landlock: Fix landlock_add_rule(2) documentation

It is not mandatory to pass a file descriptor obtained with the O_PATH
flag.  Also, replace rule's accesses with ruleset's accesses.

Link: https://lore.kernel.org/r/20220506160820.524344-2-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>

include/uapi/linux/landlock.h

@@ -62,8 +62,9 @@ struct landlock_path_beneath_attr {
 	 */
 	__u64 allowed_access;
 	/**
-	 * @parent_fd: File descriptor, open with ``O_PATH``, which identifies
-	 * the parent directory of a file hierarchy, or just a file.
+	 * @parent_fd: File descriptor, preferably opened with ``O_PATH``,
+	 * which identifies the parent directory of a file hierarchy, or just a
+	 * file.
 	 */
 	__s32 parent_fd;
 	/*

security/landlock/syscalls.c

@@ -292,14 +292,13 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
  *
  * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
  * - EINVAL: @flags is not 0, or inconsistent access in the rule (i.e.
- *   &landlock_path_beneath_attr.allowed_access is not a subset of the rule's
- *   accesses);
+ *   &landlock_path_beneath_attr.allowed_access is not a subset of the
+ *   ruleset handled accesses);
  * - ENOMSG: Empty accesses (e.g. &landlock_path_beneath_attr.allowed_access);
  * - EBADF: @ruleset_fd is not a file descriptor for the current thread, or a
  *   member of @rule_attr is not a file descriptor as expected;
  * - EBADFD: @ruleset_fd is not a ruleset file descriptor, or a member of
- *   @rule_attr is not the expected file descriptor type (e.g. file open
- *   without O_PATH);
+ *   @rule_attr is not the expected file descriptor type;
  * - EPERM: @ruleset_fd has no write access to the underlying ruleset;
  * - EFAULT: @rule_attr inconsistency.
  */