On Monday 24 November 2003 19:17, Steven Leikeim wrote: > On Mon, Nov 24, 2003 at 05:36:29PM +0100, Jakob Lell wrote: > > Hello, > > on Linux it is possible for any user to create a hard link to a file > > belonging to another user. This hard link continues to exist even if the > > original file is removed by the owner. However, as the link still belongs > > to the original owner, it is still counted to his quota. If a malicious > > user creates hard links for every temp file created by another user, this > > can make the victim run out of quota (or even fill up the hard disk). > > This makes a local DoS attack possible. > > Actually, this is a problem with ALL UNIX/UNIX like systems. And has been > since the beginning. > > > To solve the problem, the kernel shouldn't allow users to create hard > > links to files belonging to someone else. > > There is a simpler solution. Place user files on a separate filesystem > from system files. This includes putting all temporary files on separate > filesystems of their own. (Both /tmp and /var/tmp.) Since hard links > cannot cross filesystems the problem disappears. Mounting user filesystems > nosuid and nodev will prevent security problems should a setuid binary > appear in that filesystem.
There are still many administrators which don't do this. > > Of course, this does not eliminate the first "DoS" problem noted above, but > it is simple for an administrator to find where the extraneous links are > and deal with the offending party. This is no reason why it shouldn't be fixed. The victim can't solve the problem if the admin isn't available at the moment. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
