Multicast packets sent to inappropriate sockets (patch)

[Matthew Dillon]

:The FreeBSD folks have apparently had a some amount of trepidation 
:surrounding the patch I presented on this issue.  The old behavior dates 
:back to BSD4.3.  Tradition.
:
:Anyway, I've made a new patch which I hope you'll consider.
:(a) provides a sysctl to toggle between the traditional BSD4.3 handling 
:and the Solaris-style strict membership handling implied by man ip(4) 
:and UNPv1.
:(b) solves a kernel panic in the first patch
:
:And with the new behavior enabled with the sysctl this will prevent 
:unicast listeners from getting multicast traffic delivered to them if 
:they are not multicast-aware (i.e. if they don't actually have any mcast 
:memberships).  This means that if some socket on your system is 
:listening to a multicast address, this patch (when enabled) will prevent 
:your nfsd from seeing traffic to multicast-address:2049, which it would 
:otherwise receive.
:
:The patch follows.  Be sure to let me know if you have any concerns or 
:questions.  Thanks for reading.

    Heh.  They always have trepidation.

    In anycase, your solution is the correct one... adding a sysctl to
    toggle the change.  I have CC'd Jeffrey Hsu who is our resident 
    network stack expert.  If he has no issues I would like to commit
    the patch into DFly with the strict_mcast_mship default set to 1.

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>

:--- freebsd_stable_udp_usrreq.c.orig   Fri Oct 24 12:35:46 2003
:+++ freebsd_stable_udp_usrreq.c  Fri Oct 24 23:22:01 2003
:@@ -102,6 +102,10 @@
: SYSCTL_INT(_net_inet_udp, OID_AUTO, blackhole, CTLFLAG_RW,
:   &blackhole, 0, "Do not send port unreachables for refused connects");
: 
:+static int strict_mcast_mship = 0;
:+SYSCTL_INT(_net_inet_udp, OID_AUTO, strict_mcast_mship, CTLFLAG_RW,
:+  &strict_mcast_mship, 0, "Only send multicast to member sockets");
:+
: struct  inpcbhead udb;    /* from udp_var.h */
: #define udb6  udb  /* for KAME src sync over BSD*'s */
: struct  inpcbinfo udbinfo;
:@@ -290,6 +294,27 @@
:            if (inp->inp_faddr.s_addr !=
:                ip->ip_src.s_addr ||
:                inp->inp_fport != uh->uh_sport)
:+              continue;
:+        }
:+        /*
:+         * Check multicast packets to make sure they are only
:+         * sent to sockets with multicast memberships for the
:+         * packet's destination address and arrival interface
:+         */
:+        if (strict_mcast_mship &&
:+            IN_MULTICAST(ntohl(ip->ip_dst.s_addr)) &&
:+            inp->inp_moptions != NULL) {
:+           int mshipno;
:+           
:+           for (mshipno = 0;
:+                mshipno <= 
:+                   inp->inp_moptions->imo_num_memberships;
:+                ++mshipno) {
:+              if (ip->ip_dst.s_addr == 
:inp->inp_moptions->imo_membership[mshipno]->inm_addr.s_addr && 
:m->m_pkthdr.rcvif == inp->inp_moptions->imo_membership[mshipno]->inm_ifp)
:+                 break;
:+           }
:+           if (mshipno ==
:+               inp->inp_moptions->imo_num_memberships)
:               continue;
:         }
: