[PATCH security-next v4 25/32] LSM: Introduce CONFIG_LSM_ORDER

[Kees Cook]

This provides a way to declare LSM initialization order via Kconfig.

Signed-off-by: Kees Cook <keescook at chromium.org>
Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>
---
 security/Kconfig    | 16 ++++++++++++++++
 security/security.c | 40 +++++++++++++++++++++++++++++++++++++---
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/security/Kconfig b/security/Kconfig
index 1e57619fd561..c68520d97fd7 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -286,5 +286,21 @@ config LSM_ENABLE
 	  changed with the "lsm.enable=" and "lsm.disable=" boot
 	  parameters.
 
+	  Note that any enabled exclusive LSM modules will be initialized
+	  based on LSM ordering, automatically disabling any following
+	  exclusive LSMs. See CONFIG_LSM_ORDER for more details on
+	  changing LSM initialization order.
+
+config LSM_ORDER
+	string "Default initialization order of builtin LSMs"
+	default "integrity"
+	help
+	  A comma-separated list of LSMs, in initialization order.
+	  Any LSMs left off this list will be link-order initialized
+	  after any listed LSMs. Any LSMs listed here but not built in
+	  the kernel will be ignored.
+
+	  If unsure, leave this as the default.
+
 endmenu
 
diff --git a/security/security.c b/security/security.c
index 8706b42b4d44..0510bb8e0af0 100644
--- a/security/security.c
+++ b/security/security.c
@@ -47,6 +47,7 @@ static __initdata const char *chosen_lsm_disable;
 static __initdata const char *chosen_major_lsm;
 
 static __initconst const char * const builtin_lsm_enable = CONFIG_LSM_ENABLE;
+static __initconst const char * const builtin_lsm_order = CONFIG_LSM_ORDER;
 
 /* Ordered list of LSMs to initialize. */
 static __initdata struct lsm_info **ordered_lsms;
@@ -122,14 +123,47 @@ static void __init append_ordered_lsm(struct lsm_info *lsm, const char *from)
 		   is_enabled(lsm) ? "en" : "dis");
 }
 
-/* Populate ordered LSMs list from hard-coded list of LSMs. */
+/* Populate ordered LSMs list from given string. */
+static void __init parse_lsm_order(const char *order, const char *origin)
+{
+	struct lsm_info *lsm;
+	char *sep, *name, *next;
+
+	if (!order)
+		return;
+
+	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;
+			}
+		}
+
+		if (!found)
+			init_debug("%s ignored: %s\n", origin, name);
+	}
+	kfree(sep);
+}
+
+/* Populate ordered LSMs list from builtin list of LSMs. */
 static void __init prepare_lsm_order(void)
 {
 	struct lsm_info *lsm;
 
+	/* Parse order from builtin list. */
+	parse_lsm_order(builtin_lsm_order, "builtin");
+
+	/* Add any missing LSMs, in link order. */
 	for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
-		if (strcmp(lsm->name, "integrity") == 0)
-			append_ordered_lsm(lsm, "builtin");
+		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
+			append_ordered_lsm(lsm, "link-time");
 	}
 }
 
-- 
2.17.1