linux-kernel - Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

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Message-ID: <20190313235534.GK25147@redhat.com>
Date:   Wed, 13 Mar 2019 19:55:34 -0400
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Maxime Coquelin <maxime.coquelin@...hat.com>,
        kvm@...r.kernel.org, Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>, linux-mm@...ck.org,
        Marty McFadden <mcfadden8@...l.gov>,
        Maya Gokhale <gokhale2@...l.gov>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Kees Cook <keescook@...omium.org>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-fsdevel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users

On Wed, Mar 13, 2019 at 01:01:40PM -0700, Mike Kravetz wrote:
> On 3/13/19 11:52 AM, Andrea Arcangeli wrote:
> > 
> > hugetlbfs is more complicated to detect, because even if you inherit
> > it from fork(), the services that mounts the fs may be in a different
> > container than the one that Oracle that uses userfaultfd later on down
> > the road from a different context. And I don't think it would be ok to
> > allow running userfaultfd just because you can open a file in an
> > hugetlbfs file system. With /dev/kvm it's a bit different, that's
> > chmod o-r by default.. no luser should be able to open it.
> > 
> > Unless somebody suggests a consistent way to make hugetlbfs "just
> > work" (like we could achieve clean with CRIU and KVM), I think Oracle
> > will need a one liner change in the Oracle setup to echo into that
> > file in addition of running the hugetlbfs mount.
> 
> I think you are suggesting the DB setup process enable uffd for all users.
> Correct?

Yes. In addition of the hugetlbfs setup, various apps requires to also
increase fs.inotify.max_user_watches or file-max and other tweaks,
this would be one of those tweaks.

> This may be too simple, and I don't really like group access, but how about
> just defining a uffd group?  If you are in the group you can make uffd
> system calls.

Everything is possible, I'm just afraid it gets too complex.

So you suggest to echo a gid into the file?