Smack: Fix the issue of wrong SMACK label update in socket bind fail case

Fix the issue of wrong SMACK label (SMACK64IPIN) update when a second bind
call is made to same IP address & port, but with different SMACK label
(SMACK64IPIN) by second instance of server. In this case server returns
with "Bind:Address already in use" error but before returning, SMACK label
is updated in SMACK port-label mapping list inside smack_socket_bind() hook

To fix this issue a new check has been added in smk_ipv6_port_label()
function before updating the existing port entry. It checks whether the
socket for matching port entry is closed or not. If it is closed then it
means port is not bound and it is safe to update the existing port entry
else return if port is still getting used. For checking whether socket is
closed or not, one more field "smk_can_reuse" has been added in the
"smk_port_label" structure. This field will be set to '1' in
"smack_sk_free_security()" function which is called to free the socket
security blob when the socket is being closed. In this function, port entry
is searched in the SMACK port-label mapping list for the closing socket.
If entry is found then "smk_can_reuse" field is set to '1'.Initially
"smk_can_reuse" field is set to '0' in smk_ipv6_port_label() function after
creating a new entry in the list which indicates that socket is in use.

Signed-off-by: Vishal Goel <vishal.goel@samsung.com>
Signed-off-by: Himanshu Shukla <himanshu.sh@samsung.com>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

security/smack/smack.h

@@ -174,6 +174,7 @@ struct smk_port_label {
 	struct smack_known	*smk_in;	/* inbound label */
 	struct smack_known	*smk_out;	/* outgoing label */
 	short			smk_sock_type;	/* Socket type */
+	short			smk_can_reuse;
 };
 #endif /* SMACK_IPV6_PORT_LABELING */
 

security/smack/smack_lsm.c

@@ -2354,6 +2354,20 @@ static int smack_sk_alloc_security(struct sock *sk, int family, gfp_t gfp_flags)
  */
 static void smack_sk_free_security(struct sock *sk)
 {
+#ifdef SMACK_IPV6_PORT_LABELING
+	struct smk_port_label *spp;
+
+	if (sk->sk_family == PF_INET6) {
+		rcu_read_lock();
+		list_for_each_entry_rcu(spp, &smk_ipv6_port_list, list) {
+			if (spp->smk_sock != sk)
+				continue;
+			spp->smk_can_reuse = 1;
+			break;
+		}
+		rcu_read_unlock();
+	}
+#endif
 	kfree(sk->sk_security);
 }
 
@@ -2637,10 +2651,15 @@ static void smk_ipv6_port_label(struct socket *sock, struct sockaddr *address)
 	list_for_each_entry_rcu(spp, &smk_ipv6_port_list, list) {
 		if (spp->smk_port != port || spp->smk_sock_type != sock->type)
 			continue;
+		if (spp->smk_can_reuse != 1) {
+			rcu_read_unlock();
+			return;
+		}
 		spp->smk_port = port;
 		spp->smk_sock = sk;
 		spp->smk_in = ssp->smk_in;
 		spp->smk_out = ssp->smk_out;
+		spp->smk_can_reuse = 0;
 		rcu_read_unlock();
 		return;
 	}
@@ -2657,6 +2676,7 @@ static void smk_ipv6_port_label(struct socket *sock, struct sockaddr *address)
 	spp->smk_in = ssp->smk_in;
 	spp->smk_out = ssp->smk_out;
 	spp->smk_sock_type = sock->type;
+	spp->smk_can_reuse = 0;
 
 	mutex_lock(&smack_ipv6_lock);
 	list_add_rcu(&spp->list, &smk_ipv6_port_list);