test SYN cookies (was Re: SYN cookies security bugfix?)

[Ed L Cashin <ecashin@terry.uga.edu>]

Alan Cox <alan@lxorguk.ukuu.org.uk> writes:

> > I received a forwarded message from SuSE regarding a security vulnerability
> > with respect to randomization of the ISN for SYN cookies - or something to
> > that effect.  I have not been able to find the patch which addresses this
> > problem; if anyone can point me towards it, I would be appreciative.
> 
> Its fixed in 2.2.20, you can grab the 2.2 patch from there

What is a good way to test SYN cookies?  I can induce a three-second
delay (on victim host V) before new TCP connections are accepted by
sending a burst of 2000 SYN packets (from attacker A), where V is
running a 2.2.14 or 2.2.17 kernel.  During the three seconds ICMP echo
requests from A to V are being answered.

Turning on SYN cookies after /proc is mounted does not affect the
three-second pause, though, so I figure that either the pause is not
on account of a full half-open connection queue or SYN cookies are not
working.

-- 
--Ed Cashin                   PGP public key:
  ecashin@terry.uga.edu       http://www.terry.uga.edu/~ecashin/pgp/