lsm: add security_inode_setintegrity() hook

This patch introduces a new hook to save inode's integrity
data. For example, for fsverity enabled files, LSMs can use this hook to
save the existence of verified fsverity builtin signature into the inode's
security blob, and LSMs can make access decisions based on this data.

Signed-off-by: Fan Wu <[e-mail]>
[PM: subject line tweak, removed changelog]
Signed-off-by: Paul Moore <[e-mail]>

include/linux/lsm_hook_defs.h

···
 LSM_HOOK(int, 0, inode_copy_up, struct dentry *src, struct cred **new)
 LSM_HOOK(int, -EOPNOTSUPP, inode_copy_up_xattr, struct dentry *src,
 	 const char *name)
+LSM_HOOK(int, 0, inode_setintegrity, const struct inode *inode,
+	 enum lsm_integrity_type type, const void *value, size_t size)
 LSM_HOOK(int, 0, kernfs_init_security, struct kernfs_node *kn_dir,
 	 struct kernfs_node *kn)
 LSM_HOOK(int, 0, file_permission, struct file *file, int mask)

include/linux/security.h

···
 void security_inode_getsecid(struct inode *inode, u32 *secid);
 int security_inode_copy_up(struct dentry *src, struct cred **new);
 int security_inode_copy_up_xattr(struct dentry *src, const char *name);
+int security_inode_setintegrity(const struct inode *inode,
+				enum lsm_integrity_type type, const void *value,
+				size_t size);
 int security_kernfs_init_security(struct kernfs_node *kn_dir,
 				  struct kernfs_node *kn);
 int security_file_permission(struct file *file, int mask);
···
 }
 
 static inline int security_inode_copy_up(struct dentry *src, struct cred **new)
+{
+	return 0;
+}
+
+static inline int security_inode_setintegrity(const struct inode *inode,
+					      enum lsm_integrity_type type,
+					      const void *value, size_t size)
 {
 	return 0;
 }

security/security.c

···
 EXPORT_SYMBOL(security_inode_copy_up_xattr);
 
 /**
+ * security_inode_setintegrity() - Set the inode's integrity data
+ * @inode: inode
+ * @type: type of integrity, e.g. hash digest, signature, etc
+ * @value: the integrity value
+ * @size: size of the integrity value
+ *
+ * Register a verified integrity measurement of a inode with LSMs.
+ * LSMs should free the previously saved data if @value is NULL.
+ *
+ * Return: Returns 0 on success, negative values on failure.
+ */
+int security_inode_setintegrity(const struct inode *inode,
+				enum lsm_integrity_type type, const void *value,
+				size_t size)
+{
+	return call_int_hook(inode_setintegrity, inode, type, value, size);
+}
+EXPORT_SYMBOL(security_inode_setintegrity);
+
+/**
  * security_kernfs_init_security() - Init LSM context for a kernfs node
  * @kn_dir: parent kernfs node
  * @kn: the kernfs node to initialize