From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f49.google.com (mail-wm0-f49.google.com [74.125.82.49]) by kanga.kvack.org (Postfix) with ESMTP id 2CBBC6B0255 for ; Thu, 19 Nov 2015 20:15:59 -0500 (EST) Received: by wmww144 with SMTP id w144so1739373wmw.1 for ; Thu, 19 Nov 2015 17:15:58 -0800 (PST) Received: from 1wt.eu (wtarreau.pck.nerim.net. [62.212.114.60]) by mx.google.com with ESMTP id m135si712329wmb.47.2015.11.19.17.15.56 for ; Thu, 19 Nov 2015 17:15:56 -0800 (PST) Date: Fri, 20 Nov 2015 02:06:24 +0100 From: Willy Tarreau Subject: Re: [PATCH] fs: clear file set[ug]id when writing via mmap Message-ID: <20151120010624.GA31732@1wt.eu> References: <20151120001043.GA28204@www.outflux.net> <20151120010016.GB31694@1wt.eu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Kees Cook Cc: LKML , 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 On Thu, Nov 19, 2015 at 05:03:15PM -0800, Kees Cook wrote: > On Thu, Nov 19, 2015 at 5:00 PM, Willy Tarreau 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 > >> 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. > > 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. Ah OK, thanks for the explanation, I didn't understand it like this at all last time I read it. Cheers, 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