From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FB88313263; Mon, 15 Dec 2025 14:58:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765810728; cv=none; b=crmzIxKkMuQVE6+8ZTa8vCH1wIOZz1+smP2AMR3ltuq0lwgI3rdxpNoLZG1QVskqnZmESo7YJaR/Z00qXFMEcaBNk7FYCKpjPiOr3qoL6sMeBTv8rIOFoGiPnOsk0Uq1bfvg7zKWCSTXOb8MiHSdLHhHH4PHJExoJ3XrLZBrkD4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765810728; c=relaxed/simple; bh=PCV8sd44c/5aFC/WUSRWenozpYDDIq0lVJk8xWbAOpE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gfLNFoDtdmx+/6IJxla2gmaM6Q/HlUS9Y+IDiDR0dSMWeOIx/QGXNuCr9K6YU/ySJCzndQSlfbPYtm83fudfZ2NObV7y3s2q8uyxJxQlmzV5Ohrol6gSPGYzWC7dFu7oAJWS8OuI7xfbrArl7rjpRm5NiJvygzRqdVx7410aQnU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d/8uG09n; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d/8uG09n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB115C4CEF5; Mon, 15 Dec 2025 14:58:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765810727; bh=PCV8sd44c/5aFC/WUSRWenozpYDDIq0lVJk8xWbAOpE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=d/8uG09n3GqrHPuGLyYc3q1dqzmBBEOTWCd9i+FnKQOMMSTjeJDwE0L+0b1adnIy2 w775w+vPDAm6FxAOTA492Wcfd6FJUWdj+XqdiUms/PTdMQz5pj4E6J3s4lx8C/GHsD KYQ2jdPdvviwKYVNk1oPbdqxNnDhVB98ACJhWBv/7ZMdyd3Osk8xkqbFLCZXD/F6V6 7y33ugbbqHElrv1q3L1jBQHWqyUaGlRW2WmvoCDA+rMKiGBpqP0AF1FrIfvZ1sxpvy Q2ZsdrvstU60EfX4Pavx2np7OwKQPHAKTzeU86IyH3JxlBgUnNwyvl6kTe/7ja1hkO J/euzD4p8MOGA== Date: Mon, 15 Dec 2025 15:58:42 +0100 From: Alexey Gladkov To: Dan Klishch Cc: brauner@kernel.org, containers@lists.linux-foundation.org, ebiederm@xmission.com, keescook@chromium.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk Subject: Re: [RESEND PATCH v6 0/5] proc: subset=pid: Relax check of mount visibility Message-ID: References: <20251215144600.911100-1-danilklishch@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251215144600.911100-1-danilklishch@gmail.com> On Mon, Dec 15, 2025 at 09:46:00AM -0500, Dan Klishch wrote: > On 12/15/25 5:10 AM, Alexey Gladkov wrote: > > On Sun, Dec 14, 2025 at 01:02:54PM -0500, Dan Klishch wrote: > >> On 12/14/25 11:40 AM, Alexey Gladkov wrote: > >>> But then, if I understand you correctly, this patch will not be enough > >>> for you. procfs with subset=pid will not allow you to have /proc/meminfo, > >>> /proc/cpuinfo, etc. > >> > >> Hmm, I didn't think of this. sunwalker-box only exposes cpuinfo and PID > >> tree to the sandboxed programs (empirically, this is enough for most of > >> programs you want sandboxing for). With that in mind, this patch and a > >> FUSE providing an overlay with cpuinfo / seccomp intercepting opens of > >> /proc/cpuinfo / a small kernel patch with a new mount option for procfs > >> to expose more static files still look like a clean solution to me. > > > > I don't think you'll be able to do that. procfs doesn't allow itself to > > be overlayed [1]. What should block mounting overlayfs and fuse on top > > of procfs. > > > > [1] https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/proc/root.c#n274 > > This is why I have been careful not to say overlayfs. With [2] (warning: > zero-shot ChatGPT output), I can do: > > $ ./fuse-overlay target --source=/proc > $ ls target > 1 88 194 1374 889840 908552 > 2 90 195 1375 889987 908619 > 3 91 196 1379 890031 908658 > 4 92 203 1412 890063 908756 > 5 93 205 1590 890085 908804 > 6 94 233 1644 890139 908951 > 7 96 237 1802 890246 909848 > 8 97 239 1850 890271 909914 > 10 98 240 1852 894665 909924 > 13 99 243 1865 895854 909926 > 15 100 244 1888 895864 910005 > 16 102 246 1889 896030 acpi > 17 103 262 1891 896205 asound > 18 104 263 1895 896508 bus > 19 105 264 1896 896544 driver > 20 106 265 1899 896706 dynamic_debug > <...> > > [2] https://gist.github.com/DanShaders/547eeb74a90315356b98472feae47474 > > This requires a much more careful thought wrt magic symlinks > and permission checks. The fact that I am highly unlikely to 100% > correctly reimplement the checks and special behavior of procfs makes me > not want to proceed with the FUSE route. > > On 12/15/25 6:30 AM, Christian Brauner wrote: > > The standard way of making it possible to mount procfs inside of a > > container with a separate mount namespace that has a procfs inside it > > with overmounted entries is to ensure that a fully-visible procfs > > instance is present. > > Yes, this is a solution. However, this is only marginally better than > passing --privileged to the outer container (in a sense that we require > outer sandbox to remove some protections for the inner sandbox to work). > > > The container needs to inherit a fully-visible instance somehow if you > > want nesting. Using an unprivileged LSM such as landlock to prevent any > > access to the fully visible procfs instance is usually the better way. > > > > My hope is that once signed bpf is more widely adopted that distros will > > just start enabling blessed bpf programs that will just take on the > > access protecting instead of the clumsy bind-mount protection mechanism. > > These are big changes to container runtimes that are unlikely to happen > soon. In contrast, the patch we are discussing will be available in 2 > months after the merge for me to use on ArchLinux, and in a couple more > months on Ubuntu. > > So, is there any way forward with the patch or should I continue trying > to find a userspace solution? I still consider these patches useful. I made them precisely to remove some of the restrictions we have for procfs because of global files in the root of this filesystem. I can update and prepare a new version of patchset if Christian thinks it's useful too. -- Rgrds, legion