LSM: Switch to lists of hooks

Instead of using a vector of security operations
with explicit, special case stacking of the capability
and yama hooks use lists of hooks with capability and
yama hooks included as appropriate.

The security_operations structure is no longer required.
Instead, there is a union of the function pointers that
allows all the hooks lists to use a common mechanism for
list management while retaining typing. Each module
supplies an array describing the hooks it provides instead
of a sparsely populated security_operations structure.
The description includes the element that gets put on
the hook list, avoiding the issues surrounding individual
element allocation.

The method for registering security modules is changed to
reflect the information available. The method for removing
a module, currently only used by SELinux, has also changed.
It should be generic now, however if there are potential
race conditions based on ordering of hook removal that needs
to be addressed by the calling module.

The security hooks are called from the lists and the first
failure is returned.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by:  Stephen Smalley <sds@tycho.nsa.gov>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: James Morris <james.l.morris@oracle.com>

1 files changed, 53 insertions, 24 deletions

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 27dd6fcacccc..f014f2596e22 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -25,21 +25,10 @@
 #define __LINUX_LSM_HOOKS_H
 
 #include <linux/security.h>
-
-/* Maximum number of letters for an LSM name string */
-#define SECURITY_NAME_MAX	10
-
-#ifdef CONFIG_SECURITY
+#include <linux/init.h>
+#include <linux/rculist.h>
 
 /**
- * struct security_operations - main security structure
- *
- * Security module identifier.
- *
- * @name:
- *	A string that acts as a unique identifier for the LSM with max number
- *	of characters = SECURITY_NAME_MAX.
- *
  * Security hooks for program execution operations.
  *
  * @bprm_set_creds:
@@ -1310,9 +1299,7 @@
  * This is the main security structure.
  */
 
-struct security_operations {
-	char name[SECURITY_NAME_MAX + 1];
-
+union security_list_options {
 	int (*binder_set_context_mgr)(struct task_struct *mgr);
 	int (*binder_transaction)(struct task_struct *from,
 					struct task_struct *to);
@@ -1838,20 +1825,62 @@ struct security_hook_heads {
 };
 
 /*
+ * Security module hook list structure.
+ * For use with generic list macros for common operations.
+ */
+struct security_hook_list {
+	struct list_head		list;
+	struct list_head		*head;
+	union security_list_options	hook;
+};
+
+/*
  * Initializing a security_hook_list structure takes
  * up a lot of space in a source file. This macro takes
  * care of the common case and reduces the amount of
  * text involved.
- * Casey says: Comment is true in the next patch.
  */
-#define LSM_HOOK_INIT(HEAD, HOOK)	.HEAD = HOOK
+#define LSM_HOOK_INIT(HEAD, HOOK) \
+	{ .head = &security_hook_heads.HEAD, .hook = { .HEAD = HOOK } }
+
+extern struct security_hook_heads security_hook_heads;
+
+static inline void security_add_hooks(struct security_hook_list *hooks,
+				      int count)
+{
+	int i;
 
-/* prototypes */
-extern int security_module_enable(struct security_operations *ops);
-extern int register_security(struct security_operations *ops);
-extern void __init security_fixup_ops(struct security_operations *ops);
-extern void reset_security_ops(void);
+	for (i = 0; i < count; i++)
+		list_add_tail_rcu(&hooks[i].list, hooks[i].head);
+}
 
-#endif /* CONFIG_SECURITY */
+#ifdef CONFIG_SECURITY_SELINUX_DISABLE
+/*
+ * Assuring the safety of deleting a security module is up to
+ * the security module involved. This may entail ordering the
+ * module's hook list in a particular way, refusing to disable
+ * the module once a policy is loaded or any number of other
+ * actions better imagined than described.
+ *
+ * The name of the configuration option reflects the only module
+ * that currently uses the mechanism. Any developer who thinks
+ * disabling their module is a good idea needs to be at least as
+ * careful as the SELinux team.
+ */
+static inline void security_delete_hooks(struct security_hook_list *hooks,
+						int count)
+{
+	int i;
+
+	for (i = 0; i < count; i++)
+		list_del_rcu(&hooks[i].list);
+}
+#endif /* CONFIG_SECURITY_SELINUX_DISABLE */
+
+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);
+#endif
 
 #endif /* ! __LINUX_LSM_HOOKS_H */