Re: [PATCH v28 07/12] landlock: Support filesystem access-control

[Mickaël Salaün]

On 10/02/2021 20:36, Serge E. Hallyn wrote:
> On Tue, Feb 02, 2021 at 05:27:05PM +0100, Mickaël Salaün wrote:
>> From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
>>
>> Thanks to the Landlock objects and ruleset, it is possible to identify
>> inodes according to a process's domain.  To enable an unprivileged
> 
> This throws me off a bit.  "identify inodes according to a process's domain".
> What exactly does it mean?  "identify" how ?

A domain is a set of rules (i.e. layers of rulesets) enforced on a set
of threads. Inodes are tagged per domain (i.e. not system-wide) and
actions are restricted thanks to these tags, which form rules. It means
that the created access-controls are scoped to a set of threads.

> 
>> process to express a file hierarchy, it first needs to open a directory
>> (or a file) and pass this file descriptor to the kernel through
>> landlock_add_rule(2).  When checking if a file access request is
>> allowed, we walk from the requested dentry to the real root, following
>> the different mount layers.  The access to each "tagged" inodes are
>> collected according to their rule layer level, and ANDed to create
>> access to the requested file hierarchy.  This makes possible to identify
>> a lot of files without tagging every inodes nor modifying the
>> filesystem, while still following the view and understanding the user
>> has from the filesystem.
>>
>> Add a new ARCH_EPHEMERAL_INODES for UML because it currently does not
>> keep the same struct inodes for the same inodes whereas these inodes are
>> in use.
> 
> -serge
>