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In ip_forward(): 

Avoid forwarding ip unicast packets which were contained inside
link-level multicast packets; having M_MCAST still set in the packet
header flags will mean that the packet will get multicast to a bogus
group instead of unicast to the next hop.

Malformed packets like this have occasionally been spotted "in the
wild" on a mediaone cable modem segment which also had multiple netbsd
machines running as router/NAT boxes.

Without this, any subnet with multiple netbsd routers receiving all
multicasts will generate a packet storm on receipt of such a
multicast.  Note that we already do the same check here for link-level
broadcasts; ip6_forward already does this as well.

Note that multicast forwarding does not go through ip_forward().

Adding some code to if_ethersubr to sanity check link-level
vs. ip-level multicast addresses might also be worthwhile.
This commit is contained in:
sommerfeld 1999-10-17 16:00:00 +00:00
parent db3b140df8
commit c2accd9f9c
1 changed files with 2 additions and 2 deletions
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4
sys/netinet/ip_input.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: ip_input.c,v 1.92 1999/07/23 15:21:17 itojun Exp $ */
/* $NetBSD: ip_input.c,v 1.93 1999/10/17 16:00:00 sommerfeld Exp $ */
/*
* Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
@ -1299,7 +1299,7 @@ ip_forward(m, srcrt)
ntohl(ip->ip_src.s_addr),
ntohl(ip->ip_dst.s_addr), ip->ip_ttl);
#endif
if (m->m_flags & M_BCAST || in_canforward(ip->ip_dst) == 0) {
if (m->m_flags & (M_BCAST|M_MCAST) || in_canforward(ip->ip_dst) == 0) {
ipstat.ips_cantforward++;
m_freem(m);
return;