smack: dont compile ipv6 code unless ipv6 is configured

I want to be sure that ipv6-specific code
is not compiled in kernel binaries
if ipv6 is not configured.

[1] was getting rid of "unused variable" warning, but,
with that, it also mandated compilation of a handful ipv6-
specific functions in ipv4-only kernel configurations:

smk_ipv6_localhost, smack_ipv6host_label, smk_ipv6_check.

Their compiled bodies are likely to be removed by compiler
from the resulting binary, but, to be on the safe side,
I remove them from the compiler view.

[1]
Fixes: 00720f0 ("smack: avoid unused 'sip' variable warning")

Signed-off-by: Konstantin Andreev <andreev@swemel.ru>
Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>

Author: goongas

security/smack/smack.h

@@ -152,6 +152,7 @@ struct smk_net4addr {
 	struct smack_known	*smk_label;	/* label */
 };
 
+#if IS_ENABLED(CONFIG_IPV6)
 /*
  * An entry in the table identifying IPv6 hosts.
  */
@@ -162,7 +163,9 @@ struct smk_net6addr {
 	int			smk_masks;	/* mask size */
 	struct smack_known	*smk_label;	/* label */
 };
+#endif /* CONFIG_IPV6 */
 
+#ifdef SMACK_IPV6_PORT_LABELING
 /*
  * An entry in the table identifying ports.
  */
@@ -175,6 +178,7 @@ struct smk_port_label {
 	short			smk_sock_type;	/* Socket type */
 	short			smk_can_reuse;
 };
+#endif /* SMACK_IPV6_PORT_LABELING */
 
 struct smack_known_list_elem {
 	struct list_head	list;
@@ -315,7 +319,9 @@ extern struct smack_known smack_known_web;
 extern struct mutex	smack_known_lock;
 extern struct list_head smack_known_list;
 extern struct list_head smk_net4addr_list;
+#if IS_ENABLED(CONFIG_IPV6)
 extern struct list_head smk_net6addr_list;
+#endif /* CONFIG_IPV6 */
 
 extern struct mutex     smack_onlycap_lock;
 extern struct list_head smack_onlycap_list;

security/smack/smack_lsm.c

@@ -2492,6 +2492,7 @@ static struct smack_known *smack_ipv4host_label(struct sockaddr_in *sip)
 	return NULL;
 }
 
+#if IS_ENABLED(CONFIG_IPV6)
 /*
  * smk_ipv6_localhost - Check for local ipv6 host address
  * @sip: the address
@@ -2559,6 +2560,7 @@ static struct smack_known *smack_ipv6host_label(struct sockaddr_in6 *sip)
 
 	return NULL;
 }
+#endif /* CONFIG_IPV6 */
 
 /**
  * smack_netlbl_add - Set the secattr on a socket
@@ -2663,6 +2665,7 @@ static int smk_ipv4_check(struct sock *sk, struct sockaddr_in *sap)
 	return rc;
 }
 
+#if IS_ENABLED(CONFIG_IPV6)
 /**
  * smk_ipv6_check - check Smack access
  * @subject: subject Smack label
@@ -2695,6 +2698,7 @@ static int smk_ipv6_check(struct smack_known *subject,
 	rc = smk_bu_note("IPv6 check", subject, object, MAY_WRITE, rc);
 	return rc;
 }
+#endif /* CONFIG_IPV6 */
 
 #ifdef SMACK_IPV6_PORT_LABELING
 /**
@@ -3027,7 +3031,9 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 		return 0;
 	if (addrlen < offsetofend(struct sockaddr, sa_family))
 		return 0;
-	if (IS_ENABLED(CONFIG_IPV6) && sap->sa_family == AF_INET6) {
+
+#if IS_ENABLED(CONFIG_IPV6)
+	if (sap->sa_family == AF_INET6) {
 		struct sockaddr_in6 *sip = (struct sockaddr_in6 *)sap;
 		struct smack_known *rsp = NULL;
 
@@ -3047,6 +3053,8 @@ static int smack_socket_connect(struct socket *sock, struct sockaddr *sap,
 
 		return rc;
 	}
+#endif /* CONFIG_IPV6 */
+
 	if (sap->sa_family != AF_INET || addrlen < sizeof(struct sockaddr_in))
 		return 0;
 	rc = smk_ipv4_check(sock->sk, (struct sockaddr_in *)sap);