[PATCH v3] landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right
From: Günther Noack <hidden>
Date: 2023-02-16 20:07:38
Subsystem:
landlock security module, the rest · Maintainers:
Mickaël Salaün, Linus Torvalds
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. Includes wording and semantics corrections by Mickaël Salaün. Signed-off-by: Günther Noack <redacted> --- include/uapi/linux/landlock.h | 45 +++++++++++++++++++++++------------ 1 file changed, 30 insertions(+), 15 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index f3223f96469..e549ad6360b 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h@@ -130,21 +130,36 @@ 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 also the only access right which is implicitly handled by any + * ruleset, even if the right is not specified at the time of creating the + * ruleset. So, by default, Landlock will deny linking and reparenting files + * between different directories, and will only grant this right when it is + * explicitly permitted for a directory by adding a rule. + * + * When using the first Landlock ABI version, Landlock will always deny the + * reparenting of 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:: *
base-commit: ceaa837f96adb69c0df0397937cd74991d5d821a -- 2.39.1