kernel/2163: IPv4 multicast packets not looped back to host

[Göran Bengtson <goeran@cdg.chalmers.se>]

>Number:         2163
>Category:       kernel
>Synopsis:       IPv4 multicast packets not looped back to host
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Nov  1 10:50:01 MST 2001
>Last-Modified:
>Originator:     Goeran Bengtson
>Organization:
Chalmers
>Release:        current
>Environment:
	System      : OpenBSD 3.0
	Architecture: OpenBSD.any
	Machine     : any
>Description:
	IP multicast (IPv4) packets sent by an OpenBSD host are not correctly
	looped back to the host even if IP_MULTICAST_LOOP is set (the default).

	The reason is that after delayed checksumming was introduced,
	checksumming isn't done before ip_mloopback is called resulting in
	checksum errors on receive.
>How-To-Repeat:
	Send IPv4 multicast packets on a socket with IP_MULTICAST_LOOP set.
>Fix:

Suggested fix follows:


Index: ip_output.c
===================================================================
RCS file: /cvs/src/sys/netinet/ip_output.c,v
retrieving revision 1.137
diff -u -r1.137 ip_output.c
--- ip_output.c	2001/08/26 21:12:06	1.137
+++ ip_output.c	2001/11/01 17:22:04
@@ -453,6 +453,15 @@
 			 * on the outgoing interface, and the caller did not
 			 * forbid loopback, loop back a copy.
 			 */
+			/*
+		 	 * Can't defer TCP/UDP checksumming, do the
+		 	 * computation now.
+		 	*/
+			if (m->m_pkthdr.csum & (M_TCPV4_CSUM_OUT | M_UDPV4_CSUM_OUT)) {
+				in_delayed_cksum(m);
+				m->m_pkthdr.csum &=
+			    	~(M_UDPV4_CSUM_OUT | M_TCPV4_CSUM_OUT);
+			}	
 			ip_mloopback(ifp, m, dst);
 		}
 #ifdef MROUTING



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