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 007833168E1; Wed, 24 Dec 2025 12:55:24 +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=1766580925; cv=none; b=Jz0gmWdfQ6xHQ6tdSBa+KyQv8d7iYThjiFM1W62GO/2gCjIs+6NANt4dn+dOWXQzX/ISC8FtIO+JWvnDGjQ6TNgqt1q/VC02BiTHPAgYorxN0hSqNOBB+y3aVRrM1gDti21oHUEEnXno0C66dkp+FHv+rQD91T6qXBBBZa9APGc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1766580925; c=relaxed/simple; bh=HV+jkR2aJYrANOhevyxDonjSyw59TeocYws8AvK7aww=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NzTf54aLFxnsw9yKoLy0aNBpEUzm+2bLuMvvKcO0WCVi0p3KDLwfyJJy78DHuFTfRdwLNngUzR6octELJjXSVqhYSbN5Lh5X4AMVKxlQLVp4P05U/O+TWmql+4/dDVSclYDU0QqOfQ7bgZFwqpTF9m+YsGgSv0A+X6cWq8HLNJI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SxNhUCGH; 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="SxNhUCGH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 97A3CC4CEFB; Wed, 24 Dec 2025 12:55:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1766580924; bh=HV+jkR2aJYrANOhevyxDonjSyw59TeocYws8AvK7aww=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=SxNhUCGHVmDGgFhy8UcCl8YjGtq7s/BkH+GSC/QKIYiOGj5NZV1R+y0tEgFbKCwCG VId+7xjJqon3iigh1x+LzLPl8Hyo4DgZbsL/W3PiTR8G5nGBUwZEcIEPi9BgB/NzIa LpqzfUolC3ZZ9bWMB3PFZo9l/BUw1h+tER7KZt9QPJPDJQfSMDvn9ozUMF9lT0pfw7 2YEZxRn/JeJ9dKLab7cTLHcigf2Wh5u32V0mWerkrfbZXmyMlzY8vqmWVJVpukpIXb FMHOQT7ySmU5IV5B5E3mAxySP7AfPcd08QYWFbyFexBS8PzkTO3VrGJ6OzgHsnVcP7 iHW/Poce03KJQ== Date: Wed, 24 Dec 2025 13:55:20 +0100 From: Christian Brauner To: Alexey Gladkov Cc: Dan Klishch , 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: <20251224-glasbruch-mahnmal-ef7e9e10bceb@brauner> References: <20251215144600.911100-1-danilklishch@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Mon, Dec 15, 2025 at 03:58:42PM +0100, Alexey Gladkov wrote: > 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. Let's see it at least! No need to preemptively dismiss it. :)