1 files changed, 37 insertions, 1 deletions

diff --git a/security/security.c b/security/security.c
index 2ef593ec70f3..dd0c6baed494 100644
--- a/security/security.c
+++ b/security/security.c
@@ -17,6 +17,8 @@
 #include <linux/kernel.h>
 #include <linux/security.h>
 
+/* Boot-time LSM user choice */
+static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1];
 
 /* things that live in dummy.c */
 extern struct security_operations dummy_security_ops;
@@ -67,13 +69,47 @@ int __init security_init(void)
         return 0;
 }
 
+/* Save user chosen LSM */
+static int __init choose_lsm(char *str)
+{
+        strncpy(chosen_lsm, str, SECURITY_NAME_MAX);
+        return 1;
+}
+__setup("security=", choose_lsm);
+
+/**
+ * security_module_enable - Load given security module on boot ?
+ * @ops: a pointer to the struct security_operations that is to be checked.
+ *
+ * Each LSM must pass this method before registering its own operations
+ * to avoid security registration races. This method may also be used
+ * to check if your LSM is currently loaded.
+ *
+ * Return true if:
+ *      -The passed LSM is the one chosen by user at boot time,
+ *      -or user didsn't specify a specific LSM and we're the first to ask
+ *       for registeration permissoin,
+ *      -or the passed LSM is currently loaded.
+ * Otherwise, return false.
+ */
+int __init security_module_enable(struct security_operations *ops)
+{
+        if (!*chosen_lsm)
+                strncpy(chosen_lsm, ops->name, SECURITY_NAME_MAX);
+        else if (strncmp(ops->name, chosen_lsm, SECURITY_NAME_MAX))
+                return 0;
+
+        return 1;
+}
+
 /**
  * register_security - registers a security framework with the kernel
  * @ops: a pointer to the struct security_options that is to be registered
  *
  * This function is to allow a security module to register itself with the
  * kernel security subsystem.  Some rudimentary checking is done on the @ops
- * value passed to this function.
+ * value passed to this function. You'll need to check first if your LSM
+ * is allowed to register its @ops by calling security_module_enable(@ops).
  *
  * If there is already a security module registered with the kernel,
  * an error will be returned.  Otherwise 0 is returned on success.