[PATCH 11/18] LSM: Lift LSM selection out of individual LSMs

[Kees Cook]

In order to adjust LSM selection logic in the future, this moves the
selection logic up out of the individual LSMs, making their init functions
only run when actually enabled.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/linux/lsm_hooks.h  |  1 -
 security/apparmor/lsm.c    |  6 ---
 security/security.c        | 75 ++++++++++++++++++++++++++------------
 security/selinux/hooks.c   | 10 -----
 security/smack/smack_lsm.c |  3 --
 security/tomoyo/tomoyo.c   |  2 -
 6 files changed, 51 insertions(+), 46 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 8a3a6cd26f03..6e71e1c47fa1 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2094,7 +2094,6 @@ static inline void security_delete_hooks(struct security_hook_list *hooks,
 #define __lsm_ro_after_init	__ro_after_init
 #endif /* CONFIG_SECURITY_WRITABLE_HOOKS */
 
-extern int __init security_module_enable(const char *module);
 extern void __init capability_add_hooks(void);
 #ifdef CONFIG_SECURITY_YAMA
 extern void __init yama_add_hooks(void);
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 6cd630b34c3b..56c0982b48cd 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1542,12 +1542,6 @@ static int __init apparmor_init(void)
 {
 	int error;
 
-	if (!apparmor_enabled || !security_module_enable("apparmor")) {
-		aa_info_message("AppArmor disabled by boot time parameter");
-		apparmor_enabled = false;
-		return 0;
-	}
-
 	aa_secids_init();
 
 	error = aa_setup_dfa_engine();
diff --git a/security/security.c b/security/security.c
index da2a923f2609..3fedbee5f3ec 100644
--- a/security/security.c
+++ b/security/security.c
@@ -43,13 +43,63 @@ char *lsm_names;
 static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
 	CONFIG_DEFAULT_SECURITY;
 
+static struct lsm_info *exclusive __initdata;
+
+/* Mark an LSM's enabled flag, if it exists. */
+static void __init set_enabled(struct lsm_info *lsm, bool enabled)
+{
+	if (lsm->enabled)
+		*lsm->enabled = enabled;
+}
+
+/* Is an LSM allowed to be enabled? */
+static bool __init lsm_enabled(struct lsm_info *lsm)
+{
+	/* Report explicit disabling. */
+	if (lsm->enabled && !*lsm->enabled) {
+		pr_info("%s disabled with boot parameter\n", lsm->name);
+		return false;
+	}
+
+	/* If LSM isn't exclusive, ignore exclusive LSM selection rules. */
+	if (lsm->type != LSM_TYPE_EXCLUSIVE)
+		return true;
+
+	/* Disabled if another exclusive LSM already selected. */
+	if (exclusive)
+		return false;
+
+	/* Disabled if this LSM isn't the chosen one. */
+	if (strcmp(lsm->name, chosen_lsm) != 0)
+		return false;
+
+	return true;
+}
+
+/* Check if LSM should be enabled. Mark any that are disabled. */
+static void __init maybe_enable_lsm(struct lsm_info *lsm)
+{
+	int enabled = lsm_enabled(lsm);
+
+	/* Record enablement. */
+	set_enabled(lsm, enabled);
+
+	/* If selected, initialize the LSM. */
+	if (enabled) {
+		if (lsm->type == LSM_TYPE_EXCLUSIVE) {
+			exclusive = lsm;
+		}
+		lsm->init();
+	}
+}
+
 static void __init lsm_init(enum lsm_type type)
 {
 	struct lsm_info *lsm;
 
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
 		if (lsm->type == type)
-			lsm->init();
+			maybe_enable_lsm(lsm);
 	}
 }
 
@@ -128,29 +178,6 @@ static int lsm_append(char *new, char **result)
 	return 0;
 }
 
-/**
- * security_module_enable - Load given security module on boot ?
- * @module: the name of the module
- *
- * Each LSM must pass this method before registering its own operations
- * to avoid security registration races. This method may also be used
- * to check if your LSM is currently loaded during kernel initialization.
- *
- * Returns:
- *
- * true if:
- *
- * - The passed LSM is the one chosen by user at boot time,
- * - or the passed LSM is configured as the default and the user did not
- *   choose an alternate LSM at boot time.
- *
- * Otherwise, return false.
- */
-int __init security_module_enable(const char *module)
-{
-	return !strcmp(module, chosen_lsm);
-}
-
 /**
  * security_add_hooks - Add a modules hooks to the hook lists.
  * @hooks: the hooks to add
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 78b5afc188f3..5478abf51f3a 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7133,16 +7133,6 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 
 static __init int selinux_init(void)
 {
-	if (!security_module_enable("selinux")) {
-		selinux_enabled = 0;
-		return 0;
-	}
-
-	if (!selinux_enabled) {
-		pr_info("SELinux:  Disabled at boot.\n");
-		return 0;
-	}
-
 	pr_info("SELinux:  Initializing.\n");
 
 	memset(&selinux_state, 0, sizeof(selinux_state));
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 1e1ace718e75..6e127c357ca2 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4834,9 +4834,6 @@ static __init int smack_init(void)
 	struct cred *cred;
 	struct task_smack *tsp;
 
-	if (!security_module_enable("smack"))
-		return 0;
-
 	smack_inode_cache = KMEM_CACHE(inode_smack, 0);
 	if (!smack_inode_cache)
 		return -ENOMEM;
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index a280d4eab456..0471390409c5 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -540,8 +540,6 @@ static int __init tomoyo_init(void)
 {
 	struct cred *cred = (struct cred *) current_cred();
 
-	if (!security_module_enable("tomoyo"))
-		return 0;
 	/* register ourselves with the security framework */
 	security_add_hooks(tomoyo_hooks, ARRAY_SIZE(tomoyo_hooks), "tomoyo");
 	printk(KERN_INFO "TOMOYO Linux initialized\n");
-- 
2.17.1