lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
From: jlell at (Jakob Lell)
Subject: Re: hard links on Linux create local DoS vulnerability and security problems

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.

Powered by blists - more mailing lists