Yama: remove needless CONFIG_SECURITY_YAMA_STACKED

Now that minor LSMs can cleanly stack with major LSMs, remove the unneeded
config for Yama to be made to explicitly stack. Just selecting the main
Yama CONFIG will allow it to work, regardless of the major LSM. Since
distros using Yama are already forcing it to stack, this is effectively
a no-op change.

Additionally add MAINTAINERS entry.

Signed-off-by: Kees Cook <[e-mail]>
Signed-off-by: James Morris <[e-mail]>

Documentation/security/Yama.txt

···
-Yama is a Linux Security Module that collects a number of system-wide DAC
-security protections that are not handled by the core kernel itself. To
-select it at boot time, specify "security=yama" (though this will disable
-any other LSM).
-
-Yama is controlled through sysctl in /proc/sys/kernel/yama:
+Yama is a Linux Security Module that collects system-wide DAC security
+protections that are not handled by the core kernel itself. This is
+selectable at build-time with CONFIG_SECURITY_YAMA, and can be controlled
+at run-time through sysctls in /proc/sys/kernel/yama:
 
 - ptrace_scope
 

MAINTAINERS

···
 S:	Supported
 F:	security/apparmor/
 
+YAMA SECURITY MODULE
+M:	Kees Cook <[e-mail]>
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git yama/tip
+S:	Supported
+F:	security/yama/
+
 SENSABLE PHANTOM
 M:	Jiri Slaby <[e-mail]>
 S:	Maintained

arch/mips/configs/pistachio_defconfig

···
 CONFIG_SECURITY=y
 CONFIG_SECURITY_NETWORK=y
 CONFIG_SECURITY_YAMA=y
-CONFIG_SECURITY_YAMA_STACKED=y
 CONFIG_DEFAULT_SECURITY_DAC=y
 CONFIG_CRYPTO_AUTHENC=y
 CONFIG_CRYPTO_HMAC=y

include/linux/lsm_hooks.h

···
 
 extern int __init security_module_enable(const char *module);
 extern void __init capability_add_hooks(void);
-#ifdef CONFIG_SECURITY_YAMA_STACKED
-void __init yama_add_hooks(void);
+#ifdef CONFIG_SECURITY_YAMA
+extern void __init yama_add_hooks(void);
+#else
+static inline void __init yama_add_hooks(void) { }
 #endif
 
 #endif /* ! __LINUX_LSM_HOOKS_H */

security/Kconfig

···
 	default DEFAULT_SECURITY_SMACK if SECURITY_SMACK
 	default DEFAULT_SECURITY_TOMOYO if SECURITY_TOMOYO
 	default DEFAULT_SECURITY_APPARMOR if SECURITY_APPARMOR
-	default DEFAULT_SECURITY_YAMA if SECURITY_YAMA
 	default DEFAULT_SECURITY_DAC
 
 	help
···
 	config DEFAULT_SECURITY_APPARMOR
 		bool "AppArmor" if SECURITY_APPARMOR=y
 
-	config DEFAULT_SECURITY_YAMA
-		bool "Yama" if SECURITY_YAMA=y
-
 	config DEFAULT_SECURITY_DAC
 		bool "Unix Discretionary Access Controls"
 
···
 	default "smack" if DEFAULT_SECURITY_SMACK
 	default "tomoyo" if DEFAULT_SECURITY_TOMOYO
 	default "apparmor" if DEFAULT_SECURITY_APPARMOR
-	default "yama" if DEFAULT_SECURITY_YAMA
 	default "" if DEFAULT_SECURITY_DAC
 
 endmenu

security/security.c

···
 	pr_info("Security Framework initialized\n");
 
 	/*
-	 * Always load the capability module.
+	 * Load minor LSMs, with the capability module always first.
 	 */
 	capability_add_hooks();
-#ifdef CONFIG_SECURITY_YAMA_STACKED
-	/*
-	 * If Yama is configured for stacking load it next.
-	 */
 	yama_add_hooks();
-#endif
+
 	/*
-	 * Load the chosen module if there is one.
-	 * This will also find yama if it is stacking
+	 * Load all the remaining security modules.
 	 */
 	do_security_initcalls();
 

security/yama/Kconfig

···
 	  This selects Yama, which extends DAC support with additional
 	  system-wide security settings beyond regular Linux discretionary
 	  access controls. Currently available is ptrace scope restriction.
+	  Like capabilities, this security module stacks with other LSMs.
 	  Further information can be found in Documentation/security/Yama.txt.
 
 	  If you are unsure how to answer this question, answer N.
-
-config SECURITY_YAMA_STACKED
-	bool "Yama stacked with other LSMs"
-	depends on SECURITY_YAMA
-	default n
-	help
-	  When Yama is built into the kernel, force it to stack with the
-	  selected primary LSM.

security/yama/yama_lsm.c

···
 	LSM_HOOK_INIT(task_free, yama_task_free),
 };
 
-void __init yama_add_hooks(void)
-{
-	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks));
-}
-
 #ifdef CONFIG_SYSCTL
 static int yama_dointvec_minmax(struct ctl_table *table, int write,
 				void __user *buffer, size_t *lenp, loff_t *ppos)
···
 	},
 	{ }
 };
-#endif /* CONFIG_SYSCTL */
-
-static __init int yama_init(void)
+static void __init yama_init_sysctl(void)
 {
-#ifndef CONFIG_SECURITY_YAMA_STACKED
-	/*
-	 * If yama is being stacked this is already taken care of.
-	 */
-	if (!security_module_enable("yama"))
-		return 0;
-#endif
-	pr_info("Yama: becoming mindful.\n");
-
-#ifdef CONFIG_SYSCTL
 	if (!register_sysctl_paths(yama_sysctl_path, yama_sysctl_table))
 		panic("Yama: sysctl registration failed.\n");
-#endif
-
-	return 0;
 }
+#else
+static inline void yama_init_sysctl(void) { }
+#endif /* CONFIG_SYSCTL */
 
-security_initcall(yama_init);
+void __init yama_add_hooks(void)
+{
+	pr_info("Yama: becoming mindful.\n");
+	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks));
+	yama_init_sysctl();
+}