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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 A2817C00523 for ; Wed, 8 Jan 2020 04:39:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 734DB2072B for ; Wed, 8 Jan 2020 04:39:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578458368; bh=dPkwsTHDSFh/AlhLKMu8SfXypcftv+MrrSXdjB8TlCg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=RB0TjepMGcuQ8bYqcn1R6KfVMqbyxbW4RWdg0OcbKHxYOhtlr4e3RM/Vc695bbWW3 agb8MmC3FxxCPA3CRBsJkVK49PzEpOPMDsRfog1NesKdZVK+r510KJK0uE6GOogQtO sL4K9CzbnwQde9Vi/fJpxHpgOjfqmSjTM+am+i9Q= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726742AbgAHEj1 (ORCPT ); Tue, 7 Jan 2020 23:39:27 -0500 Received: from mail.kernel.org ([198.145.29.99]:58168 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726149AbgAHEj1 (ORCPT ); Tue, 7 Jan 2020 23:39:27 -0500 Received: from mail-wm1-f54.google.com (mail-wm1-f54.google.com [209.85.128.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8E17920848 for ; Wed, 8 Jan 2020 04:39:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1578458366; bh=dPkwsTHDSFh/AlhLKMu8SfXypcftv+MrrSXdjB8TlCg=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=zo2q/guK0Te/iTqGXf3SvyqyWLZnZryXPvlKdFXdNJdGBBy8ctLeTY2cPwgEHE06N NPJbRd8JxRD23NLJgsLXpSJawO2dNwLgMoXyn5etXhzNfdNtiX8KV8gXLwFHH5Jmj7 K3TYOsWq2pU0Xxc8rWGq+IHMRapADDP2TTdSFTko= Received: by mail-wm1-f54.google.com with SMTP id m24so1043344wmc.3 for ; Tue, 07 Jan 2020 20:39:26 -0800 (PST) X-Gm-Message-State: APjAAAXIgqyJqw/AZVuWRjyJAUtnEJSxsZ5n0rjWSH+LbVnlBKmXc2Cb OOPdAuF1CP6CtQDuHXdjeytzqdsP+5QPscB1X6zbiA== X-Google-Smtp-Source: APXvYqz/SlzA6q8BHzR8wgKeCu5YF8gd0+SAe8SHOFxrPyQnlZmV8Zsm1JVs0cwdLErhzYcGzMfm2lHs87ilm/bZZrU= X-Received: by 2002:a1c:7ed0:: with SMTP id z199mr1421925wmc.58.1578458364943; Tue, 07 Jan 2020 20:39:24 -0800 (PST) MIME-Version: 1.0 References: <20191230052036.8765-1-cyphar@cyphar.com> <20191230052036.8765-2-cyphar@cyphar.com> <20191230082847.dkriyisvu7wwxqqu@yavin.dot.cyphar.com> In-Reply-To: <20191230082847.dkriyisvu7wwxqqu@yavin.dot.cyphar.com> From: Andy Lutomirski Date: Tue, 7 Jan 2020 20:39:10 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH RFC 1/1] mount: universally disallow mounting over symlinks To: Aleksa Sarai Cc: Linus Torvalds , Al Viro , David Howells , Eric Biederman , stable , Christian Brauner , Serge Hallyn , dev@opencontainers.org, Linux Containers , Linux API , linux-fsdevel , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 30, 2019 at 12:29 AM Aleksa Sarai wrote: > > On 2019-12-29, Linus Torvalds wrote: > > On Sun, Dec 29, 2019 at 9:21 PM Aleksa Sarai wrote: > > If allowing bind-mounts over symlinks is allowed (which I don't have a > problem with really), it just means we'll need a few more kernel pieces > to get this hardening to work. But these features would be useful > outside of the problems I'm dealing with (O_EMPTYPATH and some kind of > pidfd-based interface to grab the equivalent of /proc/self/exe and a few > other such magic-link targets). As one data point, I would use this ability in virtme: this would allow me to more reliably mount over /etc/resolve.conf even when it's a symlink. (Perhaps I should use overlayfs instead. Hmm.)