[bgpd] Fix number of DoS security issues, restricted to configured peers.

[bgpd] Fix number of DoS security issues, restricted to configured peers.

2007-12-22 Paul Jakma <paul.jakma@sun.com>

	* Fix series of vulnerabilities reported by "Mu Security
	  Research Team", where bgpd can be made to crash by sending
	  malformed packets - requires that bgpd be configured with a
	  session to the peer.
	* bgp_attr.c: (bgp_attr_as4_path) aspath_parse may fail, only
	  set the attribute flag indicating AS4_PATH if we actually managed
	  to parse one.
	  (bgp_attr_munge_as4_attrs) Assert was too general, it is possible
	  to receive AS4_AGGREGATOR before AGGREGATOR.
	  (bgp_attr_parse) Check that we have actually received the extra
	  byte of header for Extended-Length attributes.
	* bgp_attr.h: Fix BGP_ATTR_MIN_LEN to account for the length byte.
	* bgp_open.c: (cap_minsizes) Fix size of CAPABILITY_CODE_RESTART,
	  incorrect -2 left in place from a development version of as4-path
	  patch.
	* bgp_packet.c: (bgp_route_refresh_receive) ORF length parameter
	  needs to be properly sanity checked.
	* tests/bgp_capability_test.c: Test for empty capabilities.