When fed a broadcast address, ifa_ifwitaddr() returns the unicast ifa
whose broadcast address match the input. This is used mainly to select
ifa, and there can be trouble when you have 2 ifas on the same range
(e.g. 10.0.0.1/24@em0 & 10.0.0.20/24@em1) :

netinet/ip_mroute.c:814
net/route.c:785
netinet/ip_divert.c:143
net/if_vxlan.c:241

There are also places where broadcast addresses should not be tolerated :

netinet/ip_input.c:1061  broadcast address is not a module identifier
netinet/ip_input.c:1141  see above
netinet/ip_input.c:1197  see above
netinet6/*:              no broadcast in ipv6
net/route.c:562:         gateway shall never be a broadcast addr
net/route.c:713:         see above

This diff removes broadcast matching from ifa_ifwithaddr, and
adds or rewrites checks where necessary.

Comments ? Ok ?

Index: sys/net/if.c
===================================================================
RCS file: /cvs/src/sys/net/if.c,v
retrieving revision 1.416
diff -u -p -r1.416 if.c
--- sys/net/if.c        2 Dec 2015 08:47:00 -0000       1.416
+++ sys/net/if.c        2 Dec 2015 15:17:26 -0000
@@ -1178,13 +1178,6 @@ ifa_ifwithaddr(struct sockaddr *addr, u_
 
                        if (equal(addr, ifa->ifa_addr))
                                return (ifa);
-
-                       /* IPv6 doesn't have broadcast */
-                       if ((ifp->if_flags & IFF_BROADCAST) &&
-                           ifa->ifa_broadaddr &&
-                           ifa->ifa_broadaddr->sa_len != 0 &&
-                           equal(ifa->ifa_broadaddr, addr))
-                               return (ifa);
                }
        }
        return (NULL);
Index: sys/netinet/in_pcb.c
===================================================================
RCS file: /cvs/src/sys/netinet/in_pcb.c,v
retrieving revision 1.188
diff -u -p -r1.188 in_pcb.c
--- sys/netinet/in_pcb.c        30 Oct 2015 09:39:42 -0000      1.188
+++ sys/netinet/in_pcb.c        2 Dec 2015 15:17:26 -0000
@@ -328,14 +328,12 @@ in_pcbbind(struct inpcb *inp, struct mbu
 
                                ia = ifatoia(ifa_ifwithaddr(sintosa(sin),
                                    inp->inp_rtableid));
-                               if (ia == NULL)
-                                       return (EADDRNOTAVAIL);
 
                                /* SOCK_RAW does not use in_pcbbind() */
-                               if (so->so_type != SOCK_DGRAM &&
-                                   sin->sin_addr.s_addr !=
-                                   ia->ia_addr.sin_addr.s_addr)
-                                       return (EADDRNOTAVAIL);
+                               if (ia == NULL &&
+                                   (so->so_type != SOCK_DGRAM ||
+                                   !in_broadcast(sin->sin_addr, 
inp->inp_rtableid)))
+                                               return (EADDRNOTAVAIL);
                        }
                }
                if (lport) {
Index: sys/netinet/ip_output.c
===================================================================
RCS file: /cvs/src/sys/netinet/ip_output.c,v
retrieving revision 1.310
diff -u -p -r1.310 ip_output.c
--- sys/netinet/ip_output.c     2 Dec 2015 13:29:26 -0000       1.310
+++ sys/netinet/ip_output.c     2 Dec 2015 15:17:27 -0000
@@ -1387,9 +1387,8 @@ ip_setmoptions(int optname, struct ip_mo
                sin.sin_family = AF_INET;
                sin.sin_addr = addr;
                ia = ifatoia(ifa_ifwithaddr(sintosa(&sin), rtableid));
-               if (ia && in_hosteq(sin.sin_addr, ia->ia_addr.sin_addr))
-                       ifp = ia->ia_ifp;
-               if (ifp == NULL || (ifp->if_flags & IFF_MULTICAST) == 0) {
+               if (ia == NULL || (ifp = ia->ia_ifp) == NULL ||
+                   (ia->ia_ifp->if_flags & IFF_MULTICAST) == 0) {
                        error = EADDRNOTAVAIL;
                        break;
                }
@@ -1561,12 +1560,11 @@ ip_setmoptions(int optname, struct ip_mo
                        sin.sin_family = AF_INET;
                        sin.sin_addr = mreq->imr_interface;
                        ia = ifatoia(ifa_ifwithaddr(sintosa(&sin), rtableid));
-                       if (ia && in_hosteq(sin.sin_addr, ia->ia_addr.sin_addr))
-                               ifp = ia->ia_ifp;
-                       else {
+                       if (ia == NULL) {
                                error = EADDRNOTAVAIL;
                                break;
                        }
+                       ifp = ia->ia_ifp;
                }
                /*
                 * Find the membership in the membership array.
Index: sys/netinet/raw_ip.c
===================================================================
RCS file: /cvs/src/sys/netinet/raw_ip.c,v
retrieving revision 1.84
diff -u -p -r1.84 raw_ip.c
--- sys/netinet/raw_ip.c        28 Jul 2015 12:22:07 -0000      1.84
+++ sys/netinet/raw_ip.c        2 Dec 2015 15:17:27 -0000
@@ -473,6 +473,7 @@ rip_usrreq(struct socket *so, int req, s
                if (!((so->so_options & SO_BINDANY) ||
                    addr->sin_addr.s_addr == INADDR_ANY ||
                    addr->sin_addr.s_addr == INADDR_BROADCAST ||
+                   in_broadcast(addr->sin_addr, inp->inp_rtableid) ||
                    ifa_ifwithaddr(sintosa(addr), inp->inp_rtableid))) {
                        error = EADDRNOTAVAIL;
                        break;

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