Let's help users by documenting how to enable and check for Landlock in
the kernel and the running system. The userspace-api section may not be
the best place for this but it still makes sense to put all the user
documentation at the same place.
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220513112743.156414-1-mic@digikod.net
Reviewed-by: Paul Moore <paul@paul-moore.com>
Add LANDLOCK_ACCESS_FS_REFER in the example and properly check to only
use it if the current kernel support it thanks to the Landlock ABI
version.
Move the file renaming and linking limitation to a new "Previous
limitations" section.
Improve documentation about the backward and forward compatibility,
including the rational for ruleset's handled_access_fs.
Update the document date.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20220506161102.525323-11-mic@digikod.net
The maximum number of nested Landlock domains is currently 64. Because
of the following fix and to help reduce the stack size, let's reduce it
to 16. This seems large enough for a lot of use cases (e.g. sandboxed
init service, spawning a sandboxed SSH service, in nested sandboxed
containers). Reducing the number of nested domains may also help to
discover misuse of Landlock (e.g. creating a domain per rule).
Add and use a dedicated layer_mask_t typedef to fit with the number of
layers. This might be useful when changing it and to keep it consistent
with the maximum number of layers.
Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-3-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>
