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Date: Sat, 7 Nov 2015 21:02:06 -0500 From: Theodore Ts'o <tytso@....edu> To: Kees Cook <keescook@...omium.org> Cc: Andy Lutomirski <luto@...capital.net>, Theodore Tso <tytso@...gle.com>, Willy Tarreau <w@....eu>, Dirk Steinmetz <public@...tdrjgfuzkfg.com>, Michael Kerrisk-manpages <mtk.manpages@...il.com>, Serge Hallyn <serge.hallyn@...ntu.com>, Seth Forshee <seth.forshee@...onical.com>, Alexander Viro <viro@...iv.linux.org.uk>, Linux FS Devel <linux-fsdevel@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, "Eric W . Biederman" <ebiederm@...ssion.com>, Serge Hallyn <serge.hallyn@...onical.com>, "security@...nel.org" <security@...nel.org> Subject: Re: [RFC] namei: prevent sgid-hardlinks for unmapped gids 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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