From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D9C0C54FD0 for ; Fri, 24 Apr 2020 17:38:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 65FFC206B9 for ; Fri, 24 Apr 2020 17:38:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728524AbgDXRik (ORCPT ); Fri, 24 Apr 2020 13:38:40 -0400 Received: from mother.openwall.net ([195.42.179.200]:54079 "HELO mother.openwall.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1726813AbgDXRik (ORCPT ); Fri, 24 Apr 2020 13:38:40 -0400 Received: (qmail 12213 invoked from network); 24 Apr 2020 17:38:38 -0000 Received: from localhost (HELO pvt.openwall.com) (127.0.0.1) by localhost with SMTP; 24 Apr 2020 17:38:38 -0000 Received: by pvt.openwall.com (Postfix, from userid 503) id CF163AB5C7; Fri, 24 Apr 2020 19:38:28 +0200 (CEST) Date: Fri, 24 Apr 2020 19:38:28 +0200 From: Solar Designer To: Ben Hutchings Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, akpm@linux-foundation.org, Denis Kirjanov , Dan Carpenter , Al Viro , Kees Cook , Salvatore Mesoraca , Linus Torvalds Subject: Re: [PATCH 3.16 208/245] namei: allow restricted O_CREAT of FIFOs and regular files Message-ID: <20200424173828.GA27528@openwall.com> References: <20200424135205.GA27204@openwall.com> <8783c94cb802ade8a45cdf4233fe3b7341cca5c9.camel@decadent.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8783c94cb802ade8a45cdf4233fe3b7341cca5c9.camel@decadent.org.uk> User-Agent: Mutt/1.4.2.3i Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 24, 2020 at 04:13:22PM +0100, Ben Hutchings wrote: > On Fri, 2020-04-24 at 15:52 +0200, Solar Designer wrote: > > On Fri, Apr 24, 2020 at 12:07:15AM +0100, Ben Hutchings wrote: > > > 3.16.83-rc1 review patch. If anyone has any objections, please let me know. > > > > I do. This patch is currently known-buggy, see this thread: > > > > https://www.openwall.com/lists/oss-security/2020/01/28/2 > > > > It is (partially) fixed with these newer commits in 5.5 and 5.5.2: > > > > commit d0cb50185ae942b03c4327be322055d622dc79f6 > > Author: Al Viro > > Date: Sun Jan 26 09:29:34 2020 -0500 > > > > do_last(): fetch directory ->i_mode and ->i_uid before it's too late > > > > may_create_in_sticky() call is done when we already have dropped the > > reference to dir. > > > > Fixes: 30aba6656f61e (namei: allow restricted O_CREAT of FIFOs and regular files) > > Signed-off-by: Al Viro > > > > commit d76341d93dedbcf6ed5a08dfc8bce82d3e9a772b > > Author: Al Viro > > Date: Sat Feb 1 16:26:45 2020 +0000 > > > > vfs: fix do_last() regression > > > > commit 6404674acd596de41fd3ad5f267b4525494a891a upstream. > [...] > > At least inclusion of the above fixes is mandatory for any backports. > > I know, and those are the next 2 patches in the series. Ah, then no objections from me. > > Also, I think no one has fixed the logic of may_create_in_sticky() so > > that it wouldn't unintentionally apply the "protection" when the file > > is neither a FIFO nor a regular file (something I found and mentioned in > > the oss-security posting above). > [...] > > I think the implementation of may_create_in_sticky() should be rewritten > > such that it'd directly correspond to the textual description in the > > comment above. As we've seen, trying to write the code "more optimally" > > resulted in its logic actually being different from the description. > > > > Meanwhile, I think backporting known-so-buggy code is a bad idea. > > I can see that it's not quite right, but does it matter in practice? > Directories and symlinks are handled separately; sockets can't be > opened anyway; block and character devices wonn't normally appear in a > sticky directory. Clearly, it doesn't matter all that much in practice - I'm not aware of anyone having complained about it causing issues on their system. I think it primarily mattered as an attack vector on the issue fixed with Al's commits above. I think we should nevertheless fix the code to match its intent and the comment, but meanwhile this isn't a blocker for the backport. Alexander