ipvs: use skb_to_full_sk() helper

SYNACK packets might be attached to request sockets.

Use skb_to_full_sk() helper to avoid illegal accesses to
inet_sk(skb->sk)

Fixes: ca6fb065 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Sander Eikelenboom <linux@eikelenboom.it>
Acked-by: Julian Anastasov <ja@ssi.bg>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/ipvs/ip_vs_core.c

@@ -1176,6 +1176,7 @@ ip_vs_out(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, in
 	struct ip_vs_protocol *pp;
 	struct ip_vs_proto_data *pd;
 	struct ip_vs_conn *cp;
+	struct sock *sk;
 
 	EnterFunction(11);
 
@@ -1183,13 +1184,12 @@ ip_vs_out(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, in
 	if (skb->ipvs_property)
 		return NF_ACCEPT;
 
+	sk = skb_to_full_sk(skb);
 	/* Bad... Do not break raw sockets */
-	if (unlikely(skb->sk != NULL && hooknum == NF_INET_LOCAL_OUT &&
+	if (unlikely(sk && hooknum == NF_INET_LOCAL_OUT &&
 		     af == AF_INET)) {
-		struct sock *sk = skb->sk;
-		struct inet_sock *inet = inet_sk(skb->sk);
 
-		if (inet && sk->sk_family == PF_INET && inet->nodefrag)
+		if (sk->sk_family == PF_INET && inet_sk(sk)->nodefrag)
 			return NF_ACCEPT;
 	}
 
@@ -1681,6 +1681,7 @@ ip_vs_in(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, int
 	struct ip_vs_conn *cp;
 	int ret, pkts;
 	int conn_reuse_mode;
+	struct sock *sk;
 
 	/* Already marked as IPVS request or reply? */
 	if (skb->ipvs_property)
@@ -1708,12 +1709,11 @@ ip_vs_in(struct netns_ipvs *ipvs, unsigned int hooknum, struct sk_buff *skb, int
 	ip_vs_fill_iph_skb(af, skb, false, &iph);
 
 	/* Bad... Do not break raw sockets */
-	if (unlikely(skb->sk != NULL && hooknum == NF_INET_LOCAL_OUT &&
+	sk = skb_to_full_sk(skb);
+	if (unlikely(sk && hooknum == NF_INET_LOCAL_OUT &&
 		     af == AF_INET)) {
-		struct sock *sk = skb->sk;
-		struct inet_sock *inet = inet_sk(skb->sk);
 
-		if (inet && sk->sk_family == PF_INET && inet->nodefrag)
+		if (sk->sk_family == PF_INET && inet_sk(sk)->nodefrag)
 			return NF_ACCEPT;
 	}