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

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Date:   Wed, 10 Feb 2021 21:17:25 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     "Serge E. Hallyn" <serge@...lyn.com>
Cc:     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 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.

> 
>> 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
>