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Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids

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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
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Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-02 16:20 +0100
  Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Serge Hallyn <serge.hallyn@ubuntu.com> - 2015-11-02 19:10 +0100
    Re: [PATCH] namei: permit linking with CAP_FOWNER in userns Andy Lutomirski <luto@amacapital.net> - 2015-11-02 21:00 +0100
      [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-03 01:50 +0100
        Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Serge Hallyn <serge.hallyn@ubuntu.com> - 2015-11-03 16:50 +0100
        Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-03 19:30 +0100
          Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Dirk Steinmetz <public@rsjtdrjgfuzkfg.com> - 2015-11-04 00:30 +0100
            Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-04 00:40 +0100
              Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 08:00 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-04 19:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-04 19:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 19:30 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Willy Tarreau <w@1wt.eu> - 2015-11-04 19:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-06 23:00 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-06 23:40 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 01:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 01:20 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Andy Lutomirski <luto@amacapital.net> - 2015-11-07 01:50 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Kees Cook <keescook@chromium.org> - 2015-11-07 06:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Theodore Ts'o <tytso@mit.edu> - 2015-11-08 03:10 +0100
                Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids Jan Kara <jack@suse.cz> - 2015-11-10 16:10 +0100
          Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids "Serge E. Hallyn" <serge@hallyn.com> - 2015-11-04 15:50 +0100

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