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    SubjectRe: [PATCH] namespace.c: fix bind mount from foreign namespace
    Ram wrote:
    > Under the premise that bind mounts across namespace should be allowed;
    > any insight why the "founding fathers" :) allowed only bind
    > and not recursive bind? What issue would that create?

    Recursive bind traverses the subtree of vfsmnts rooted at the source
    mount (following mnt->mnt_mounts, see copy_tree()). That requires the
    source mount's namespace semaphore to be held.

    > One can easily workaround that restriction by manually binding
    > recursively.

    Yes, if you know which mounts they are.

    > I remember Miklos saying its not a security issue but a
    > implementation/locking issue. That can be fixed aswell.

    Yes, by taking the source namespace semaphore while traversing the
    subtree. That involves taking _two_ semaphores, so they have to be
    ordered to avoid deadlock (see double-locking elsewhere in the kernel).

    - Jamie
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