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Date:   Fri, 15 Jan 2021 16:24:23 +0000
From:   Christoph Hellwig <>
To:     Dave Chinner <>
Cc:     "Darrick J. Wong" <>,
        Christian Brauner <>,
        Alexander Viro <>,
        Christoph Hellwig <>,,
        John Johansen <>,
        James Morris <>,
        Mimi Zohar <>,
        Dmitry Kasatkin <>,
        Stephen Smalley <>,
        Casey Schaufler <>,
        Arnd Bergmann <>,
        Andreas Dilger <>,
        OGAWA Hirofumi <>,
        Geoffrey Thomas <>,
        Mrunal Patel <>,
        Josh Triplett <>,
        Andy Lutomirski <>,
        Theodore Tso <>, Alban Crequy <>,
        Tycho Andersen <>,
        David Howells <>,
        James Bottomley <>,
        Seth Forshee <>,
        St?phane Graber <>,
        Linus Torvalds <>,
        Aleksa Sarai <>,
        Lennart Poettering <>,
        "Eric W. Biederman" <>,,
        Phil Estes <>, Serge Hallyn <>,
        Kees Cook <>,
        Todd Kjos <>, Paul Moore <>,
        Jonathan Corbet <>,,,,,,,
Subject: Re: [PATCH v5 00/42] idmapped mounts

On Fri, Jan 15, 2021 at 07:43:34AM +1100, Dave Chinner wrote:
> > That sounds neat.  AFAICT, the VFS passes the filesystem a mount userns
> > structure, which is then carried down the call stack to whatever
> > functions actually care about mapping kernel [ug]ids to their ondisk
> > versions?
> > 
> > Does quota still work after this patchset is applied?  There isn't any
> > mention of that in the cover letter and I don't see a code patch, so
> > does that mean everything just works?  I'm particularly curious about
> > whether there can exist processes with CAP_SYS_ADMIN and an idmapped
> > mount?  Syscalls like bulkstat and quotactl present file [ug]ids to
> > programs, but afaict there won't be any translating going on?
> bulkstat is not allowed inside user namespaces. It's an init
> namespace only thing because it provides unchecked/unbounded access
> to all inodes in the filesystem, not just those contained within a
> specific mount container.
> Hence I don't think bulkstat output (and other initns+root only
> filesystem introspection APIs) should be subject to or concerned
> about idmapping.

That is what the capabilities are designed for and we already check
for them.

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