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    SubjectRe: unprivileged mounts vs. rmdir (was: VFS, NFS security bug? ...)
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    Pavel Machek <pavel@ucw.cz> writes:

    > On Mon 2009-03-23 14:21:30, Miklos Szeredi wrote:
    >> [CCs trimmed]
    >>
    >> On Mon, 16 Mar 2009, Serge E. Hallyn wrote:
    >> > Quoting J. Bruce Fields (bfields@fieldses.org):
    >> > > special privilege, so don't consult filesystem permissions (do I have
    >> > > that right? What happened to the attempt to allow ordinary users to
    >> > > mount?).
    >> >
    >> > Well, they keep getting stalled because we don't have a good answer for
    >> > what to do about the fact that an unprivileged user can make trees
    >> > undeletable by pinning them with mounts. (Miklos and Eric cc'd in case
    >> > I didn't explain that well enough).
    >>
    >> That's correct.
    >>
    >> The best answer I can come up with is to allow rmdir/unlink to
    >> automatically umount trees from their respective dentries. Obviously
    >> this can't be done for regular (privileged) mounts, which must keep
    >> returning EBUSY in such situations.
    >>
    >> But for unprivileged mounts I can't see any fundamental issue with
    >> such an approach.
    >>
    >> Does anyone see a problem with this? Is there a better solution?
    >
    > Well... traditionally if you have an open file or cwd inside mounted
    > tree... that blocks unmount, right?
    >
    > What will you do with processes that have open (deleted) files inside
    > the mount? What about cwd?

    That is a backwards understanding, of the problem.

    Currently I can not delete my mount point if I have something mounted on it in another
    mount namespace.

    Generally lazy unmounts solve the deleted inodes problem, your were talking about.

    Eric




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