From: Theodore Ts'o <tytso@mit.edu>
To: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
Theodore Tso <tytso@google.com>, Willy Tarreau <w@1wt.eu>,
Dirk Steinmetz <public@rsjtdrjgfuzkfg.com>,
Michael Kerrisk-manpages <mtk.manpages@gmail.com>,
Serge Hallyn <serge.hallyn@ubuntu.com>,
Seth Forshee <seth.forshee@canonical.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
"security@kernel.org" <security@kernel.org>
Subject: Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids
Date: Sat, 7 Nov 2015 21:02:06 -0500 [thread overview]
Message-ID: <20151108020206.GA3880@thunk.org> (raw)
In-Reply-To: <CAGXu5j++4L3BLNPmBDwU9JA3UdqmFAWEKxDcveLOmJmxwgNiVA@mail.gmail.com>
On Fri, Nov 06, 2015 at 09:05:57PM -0800, Kees Cook wrote:
> >>>> They're certainly not used early enough -- we need to remove suid when
> >>>> the page becomes writable via mmap (wp_page_shared), not when
> >>>> writeback happens, or at least not only when writeback happens.
> >>>
> >>> Well, I'm shy about the change there. For example, we don't strip in
> >>> on open(RDWR), just on write().
> >>
> >> I take it back. Hooking wp_page_shared looks expensive. :) Maybe we do
> >> need to hook the mmap?
> >
> > But file_update_time already pokes at the same (or nearby) cachelines,
> > I think -- why would it be expensive? The whole thing could be
> > guarded by if (unlikely(is setuid)), right?
>
> Yeah, true. I added file_remove_privs calls near all the
> file_update_time calls, to no effect. Added to wp_page_shared too,
> nothing. Hmmm.
Why not put the the should_remove_suid() call in
filemap_page_mkwrite(), or maybe do_page_mkwrite()?
Cheers,
- Ted
next prev parent reply other threads:[~2015-11-08 2:02 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-10 14:59 [PATCH] namei: permit linking with CAP_FOWNER in userns Dirk Steinmetz
2015-10-20 14:09 ` Dirk Steinmetz
2015-10-27 14:33 ` Seth Forshee
2015-10-27 18:08 ` Dirk Steinmetz
2015-10-27 20:28 ` Serge Hallyn
2015-10-28 15:07 ` Dirk Steinmetz
2015-10-28 17:33 ` Serge Hallyn
2015-11-02 15:10 ` Dirk Steinmetz
2015-11-02 18:02 ` Serge Hallyn
2015-11-02 19:57 ` Andy Lutomirski
2015-11-03 0:39 ` [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz
2015-11-03 15:44 ` Serge Hallyn
2015-11-03 18:20 ` Kees Cook
2015-11-03 23:21 ` Dirk Steinmetz
2015-11-03 23:29 ` Kees Cook
2015-11-04 6:58 ` Willy Tarreau
2015-11-04 17:59 ` Andy Lutomirski
2015-11-04 18:15 ` Willy Tarreau
2015-11-04 18:17 ` Andy Lutomirski
2015-11-04 18:28 ` Willy Tarreau
2015-11-06 21:59 ` Kees Cook
2015-11-06 22:30 ` Andy Lutomirski
2015-11-07 0:11 ` Kees Cook
2015-11-07 0:16 ` Kees Cook
2015-11-07 0:48 ` Andy Lutomirski
2015-11-07 5:05 ` Kees Cook
2015-11-08 2:02 ` Theodore Ts'o [this message]
2015-11-10 15:08 ` Jan Kara
2015-11-19 20:11 ` Kees Cook
2015-11-19 21:57 ` Andy Lutomirski
2015-11-19 22:02 ` Dave Chinner
2015-11-20 0:11 ` Kees Cook
2015-11-04 14:46 ` Serge E. Hallyn
2015-10-27 21:04 ` [PATCH] namei: permit linking with CAP_FOWNER in userns Eric W. Biederman
2015-11-03 17:51 ` Kees Cook
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