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Date: Thu, 19 Nov 2015 17:03:15 -0800 From: Kees Cook <keescook@...omium.org> To: Willy Tarreau <w@....eu> Cc: LKML <linux-kernel@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Dave Chinner <david@...morbit.com>, Andy Lutomirski <luto@...capital.net>, Jan Kara <jack@...e.cz>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Mel Gorman <mgorman@...e.de>, Johannes Weiner <hannes@...xchg.org>, Rik van Riel <riel@...hat.com>, Matthew Wilcox <willy@...ux.intel.com>, Shachar Raindel <raindel@...lanox.com>, Boaz Harrosh <boaz@...xistor.com>, Michal Hocko <mhocko@...e.cz>, Haggai Eran <haggaie@...lanox.com>, Theodore Tso <tytso@...gle.com>, 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>, "Eric W . Biederman" <ebiederm@...ssion.com>, Serge Hallyn <serge.hallyn@...onical.com>, Linux-MM <linux-mm@...ck.org> Subject: Re: [PATCH] fs: clear file set[ug]id when writing via mmap On Thu, Nov 19, 2015 at 5:00 PM, Willy Tarreau <w@....eu> wrote: > Hi Kees, > > On Thu, Nov 19, 2015 at 04:10:43PM -0800, Kees Cook wrote: >> Normally, when a user can modify a file that has setuid or setgid bits, >> those bits are cleared when they are not the file owner or a member of the >> group. This is enforced when using write() directly but not when writing >> to a shared mmap on the file. This could allow the file writer to gain >> privileges by changing the binary without losing the setuid/setgid bits. >> >> Signed-off-by: Kees Cook <keescook@...omium.org> >> Cc: stable@...r.kernel.org >> --- >> mm/memory.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index deb679c31f2a..4c970a4e0057 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -2036,6 +2036,7 @@ static inline int wp_page_reuse(struct mm_struct *mm, >> >> if (!page_mkwrite) >> file_update_time(vma->vm_file); >> + file_remove_privs(vma->vm_file); > > I thought you said in one of the early mails of this thread that it > didn't work. Or maybe I misunderstood. I had a think-o in my earlier attempts. I understood the meaning of page_mkwrite incorrectly. > Also, don't you think we should move that into the if (!page_mkwrite) > just like for the time update ? Nope, page_mkwrite indicates if there was a vmops call to page_mkwrite. In this case, it means "I will update the file time if the filesystem driver didn't take care of it like it should". For file_remove_privs, we want to always do it, since we should not depend on filesystems to do it. -Kees -- Kees Cook Chrome OS Security -- 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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