[PATCH v6 1/1] security: Add mechanism to safely (un)load LSMs after boot time

[penguin-kernel@I-love.SAKURA.ne.jp (Tetsuo Handa)]

I think we can introduce a struct for passing arguments of
security_add_hooks()/security_delete_hooks(). Then, we don't
need to increment module usage count as many as hooks used.

---
 include/linux/lsm_hooks.h                     |  37 +++++---
 scripts/gcc-plugins/randomize_layout_plugin.c |   2 -
 security/apparmor/lsm.c                       |   6 +-
 security/commoncap.c                          |   7 +-
 security/loadpin/loadpin.c                    |   5 +-
 security/security.c                           | 117 ++++++++++++++------------
 security/selinux/hooks.c                      |  10 +--
 security/smack/smack_lsm.c                    |   4 +-
 security/tomoyo/tomoyo.c                      |   5 +-
 security/yama/yama_lsm.c                      |   5 +-
 10 files changed, 112 insertions(+), 86 deletions(-)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index c577d3d..4df62dd 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2007,10 +2007,17 @@ struct security_hook_heads {
  */
 struct security_hook_list {
 	struct hlist_node			list;
-	const unsigned int			hook_idx;
+	const unsigned int			offset;
 	const union security_list_options	hook;
-	struct module				*owner;
-	char					*lsm;
+	const char				*lsm; /* Currently unused. */
+} __randomize_layout;
+
+struct lsm_info {
+	struct list_head		list;
+	const char			*name;
+	struct module			*owner;
+	const int			count;
+	struct security_hook_list	*hooks;
 } __randomize_layout;
 
 /*
@@ -2020,20 +2027,27 @@ struct security_hook_list {
  * text involved.
  */
 #define HOOK_OFFSET(HEAD)	offsetof(struct security_hook_heads, HEAD)
-#define HOOK_SIZE(HEAD)		FIELD_SIZEOF(struct security_hook_heads, HEAD)
-#define LSM_HOOK_IDX(HEAD)	(HOOK_OFFSET(HEAD) / HOOK_SIZE(HEAD))
 
 #define LSM_HOOK_INIT(HEAD, HOOK) \
 	{						\
 		.hook = { .HEAD = HOOK },		\
-		.owner = THIS_MODULE,			\
-		.hook_idx = LSM_HOOK_IDX(HEAD),		\
+		.offset = HOOK_OFFSET(HEAD),		\
 	}
 extern char *lsm_names;
 
-extern int __must_check security_add_hooks(struct security_hook_list *hooks,
-						const int count, char *lsm,
-						const bool is_mutable);
+#define LSM_MODULE_INIT(NAME, HOOKS)		\
+	{					\
+		.name = NAME,			\
+		.hooks = HOOKS,			\
+		.count = ARRAY_SIZE(HOOKS),	\
+		.owner = THIS_MODULE,		\
+	}
+
+extern int __must_check security_add_hooks(struct lsm_info *lsm,
+					   const bool is_mutable);
+#ifdef CONFIG_SECURITY_SELINUX_DISABLE
+extern void __security_delete_hooks(struct lsm_info *lsm);
+#endif
 #ifdef CONFIG_SECURITY_UNREGISTRABLE_HOOKS
 /*
  * Used to facilitate runtime hook unloading
@@ -2049,8 +2063,7 @@ extern int __must_check security_add_hooks(struct security_hook_list *hooks,
  * disabling their module is a good idea needs to be at least as
  * careful as the SELinux team.
  */
-extern int __must_check security_delete_hooks(struct security_hook_list *hooks,
-						int count);
+extern int __must_check security_delete_hooks(struct lsm_info *lsm);
 #endif /* CONFIG_SECURITY_UNREGISTRABLE_HOOKS */
 
 extern int __init security_module_enable(const char *module);
diff --git a/scripts/gcc-plugins/randomize_layout_plugin.c b/scripts/gcc-plugins/randomize_layout_plugin.c
index 6d5bbd3..d941389 100644
--- a/scripts/gcc-plugins/randomize_layout_plugin.c
+++ b/scripts/gcc-plugins/randomize_layout_plugin.c
@@ -52,8 +52,6 @@ struct whitelist_entry {
 	{ "net/unix/af_unix.c", "unix_skb_parms", "char" },
 	/* big_key payload.data struct splashing */
 	{ "security/keys/big_key.c", "path", "void *" },
-	/* walk struct security_hook_heads as an array of struct hlist_head */
-	{ "security/security.c", "hlist_head", "security_hook_heads" },
 	{ }
 };
 
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 2a591bd..12c98aa8 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1191,6 +1191,9 @@ static void apparmor_sock_graft(struct sock *sk, struct socket *parent)
 	LSM_HOOK_INIT(task_kill, apparmor_task_kill),
 };
 
+static struct lsm_info apparmor_module =
+	LSM_MODULE_INIT("apparmor", apparmor_hooks);
+
 /*
  * AppArmor sysfs module parameters
  */
@@ -1562,8 +1565,7 @@ static int __init apparmor_init(void)
 		aa_free_root_ns();
 		goto buffers_out;
 	}
-	BUG_ON(security_add_hooks(apparmor_hooks, ARRAY_SIZE(apparmor_hooks),
-					"apparmor", false));
+	BUG_ON(security_add_hooks(&apparmor_module, false));
 
 	/* Report that AppArmor successfully initialized */
 	apparmor_initialized = 1;
diff --git a/security/commoncap.c b/security/commoncap.c
index a215059..8c0df17 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1362,11 +1362,12 @@ struct security_hook_list capability_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(vm_enough_memory, cap_vm_enough_memory),
 };
 
+static struct lsm_info capability_module =
+	LSM_MODULE_INIT("capability", capability_hooks);
+
 void __init capability_add_hooks(void)
 {
-	BUG_ON(security_add_hooks(capability_hooks,
-					ARRAY_SIZE(capability_hooks),
-					"capability", false));
+	BUG_ON(security_add_hooks(&capability_module, false));
 }
 
 #endif /* CONFIG_SECURITY */
diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 7c84ca8..60f85a5 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -178,10 +178,13 @@ static int loadpin_read_file(struct file *file, enum kernel_read_file_id id)
 	LSM_HOOK_INIT(kernel_read_file, loadpin_read_file),
 };
 
+static struct lsm_info loadpin_module =
+	LSM_MODULE_INIT("loadpin", 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), "loadpin");
+	BUG_ON(security_add_hooks(&loadpin_module, false));
 }
 
 /* Should not be mutable after boot, so not listed in sysfs (perm == 0). */
diff --git a/security/security.c b/security/security.c
index dd69889..c4e5437 100644
--- a/security/security.c
+++ b/security/security.c
@@ -32,9 +32,6 @@
 #include <linux/srcu.h>
 #include <linux/mutex.h>
 
-#define SECURITY_HOOK_COUNT \
-	(sizeof(security_hook_heads) / sizeof(struct hlist_head))
-
 #include <trace/events/initcall.h>
 
 #define MAX_LSM_EVM_XATTR	2
@@ -43,7 +40,7 @@
 #define SECURITY_NAME_MAX	10
 
 static struct security_hook_heads security_hook_heads __ro_after_init;
-
+static LIST_HEAD(registered_lsm_modules);
 static ATOMIC_NOTIFIER_HEAD(lsm_notifier_chain);
 static DEFINE_MUTEX(security_hook_mutex);
 /*
@@ -93,20 +90,20 @@ static void __init do_security_initcalls(void)
 #define FOR_EACH_SECURITY_HOOK_MUTABLE(ITERATOR, HEAD) \
 	hlist_for_each_entry(ITERATOR, &security_hook_heads_mutable.HEAD, list)
 
-static struct hlist_head *get_heads(bool is_mutable)
+static struct security_hook_heads *get_heads(bool is_mutable)
 {
 	if (is_mutable)
-		return (struct hlist_head *)&security_hook_heads_mutable;
-	return (struct hlist_head *)&security_hook_heads;
+		return &security_hook_heads_mutable;
+	return &security_hook_heads;
 }
 #else
 #define FOR_EACH_SECURITY_HOOK_MUTABLE(ITERATOR, HEAD)	while (0)
 
-static struct hlist_head *get_heads(bool is_mutable)
+static struct security_hook_heads *get_heads(bool is_mutable)
 {
 	if (is_mutable)
 		return ERR_PTR(-EINVAL);
-	return (struct hlist_head *)&security_hook_heads;
+	return &security_hook_heads;
 }
 #endif /* CONFIG_SECURITY_WRITABLE_HOOKS */
 
@@ -129,8 +126,7 @@ static inline void synchronize_lsm(void)
 
 /**
  * security_delete_hooks - Remove modules hooks from the mutable hooks lists.
- * @hooks: the hooks to remove
- * @count: the number of hooks to remove
+ * @lsm: Module info,
  *
  * 0 is returned on success, otherwise -errno is returned on failure.
  * If an error is returned, it is up to the LSM author to handle the error
@@ -142,31 +138,29 @@ static inline void synchronize_lsm(void)
  * authors check the return code here, and act appropriately. In most cases
  * a failure should result in panic.
  */
-int __must_check security_delete_hooks(struct security_hook_list *hooks,
-					int count)
+int __must_check security_delete_hooks(struct lsm_info *lsm)
 {
-	int i, ret = 0;
+	struct security_hook_list *hooks = lsm->hooks;
+	const int count = lsm->count;
+	int i, ret = -EPERM;
 
-	mutex_lock(&security_hook_mutex);
-	if (security_allow_unregister_hooks)
+	if (mutex_lock_killable(&security_hook_mutex))
+		return -EINTR;
+	if (security_allow_unregister_hooks) {
 		for (i = 0; i < count; i++)
 			hlist_del_rcu(&hooks[i].list);
-	else
-		ret = -EPERM;
-	mutex_unlock(&security_hook_mutex);
-
-	if (!ret)
+		list_del(&lsm->list);
 		synchronize_lsm();
+		ret = 0;
+	}
+	mutex_unlock(&security_hook_mutex);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(security_delete_hooks);
 
 static void lock_existing_hooks(void)
 {
-	struct hlist_head *list = (struct hlist_head *)
-					&security_hook_heads_mutable;
-	struct security_hook_list *P;
-	int i;
+	struct lsm_info *lsm;
 
 	/*
 	 * Prevent module unloading while we're doing this
@@ -174,10 +168,8 @@ static void lock_existing_hooks(void)
 	 * is already unloading -- allow that.
 	 */
 	mutex_lock(&module_mutex);
-	for (i = 0; i < SECURITY_HOOK_COUNT; i++)
-		hlist_for_each_entry(P, &list[i], list)
-			if (P->owner)
-				WARN_ON(!try_module_get(P->owner));
+	list_foreach_entry(lsm, &registered_lsm_modules, list)
+		try_module_get(lsm->owner);
 	mutex_unlock(&module_mutex);
 }
 #else
@@ -198,16 +190,19 @@ static inline void synchronize_lsm(void) {}
  * Only to be called by legacy code, like SELinux's delete hooks mechanism
  * as it ignores whether or not allow_unregister_hooks is set.
  */
-void __security_delete_hooks(struct security_hook_list *hooks, int count)
+void __security_delete_hooks(struct lsm_info *lsm)
 {
 	int i;
+	struct security_hook_list *hooks = lsm->hooks;
+	const int count = lsm->count;
 
 	mutex_lock(&security_hook_mutex);
 	for (i = 0; i < count; i++)
 		hlist_del_rcu(&hooks[i].list);
+	list_del(&lsm->list);
+	synchronize_lsm();
 	mutex_unlock(&security_hook_mutex);
 
-	synchronize_lsm();
 }
 #endif /* CONFIG_SECURITY_SELINUX_DISABLE */
 
@@ -314,7 +309,7 @@ static bool match_last_lsm(const char *list, const char *lsm)
 	return !strcmp(last, lsm);
 }
 
-static int lsm_append(char *new, char **result)
+static int lsm_append(const char *new, char **result)
 {
 	char *cp;
 
@@ -358,41 +353,53 @@ int __init security_module_enable(const char *module)
 
 /**
  * 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
+ * @lsm: Module info,
  * @is_mutable: True if dynamic registration and/or unregistration is needed.
  *
  * Each LSM has to register its hooks with the infrastructure.
  * 0 is returned on success, otherwise -errno is returned on failure.
  */
-int __must_check security_add_hooks(struct security_hook_list *hooks,
-					const int count, char *lsm,
-					const bool is_mutable)
+int __must_check security_add_hooks(struct lsm_info *lsm,
+				    const bool is_mutable)
 {
-	struct hlist_head *heads;
-	int i, hook_idx, ret = 0;
+	struct security_hook_heads *heads = get_heads(is_mutable);
+	struct security_hook_list *hooks = lsm->hooks;
+	const int count = lsm->count;
+	int i, ret;
 
-	mutex_lock(&security_hook_mutex);
-	heads = get_heads(is_mutable);
-	if (IS_ERR(heads)) {
-		ret = PTR_ERR(heads);
+	INIT_LIST_HEAD(&lsm->list);
+	if (IS_ERR(heads))
+		return PTR_ERR(heads);
+	for (i = 0; i < count; i++) {
+		unsigned int offset = hooks[i].offset;
+
+		if (offset % sizeof(struct hlist_head) ||
+		    offset + sizeof(struct hlist_head) >
+		    sizeof(struct security_hook_heads))
+			return -EINVAL;
+	}
+	if (!security_allow_unregister_hooks &&
+	    !try_module_get(lsm->owner))
+		return -EINVAL;
+	if (mutex_lock_killable(&security_hook_mutex)) {
+		module_put(lsm->owner);
+		return -EINTR;
+	}
+	ret = lsm_append(lsm->name, &lsm_names);
+	if (ret) {
+		module_put(lsm->owner);
 		goto out;
 	}
-
+	list_add(&lsm->list, &registered_lsm_modules);
 	for (i = 0; i < count; i++) {
-		hook_idx = hooks[i].hook_idx;
-		hooks[i].lsm = lsm;
-		hlist_add_tail_rcu(&hooks[i].list, &heads[hook_idx]);
-		if (!security_allow_unregister_hooks && hooks[i].owner)
-			WARN_ON(!try_module_get(hooks->owner));
-	}
+		struct hlist_head *head = (struct hlist_head *)
+			(((char *) heads) + hooks[i].offset);
 
-	if (lsm_append(lsm, &lsm_names) < 0)
-		panic("%s - Cannot get memory.\n", __func__);
-out:
+		hooks[i].lsm = lsm->name;
+		hlist_add_tail_rcu(&hooks[i].list, head);
+	}
+ out:
 	mutex_unlock(&security_hook_mutex);
-
 	return ret;
 }
 EXPORT_SYMBOL_GPL(security_add_hooks);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 72466eb..0140e2b 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -7090,6 +7090,9 @@ static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
 #endif
 };
 
+static struct lsm_info selinux_module =
+	LSM_MODULE_INIT("selinux", selinux_hooks);
+
 static __init int selinux_init(void)
 {
 	const bool is_mutable = IS_ENABLED(CONFIG_SECURITY_SELINUX_DISABLE);
@@ -7131,8 +7134,7 @@ static __init int selinux_init(void)
 
 	hashtab_cache_init();
 
-	BUG_ON(security_add_hooks(selinux_hooks, ARRAY_SIZE(selinux_hooks),
-					"selinux", is_mutable));
+	BUG_ON(security_add_hooks(&selinux_module, is_mutable));
 
 	if (avc_add_callback(selinux_netcache_avc_callback, AVC_CALLBACK_RESET))
 		panic("SELinux: Unable to register AVC netcache callback\n");
@@ -7266,8 +7268,6 @@ static void selinux_nf_ip_exit(void)
  * it not meant to be  used by new LSMs. Therefore, this is defined here, rather
  * than in a shared header.
  */
-extern void __security_delete_hooks(struct security_hook_list *hooks,
-					int count);
 int selinux_disable(struct selinux_state *state)
 {
 	if (state->initialized) {
@@ -7286,7 +7286,7 @@ int selinux_disable(struct selinux_state *state)
 
 	selinux_enabled = 0;
 
-	__security_delete_hooks(selinux_hooks, ARRAY_SIZE(selinux_hooks));
+	__security_delete_hooks(&selinux_module);
 
 	/* Try to destroy the avc node cache */
 	avc_disable();
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index f69b4d9..6b9566e 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -4764,6 +4764,7 @@ static int smack_dentry_create_files_as(struct dentry *dentry, int mode,
 	LSM_HOOK_INIT(dentry_create_files_as, smack_dentry_create_files_as),
 };
 
+static struct lsm_info smack_module = LSM_MODULE_INIT("smack", smack_hooks);
 
 static __init void init_smack_known_list(void)
 {
@@ -4842,8 +4843,7 @@ static __init int smack_init(void)
 	/*
 	 * Register with LSM
 	 */
-	BUG_ON(security_add_hooks(smack_hooks, ARRAY_SIZE(smack_hooks), "smack",
-					false));
+	BUG_ON(security_add_hooks(&smack_module, false));
 
 	return 0;
 }
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 544a614..0917f71 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -528,6 +528,8 @@ static int tomoyo_socket_sendmsg(struct socket *sock, struct msghdr *msg,
 	LSM_HOOK_INIT(socket_sendmsg, tomoyo_socket_sendmsg),
 };
 
+static struct lsm_info tomoyo_module = LSM_MODULE_INIT("tomoyo", tomoyo_hooks);
+
 /* Lock for GC. */
 DEFINE_SRCU(tomoyo_ss);
 
@@ -543,8 +545,7 @@ static int __init tomoyo_init(void)
 	if (!security_module_enable("tomoyo"))
 		return 0;
 	/* register ourselves with the security framework */
-	BUG_ON(security_add_hooks(tomoyo_hooks, ARRAY_SIZE(tomoyo_hooks), "tomoyo",
-					false));
+	BUG_ON(security_add_hooks(&tomoyo_module, false));
 	printk(KERN_INFO "TOMOYO Linux initialized\n");
 	cred->security = &tomoyo_kernel_domain;
 	tomoyo_mm_init();
diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
index 2e4bbb0..ee520b0 100644
--- a/security/yama/yama_lsm.c
+++ b/security/yama/yama_lsm.c
@@ -430,6 +430,8 @@ int yama_ptrace_traceme(struct task_struct *parent)
 	LSM_HOOK_INIT(task_free, yama_task_free),
 };
 
+static struct lsm_info yama_module = LSM_MODULE_INIT("yama", 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)
@@ -480,7 +482,6 @@ static inline void yama_init_sysctl(void) { }
 void __init yama_add_hooks(void)
 {
 	pr_info("Yama: becoming mindful.\n");
-	BUG_ON(security_add_hooks(yama_hooks, ARRAY_SIZE(yama_hooks), "yama",
-					false));
+	BUG_ON(security_add_hooks(&yama_module, false));
 	yama_init_sysctl();
 }
-- 
1.8.3.1
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