linux-kernel - Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter

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-=wjMyZLH+ta5SohAViSc10iPj-hRnHc-KPDoj1XZCmxdBg@mail.gmail.com>
Date:   Fri, 27 Aug 2021 12:33:00 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andreas Gruenbacher <agruenba@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J. Wong" <djwong@...nel.org>, Jan Kara <jack@...e.cz>,
        Matthew Wilcox <willy@...radead.org>,
        cluster-devel <cluster-devel@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ocfs2-devel@....oracle.com
Subject: Re: [PATCH v7 05/19] iov_iter: Introduce fault_in_iov_iter_writeable

On Fri, Aug 27, 2021 at 12:23 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Could you show the cases where "partial copy, so it's OK" behaviour would
> break anything?

Absolutely.

For example, i t would cause an infinite loop in
restore_fpregs_from_user() if the "buf" argument is a situation where
the first page is fine, but the next page is not.

Why? Because __restore_fpregs_from_user() would take a fault, but then
fault_in_pages_readable() (renamed) would succeed, so you'd just do
that "retry" forever and ever.

Probably there are a number of other places too. That was literally
the *first* place I looked at.

Seriously. The current semantics are "check the whole area".

THOSE MUST NOT CHANGE.

              Linus