[PATCH security-next v2 14/26] LSM: Lift LSM selection out of individual LSMs

[Kees Cook]

As a prerequisite to adjusting LSM selection logic in the future, this
moves the selection logic up out of the individual major 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        | 76 ++++++++++++++++++++++----------------
 security/selinux/hooks.c   | 10 -----
 security/smack/smack_lsm.c |  3 --
 security/tomoyo/tomoyo.c   |  2 -
 6 files changed, 45 insertions(+), 53 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 118e12f678df..ec1c0a97dfe3 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2091,7 +2091,6 @@ 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 d03133a267f2..5399c2f03536 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 a886a978214a..85533d4e534a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -52,33 +52,70 @@ static bool debug __initdata;
 			pr_info(__VA_ARGS__);			\
 	} while (0)
 
+/* 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_allowed(struct lsm_info *lsm)
+{
+	/* Skip if the LSM is disabled. */
+	if (lsm->enabled && !*lsm->enabled)
+		return false;
+
+	/* Skip major-specific checks if not a major LSM. */
+	if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
+		return true;
+
+	/* 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_initialize_lsm(struct lsm_info *lsm)
+{
+	int enabled = lsm_allowed(lsm);
+
+	/* Record enablement. */
+	set_enabled(lsm, enabled);
+
+	/* If selected, initialize the LSM. */
+	if (enabled) {
+		int ret;
+
+		init_debug("initializing %s\n", lsm->name);
+		ret = lsm->init();
+		WARN(ret, "%s failed to initialize: %d\n", lsm->name, ret);
+	}
+}
+
 static void __init ordered_lsm_init(void)
 {
 	struct lsm_info *lsm;
-	int ret;
 
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
 		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) != 0)
 			continue;
 
-		init_debug("initializing %s\n", lsm->name);
-		ret = lsm->init();
-		WARN(ret, "%s failed to initialize: %d\n", lsm->name, ret);
+		maybe_initialize_lsm(lsm);
 	}
 }
 
 static void __init major_lsm_init(void)
 {
 	struct lsm_info *lsm;
-	int ret;
 
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
 		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
 			continue;
 
-		init_debug("initializing %s\n", lsm->name);
-		ret = lsm->init();
-		WARN(ret, "%s failed to initialize: %d\n", lsm->name, ret);
+		maybe_initialize_lsm(lsm);
 	}
 }
 
@@ -168,29 +205,6 @@ 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 3f999ed98cfd..409a9252aeb6 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 4aef844fc0e2..e79fad43a8e3 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 528b6244a648..39bb994ebe09 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