Smack: Fix handling of IPv4 traffic received by PF_INET6 sockets

A socket which has sk_family set to PF_INET6 is able to receive not
only IPv6 but also IPv4 traffic (IPv4-mapped IPv6 addresses).

Prior to this patch, the smk_skb_to_addr_ipv6() could have been
called for socket buffers containing IPv4 packets, in result such
traffic was allowed.

Signed-off-by: Piotr Sawicki <p.sawicki2@partner.samsung.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack_lsm.c

@@ -3923,15 +3923,19 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	struct smack_known *skp = NULL;
 	int rc = 0;
 	struct smk_audit_info ad;
+	u16 family = sk->sk_family;
 #ifdef CONFIG_AUDIT
 	struct lsm_network_audit net;
 #endif
 #if IS_ENABLED(CONFIG_IPV6)
 	struct sockaddr_in6 sadd;
 	int proto;
+
+	if (family == PF_INET6 && skb->protocol == htons(ETH_P_IP))
+		family = PF_INET;
 #endif /* CONFIG_IPV6 */
 
-	switch (sk->sk_family) {
+	switch (family) {
 	case PF_INET:
 #ifdef CONFIG_SECURITY_SMACK_NETFILTER
 		/*
@@ -3949,7 +3953,7 @@ static int smack_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 		 */
 		netlbl_secattr_init(&secattr);
 
-		rc = netlbl_skbuff_getattr(skb, sk->sk_family, &secattr);
+		rc = netlbl_skbuff_getattr(skb, family, &secattr);
 		if (rc == 0)
 			skp = smack_from_secattr(&secattr, ssp);
 		else
@@ -3962,7 +3966,7 @@ access_check:
 #endif
 #ifdef CONFIG_AUDIT
 		smk_ad_init_net(&ad, __func__, LSM_AUDIT_DATA_NET, &net);
-		ad.a.u.net->family = sk->sk_family;
+		ad.a.u.net->family = family;
 		ad.a.u.net->netif = skb->skb_iif;
 		ipv4_skb_to_auditdata(skb, &ad.a, NULL);
 #endif
@@ -3976,7 +3980,7 @@ access_check:
 		rc = smk_bu_note("IPv4 delivery", skp, ssp->smk_in,
 					MAY_WRITE, rc);
 		if (rc != 0)
-			netlbl_skbuff_err(skb, sk->sk_family, rc, 0);
+			netlbl_skbuff_err(skb, family, rc, 0);
 		break;
 #if IS_ENABLED(CONFIG_IPV6)
 	case PF_INET6:
@@ -3992,7 +3996,7 @@ access_check:
 			skp = smack_net_ambient;
 #ifdef CONFIG_AUDIT
 		smk_ad_init_net(&ad, __func__, LSM_AUDIT_DATA_NET, &net);
-		ad.a.u.net->family = sk->sk_family;
+		ad.a.u.net->family = family;
 		ad.a.u.net->netif = skb->skb_iif;
 		ipv6_skb_to_auditdata(skb, &ad.a, NULL);
 #endif /* CONFIG_AUDIT */