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    SubjectRe: [PATCH v6 0/3] SELinux support for anonymous inodes and UFFD
    On Thu, Aug 20, 2020 at 11:36 AM James Morris <jmorris@namei.org> wrote:
    >
    > On Fri, 7 Aug 2020, Lokesh Gidra wrote:
    >
    > > Userfaultfd in unprivileged contexts could be potentially very
    > > useful. We'd like to harden userfaultfd to make such unprivileged use
    > > less risky. This patch series allows SELinux to manage userfaultfd
    > > file descriptors and in the future, other kinds of
    > > anonymous-inode-based file descriptor. SELinux policy authors can
    > > apply policy types to anonymous inodes by providing name-based
    > > transition rules keyed off the anonymous inode internal name (
    > > "[userfaultfd]" in the case of userfaultfd(2) file descriptors) and
    > > applying policy to the new SIDs thus produced.
    >
    > Can you expand more on why this would be useful, e.g. use-cases?
    >
    With SELinux managed userfaultfd file descriptors, an administrator
    can control creation and movement of them. In particular, handling of
    a userfaultfd descriptor by a different process is essentially a
    ptrace access into the process, without any of the
    corresponding security_ptrace_access_check() checks. For privacy, the
    admin may want to deny such accesses,
    which is possible with SELinux support.

    I'll add this use case in the cover letter too in the next version.

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