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    SubjectRe: hard links create local DoS vulnerability and security problems
    Date
    On Monday 24 November 2003 19:13, Richard B. Johnson wrote:
    > On Mon, 24 Nov 2003 splite@purdue.edu wrote:
    > > On Mon, Nov 24, 2003 at 06:57:41PM +0100, Jakob Lell wrote:
    > > > [...]
    > > > Setuid-root binaries also work in a home directory.
    > > > You can try it by doing this test:
    > > > ln /bin/ping $HOME/ping
    > > > $HOME/ping localhost
    > > > [...]
    > >
    > > That's why you don't put user-writable directories on the root or /usr
    > > partitions.  (For extra points, mount your /tmp and /var/tmp partitions
    > > nodev,nosuid.)  Seriously guys, this is Unix Admin 101, not a major new
    > > security problem.
    >
    > And if the inode that was referenced in the root-owned directory
    > was deleted, it would no longer function as setuid root.
    Hello,
    I've just checked it out. It still works as setuid root. Just try this (as
    root):
    cp /bin/ping /tmp/ping
    chmod 4755 /tmp/ping
    su user
    ln /tmp/ping $HOME/ping
    exit
    rm /tmp/ping
    su user
    $HOME/ping localhost
    rm $HOME/ping

    Regards
    Jakob

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