linux-kernel - Re: [RFC PATCH RESEND] userfaultfd: open userfaultfds with O

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Message-ID: <CAHC9VhRv2VPvUAbpDo0D0oK9gEHL=vcOh84M9Fg+AN1c1SR0pA@mail.gmail.com>
Date:   Tue, 12 Jul 2022 17:16:45 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     Ondrej Mosnacek <omosnace@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Robert O'Callahan" <roc@...llahan.org>
Subject: Re: [RFC PATCH RESEND] userfaultfd: open userfaultfds with O_RDONLY

On Tue, Jul 12, 2022 at 10:22 AM Peter Xu <peterx@...hat.com> wrote:
> On Fri, Jul 08, 2022 at 11:34:51AM +0200, Ondrej Mosnacek wrote:
> > Since userfaultfd doesn't implement a write operation, it is more
> > appropriate to open it read-only.
> >
> > When userfaultfds are opened read-write like it is now, and such fd is
> > passed from one process to another, SELinux will check both read and
> > write permissions for the target process, even though it can't actually
> > do any write operation on the fd later.
> >
> > Inspired by the following bug report, which has hit the SELinux scenario
> > described above:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1974559
> >
> > Reported-by: Robert O'Callahan <roc@...llahan.org>
> > Fixes: 86039bd3b4e6 ("userfaultfd: add new syscall to provide memory externalization")
> > Signed-off-by: Ondrej Mosnacek <omosnace@...hat.com>
>
> Acked-by: Peter Xu <peterx@...hat.com>

Thanks Peter.

-- 
paul-moore.com