From fd963b992986bba83e344396c5d7dcff4ea6c1c0 Mon Sep 17 00:00:00 2001
From: Bruce M Simpson <bms@FreeBSD.org>
Date: Tue, 27 Apr 2010 14:14:21 +0000
Subject: [PATCH] Fix a regression where DVMRP diagnostic traffic, such as that
 used by mrinfo and mtrace, was dropped by the IGMP TTL check. IGMP control
 traffic must always have a TTL of 1.

Submitted by:	Matthew Luckie
MFC after:	3 days
---
 sys/netinet/igmp.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/sys/netinet/igmp.c b/sys/netinet/igmp.c
index f9f6381f3fc6..d4c8e99cdab1 100644
--- a/sys/netinet/igmp.c
+++ b/sys/netinet/igmp.c
@@ -1468,12 +1468,6 @@ igmp_input(struct mbuf *m, int off)
 	}
 	ip = mtod(m, struct ip *);
 
-	if (ip->ip_ttl != 1) {
-		IGMPSTAT_INC(igps_rcv_badttl);
-		m_freem(m);
-		return;
-	}
-
 	/*
 	 * Validate checksum.
 	 */
@@ -1488,6 +1482,17 @@ igmp_input(struct mbuf *m, int off)
 	m->m_data -= iphlen;
 	m->m_len += iphlen;
 
+	/*
+	 * IGMP control traffic is link-scope, and must have a TTL of 1.
+	 * DVMRP traffic (e.g. mrinfo, mtrace) is an exception;
+	 * probe packets may come from beyond the LAN.
+	 */
+	if (igmp->igmp_type != IGMP_DVMRP && ip->ip_ttl != 1) {
+		IGMPSTAT_INC(igps_rcv_badttl);
+		m_freem(m);
+		return;
+	}
+
 	switch (igmp->igmp_type) {
 	case IGMP_HOST_MEMBERSHIP_QUERY:
 		if (igmplen == IGMP_MINLEN) {