Re: hard links create local DoS vulnerability and security problems

[Jakob Lell]

On Monday 24 November 2003 19:13, Richard B. Johnson wrote:
> On Mon, 24 Nov 2003 splite@xxxxxxxxxx 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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