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    SubjectRe: Proposal: restrict link(2)


    On Thu, 12 Dec 1996, Thomas Koenig wrote:

    > The Deviant wrote:
    > >Exactly. since /etc/passwd is root.root (or root.shadow, or whatever),
    > >anything linked to it (/tmp/foo in this example) is also owned root.root.
    > >As the original author of this thread should have observed before posting,
    > >a user may not chown something he to or from a user or group he does not
    > >belong to. This "crack" will not work.
    > Uh, sure. Unless, that is, I can trick a root-privileged program into
    > chowning something in /tmp, for example. Can anybody say "xterm logging
    > bug"?

    Thats not a kernel problem. Thats a userspace problem. xterm needs to be
    fixed, not the kernel.

    > Alternatively, consider the possibilities when a root-privileged does an
    > open() on a file in /tmp. I feel much more secure when I know that this
    > CAN'T open any valuable configuration file.

    If you don't want your machine to be hacked, and you're willing to
    sacrafice functionality, don't network it.

    > Some programs use mktemp(3). The filenames generated are predictable.
    > Soft links are one way of exploiting this; hard links are another.

    Then mktemp(3) needs to be fixed... A concept which I am all for. But
    again, this is userland, not kernel. If you want to go fix libc so that
    mktemp(3) doesn't produice predictable filenames, go right ahead. This
    would, IMHO, be a Good Thing. Its still not a kernel problem.

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