[PATCH v5 08/38] LSM: Tie enabling logic to presence in ordered list

[Casey Schaufler]

From: Kees Cook <keescook at chromium.org>

Until now, any LSM without an enable storage variable was considered
enabled. This inverts the logic and sets defaults to true only if the
LSM gets added to the ordered initialization list. (And an exception
continues for the major LSMs until they are integrated into the ordered
initialization in a later patch.)

Signed-off-by: Kees Cook <keescook at chromium.org>
---
 include/linux/lsm_hooks.h |  2 +-
 security/security.c       | 14 +++++++++++---
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index dabd2761acfc..272791fdd26e 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2044,7 +2044,7 @@ extern void security_add_hooks(struct security_hook_list *hooks, int count,
 struct lsm_info {
 	const char *name;	/* Required. */
 	unsigned long flags;	/* Optional: flags describing LSM */
-	int *enabled;		/* Optional: NULL means enabled. */
+	int *enabled;		/* Optional: controlled by CONFIG_LSM */
 	int (*init)(void);	/* Required. */
 };
 
diff --git a/security/security.c b/security/security.c
index 38fc436e8b4b..ea760d625af6 100644
--- a/security/security.c
+++ b/security/security.c
@@ -63,10 +63,10 @@ static __initdata bool debug;
 
 static bool __init is_enabled(struct lsm_info *lsm)
 {
-	if (!lsm->enabled || *lsm->enabled)
-		return true;
+	if (!lsm->enabled)
+		return false;
 
-	return false;
+	return *lsm->enabled;
 }
 
 /* Mark an LSM's enabled flag. */
@@ -117,7 +117,11 @@ static void __init append_ordered_lsm(struct lsm_info *lsm, const char *from)
 	if (WARN(last_lsm == LSM_COUNT, "%s: out of LSM slots!?\n", from))
 		return;
 
+	/* Enable this LSM, if it is not already set. */
+	if (!lsm->enabled)
+		lsm->enabled = &lsm_enabled_true;
 	ordered_lsms[last_lsm++] = lsm;
+
 	init_debug("%s ordering: %s (%sabled)\n", from, lsm->name,
 		   is_enabled(lsm) ? "en" : "dis");
 }
@@ -210,6 +214,10 @@ static void __init major_lsm_init(void)
 		if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
 			continue;
 
+		/* Enable this LSM, if it is not already set. */
+		if (!lsm->enabled)
+			lsm->enabled = &lsm_enabled_true;
+
 		maybe_initialize_lsm(lsm);
 	}
 }
-- 
2.14.5