linux-kernel - Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHk-=wi81ujYGP0gmyy2kDke_ExL742Lo_hLepGjCa8mS81A7w@mail.gmail.com>
Date:   Tue, 9 Aug 2022 11:40:50 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW

On Mon, Aug 8, 2022 at 12:32 AM David Hildenbrand <david@...hat.com> wrote:
>
> For example, a write() via /proc/self/mem to a uffd-wp-protected range has
> to fail instead of silently granting write access and bypassing the
> userspace fault handler. Note that FOLL_FORCE is not only used for debug
> access, but also triggered by applications without debug intentions, for
> example, when pinning pages via RDMA.

So this made me go "Whaa?"

I didn't even realize that the media drivers and rdma used FOLL_FORCE.

That's just completely bogus.

Why do they do that?

It seems to be completely bogus, and seems to have no actual valid
reason for it. Looking through the history, it goes back to the
original code submission in 2006, and doesn't have a mention of why.

I think the original reason was that the code didn't have pinning, so
it used "do a write" as a pin mechanism - even for reads.

IOW, I think the non-ptrace use of FOLL_FORCE should just be removed.

                 Linus