Unverified Commit ed35e2f2 authored by Günther Noack's avatar Günther Noack Committed by Mickaël Salaün
Browse files

landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right 



Clarify the "refer" documentation by splitting up a big paragraph of
text.

- Call out specifically that the denial by default applies to ABI v1 as
  well.
- Turn the three additional constraints for link/rename operations
  into bullet points, to give it more structure.

Signed-off-by: default avatarGünther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20230221165205.4231-1-gnoack3000@gmail.com


Signed-off-by: default avatarMickaël Salaün <mic@digikod.net>
parent 1c1ea1c3

include/uapi/linux/landlock.h

+31 −15
Original line number Diff line number Diff line
@@ -130,21 +130,37 @@ struct landlock_path_beneath_attr { 
 * - %LANDLOCK_ACCESS_FS_MAKE_BLOCK: Create (or rename or link) a block device.

 * - %LANDLOCK_ACCESS_FS_MAKE_SYM: Create (or rename or link) a symbolic link.

 * - %LANDLOCK_ACCESS_FS_REFER: Link or rename a file from or to a different

 *   directory (i.e. reparent a file hierarchy).  This access right is

 *   available since the second version of the Landlock ABI.  This is also the

 *   only access right which is always considered handled by any ruleset in

 *   such a way that reparenting a file hierarchy is always denied by default.

 *   To avoid privilege escalation, it is not enough to add a rule with this

 *   access right.  When linking or renaming a file, the destination directory

 *   hierarchy must also always have the same or a superset of restrictions of

 *   the source hierarchy.  If it is not the case, or if the domain doesn't

 *   handle this access right, such actions are denied by default with errno

 *   set to ``EXDEV``.  Linking also requires a ``LANDLOCK_ACCESS_FS_MAKE_*``

 *   access right on the destination directory, and renaming also requires a

 *   ``LANDLOCK_ACCESS_FS_REMOVE_*`` access right on the source's (file or

 *   directory) parent.  Otherwise, such actions are denied with errno set to

 *   ``EACCES``.  The ``EACCES`` errno prevails over ``EXDEV`` to let user space

 *   efficiently deal with an unrecoverable error.

 *   directory (i.e. reparent a file hierarchy).

 *

 *   This access right is available since the second version of the Landlock

 *   ABI.

 *

 *   This is the only access right which is denied by default by any ruleset,

 *   even if the right is not specified as handled at ruleset creation time.

 *   The only way to make a ruleset grant this right is to explicitly allow it

 *   for a specific directory by adding a matching rule to the ruleset.

 *

 *   In particular, when using the first Landlock ABI version, Landlock will

 *   always deny attempts to reparent files between different directories.

 *

 *   In addition to the source and destination directories having the

 *   %LANDLOCK_ACCESS_FS_REFER access right, the attempted link or rename

 *   operation must meet the following constraints:

 *

 *   * The reparented file may not gain more access rights in the destination

 *     directory than it previously had in the source directory.  If this is

 *     attempted, the operation results in an ``EXDEV`` error.

 *

 *   * When linking or renaming, the ``LANDLOCK_ACCESS_FS_MAKE_*`` right for the

 *     respective file type must be granted for the destination directory.

 *     Otherwise, the operation results in an ``EACCES`` error.

 *

 *   * When renaming, the ``LANDLOCK_ACCESS_FS_REMOVE_*`` right for the

 *     respective file type must be granted for the source directory.  Otherwise,

 *     the operation results in an ``EACCES`` error.

 *

 *   If multiple requirements are not met, the ``EACCES`` error code takes

 *   precedence over ``EXDEV``.

 *

 * .. warning::

 *