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    SubjectRe: [PATCH -mm 5/7] add user namespace
    Date
    Dave Hansen <haveblue@us.ibm.com> writes:

    > On Thu, 2006-07-13 at 13:02 -0600, Eric W. Biederman wrote:
    >> All comparisons of a user equality need to be of the tuple (user namespace,
    > user id).
    >> Any comparison that does not do that is an optimization.
    > ...
    >> So my impression was that Cedric's patchset was overoptimized because
    >> it did not change most of the uid comparisons, to (user namespace, user id).
    >
    > I might just be tempted to call them bugs so people understand what I'm
    > talking about ;)
    >
    >> Because you can have access to files created in another user namespace it
    >> is very unlikely that optimization will apply very frequently. The easy
    > scenario
    >> to get access to a file descriptor from another context is to consider unix
    >> domain sockets.
    >
    > OK, so you're saying that the lack of checks will cause problems rarely,
    > and that passing a fd across a unix domain sockets is one of the times
    > when you _could_ encounter this problem?

    I think for filesystems like /proc and /sys that there will normally
    be problems. However many of those problems can be rationalized away
    as a reasonable optimization, or are not immediately apparent.

    Passing a file descriptor between process in a unix domain socket is
    a case where I can easily construct scenarios where there are
    indisputable problems. It is one of my standard thought experiments
    to see if a namespace is sound.

    Eric
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