LSM: Add /sys/kernel/security/lsm

I am still tired of having to find indirect ways to determine
what security modules are active on a system. I have added
/sys/kernel/security/lsm, which contains a comma separated
list of the active security modules. No more groping around
in /proc/filesystems or other clever hacks.

Unchanged from previous versions except for being updated
to the latest security next branch.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>

Documentation/security/LSM.txt

@@ -22,6 +22,13 @@ system, building their checks on top of the defined capability hooks.
 For more details on capabilities, see capabilities(7) in the Linux
 man-pages project.
 
+A list of the active security modules can be found by reading
+/sys/kernel/security/lsm. This is a comma separated list, and
+will always include the capability module. The list reflects the
+order in which checks are made. The capability module will always
+be first, followed by any "minor" modules (e.g. Yama) and then
+the one "major" module (e.g. SELinux) if there is one configured.
+
 Based on https://lkml.org/lkml/2007/10/26/215,
 a new LSM is accepted into the kernel when its intent (a description of
 what it tries to protect against and in what cases one would expect to

include/linux/lsm_hooks.h

@@ -1875,6 +1875,7 @@ struct security_hook_list {
 	struct list_head		list;
 	struct list_head		*head;
 	union security_list_options	hook;
+	char				*lsm;
 };
 
 /*
@@ -1887,15 +1888,10 @@ struct security_hook_list {
 	{ .head = &security_hook_heads.HEAD, .hook = { .HEAD = HOOK } }
 
 extern struct security_hook_heads security_hook_heads;
+extern char *lsm_names;
 
-static inline void security_add_hooks(struct security_hook_list *hooks,
-				      int count)
-{
-	int i;
-
-	for (i = 0; i < count; i++)
-		list_add_tail_rcu(&hooks[i].list, hooks[i].head);
-}
+extern void security_add_hooks(struct security_hook_list *hooks, int count,
+				char *lsm);
 
 #ifdef CONFIG_SECURITY_SELINUX_DISABLE
 /*

security/apparmor/lsm.c

@@ -999,7 +999,8 @@ static int __init apparmor_init(void)
 		aa_free_root_ns();
 		goto buffers_out;
 	}
-	security_add_hooks(apparmor_hooks, ARRAY_SIZE(apparmor_hooks));
+	security_add_hooks(apparmor_hooks, ARRAY_SIZE(apparmor_hooks),
+				"apparmor");
 
 	/* Report that AppArmor successfully initialized */
 	apparmor_initialized = 1;

security/commoncap.c

@@ -1093,7 +1093,8 @@ struct security_hook_list capability_hooks[] = {
 
 void __init capability_add_hooks(void)
 {
-	security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks));
+	security_add_hooks(capability_hooks, ARRAY_SIZE(capability_hooks),
+				"capability");
 }
 
 #endif /* CONFIG_SECURITY */

security/inode.c

@@ -20,6 +20,7 @@
 #include <linux/init.h>
 #include <linux/namei.h>
 #include <linux/security.h>
+#include <linux/lsm_hooks.h>
 #include <linux/magic.h>
 
 static struct vfsmount *mount;
@@ -204,6 +205,21 @@ void securityfs_remove(struct dentry *dentry)
 }
 EXPORT_SYMBOL_GPL(securityfs_remove);
 
+#ifdef CONFIG_SECURITY
+static struct dentry *lsm_dentry;
+static ssize_t lsm_read(struct file *filp, char __user *buf, size_t count,
+			loff_t *ppos)
+{
+	return simple_read_from_buffer(buf, count, ppos, lsm_names,
+		strlen(lsm_names));
+}
+
+static const struct file_operations lsm_ops = {
+	.read = lsm_read,
+	.llseek = generic_file_llseek,
+};
+#endif
+
 static int __init securityfs_init(void)
 {
 	int retval;
@@ -213,9 +229,15 @@ static int __init securityfs_init(void)
 		return retval;
 
 	retval = register_filesystem(&fs_type);
-	if (retval)
+	if (retval) {
 		sysfs_remove_mount_point(kernel_kobj, "security");
-	return retval;
+		return retval;
+	}
+#ifdef CONFIG_SECURITY
+	lsm_dentry = securityfs_create_file("lsm", 0444, NULL, NULL,
+						&lsm_ops);
+#endif
+	return 0;
 }
 
 core_initcall(securityfs_init);

security/loadpin/loadpin.c

@@ -182,7 +182,7 @@ static struct security_hook_list loadpin_hooks[] = {
 void __init loadpin_add_hooks(void)
 {
 	pr_info("ready to pin (currently %sabled)", enabled ? "en" : "dis");
-	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks));
+	security_add_hooks(loadpin_hooks, ARRAY_SIZE(loadpin_hooks), "loadpin");
 }
 
 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */

security/security.c

@@ -32,6 +32,7 @@
 /* Maximum number of letters for an LSM name string */
 #define SECURITY_NAME_MAX	10
 
+char *lsm_names;
 /* Boot-time LSM user choice */
 static __initdata char chosen_lsm[SECURITY_NAME_MAX + 1] =
 	CONFIG_DEFAULT_SECURITY;
@@ -78,6 +79,22 @@ static int __init choose_lsm(char *str)
 }
 __setup("security=", choose_lsm);
 
+static int lsm_append(char *new, char **result)
+{
+	char *cp;
+
+	if (*result == NULL) {
+		*result = kstrdup(new, GFP_KERNEL);
+	} else {
+		cp = kasprintf(GFP_KERNEL, "%s,%s", *result, new);
+		if (cp == NULL)
+			return -ENOMEM;
+		kfree(*result);
+		*result = cp;
+	}
+	return 0;
+}
+
 /**
  * security_module_enable - Load given security module on boot ?
  * @module: the name of the module
@@ -97,6 +114,27 @@ int __init security_module_enable(const char *module)
 	return !strcmp(module, chosen_lsm);
 }
 
+/**
+ * security_add_hooks - Add a modules hooks to the hook lists.
+ * @hooks: the hooks to add
+ * @count: the number of hooks to add
+ * @lsm: the name of the security module
+ *
+ * Each LSM has to register its hooks with the infrastructure.
+ */
+void __init security_add_hooks(struct security_hook_list *hooks, int count,
+				char *lsm)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+		hooks[i].lsm = lsm;
+		list_add_tail_rcu(&hooks[i].list, hooks[i].head);
+	}
+	if (lsm_append(lsm, &lsm_names) < 0)
+		panic("%s - Cannot get early memory.\n", __func__);
+}
+
 /*
  * Hook list operation macros.
  *

security/selinux/hooks.c

@@ -6349,7 +6349,7 @@ static __init int selinux_init(void)
 					    0, SLAB_PANIC, NULL);
 	avc_init();
 
-	security_add_hooks(selinux_hooks, ARRAY_SIZE(selinux_hooks));
+	security_add_hooks(selinux_hooks, ARRAY_SIZE(selinux_hooks), "selinux");
 
 	if (avc_add_callback(selinux_netcache_avc_callback, AVC_CALLBACK_RESET))
 		panic("SELinux: Unable to register AVC netcache callback\n");

security/smack/smack_lsm.c

@@ -4819,7 +4819,7 @@ static __init int smack_init(void)
 	/*
 	 * Register with LSM
 	 */
-	security_add_hooks(smack_hooks, ARRAY_SIZE(smack_hooks));
+	security_add_hooks(smack_hooks, ARRAY_SIZE(smack_hooks), "smack");
 
 	return 0;
 }

security/tomoyo/tomoyo.c

@@ -542,7 +542,7 @@ static int __init tomoyo_init(void)
 	if (!security_module_enable("tomoyo"))
 		return 0;
 	/* register ourselves with the security framework */
-	security_add_hooks(tomoyo_hooks, ARRAY_SIZE(tomoyo_hooks));
+	security_add_hooks(tomoyo_hooks, ARRAY_SIZE(tomoyo_hooks), "tomoyo");
 	printk(KERN_INFO "TOMOYO Linux initialized\n");
 	cred->security = &tomoyo_kernel_domain;
 	tomoyo_mm_init();

security/yama/yama_lsm.c

@@ -485,6 +485,6 @@ static inline void yama_init_sysctl(void) { }
 void __init yama_add_hooks(void)
 {
 	pr_info("Yama: becoming mindful.\n");
-	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks));
+	security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama");
 	yama_init_sysctl();
 }