security: rework selinux, smack, ima, apparmor detection logic

Always cache the results, and bypass low-level security calls when the
respective subsystem is not enabled.

src/shared/apparmor-util.c

@@ -0,0 +1,41 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <unistd.h>
+
+#include "util.h"
+#include "fileio.h"
+#include "apparmor-util.h"
+
+static int use_apparmor_cached = -1;
+
+bool use_apparmor(void) {
+
+        if (use_apparmor_cached < 0) {
+                _cleanup_free_ char *p = NULL;
+
+                use_apparmor_cached =
+                        read_one_line_file("/sys/module/apparmor/parameters/enabled", &p) >= 0 &&
+                        parse_boolean(p) > 0;
+        }
+
+        return use_apparmor_cached;
+}

src/shared/apparmor-util.h

@@ -0,0 +1,26 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdbool.h>
+
+bool use_apparmor(void);

src/shared/ima-util.c

@@ -0,0 +1,35 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <unistd.h>
+
+#include "apparmor-util.h"
+
+
+static int use_ima_cached = -1;
+
+bool use_ima(void) {
+
+        if (use_ima_cached < 0)
+                use_ima_cached = access("/sys/kernel/security/ima/", F_OK) >= 0;
+
+        return use_ima_cached;
+}

src/shared/ima-util.h

@@ -0,0 +1,26 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdbool.h>
+
+bool use_ima(void);

src/shared/selinux-util.c

@@ -39,4 +39,13 @@ void retest_selinux(void) {
         use_selinux_cached = -1;
 }
 
+#else
+
+bool use_selinux(void) {
+        return false;
+}
+
+void retest_selinux(void) {
+}
+
 #endif

src/shared/smack-util.c

@@ -21,16 +21,21 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
-#include "smack-util.h"
-
 #include <unistd.h>
 
-static int use_smack_cached = -1;
+#include "smack-util.h"
 
 bool use_smack(void) {
 
+#ifdef HAVE_SMACK
+        static int use_smack_cached = -1;
+
         if (use_smack_cached < 0)
-                use_smack_cached = (access("/sys/fs/smackfs", F_OK) >= 0);
+                use_smack_cached = access("/sys/fs/smackfs/", F_OK) >= 0;
 
         return use_smack_cached;
+#else
+        return false;
+#endif
+
 }