From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f41.google.com (mail-wm0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id EA3DB6B0254 for ; Thu, 19 Nov 2015 20:15:56 -0500 (EST) Received: by wmec201 with SMTP id c201so51464441wme.0 for ; Thu, 19 Nov 2015 17:15:56 -0800 (PST) Received: from 1wt.eu (wtarreau.pck.nerim.net. [62.212.114.60]) by mx.google.com with ESMTP id m135si712329wmb.47.2015.11.19.17.15.55 for ; Thu, 19 Nov 2015 17:15:55 -0800 (PST) Date: Fri, 20 Nov 2015 02:00:16 +0100 From: Willy Tarreau Subject: Re: [PATCH] fs: clear file set[ug]id when writing via mmap Message-ID: <20151120010016.GB31694@1wt.eu> References: <20151120001043.GA28204@www.outflux.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151120001043.GA28204@www.outflux.net> Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: linux-kernel@vger.kernel.org, Andrew Morton , Dave Chinner , Andy Lutomirski , Jan Kara , "Kirill A. Shutemov" , Mel Gorman , Johannes Weiner , Rik van Riel , Matthew Wilcox , Shachar Raindel , Boaz Harrosh , Michal Hocko , Haggai Eran , Theodore Tso , Dirk Steinmetz , Michael Kerrisk-manpages , Serge Hallyn , Seth Forshee , Alexander Viro , Linux FS Devel , "Eric W . Biederman" , Serge Hallyn , linux-mm@kvack.org 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 > Cc: stable@vger.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. Also, don't you think we should move that into the if (!page_mkwrite) just like for the time update ? Willy -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org