From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.bugs Subject: bug#27986: 26.0.50; 'rename-file' can rename files without confirmation Date: Tue, 15 Aug 2017 12:27:52 -0700 Organization: UCLA Computer Science Department Message-ID: <2bb4b7ee-6bf9-df3d-5cd8-ae7992b9f2e7@cs.ucla.edu> References: <61980dde-3d68-7200-e7f4-98f62e410060@cs.ucla.edu> <1002ee73-0ab5-409b-831f-0c283c322264@cs.ucla.edu> <83o9rignt6.fsf@gnu.org> <83d17whl72.fsf@gnu.org> <8e6de468-600c-4f2d-a21a-c2ff3a63d065@cs.ucla.edu> <83zib0g221.fsf@gnu.org> NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1502825365 29084 195.159.176.226 (15 Aug 2017 19:29:25 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 15 Aug 2017 19:29:25 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 Cc: p.stephani2@gmail.com, 27986@debbugs.gnu.org To: Eli Zaretskii Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Tue Aug 15 21:29:21 2017 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dhhWY-0006jf-0X for geb-bug-gnu-emacs@m.gmane.org; Tue, 15 Aug 2017 21:29:10 +0200 Original-Received: from localhost ([::1]:59644 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dhhWe-0006ht-FC for geb-bug-gnu-emacs@m.gmane.org; Tue, 15 Aug 2017 15:29:16 -0400 Original-Received: from eggs.gnu.org ([2001:4830:134:3::10]:54819) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dhhWV-0006cA-Ga for bug-gnu-emacs@gnu.org; Tue, 15 Aug 2017 15:29:08 -0400 Original-Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dhhWQ-00088G-G0 for bug-gnu-emacs@gnu.org; Tue, 15 Aug 2017 15:29:07 -0400 Original-Received: from debbugs.gnu.org ([208.118.235.43]:58832) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1dhhWQ-000880-Cm for bug-gnu-emacs@gnu.org; Tue, 15 Aug 2017 15:29:02 -0400 Original-Received: from Debian-debbugs by debbugs.gnu.org with local (Exim 4.84_2) (envelope-from ) id 1dhhWQ-0002et-6s for bug-gnu-emacs@gnu.org; Tue, 15 Aug 2017 15:29:02 -0400 X-Loop: help-debbugs@gnu.org Resent-From: Paul Eggert Original-Sender: "Debbugs-submit" Resent-CC: bug-gnu-emacs@gnu.org Resent-Date: Tue, 15 Aug 2017 19:29:02 +0000 Resent-Message-ID: Resent-Sender: help-debbugs@gnu.org X-GNU-PR-Message: followup 27986 X-GNU-PR-Package: emacs X-GNU-PR-Keywords: security Original-Received: via spool by 27986-submit@debbugs.gnu.org id=B27986.150282528210202 (code B ref 27986); Tue, 15 Aug 2017 19:29:02 +0000 Original-Received: (at 27986) by debbugs.gnu.org; 15 Aug 2017 19:28:02 +0000 Original-Received: from localhost ([127.0.0.1]:39275 helo=debbugs.gnu.org) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dhhVS-0002eU-Fm for submit@debbugs.gnu.org; Tue, 15 Aug 2017 15:28:02 -0400 Original-Received: from zimbra.cs.ucla.edu ([131.179.128.68]:55448) by debbugs.gnu.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dhhVQ-0002e7-3q for 27986@debbugs.gnu.org; Tue, 15 Aug 2017 15:28:00 -0400 Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 15D85160875; Tue, 15 Aug 2017 12:27:54 -0700 (PDT) Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10032) with ESMTP id TIcXz_WA-kuS; Tue, 15 Aug 2017 12:27:53 -0700 (PDT) Original-Received: from localhost (localhost [127.0.0.1]) by zimbra.cs.ucla.edu (Postfix) with ESMTP id 4571E160881; Tue, 15 Aug 2017 12:27:53 -0700 (PDT) X-Virus-Scanned: amavisd-new at zimbra.cs.ucla.edu Original-Received: from zimbra.cs.ucla.edu ([127.0.0.1]) by localhost (zimbra.cs.ucla.edu [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id kzN65nG3_Qtt; Tue, 15 Aug 2017 12:27:53 -0700 (PDT) Original-Received: from [192.168.1.9] (unknown [47.153.184.153]) by zimbra.cs.ucla.edu (Postfix) with ESMTPSA id 21101160875; Tue, 15 Aug 2017 12:27:53 -0700 (PDT) In-Reply-To: <83zib0g221.fsf@gnu.org> Content-Language: en-US X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 208.118.235.43 X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.org gmane.emacs.bugs:135788 Archived-At: Eli Zaretskii wrote: > How would they know to create B before Emacs issues any system call > that uses B? Because the attackers know how Emacs work and are attempting to exploit i= ts=20 security hole. > And how is this case different from the case that Emacs calls > (rename-file A B) thinking B doesn't exist (e.g., because some prior > code tested that)? The case in question trashes a directory that the attacker lacks permissi= on to.=20 The case you're talking about does not: it merely causes rename-file to f= ail. > we should be backward compatible as a fallback. I don't see how this can work, if the fallback method relies on two syste= m calls=20 that can fall victim to a race. I tried pretty hard to come up with secur= e and=20 backward-compatible approaches before proposing the change. I could not c= ome up=20 with any, and doubt whether anyone else could either. Another possibility is to implement new functions (say: file-copy, file-r= ename,=20 file-link, file-symlink, and directory-copy) that behave like the existin= g=20 functions except without the security hole, modify callers to use these n= ew=20 functions, and then mark the existing functions as deprecated due to secu= rity=20 concerns. I suspect that this would be more disruptive overall than the p= roposed=20 change, though (albeit disruptive in a different way).