[PATCH security-next v5 15/30] 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. This considers all
LSMs enabled by default unless they specified an external "enable"
variable.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
Reviewed-by: John Johansen <john.johansen@xxxxxxxxxxxxx>
---
 include/linux/lsm_hooks.h  |   1 -
 security/apparmor/lsm.c    |   6 ---
 security/security.c        | 102 ++++++++++++++++++++++++++-----------
 security/selinux/hooks.c   |  10 ----
 security/smack/smack_lsm.c |   3 --
 security/tomoyo/tomoyo.c   |   2 -
 6 files changed, 71 insertions(+), 53 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 6ec5a0266f21..9ecb623fb39d 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2085,7 +2085,6 @@ 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 6ace45704cb6..bc56b058dc75 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 ebbbb672ced5..8968c98e0a0e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -52,33 +52,96 @@ static __initdata bool debug;
 			pr_info(__VA_ARGS__);			\
 	} while (0)
 
+static bool __init is_enabled(struct lsm_info *lsm)
+{
+	if (!lsm->enabled || *lsm->enabled)
+		return true;
+
+	return false;
+}
+
+/* Mark an LSM's enabled flag. */
+static int lsm_enabled_true __initdata = 1;
+static int lsm_enabled_false __initdata = 0;
+static void __init set_enabled(struct lsm_info *lsm, bool enabled)
+{
+	/*
+	 * When an LSM hasn't configured an enable variable, we can use
+	 * a hard-coded location for storing the default enabled state.
+	 */
+	if (!lsm->enabled) {
+		if (enabled)
+			lsm->enabled = &lsm_enabled_true;
+		else
+			lsm->enabled = &lsm_enabled_false;
+	} else if (lsm->enabled == &lsm_enabled_true) {
+		if (!enabled)
+			lsm->enabled = &lsm_enabled_false;
+	} else if (lsm->enabled == &lsm_enabled_false) {
+		if (enabled)
+			lsm->enabled = &lsm_enabled_true;
+	} else {
+		*lsm->enabled = enabled;
+	}
+}
+
+/* Is an LSM allowed to be initialized? */
+static bool __init lsm_allowed(struct lsm_info *lsm)
+{
+	/* Skip if the LSM is disabled. */
+	if (!is_enabled(lsm))
+		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 initialized. */
+static void __init maybe_initialize_lsm(struct lsm_info *lsm)
+{
+	int enabled = lsm_allowed(lsm);
+
+	/* Record enablement (to handle any following exclusive LSMs). */
+	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 +231,6 @@ 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 e8da99550b67..71a10fedecb3 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 db8bc6b6d8b0..f243044d5a55 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 09f7af130d3a..a46f6bc1e97c 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