ATM: CVE-2008-5079: duplicate listen() on socket corrupts the vcc table

commit 17b24b3c97498935a2ef9777370b1151dfed3f6f upstream.

As reported by Hugo Dias that it is possible to cause a local denial
of service attack by calling the svc_listen function twice on the same
socket and reading /proc/net/atm/*vc

Signed-off-by: Chas Williams <chas@cmf.nrl.navy.mil>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>