linux-kernel - Re: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine grained access control

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Message-ID: <87k09kxi59.fsf@meer.lwn.net>
Date:   Mon, 13 Jun 2022 17:23:14 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Charan Teja Reddy <charante@...eaurora.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
        Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.com>,
        Shuah Khan <shuah@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        zhangyi <yi.zhang@...wei.com>, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Linuxkselftest <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] userfaultfd: add /dev/userfaultfd for fine
 grained access control

Axel Rasmussen <axelrasmussen@...gle.com> writes:

> I think for any approach involving syscalls, we need to be able to
> control access to who can call a syscall. Maybe there's another way
> I'm not aware of, but I think today the only mechanism to do this is
> capabilities. I proposed adding a CAP_USERFAULTFD for this purpose,
> but that approach was rejected [1]. So, I'm not sure of another way
> besides using a device node.

I take it there's a reason why this can't be done with a security module
- either a custom module or a policy in one of the existing modules?
That sort of access control is just what security modules are supposed
to be for, after all.

Thanks,

jon