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Date: Sat, 16 Jan 2021 01:27:18 +0100 From: Christian Brauner <christian.brauner@...ntu.com> To: Theodore Ts'o <tytso@....edu> Cc: Christoph Hellwig <hch@...radead.org>, Dave Chinner <david@...morbit.com>, "Darrick J. Wong" <djwong@...nel.org>, Alexander Viro <viro@...iv.linux.org.uk>, linux-fsdevel@...r.kernel.org, John Johansen <john.johansen@...onical.com>, James Morris <jmorris@...ei.org>, Mimi Zohar <zohar@...ux.ibm.com>, Dmitry Kasatkin <dmitry.kasatkin@...il.com>, Stephen Smalley <stephen.smalley.work@...il.com>, Casey Schaufler <casey@...aufler-ca.com>, Arnd Bergmann <arnd@...db.de>, Andreas Dilger <adilger.kernel@...ger.ca>, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>, Geoffrey Thomas <geofft@...reload.com>, Mrunal Patel <mpatel@...hat.com>, Josh Triplett <josh@...htriplett.org>, Andy Lutomirski <luto@...nel.org>, Alban Crequy <alban@...volk.io>, Tycho Andersen <tycho@...ho.ws>, David Howells <dhowells@...hat.com>, James Bottomley <James.Bottomley@...senpartnership.com>, Seth Forshee <seth.forshee@...onical.com>, St?phane Graber <stgraber@...ntu.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Aleksa Sarai <cyphar@...har.com>, Lennart Poettering <lennart@...ttering.net>, "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org, Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>, Kees Cook <keescook@...omium.org>, Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>, Jonathan Corbet <corbet@....net>, containers@...ts.linux-foundation.org, linux-security-module@...r.kernel.org, linux-api@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, linux-integrity@...r.kernel.org, selinux@...r.kernel.org Subject: Re: [PATCH v5 00/42] idmapped mounts On Fri, Jan 15, 2021 at 12:51:20PM -0500, Theodore Ts'o wrote: > On Fri, Jan 15, 2021 at 04:24:23PM +0000, Christoph Hellwig wrote: > > > > That is what the capabilities are designed for and we already check > > for them. > > So perhaps I'm confused, but my understanding is that in the > containers world, capabilities are a lot more complicated. There is: > > 1) The initial namespace capability set > > 2) The container's user-namespace capability set > > 3) The namespace in which the file system is mounted --- which is > "usually, but not necessarily the initial namespace" and > presumably could potentially not necessarily be the current > container's user name space, is namespaces can be hierarchically > arranged. > > Is that correct? If so, how does this patch set change things (if > any), and and how does this interact with quota administration > operations? The cases you listed are correct. The patchset doesn't change them. Simply put, the patchset doesn't alter capability checking in any way. > > On a related note, ext4 specifies a "reserved user" or "reserved > group" which can access the reserved blocks. If we have a file system > which is mounted in a namespace running a container which is running > RHEL or SLES, and in that container, we have a file system mounted (so > it was not mounted in the initial namespace), with id-mapping --- and > then there is a further sub-container created with its own user > sub-namespace further mapping uids/gids --- will the right thing > happen? For that matter, how *is* the "right thing" defined? In short, nothing changes. Whatever happened before happens now. Specifically s_resuid/s_resgid are superblock mount options and so never change on a per-mount basis and thus also aren't affected by idmapped mounts. > > Sorry if this is a potentially stupid question, but I find user > namespaces and id and capability mapping to be hopefully confusing for > my tiny brain. :-) No, I really appreciate the questions. :) My brain can most likely handle less. :) Christian
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