LSM: Refactor "security=" in terms of enable/disable

For what are marked as the Legacy Major LSMs, make them effectively
exclusive when selected on the "security=" boot parameter, to handle
the future case of when a previously major LSMs become non-exclusive
(e.g. when TOMOYO starts blob-sharing).

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

1 files changed, 20 insertions, 8 deletions

diff --git a/security/security.c b/security/security.c
index 1e1f34285e96..88de6b073246 100644
--- a/security/security.c
+++ b/security/security.c
@@ -129,14 +129,6 @@ static bool __init lsm_allowed(struct lsm_info *lsm)
         if (!is_enabled(lsm))
                 return false;
 
-        /* Skip major-specific checks if not a major LSM. */
-        if ((lsm->flags & LSM_FLAG_LEGACY_MAJOR) == 0)
-                return true;
-
-        /* Disabled if this LSM isn't the chosen one. */
-        if (strcmp(lsm->name, chosen_major_lsm) != 0)
-                return false;
-
         return true;
 }
 
@@ -164,8 +156,28 @@ static void __init ordered_lsm_parse(const char *order, const char *origin)
         struct lsm_info *lsm;
         char *sep, *name, *next;
 
+        /* Process "security=", if given. */
         if (!chosen_major_lsm)
                 chosen_major_lsm = CONFIG_DEFAULT_SECURITY;
+        if (chosen_major_lsm) {
+                struct lsm_info *major;
+
+                /*
+                 * To match the original "security=" behavior, this
+                 * explicitly does NOT fallback to another Legacy Major
+                 * if the selected one was separately disabled: disable
+                 * all non-matching Legacy Major LSMs.
+                 */
+                for (major = __start_lsm_info; major < __end_lsm_info;
+                     major++) {
+                        if ((major->flags & LSM_FLAG_LEGACY_MAJOR) &&
+                            strcmp(major->name, chosen_major_lsm) != 0) {
+                                set_enabled(major, false);
+                                init_debug("security=%s disabled: %s\n",
+                                           chosen_major_lsm, major->name);
+                        }
+                }
+        }
 
         sep = kstrdup(order, GFP_KERNEL);
         next = sep;