BACKPORT: security: add inode_init_security_anon() LSM hook

This change adds a new LSM hook, inode_init_security_anon(), that will
be used while creating secure anonymous inodes. The hook allows/denies
its creation and assigns a security context to the inode.

The new hook accepts an optional context_inode parameter that callers
can use to provide additional contextual information to security modules
for granting/denying permission to create an anon-inode of the same type.
This context_inode's security_context can also be used to initialize the
newly created anon-inode's security_context.

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
(cherry picked from commit 215b674b84dd052098fe6389e32a5afaff8b4d56)

Conflicts:
    include/linux/lsm_hook_defs.h

(1. Added LSM hook in lsm_hook.h and removd lsm_hook_defs.h as per
98e828a0650f348be85728c69875260cf78069e6, which is not merged here)

Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Bug: 160737021
Bug: 169683130
Change-Id: I83fe318c891f034b4dd7f3f357cc74964b55ffc8

include/linux/lsm_hooks.h

@@ -215,6 +215,15 @@
  *	Returns 0 if @name and @value have been successfully set,
  *	-EOPNOTSUPP if no security attribute is needed, or
  *	-ENOMEM on memory allocation failure.
+ * @inode_init_security_anon:
+ *      Set up the incore security field for the new anonymous inode
+ *      and return whether the inode creation is permitted by the security
+ *      module or not.
+ *      @inode contains the inode structure
+ *      @name name of the anonymous inode class
+ *      @context_inode optional related inode
+ *	Returns 0 on success, -EACCES if the security module denies the
+ *	creation of this inode, or another -errno upon other errors.
  * @inode_create:
  *	Check permission to create a regular file.
  *	@dir contains inode structure of the parent of the new file.
@@ -1558,6 +1567,9 @@ union security_list_options {
 					const struct qstr *qstr,
 					const char **name, void **value,
 					size_t *len);
+	int (*inode_init_security_anon)(struct inode *inode,
+					const struct qstr *name,
+					const struct inode *context_inode);
 	int (*inode_create)(struct inode *dir, struct dentry *dentry,
 				umode_t mode);
 	int (*inode_link)(struct dentry *old_dentry, struct inode *dir,
@@ -1892,6 +1904,7 @@ struct security_hook_heads {
 	struct hlist_head inode_alloc_security;
 	struct hlist_head inode_free_security;
 	struct hlist_head inode_init_security;
+	struct hlist_head inode_init_security_anon;
 	struct hlist_head inode_create;
 	struct hlist_head inode_link;
 	struct hlist_head inode_unlink;

include/linux/security.h

@@ -320,6 +320,9 @@ void security_inode_free(struct inode *inode);
 int security_inode_init_security(struct inode *inode, struct inode *dir,
 				 const struct qstr *qstr,
 				 initxattrs initxattrs, void *fs_data);
+int security_inode_init_security_anon(struct inode *inode,
+				      const struct qstr *name,
+				      const struct inode *context_inode);
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len);
@@ -724,6 +727,13 @@ static inline int security_inode_init_security(struct inode *inode,
 	return 0;
 }
 
+static inline int security_inode_init_security_anon(struct inode *inode,
+						    const struct qstr *name,
+						    const struct inode *context_inode)
+{
+	return 0;
+}
+
 static inline int security_old_inode_init_security(struct inode *inode,
 						   struct inode *dir,
 						   const struct qstr *qstr,

security/security.c

@@ -1014,6 +1014,14 @@ out:
 }
 EXPORT_SYMBOL(security_inode_init_security);
 
+int security_inode_init_security_anon(struct inode *inode,
+				      const struct qstr *name,
+				      const struct inode *context_inode)
+{
+	return call_int_hook(inode_init_security_anon, 0, inode, name,
+			     context_inode);
+}
+
 int security_old_inode_init_security(struct inode *inode, struct inode *dir,
 				     const struct qstr *qstr, const char **name,
 				     void **value, size_t *len)