net: add skb_to_full_sk() helper and use it in selinux_netlbl_skbuff_setsid()

Generalize selinux_skb_sk() added in commit 212cd0895330
("selinux: fix random read in selinux_ip_postroute_compat()")
so that we can use it other contexts.

Use it right away in selinux_netlbl_skbuff_setsid()

Fixes: ca6fb0651883 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_sock.h

@@ -210,6 +210,18 @@ struct inet_sock {
 #define IP_CMSG_ORIGDSTADDR	BIT(6)
 #define IP_CMSG_CHECKSUM	BIT(7)
 
+/* 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)
+{
+	struct sock *sk = skb->sk;
+
+	if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
+		sk = inet_reqsk(sk)->rsk_listener;
+	return sk;
+}
+
 static inline struct inet_sock *inet_sk(const struct sock *sk)
 {
 	return (struct inet_sock *)sk;

security/selinux/hooks.c

@@ -4931,23 +4931,11 @@ static unsigned int selinux_ipv4_output(void *priv,
 	return selinux_ip_output(skb, PF_INET);
 }
 
-/* SYNACK messages might be attached to request sockets.
- * To get back to sk_security, we need to look at the listener.
- */
-static struct sock *selinux_skb_sk(const struct sk_buff *skb)
-{
-	struct sock *sk = skb->sk;
-
-	if (sk && sk->sk_state == TCP_NEW_SYN_RECV)
-		sk = inet_reqsk(sk)->rsk_listener;
-	return sk;
-}
-
 static unsigned int selinux_ip_postroute_compat(struct sk_buff *skb,
 						int ifindex,
 						u16 family)
 {
-	struct sock *sk = selinux_skb_sk(skb);
+	struct sock *sk = skb_to_full_sk(skb);
 	struct sk_security_struct *sksec;
 	struct common_audit_data ad;
 	struct lsm_network_audit net = {0,};
@@ -5002,7 +4990,7 @@ static unsigned int selinux_ip_postroute(struct sk_buff *skb,
 	if (!secmark_active && !peerlbl_active)
 		return NF_ACCEPT;
 
-	sk = selinux_skb_sk(skb);
+	sk = skb_to_full_sk(skb);
 
 #ifdef CONFIG_XFRM
 	/* If skb->dst->xfrm is non-NULL then the packet is undergoing an IPsec

security/selinux/netlabel.c

@@ -245,7 +245,7 @@ int selinux_netlbl_skbuff_setsid(struct sk_buff *skb,
 
 	/* if this is a locally generated packet check to see if it is already
 	 * being labeled by it's parent socket, if it is just exit */
-	sk = skb->sk;
+	sk = skb_to_full_sk(skb);
 	if (sk != NULL) {
 		struct sk_security_struct *sksec = sk->sk_security;
 		if (sksec->nlbl_state != NLBL_REQSKB)