From ed35e2f2f0ded15df313ae6f8da21e85c8e1e493 Mon Sep 17 00:00:00 2001 From: Günther Noack Date: Tue, 21 Feb 2023 17:52:05 +0100 Subject: landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Günther Noack Link: https://lore.kernel.org/r/20230221165205.4231-1-gnoack3000@gmail.com Signed-off-by: Mickaël Salaün --- include/uapi/linux/landlock.h | 46 +++++++++++++++++++++++++++++-------------- 1 file changed, 31 insertions(+), 15 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index f3223f964691..81d09ef9aa50 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -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:: * -- cgit v1.2.3