@ -758,7 +758,7 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4)
 		uh->check = CSUM_MANGLED_0;
 
 send:
-	err = ip_send_skb(skb);
+	err = ip_send_skb(sock_net(sk), skb);
 	if (err) {
 		if (err == -ENOBUFS && !inet->recverr) {
 			UDP_INC_STATS_USER(sock_net(sk),