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    SubjectRe: Proposal: restrict link(2)


    On Wed, 11 Dec 1996, Thomas Koenig wrote:

    > The possiblities of playing around with symlinks in /tmp are well
    > known and understood.
    > However, there are also many things which can go wrong with publically
    > writable directories, such as /tmp, when hard links are employed.
    > Consider a (questionable) root-owned program which does a
    > chown("/tmp/foo", uid, gid), with the sticky bit set on /tmp.
    > If /tmp/foo is a symbolic link to /etc/passwd, all is well with Linux -
    > it changes the ownership of the symbolic link (which is meaningless in
    > most cases), and /etc/passwd still belongs to root.
    > If, however, /tmp/foo is a HARD link to /etc/passwd, chown("/tmp/foo",
    > uid, gid) will lead to the user owning /etc/passwd - not a desirable
    > thing, in general.
    > My proposal would be to disallow linking a file into a directory which
    > has the sticky bit set unless the owner of the file is attempting this.
    > In other words, Joe Random Cracker can't do a 'ln /etc/passwd /tmp/foo'
    > beforehand.
    > Comments?

    I would not like to have /etc/passwd on the same file system as /tmp. I
    think critical systems should have a really small root partition and
    everything else should reside on separate partitions, so no hard linking
    to the files mentioned is possible.

    > Thomas Koenig,, ig25@dkauni2.bitnet.


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