selinux: streamline selinux_nlmsg_lookup()

Streamline the code in selinux_nlmsg_lookup() to improve the code flow,
readability, and remove the unnecessary local variables.

Tested-by: Thiébaud Weksteen <tweek@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: pcmoore

security/selinux/nlmsgtab.c

@@ -168,34 +168,12 @@ static int nlmsg_perm(u16 nlmsg_type, u32 *perm, const struct nlmsg_perm *tab, s
 
 int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm)
 {
-	int err = 0;
-
-	if (selinux_policycap_netlink_xperm()) {
-		switch (sclass) {
-		case SECCLASS_NETLINK_ROUTE_SOCKET:
-			*perm = NETLINK_ROUTE_SOCKET__NLMSG;
-			break;
-		case SECCLASS_NETLINK_TCPDIAG_SOCKET:
-			*perm = NETLINK_TCPDIAG_SOCKET__NLMSG;
-			break;
-		case SECCLASS_NETLINK_XFRM_SOCKET:
-			*perm = NETLINK_XFRM_SOCKET__NLMSG;
-			break;
-		case SECCLASS_NETLINK_AUDIT_SOCKET:
-			*perm = NETLINK_AUDIT_SOCKET__NLMSG;
-			break;
-		/* While it is possible to add a similar permission to other
-		 * netlink classes, note that the extended permission value is
-		 * matched against the nlmsg_type field. Notably,
-		 * SECCLASS_NETLINK_GENERIC_SOCKET uses dynamic values for this
-		 * field, which means that it cannot be added as-is.
-		 */
-		default:
-			err = -ENOENT;
-			break;
-		}
-		return err;
-	}
+	/* While it is possible to add a similar permission to other netlink
+	 * classes, note that the extended permission value is matched against
+	 * the nlmsg_type field. Notably, SECCLASS_NETLINK_GENERIC_SOCKET uses
+	 * dynamic values for this field, which means that it cannot be added
+	 * as-is.
+	 */
 
 	switch (sclass) {
 	case SECCLASS_NETLINK_ROUTE_SOCKET:
@@ -205,42 +183,52 @@ int selinux_nlmsg_lookup(u16 sclass, u16 nlmsg_type, u32 *perm)
 		 * before updating the BUILD_BUG_ON() macro!
 		 */
 		BUILD_BUG_ON(RTM_MAX != (RTM_NEWTUNNEL + 3));
-		err = nlmsg_perm(nlmsg_type, perm, nlmsg_route_perms,
-				 sizeof(nlmsg_route_perms));
-		break;
 
+		if (selinux_policycap_netlink_xperm()) {
+			*perm = NETLINK_ROUTE_SOCKET__NLMSG;
+			return 0;
+		}
+		return nlmsg_perm(nlmsg_type, perm, nlmsg_route_perms,
+				  sizeof(nlmsg_route_perms));
+		break;
 	case SECCLASS_NETLINK_TCPDIAG_SOCKET:
-		err = nlmsg_perm(nlmsg_type, perm, nlmsg_tcpdiag_perms,
-				 sizeof(nlmsg_tcpdiag_perms));
+		if (selinux_policycap_netlink_xperm()) {
+			*perm = NETLINK_TCPDIAG_SOCKET__NLMSG;
+			return 0;
+		}
+		return nlmsg_perm(nlmsg_type, perm, nlmsg_tcpdiag_perms,
+				  sizeof(nlmsg_tcpdiag_perms));
 		break;
-
 	case SECCLASS_NETLINK_XFRM_SOCKET:
 		/* If the BUILD_BUG_ON() below fails you must update the
 		 * structures at the top of this file with the new mappings
 		 * before updating the BUILD_BUG_ON() macro!
 		 */
 		BUILD_BUG_ON(XFRM_MSG_MAX != XFRM_MSG_GETDEFAULT);
-		err = nlmsg_perm(nlmsg_type, perm, nlmsg_xfrm_perms,
-				 sizeof(nlmsg_xfrm_perms));
-		break;
 
+		if (selinux_policycap_netlink_xperm()) {
+			*perm = NETLINK_XFRM_SOCKET__NLMSG;
+			return 0;
+		}
+		return nlmsg_perm(nlmsg_type, perm, nlmsg_xfrm_perms,
+				  sizeof(nlmsg_xfrm_perms));
+		break;
 	case SECCLASS_NETLINK_AUDIT_SOCKET:
-		if ((nlmsg_type >= AUDIT_FIRST_USER_MSG &&
-		     nlmsg_type <= AUDIT_LAST_USER_MSG) ||
-		    (nlmsg_type >= AUDIT_FIRST_USER_MSG2 &&
-		     nlmsg_type <= AUDIT_LAST_USER_MSG2)) {
+		if (selinux_policycap_netlink_xperm()) {
+			*perm = NETLINK_AUDIT_SOCKET__NLMSG;
+			return 0;
+		} else if ((nlmsg_type >= AUDIT_FIRST_USER_MSG &&
+			    nlmsg_type <= AUDIT_LAST_USER_MSG) ||
+			   (nlmsg_type >= AUDIT_FIRST_USER_MSG2 &&
+			    nlmsg_type <= AUDIT_LAST_USER_MSG2)) {
 			*perm = NETLINK_AUDIT_SOCKET__NLMSG_RELAY;
-		} else {
-			err = nlmsg_perm(nlmsg_type, perm, nlmsg_audit_perms,
-					 sizeof(nlmsg_audit_perms));
+			return 0;
 		}
-		break;
-
-	/* No messaging from userspace, or class unknown/unhandled */
-	default:
-		err = -ENOENT;
+		return nlmsg_perm(nlmsg_type, perm, nlmsg_audit_perms,
+				  sizeof(nlmsg_audit_perms));
 		break;
 	}
 
-	return err;
+	/* No messaging from userspace, or class unknown/unhandled */
+	return -ENOENT;
 }