LSM: Introduce CONFIG_LSM

This provides a way to declare LSM initialization order via the new
CONFIG_LSM. Currently only non-major LSMs are recognized. This will
be expanded in future patches.
Signed-off-by: Kees Cook <keescook@chromium.org>

security/Kconfig

@@ -276,5 +276,14 @@ config DEFAULT_SECURITY
 	default "apparmor" if DEFAULT_SECURITY_APPARMOR
 	default "" if DEFAULT_SECURITY_DAC
 
+config LSM
+	string "Ordered list of enabled LSMs"
+	default "integrity"
+	help
+	  A comma-separated list of LSMs, in initialization order.
+	  Any LSMs left off this list will be ignored.
+
+	  If unsure, leave this as the default.
+
 endmenu
 

security/security.c

@@ -48,6 +48,8 @@ char *lsm_names;
 static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
 	CONFIG_DEFAULT_SECURITY;
 
+static __initconst const char * const builtin_lsm_order = CONFIG_LSM;
+
 /* Ordered list of LSMs to initialize. */
 static __initdata struct lsm_info **ordered_lsms;
 
@@ -155,15 +157,30 @@ static void __init maybe_initialize_lsm(struct lsm_info *lsm)
 	}
 }
 
-/* Populate ordered LSMs list from single LSM name. */
+/* Populate ordered LSMs list from comma-separated LSM name list. */
 static void __init ordered_lsm_parse(const char *order, const char *origin)
 {
 	struct lsm_info *lsm;
+	char *sep, *name, *next;
+
+	sep = kstrdup(order, GFP_KERNEL);
+	next = sep;
+	/* Walk the list, looking for matching LSMs. */
+	while ((name = strsep(&next, ",")) != NULL) {
+		bool found = false;
+
+		for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
+			if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0 &&
+			    strcmp(lsm->name, name) == 0) {
+				append_ordered_lsm(lsm, origin);
+				found = true;
+			}
+		}
 
-	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
-		if (strcmp(lsm->name, order) == 0)
-			append_ordered_lsm(lsm, origin);
+		if (!found)
+			init_debug("%s ignored: %s\n", origin, name);
 	}
+	kfree(sep);
 }
 
 static void __init ordered_lsm_init(void)
@@ -173,7 +190,7 @@ static void __init ordered_lsm_init(void)
 	ordered_lsms = kcalloc(LSM_COUNT + 1, sizeof(*ordered_lsms),
 				GFP_KERNEL);
 
-	ordered_lsm_parse("integrity", "builtin");
+	ordered_lsm_parse(builtin_lsm_order, "builtin");
 
 	for (lsm = ordered_lsms; *lsm; lsm++)
 		maybe_initialize_lsm(*lsm);