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    SubjectRe: [RFC v2 PATCH 0/8] VFS:userns: support portable root filesystems
    On Sat, May 14, 2016 at 09:21:55PM -0500, Eric W. Biederman wrote:
    > I have slowly been working with Seth Forshee on these issues as
    > the last thing I want is to introduce more security bugs right now.
    > Seth being a braver man than I am has already merged his changes into
    > the Ubuntu kernel.

    Maybe not quite so brave as you think. I also threw on a patch to
    disable the feature unless explicitly enabled by a sys admin.

    > James I think you are missing the fact that all filesystems already have
    > the make_kuid and make_kgid calls right where the data comes off disk,
    > and the from_kuid and from_kgid calls right where the on-disk data is
    > being created just before it goes on disk. Which means that the actual
    > impact on filesystems of the translation is trivial.

    It is fairly simple but a there's bit more that just id conversions to
    change. With ext4 I found that there were mount options which needed to
    be restricted, some capability checks to update, and access to external
    journal devices must be checked. In all it wasn't a whole lot of changes
    to the filesystem though. Fuse was a bit more involved, but the
    complexities there won't apply to other filesystems.

    > Djalal if you could work with Seth I think that would be very useful. I
    > know I am dragging my heels there but I really hope I can dig in and get
    > everything reviewed and merged soonish.

    That would make me very happy :-)

    I'm happy to look with Djalal for commonalities. I did skim his patches
    before, and based on that all I really expect to find are things related
    to permission checks when ids don't map. The rest seems fundamentally
    different.

    Seth

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