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

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Date:   Fri, 19 Feb 2021 09:34:14 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Mickaël Salaün <mic@...ikod.net>
Cc:     "Serge E. Hallyn" <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>, Jann Horn <jannh@...gle.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Arnd Bergmann <arnd@...db.de>,
        Casey Schaufler <casey@...aufler-ca.com>,
        Jeff Dike <jdike@...toit.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Richard Weinberger <richard@....at>,
        Shuah Khan <shuah@...nel.org>,
        Vincent Dagonneau <vincent.dagonneau@....gouv.fr>,
        kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        linux-security-module@...r.kernel.org, x86@...nel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: Re: [PATCH v28 07/12] landlock: Support filesystem access-control

On Wed, Feb 10, 2021 at 09:17:25PM +0100, Mickaël Salaün wrote:
> 
> 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@...ux.microsoft.com>
> >>
> >> 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.

Thanks, that's helpful.  To me it would be much clearer if you used the word
'tagged' :

  Using the Landlock objects and ruleset, it is possible to tag inodes
  according to a process's domain.

> >> 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
> >