LSM: Build ordered list of LSMs to initialize

This constructs an ordered list of LSMs to initialize, using a hard-coded
list of only "integrity": minor LSMs continue to have direct hook calls,
and major LSMs continue to initialize separately.
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>

security/security.c

@@ -37,6 +37,9 @@
 /* Maximum number of letters for an LSM name string */
 #define SECURITY_NAME_MAX	10
 
+/* How many LSMs were built into the kernel? */
+#define LSM_COUNT (__end_lsm_info - __start_lsm_info)
+
 struct security_hook_heads security_hook_heads __lsm_ro_after_init;
 static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
 
@@ -45,6 +48,9 @@ char *lsm_names;
 static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
 	CONFIG_DEFAULT_SECURITY;
 
+/* Ordered list of LSMs to initialize. */
+static __initdata struct lsm_info **ordered_lsms;
+
 static __initdata bool debug;
 #define init_debug(...)						\
 	do {							\
@@ -85,6 +91,34 @@ static void __init set_enabled(struct lsm_info *lsm, bool enabled)
 	}
 }
 
+/* Is an LSM already listed in the ordered LSMs list? */
+static bool __init exists_ordered_lsm(struct lsm_info *lsm)
+{
+	struct lsm_info **check;
+
+	for (check = ordered_lsms; *check; check++)
+		if (*check == lsm)
+			return true;
+
+	return false;
+}
+
+/* Append an LSM to the list of ordered LSMs to initialize. */
+static int last_lsm __initdata;
+static void __init append_ordered_lsm(struct lsm_info *lsm, const char *from)
+{
+	/* Ignore duplicate selections. */
+	if (exists_ordered_lsm(lsm))
+		return;
+
+	if (WARN(last_lsm == LSM_COUNT, "%s: out of LSM slots!?\n", from))
+		return;
+
+	ordered_lsms[last_lsm++] = lsm;
+	init_debug("%s ordering: %s (%sabled)\n", from, lsm->name,
+		   is_enabled(lsm) ? "en" : "dis");
+}
+
 /* Is an LSM allowed to be initialized? */
 static bool __init lsm_allowed(struct lsm_info *lsm)
 {
@@ -121,18 +155,32 @@ static void __init maybe_initialize_lsm(struct lsm_info *lsm)
 	}
 }
 
-static void __init ordered_lsm_init(void)
+/* Populate ordered LSMs list from single LSM name. */
+static void __init ordered_lsm_parse(const char *order, const char *origin)
 {
 	struct lsm_info *lsm;
 
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
-		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) != 0)
-			continue;
-
-		maybe_initialize_lsm(lsm);
+		if (strcmp(lsm->name, order) == 0)
+			append_ordered_lsm(lsm, origin);
 	}
 }
 
+static void __init ordered_lsm_init(void)
+{
+	struct lsm_info **lsm;
+
+	ordered_lsms = kcalloc(LSM_COUNT + 1, sizeof(*ordered_lsms),
+				GFP_KERNEL);
+
+	ordered_lsm_parse("integrity", "builtin");
+
+	for (lsm = ordered_lsms; *lsm; lsm++)
+		maybe_initialize_lsm(*lsm);
+
+	kfree(ordered_lsms);
+}
+
 static void __init major_lsm_init(void)
 {
 	struct lsm_info *lsm;