Add the IP_ONESBCAST option, to enable undirected IP broadcasts to be sent on

specific interfaces. This is required by aodvd, and may in future help us
in getting rid of the requirement for BPF from our import of isc-dhcp.

Suggested by:   fenestro
Obtained from:  BSD/OS
Reviewed by:    mini, sam
Approved by:    jake (mentor)

share/man/man4/ip.4

@@ -175,6 +175,47 @@ can be used directly as a control message for
 .Xr sendmsg 2 .
 .Pp
 If the
+.Dv IP_ONESBCAST
+option is enabled on a
+.Dv SOCK_DGRAM
+or a
+.Dv SOCK_RAW
+socket, the destination address of outgoing
+broadcast datagrams on that socket will be forced
+to the undirected broadcast address,
+.Dv INADDR_BROADCAST ,
+before transmission.
+This is in contrast to the default behavior of the
+system, which is to transmit undirected broadcasts
+via the first network interface with the
+.Dv IFF_BROADCAST flag set.
+.Pp
+This option allows applications to choose which
+interface is used to transmit an undirected broadcast
+datagram.
+For example, the following code would force an
+undirected broadcast to be transmitted via the interface
+configured with the broadcast address 192.168.2.255:
+.Bd -literal
+char msg[512];
+struct sockaddr_in sin;
+u_char onesbcast = 1;	/* 0 = disable (default), 1 = enable */
+
+setsockopt(s, IPPROTO_IP, IP_ONESBCAST, &onesbcast, sizeof(onesbcast));
+sin.sin_addr.s_addr = inet_addr("192.168.2.255");
+sin.sin_port = htons(1234);
+sendto(s, msg, sizeof(msg), 0, &sin, sizeof(sin));
+.Ed
+.Pp
+It is the application's responsibility to set the
+.Dv IP_TTL option
+to an appropriate value in order to prevent broadcast storms.
+The application must have sufficient credentials to set the
+.Dv SO_BROADCAST
+socket level option, otherwise the
+.Dv IP_ONESBCAST option has no effect.
+.Pp
+If the
 .Dv IP_RECVTTL
 option is enabled on a
 .Dv SOCK_DGRAM

sys/netinet/in.h

@@ -388,6 +388,8 @@ __END_DECLS
 #define	IP_IPSEC_POLICY		21   /* int; set/get security policy */
 #define	IP_FAITH		22   /* bool; accept FAITH'ed connections */
 
+#define	IP_ONESBCAST		23   /* bool: send all-ones broadcast */
+
 #define	IP_FW_ADD     		50   /* add a firewall rule to chain */
 #define	IP_FW_DEL    		51   /* delete a firewall rule from chain */
 #define	IP_FW_FLUSH   		52   /* flush firewall rule chain */

sys/netinet/in_pcb.h

@@ -142,6 +142,7 @@ struct inpcb {
 #define	INP_IPV6	0x2
 #define INP_IPV6PROTO	0x4		/* opened under IPv6 protocol */
 #define INP_TIMEWAIT	0x8		/* .. probably doesn't go here */
+#define	INP_ONESBCAST	0x10		/* send all-ones broadcast */
 	u_char	inp_ip_ttl;		/* time to live proto */
 	u_char	inp_ip_p;		/* protocol proto */
 

sys/netinet/ip_output.c

@@ -477,6 +477,8 @@ ip_output(struct mbuf *m0, struct mbuf *opt, struct route *ro,
 			error = EMSGSIZE;
 			goto bad;
 		}
+		if (flags & IP_SENDONES)
+			ip->ip_dst.s_addr = INADDR_BROADCAST;
 		m->m_flags |= M_BCAST;
 	} else {
 		m->m_flags &= ~M_BCAST;
@@ -1473,6 +1475,7 @@ ip_ctloutput(so, sopt)
 		case IP_RECVTTL:
 		case IP_RECVIF:
 		case IP_FAITH:
+		case IP_ONESBCAST:
 			error = sooptcopyin(sopt, &optval, sizeof optval,
 					    sizeof optval);
 			if (error)
@@ -1515,6 +1518,10 @@ ip_ctloutput(so, sopt)
 			case IP_FAITH:
 				OPTSET(INP_FAITH);
 				break;
+
+			case IP_ONESBCAST:
+				OPTSET(INP_ONESBCAST);
+				break;
 			}
 			break;
 #undef OPTSET
@@ -1608,6 +1615,7 @@ ip_ctloutput(so, sopt)
 		case IP_RECVIF:
 		case IP_PORTRANGE:
 		case IP_FAITH:
+		case IP_ONESBCAST:
 			switch (sopt->sopt_name) {
 
 			case IP_TOS:
@@ -1652,6 +1660,10 @@ ip_ctloutput(so, sopt)
 			case IP_FAITH:
 				optval = OPTBIT(INP_FAITH);
 				break;
+
+			case IP_ONESBCAST:
+				optval = OPTBIT(INP_ONESBCAST);
+				break;
 			}
 			error = sooptcopyout(sopt, &optval, sizeof optval);
 			break;

sys/netinet/ip_var.h

@@ -139,6 +139,7 @@ struct	ipstat {
 /* flags passed to ip_output as last parameter */
 #define	IP_FORWARDING		0x1		/* most of ip header exists */
 #define	IP_RAWOUTPUT		0x2		/* raw ip header exists */
+#define	IP_SENDONES		0x4		/* send all-ones broadcast */
 #define	IP_ROUTETOIF		SO_DONTROUTE	/* bypass routing tables */
 #define	IP_ALLOWBROADCAST	SO_BROADCAST	/* can send broadcast packets */
 

sys/netinet/raw_ip.c

@@ -322,6 +322,9 @@ rip_output(m, so, dst)
 		ipstat.ips_rawout++;
 	}
 
+	if (inp->inp_flags & INP_ONESBCAST)
+		flags |= IP_SENDONES;
+
 	return (ip_output(m, inp->inp_options, &inp->inp_route, flags,
 			  inp->inp_moptions, inp));
 }

sys/netinet/udp_usrreq.c

@@ -693,6 +693,7 @@ udp_output(inp, m, addr, control, td)
 	struct cmsghdr *cm;
 	struct sockaddr_in *sin, src;
 	int error = 0;
+	int ipflags;
 	u_short fport, lport;
 
 #ifdef MAC
@@ -821,6 +822,10 @@ udp_output(inp, m, addr, control, td)
 	ui->ui_dport = fport;
 	ui->ui_ulen = htons((u_short)len + sizeof(struct udphdr));
 
+	ipflags = inp->inp_socket->so_options & (SO_DONTROUTE | SO_BROADCAST);
+	if (inp->inp_flags & INP_ONESBCAST)
+		ipflags |= IP_SENDONES;
+
 	/*
 	 * Set up checksum and output datagram.
 	 */
@@ -837,8 +842,7 @@ udp_output(inp, m, addr, control, td)
 	((struct ip *)ui)->ip_tos = inp->inp_ip_tos;	/* XXX */
 	udpstat.udps_opackets++;
 
-	error = ip_output(m, inp->inp_options, &inp->inp_route,
-	    (inp->inp_socket->so_options & (SO_DONTROUTE | SO_BROADCAST)),
+	error = ip_output(m, inp->inp_options, &inp->inp_route, ipflags,
 	    inp->inp_moptions, inp);
 	return (error);