Config option to set a default LSM

The LSM currently requires setting a kernel parameter at boot to select
a specific LSM.  This adds a config option that allows specifying a default
LSM that is used unless overridden with the security= kernel parameter.
If the the config option is not set the current behavior of first LSM
to register is used.
Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>

security/Kconfig

@@ -152,5 +152,37 @@ source security/tomoyo/Kconfig
 
 source security/integrity/ima/Kconfig
 
+choice
+	prompt "Default security module"
+	default DEFAULT_SECURITY_SELINUX if SECURITY_SELINUX
+	default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
+	default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
+	default DEFAULT_SECURITY_DAC
+
+	help
+	  Select the security module that will be used by default if the
+	  kernel parameter security= is not specified.
+
+	config DEFAULT_SECURITY_SELINUX
+		bool "SELinux" if SECURITY_SELINUX=y
+
+	config DEFAULT_SECURITY_SMACK
+		bool "Simplified Mandatory Access Control" if SECURITY_SMACK=y
+
+	config DEFAULT_SECURITY_TOMOYO
+		bool "TOMOYO" if SECURITY_TOMOYO=y
+
+	config DEFAULT_SECURITY_DAC
+		bool "Unix Discretionary Access Controls"
+
+endchoice
+
+config DEFAULT_SECURITY
+	string
+	default "selinux" if DEFAULT_SECURITY_SELINUX
+	default "smack" if DEFAULT_SECURITY_SMACK
+	default "tomoyo" if DEFAULT_SECURITY_TOMOYO
+	default "" if DEFAULT_SECURITY_DAC
+
 endmenu
 

security/security.c

@@ -19,7 +19,8 @@
 #include <linux/ima.h>
 
 /* Boot-time LSM user choice */
-static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1];
+static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
+	CONFIG_DEFAULT_SECURITY;
 
 /* things that live in capability.c */
 extern struct security_operations default_security_ops;
@@ -80,8 +81,10 @@ __setup("security=", choose_lsm);
  *
  * Return true if:
  *	-The passed LSM is the one chosen by user at boot time,
- *	-or user didn't specify a specific LSM and we're the first to ask
- *	 for registration permission,
+ *	-or the passed LSM is configured as the default and the user did not
+ *	 choose an alternate LSM at boot time,
+ *	-or there is no default LSM set and the user didn't specify a
+ *	 specific LSM and we're the first to ask for registration permission,
  *	-or the passed LSM is currently loaded.
  * Otherwise, return false.
  */