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    SubjectRe: [PATCH -mm 5/7] add user namespace
    Quoting Eric W. Biederman (ebiederm@xmission.com):
    > "Serge E. Hallyn" <serue@us.ibm.com> writes:
    > >> No. The uids in a filesystem are interpreted in some user namespace
    > >> context. We can discover that context at the first mount of the
    > >> filesystem. Assuming the uids on a filesystem are the same set
    > >> of uids your process is using is just wrong.
    > >
    > > But, when I insert a usb keychain disk into my laptop, that fs assumes
    > > the uids on it's fs are the same as uids on my laptop...
    >
    > I agree that setting the fs_user_namespace at mount time is fine.
    > However when we use a mount that a process in another user namespace
    > we need to not assume the uids are the same.
    >
    > Do you see the difference?

    Aaah - so you don't want to store this on the fs. So this is actually
    like what I had mentioned many many emails ago?

    > > much wider community on. I.e. the cifs and nifs folks. I haven't even
    > > googled to see what they say about it.
    >
    > Yes.
    >
    > >> Yes. Your patch does lay some interesting foundation work.
    > >> But we must not merge it upstream until we have a complete patchset
    > >> that handles all of the user namespace issues.
    > >
    > > Don't think Cedric expected this to be merged :) Just to start
    > > discussion, which it certainly did...
    >
    > If we could have [RFC] in front of these proof of concept patches
    > it would clear up a lot of confusion.

    Agreed.

    > > If we're going to talk about keys (which I'd like to) I think we need to
    > > decide whether we are just using them as an easy wider-than-uid
    > > identifier, or if we actually need cryptographic keys to prevent
    > > "identity theft" (heheh). I don't know that we need the latter for
    > > anything, but of course if we're going to try for a more general
    > > solution, then we do.
    >
    > Actually I was thinking something as mundane as a mapping table. This
    > uid in this namespace equals that uid in that other namespace.

    I see.

    That's also what I was imagining earlier, but it seems crass somehow.
    I'd almost prefer to just tag a mount with a user namespace implicitly,
    and only allow the mounter to say 'do' or 'don't' allow this to be read
    by users in another namespace. Then in the 'don't' case, user joe
    [1000] can't read files belonging to user jack [1000] in another
    namespace. It's stricter, but clean.

    But whether we do mapping tables or simple isolation, I do still like
    the idea of pursuing the use of the keystore for global uids.

    thanks,
    -serge
    -
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