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=-2.8 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 2BD27C43143 for ; Mon, 1 Oct 2018 16:04:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E8047204FD for ; Mon, 1 Oct 2018 16:04:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=cyphar-com.20150623.gappssmtp.com header.i=@cyphar-com.20150623.gappssmtp.com header.b="0gqaI+7n" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E8047204FD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=cyphar.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726304AbeJAWnS (ORCPT ); Mon, 1 Oct 2018 18:43:18 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:46991 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725777AbeJAWnS (ORCPT ); Mon, 1 Oct 2018 18:43:18 -0400 Received: by mail-pg1-f195.google.com with SMTP id a5-v6so1226915pgv.13 for ; Mon, 01 Oct 2018 09:04:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cyphar-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=YZTPZOesbYMxuSc+kS6QFWusaC5AEJK1lCFZDsFfBOg=; b=0gqaI+7nhwSpxzVEjfpw1RpqBnH0cilUWWTV5JvcFvO6LRfDznlOkckuqyH6FK/02O oFPT1Hm5O8sAYNtBJJxTVj5DJBAAsMEjVyrTrAWYOil44h6hoHzq+TBFqdjgQCb1b3y6 pTycsRMQMWHNUeuiNQ6K6EecQSECydCjhcvJdSOjabJL2idpNPiOzrqILY6OmWUopbg4 SfEUIDK66S7ArG0jvqw4w0Ow5r3qTeVBi7XGyzLAuC8Uo/+ZutZ0hX36sWmVKE8E/XtP PVF77i4eQeAEH5YYFEdVi4cI4mWrBY+Mfiy+/vNwZAtqpe1+60uNj7TQ90r+tm8M983d Y1nQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=YZTPZOesbYMxuSc+kS6QFWusaC5AEJK1lCFZDsFfBOg=; b=Pff/STIcc6eHYkl5+qHMFxqX02n7ntkze3WVmVzzo+NBxXyxh7os5stdxTYDuIpD5R b+yciJzdGPGNc1G4zKh0KiDX5U6/DBknC7Cs8HE44/8QteS2k7HkTDSlI+++KZ/6yc+d 6nbVYwSwFUT8G9W2vYQLfjOT5YPVXijJLuEpyOD9jhhnGDDZL1uQujKtVtUby430IeVe KJCsAUJ6pX57XoKOb2pgZtrGmP8MFhHhOdiqS40QHb8rYQVzx+OjfDeGTYmtFx0/6pXY SaHs5KQXFi+X98VnFaw4f9XMW/1Y9Dplt9oLCLkT5aUxKEK440GfG7wMiQaz31m/KBKv nISQ== X-Gm-Message-State: ABuFfoh4sIKsTd8559JcFH8Uu2Ck6I2zozYgzAjg1LAlXRRfsh6VlB+c f89rzYbhfOfb+o/BpgeV3HNLNg== X-Google-Smtp-Source: ACcGV62qIcGXIhdJvFYWhXFMkKr4Oh/9FigDhUtK2zjByRA4hChAynoWgM/du2x+zS2TC04BNwELcg== X-Received: by 2002:a63:2f81:: with SMTP id v123-v6mr10550874pgv.223.1538409887728; Mon, 01 Oct 2018 09:04:47 -0700 (PDT) Received: from ryuk ([220.240.25.129]) by smtp.gmail.com with ESMTPSA id z25-v6sm22134870pfl.58.2018.10.01.09.04.41 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 01 Oct 2018 09:04:46 -0700 (PDT) Date: Tue, 2 Oct 2018 02:04:31 +1000 From: Aleksa Sarai To: Christian Brauner Cc: Jann Horn , Al Viro , "Eric W. Biederman" , Andy Lutomirski , jlayton@kernel.org, Bruce Fields , Arnd Bergmann , shuah@kernel.org, David Howells , Tycho Andersen , kernel list , linux-fsdevel@vger.kernel.org, linux-arch , linux-kselftest@vger.kernel.org, dev@opencontainers.org, containers@lists.linux-foundation.org Subject: Re: [PATCH 1/3] namei: implement O_BENEATH-style AT_* flags Message-ID: <20181001160431.emb6b2hf32b754cl@ryuk> References: <20180929103453.12025-1-cyphar@cyphar.com> <20180929103453.12025-2-cyphar@cyphar.com> <20181001130038.s5ztphs3pl2zt3ut@brauner.io> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="l5774zw5ogijx4tv" Content-Disposition: inline In-Reply-To: <20181001130038.s5ztphs3pl2zt3ut@brauner.io> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --l5774zw5ogijx4tv Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2018-10-01, Christian Brauner wrote: > On Mon, Oct 01, 2018 at 02:28:03PM +0200, Jann Horn wrote: > > On Sat, Sep 29, 2018 at 4:28 PM Aleksa Sarai wrote: > > > * AT_BENEATH: Disallow ".." or absolute paths (either in the path or > > > found during symlink resolution) to escape the starting point of na= me > > > resolution, though ".." is permitted in cases like "foo/../bar". > > > Relative symlinks are still allowed (as long as they don't escape t= he > > > starting point). > >=20 > > As I said on the other thread, I would strongly prefer an API that > > behaves along the lines of David Drysdale's old patch > > https://lore.kernel.org/lkml/1439458366-8223-2-git-send-email-drysdale@= google.com/ > > : Forbid any use of "..". This would also be more straightforward to > > implement safely. If that doesn't work for you, I would like it if you > > could at least make that an option. I would like it if this API could > > mitigate straightforward directory traversal bugs such as > > https://bugs.chromium.org/p/project-zero/issues/detail?id=3D1583, where > > a confused deputy attempts to access a path like > > "/mnt/media_rw/../../data" while intending to access a directory under > > "/mnt/media_rw". >=20 > Oh, the semantics for this changed in this patchset, hah. I was still on > vacation so didn't get to look at it before it was sent out. From prior > discussion I remember that the original intention actual was what you > argue for. And the patchset should be as tight as possible. Having > special cases where ".." is allowed just sounds like an invitation for > userspace to get it wrong. > Aleksa, did you have a specific use-case in mind that made you change > this or was it already present in an earlier iteration of the patchset > by someone else? Al's original patchset allowed "..". A quick survey of my machine shows that there are 100k symlinks that contain ".." (~37% of all symlinks on my machine). This indicates to me that you would be restricting a large amount of reasonable resolutions because of this restriction. I posted a proposed way to protect against ".." shenanigans. If it's turns out this is not possible, I'm okay with disallowing ".." (assuming Al is also okay with that). --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --l5774zw5ogijx4tv Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEXzbGxhtUYBJKdfWmnhiqJn3bjbQFAluyRY8ACgkQnhiqJn3b jbQVKxAAmkBystPEfvPnjFxU6M2/bymYFbq5HrT6vKRRHrHGTJVo0WLeYXKCMjFq 7QYyfBoOdoMqYoPSCHM59qknyQFhiRHD66JJdF5tdf8k5wfg/aXAFfWh9pJFN85U 8uX3FI+d60svpeMmtxoTQrtpyvsWknxWBNEWl+HM7rtc5LNkOhXB6AgBpxRnLp6O 3lCzADIXPbOD5NuNhTlgDqvmbmJVOKgFv8ngdm055u2yGSR+B1GDaaqpNt4AS0rC ev7LktJ4T1yPHpty4GOpJNLka4BgetpOTUa6Iqs+zv4Uuf/zawNxP7O8NKtcgaXC jkMKUFcFwiNcYKt8BcZgQAtHyK8hbJcakmef3ZDq+05bwZ1/k1LisDRwgA0evHRS iqSnKFlB6uhRc/H6cYwc185b9lKDhUntId2vzRKYnXaF3fi+92YW2nZ/51PFSq6M PPauYn4BB9poMHQM8tnDelHraJ2btsd7+WduMlUtzcSimuUv/84CY7sNJiOuyYm9 qhxsNi2MSxMit0/LKzit/o73jfp68h8UAfl3Z592i1jPRXLo85jt3NByZWRM/qOm 4U20HegNdtbrkJpYjzDNT+8fZhtq73LfBgpaU7xqSFEX+PMqj8RM4H/af429rhqU BZ5M9yovvFgwKsr6rLkoDAgbFnUl4CWjufzhGFStPJmy1iBfGpk= =imiF -----END PGP SIGNATURE----- --l5774zw5ogijx4tv--