Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755834AbZJ1VDa (ORCPT ); Wed, 28 Oct 2009 17:03:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755813AbZJ1VD2 (ORCPT ); Wed, 28 Oct 2009 17:03:28 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:34496 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755788AbZJ1VD1 (ORCPT ); Wed, 28 Oct 2009 17:03:27 -0400 Date: Wed, 28 Oct 2009 22:03:24 +0100 From: Pavel Machek To: "Eric W. Biederman" Cc: Trond Myklebust , Jan Kara , "J. Bruce Fields" , "Serge E. Hallyn" , kernel list , linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, jamie@shareable.org Subject: Re: symlinks with permissions Message-ID: <20091028210323.GA4159@elf.ucw.cz> References: <20091025062953.GC1391@ucw.cz> <20091026163157.GB7233@duck.suse.cz> <20091026165729.GF23564@us.ibm.com> <20091026173629.GB16861@fieldses.org> <20091026174631.GD7233@duck.suse.cz> <1256579869.8576.7.camel@heimdal.trondhjem.org> <20091025093604.GA1501@ucw.cz> <20091028081653.GA18290@elf.ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2249 Lines: 59 Hi! > >> > Well, it is unexpected and mild security hole. > >> > >> /proc//fd is only viewable by the owner of the process or by > >> someone with CAP_DAC_OVERRIDE. So there appears to be no security > >> hole exploitable by people who don't have the file open. > > > > Please see bugtraq discussion at > > http://seclists.org/bugtraq/2009/Oct/179 . > > > > (In short, you get read-only fd, and you can upgrade it to read-write > > fd. Yes, you are the owner of the process, but you are not owner of > > the file the fd refers to.) > > Assuming you have permission to open it read-write. Please see the bugtraq discussion. It works even if you would not have permission to write to it with /proc unmounted. > >> Openly if you actually have permission to open the file again. The actual > >> permissions on the file should not be ignored. > > > > The actual permissions of the file are not ignored, but permissions of > > the containing directory _are_. If there's 666 file in 700 directory, > > you can reopen it read-write, in violation of directory's 700 > > permissions. > > I can see how all of this can come as a surprise. However I don't see > how any coder who is taking security seriously and being paranoid about > security would actually write code that would have a problem with > this. So, there's "surprise" that gives _you_ write access to my files. You agree that it is surprising, and you would not have write access to my file if /proc was not mounted. Call it "security surprise" if you prefer. But many people call it "security hole". > Do you know of any cases where this difference matters in practice? No. Do you have a proof that it does not matter anywhere? > It looks to me like it has been this way for better than a decade > without problems so there is no point in changing it now. Unix compatibility? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/