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Landlock updates for v6.4-rc1 

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Merge tag 'landlock-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull landlock update from Mickaël Salaün:
 "Improve user space documentation"

* tag 'landlock-6.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  landlock: Clarify documentation for the LANDLOCK_ACCESS_FS_REFER right
This commit is contained in:
Linus Torvalds 2023-04-24 11:35:15 -07:00
parent 5af4b523ba ed35e2f2f0
commit 62443646a5
1 changed files with 31 additions and 15 deletions
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46
include/uapi/linux/landlock.h
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@ -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::
*