Re: [PATCH v1 09/11] landlock: Document LANDLOCK_ACCESS_FS_REFER and ABI versioning

[Mickaël Salaün]

On 17/03/2022 02:27, Paul Moore wrote:
> On Mon, Feb 21, 2022 at 4:15 PM Mickaël Salaün <mic@xxxxxxxxxxx> wrote:
> > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> >
> > 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.
> >
> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20220221212522.320243-10-mic@xxxxxxxxxxx
> > ---
> >   Documentation/userspace-api/landlock.rst | 124 +++++++++++++++++++----
> >   1 file changed, 104 insertions(+), 20 deletions(-)
>
> Thanks for remembering to update the docs :)  I made a few phrasing
> suggestions below, but otherwise it looks good to me.

Thanks Paul! I'll take them.


> Reviewed-by: Paul Moore <paul@xxxxxxxxxxxxxx>
>
> > diff --git a/Documentation/userspace-api/landlock.rst b/Documentation/userspace-api/landlock.rst
> > index f35552ff19ba..97db09d36a5c 100644
> > --- a/Documentation/userspace-api/landlock.rst
> > +++ b/Documentation/userspace-api/landlock.rst
> > @@ -281,6 +347,24 @@ Memory usage
> >   Kernel memory allocated to create rulesets is accounted and can be restricted
> >   by the Documentation/admin-guide/cgroup-v1/memory.rst.
> >
> > +Previous limitations
> > +====================
> > +
> > +File renaming and linking (ABI 1)
> > +---------------------------------
> > +
> > +Because Landlock targets unprivileged access controls, it is needed to properly
>                                                            ^^^^^
>                                             "... controls, it needs to ..."
>
> > +handle composition of rules.  Such property also implies rules nesting.
> > +Properly handling multiple layers of ruleset, each one of them able to restrict
>                                          ^^^^^^^
>                                        "rulesets,"
>
> > +access to files, also implies to inherit the ruleset restrictions from a parent
>                                   ^^^^^^^^^^
>                      "... implies inheritance of the ..."
>
> > +to its hierarchy.  Because files are identified and restricted by their
> > +hierarchy, moving or linking a file from one directory to another implies to
> > +propagate the hierarchy constraints.
>
> "... one directory to another implies propagation of the hierarchy constraints."
>
> > +                                     To protect against privilege escalations
>
> > +through renaming or linking, and for the sake of simplicity, Landlock previously
> > +limited linking and renaming to the same directory.  Starting with the Landlock
> > +ABI version 2, it is now possible to securely control renaming and linking
> > +thanks to the new `LANDLOCK_ACCESS_FS_REFER` access right.
>
> --
> paul-moore.com