[PATCH security-next v4 24/32] LSM: Build ordered list of ordered LSMs for init

From: Kees Cook
Date: Mon Oct 01 2018 - 21:05:17 EST


This constructs a list of ordered 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@xxxxxxxxxxxx>
Reviewed-by: Casey Schaufler <casey@xxxxxxxxxxxxxxxx>
---
security/security.c | 59 +++++++++++++++++++++++++++++++++++++++------
1 file changed, 52 insertions(+), 7 deletions(-)

diff --git a/security/security.c b/security/security.c
index 40b9f508b856..8706b42b4d44 100644
--- a/security/security.c
+++ b/security/security.c
@@ -34,6 +34,9 @@

#define MAX_LSM_EVM_XATTR 2

+/* 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 @@ static __initdata const char *chosen_major_lsm;

static __initconst const char * const builtin_lsm_enable = CONFIG_LSM_ENABLE;

+/* Ordered list of LSMs to initialize. */
+static __initdata struct lsm_info **ordered_lsms;
+
static __initdata bool debug;
#define init_debug(...) \
do { \
@@ -88,6 +94,45 @@ 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");
+}
+
+/* Populate ordered LSMs list from hard-coded list of LSMs. */
+static void __init prepare_lsm_order(void)
+{
+ struct lsm_info *lsm;
+
+ for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
+ if (strcmp(lsm->name, "integrity") == 0)
+ append_ordered_lsm(lsm, "builtin");
+ }
+}
+
/* Is an LSM allowed to be initialized? */
static bool __init lsm_allowed(struct lsm_info *lsm)
{
@@ -118,14 +163,10 @@ static void __init maybe_initialize_lsm(struct lsm_info *lsm)

static void __init ordered_lsm_init(void)
{
- struct lsm_info *lsm;
-
- for (lsm = __start_lsm_info; lsm < __end_lsm_info; lsm++) {
- if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) != 0)
- continue;
+ struct lsm_info **lsm;

- maybe_initialize_lsm(lsm);
- }
+ for (lsm = ordered_lsms; *lsm; lsm++)
+ maybe_initialize_lsm(*lsm);
}

static void __init major_lsm_init(void)
@@ -207,6 +248,8 @@ int __init security_init(void)
for (i = 0; i < sizeof(security_hook_heads) / sizeof(struct hlist_head);
i++)
INIT_HLIST_HEAD(&list[i]);
+ ordered_lsms = kcalloc(LSM_COUNT + 1, sizeof(*ordered_lsms),
+ GFP_KERNEL);

/* Figure out which LSMs are enabled and disabled. */
prepare_lsm_enable();
@@ -219,6 +262,7 @@ int __init security_init(void)
loadpin_add_hooks();

/* Load LSMs in specified order. */
+ prepare_lsm_order();
ordered_lsm_init();

/*
@@ -226,6 +270,7 @@ int __init security_init(void)
*/
major_lsm_init();

+ kfree(ordered_lsms);
return 0;
}

--
2.17.1