LSM: Separate idea of "major" LSM from "exclusive" LSM

In order to both support old "security=" Legacy Major LSM selection, and
handling real exclusivity, this creates LSM_FLAG_EXCLUSIVE and updates
the selection logic to handle them.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/security/security.c b/security/security.c
index 88de6b073246..a8dd7defe30a 100644
--- a/security/security.c
+++ b/security/security.c
@@ -49,6 +49,7 @@ static __initconst const char * const builtin_lsm_order = CONFIG_LSM;
 
 /* Ordered list of LSMs to initialize. */
 static __initdata struct lsm_info **ordered_lsms;
+static __initdata struct lsm_info *exclusive;
 
 static __initdata bool debug;
 #define init_debug(...)                                         \
@@ -129,6 +130,12 @@ static bool __init lsm_allowed(struct lsm_info *lsm)
         if (!is_enabled(lsm))
                 return false;
 
+        /* Not allowed if another exclusive LSM already initialized. */
+        if ((lsm->flags & LSM_FLAG_EXCLUSIVE) && exclusive) {
+                init_debug("exclusive disabled: %s\n", lsm->name);
+                return false;
+        }
+
         return true;
 }
 
@@ -144,6 +151,11 @@ static void __init maybe_initialize_lsm(struct lsm_info *lsm)
         if (enabled) {
                 int ret;
 
+                if ((lsm->flags & LSM_FLAG_EXCLUSIVE) && !exclusive) {
+                        exclusive = lsm;
+                        init_debug("exclusive chosen: %s\n", lsm->name);
+                }
+
                 init_debug("initializing %s\n", lsm->name);
                 ret = lsm->init();
                 WARN(ret, "%s failed to initialize: %d\n", lsm->name, ret);