xfrm: take care of request sockets

TCP SYNACK messages might now be attached to request sockets.

XFRM needs to get back to a listener socket.

Adds new helpers that might be used elsewhere :
sk_to_full_sk() and sk_const_to_full_sk()

Note: We also need to add RCU protection for xfrm lookups,
now TCP/DCCP have lockless listener processing. This will
be addressed in separate patches.

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_sock.h

@@ -210,18 +210,37 @@ struct inet_sock {
 #define IP_CMSG_ORIGDSTADDR	BIT(6)
 #define IP_CMSG_CHECKSUM	BIT(7)
 
-/* SYNACK messages might be attached to request sockets.
+/**
+ * sk_to_full_sk - Access to a full socket
+ * @sk: pointer to a socket
+ *
+ * SYNACK messages might be attached to request sockets.
  * Some places want to reach the listener in this case.
  */
-static inline struct sock *skb_to_full_sk(const struct sk_buff *skb)
+static inline struct sock *sk_to_full_sk(struct sock *sk)
 {
-	struct sock *sk = skb->sk;
-
+#ifdef CONFIG_INET
 	if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
 		sk = inet_reqsk(sk)->rsk_listener;
+#endif
+	return sk;
+}
+
+/* sk_to_full_sk() variant with a const argument */
+static inline const struct sock *sk_const_to_full_sk(const struct sock *sk)
+{
+#ifdef CONFIG_INET
+	if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
+		sk = ((const struct request_sock *)sk)->rsk_listener;
+#endif
 	return sk;
 }
 
+static inline struct sock *skb_to_full_sk(const struct sk_buff *skb)
+{
+	return sk_to_full_sk(skb->sk);
+}
+
 static inline struct inet_sock *inet_sk(const struct sock *sk)
 {
 	return (struct inet_sock *)sk;

net/xfrm/xfrm_policy.c

@@ -2198,6 +2198,7 @@ struct dst_entry *xfrm_lookup(struct net *net, struct dst_entry *dst_orig,
 	xdst = NULL;
 	route = NULL;
 
+	sk = sk_const_to_full_sk(sk);
 	if (sk && sk->sk_policy[XFRM_POLICY_OUT]) {
 		num_pols = 1;
 		pols[0] = xfrm_sk_policy_lookup(sk, XFRM_POLICY_OUT, fl);
@@ -2477,6 +2478,7 @@ int __xfrm_policy_check(struct sock *sk, int dir, struct sk_buff *skb,
 	}
 
 	pol = NULL;
+	sk = sk_to_full_sk(sk);
 	if (sk && sk->sk_policy[dir]) {
 		pol = xfrm_sk_policy_lookup(sk, dir, &fl);
 		if (IS_ERR(pol)) {