1 /* vi: set sw=4 ts=4: */
3 * RFC3927 ZeroConf IPv4 Link-Local addressing
4 * (see <http://www.zeroconf.org/>)
6 * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
7 * Copyright (C) 2004 by David Brownell
9 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
13 * ZCIP just manages the 169.254.*.* addresses. That network is not
14 * routed at the IP level, though various proxies or bridges can
15 * certainly be used. Its naming is built over multicast DNS.
21 // - more real-world usage/testing, especially daemon mode
22 // - kernel packet filters to reduce scheduling noise
23 // - avoid silent script failures, especially under load...
24 // - link status monitoring (restart on link-up; stop on link-down)
26 //usage:#define zcip_trivial_usage
27 //usage: "[OPTIONS] IFACE SCRIPT"
28 //usage:#define zcip_full_usage "\n\n"
29 //usage: "Manage a ZeroConf IPv4 link-local address\n"
30 //usage: "\n -f Run in foreground"
31 //usage: "\n -q Quit after obtaining address"
32 //usage: "\n -r 169.254.x.x Request this address first"
33 //usage: "\n -l x.x.0.0 Use this range instead of 169.254"
34 //usage: "\n -v Verbose"
36 //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
37 //usage: "\nexits only on I/O errors (link down etc)"
40 #include <netinet/ether.h>
42 #include <net/if_arp.h>
43 #include <linux/sockios.h>
47 /* We don't need more than 32 bits of the counter */
48 #define MONOTONIC_US() ((unsigned)monotonic_us())
51 struct ether_header eth;
57 LINKLOCAL_ADDR = 0xa9fe0000,
59 /* protocol timeout parameters, specified in seconds */
65 RATE_LIMIT_INTERVAL = 60,
68 ANNOUNCE_INTERVAL = 2,
72 /* States during the configuration process. */
81 #define VDBG(...) do { } while (0)
89 struct sockaddr saddr;
90 struct ether_addr eth_addr;
93 #define G (*(struct globals*)&bb_common_bufsiz1)
94 #define saddr (G.saddr )
95 #define eth_addr (G.eth_addr)
96 #define INIT_G() do { } while (0)
100 * Pick a random link local IP address on 169.254/16, except that
101 * the first and last 256 addresses are reserved.
103 static uint32_t pick_nip(void)
108 tmp = rand() & IN_CLASSB_HOST;
109 } while (tmp > (IN_CLASSB_HOST - 0x0200));
110 return htonl((G.localnet_ip + 0x0100) + tmp);
114 * Broadcast an ARP packet.
117 /* int op, - always ARPOP_REQUEST */
118 /* const struct ether_addr *source_eth, - always ð_addr */
119 struct in_addr source_ip,
120 const struct ether_addr *target_eth, struct in_addr target_ip)
122 enum { op = ARPOP_REQUEST };
123 #define source_eth (ð_addr)
126 memset(&p, 0, sizeof(p));
129 p.eth.ether_type = htons(ETHERTYPE_ARP);
130 memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
131 memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
134 p.arp.arp_hrd = htons(ARPHRD_ETHER);
135 p.arp.arp_pro = htons(ETHERTYPE_IP);
136 p.arp.arp_hln = ETH_ALEN;
138 p.arp.arp_op = htons(op);
139 memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
140 memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
141 memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
142 memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
145 // Even though sock_fd is already bound to saddr, just send()
146 // won't work, because "socket is not connected"
147 // (and connect() won't fix that, "operation not supported").
148 // Thus we sendto() to saddr. I wonder which sockaddr
149 // (from bind() or from sendto()?) kernel actually uses
150 // to determine iface to emit the packet from...
151 xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr));
157 * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
159 static int run(char *argv[3], const char *param, struct in_addr *ip)
162 char *addr = addr; /* for gcc */
163 const char *fmt = "%s %s %s" + 3;
165 argv[2] = (char*)param;
167 VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
170 addr = inet_ntoa(*ip);
174 bb_info_msg(fmt, argv[2], argv[0], addr);
176 status = spawn_and_wait(argv + 1);
178 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
182 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
187 * Return milliseconds of random delay, up to "secs" seconds.
189 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
191 return rand() % (secs * 1000);
197 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
198 int zcip_main(int argc UNUSED_PARAM, char **argv)
202 const char *l_opt = "169.254.0.0";
205 // ugly trick, but I want these zeroed in one go
207 const struct in_addr null_ip;
208 const struct ether_addr null_addr;
211 int timeout_ms; /* must be signed */
218 #define null_ip (L.null_ip )
219 #define null_addr (L.null_addr )
222 #define timeout_ms (L.timeout_ms)
223 #define conflicts (L.conflicts )
224 #define nprobes (L.nprobes )
225 #define nclaims (L.nclaims )
226 #define ready (L.ready )
227 #define verbose (L.verbose )
229 memset(&L, 0, sizeof(L));
232 #define FOREGROUND (opts & 1)
233 #define QUIT (opts & 2)
234 // parse commandline: prog [options] ifname script
235 // exactly 2 args; -v accumulates and implies -f
236 opt_complementary = "=2:vv:vf";
237 opts = getopt32(argv, "fqr:l:v", &r_opt, &l_opt, &verbose);
239 // on NOMMU reexec early (or else we will rerun things twice)
241 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
243 // open an ARP socket
244 // (need to do it before openlog to prevent openlog from taking
245 // fd 3 (sock_fd==3))
246 xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
248 // do it before all bb_xx_msg calls
249 openlog(applet_name, 0, LOG_DAEMON);
250 logmode |= LOGMODE_SYSLOG;
254 if (inet_aton(l_opt, &net) == 0
255 || (net.s_addr & htonl(IN_CLASSB_NET)) != net.s_addr
257 bb_error_msg_and_die("invalid network address");
259 G.localnet_ip = ntohl(net.s_addr);
261 if (opts & 4) { // -r n.n.n.n
262 if (inet_aton(r_opt, &ip) == 0
263 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != G.localnet_ip
265 bb_error_msg_and_die("invalid link address");
270 /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
271 /* We need to make space for script argument: */
274 /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
275 #define argv_intf (argv[0])
277 xsetenv("interface", argv_intf);
279 // initialize the interface (modprobe, ifup, etc)
280 if (run(argv, "init", NULL))
284 // saddr is: { u16 sa_family; u8 sa_data[14]; }
285 //memset(&saddr, 0, sizeof(saddr));
286 //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
287 safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data));
289 // bind to the interface's ARP socket
290 xbind(sock_fd, &saddr, sizeof(saddr));
292 // get the interface's ethernet address
293 //memset(&ifr, 0, sizeof(ifr));
294 strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
295 xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
296 memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
298 // start with some stable ip address, either a function of
299 // the hardware address or else the last address we used.
300 // we are taking low-order four bytes, as top-order ones
301 // aren't random enough.
302 // NOTE: the sequence of addresses we try changes only
303 // depending on when we detect conflicts.
306 move_from_unaligned32(t, ((char *)ð_addr + 2));
310 ip.s_addr = pick_nip();
312 // FIXME cases to handle:
313 // - zcip already running!
314 // - link already has local address... just defend/update
316 // daemonize now; don't delay system startup
319 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
321 bb_info_msg("start, interface %s", argv_intf);
324 // run the dynamic address negotiation protocol,
325 // restarting after address conflicts:
326 // - start with some address we want to try
327 // - short random delay
328 // - arp probes to see if another host uses it
329 // - arp announcements that we're claiming it
331 // - defend it, within limits
333 // - address is successfully obtained and -q was given:
334 // run "<script> config", then exit with exitcode 0
335 // - poll error (when does this happen?)
336 // - read error (when does this happen?)
337 // - sendto error (in arp()) (when does this happen?)
338 // - revents & POLLERR (link down). run "<script> deconfig" first
341 struct pollfd fds[1];
342 unsigned deadline_us;
344 int source_ip_conflict;
345 int target_ip_conflict;
348 fds[0].events = POLLIN;
351 // poll, being ready to adjust current timeout
353 timeout_ms = random_delay_ms(PROBE_WAIT);
354 // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
355 // make the kernel filter out all packets except
356 // ones we'd care about.
358 // set deadline_us to the point in time when we timeout
359 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
361 VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
362 timeout_ms, argv_intf, nprobes, nclaims);
364 switch (safe_poll(fds, 1, timeout_ms)) {
367 //bb_perror_msg("poll"); - done in safe_poll
372 VDBG("state = %d\n", state);
375 // timeouts in the PROBE state mean no conflicting ARP packets
376 // have been received, so we can progress through the states
377 if (nprobes < PROBE_NUM) {
379 VDBG("probe/%u %s@%s\n",
380 nprobes, argv_intf, inet_ntoa(ip));
381 timeout_ms = PROBE_MIN * 1000;
382 timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
383 arp(/* ARPOP_REQUEST, */
384 /* ð_addr, */ null_ip,
388 // Switch to announce state.
391 VDBG("announce/%u %s@%s\n",
392 nclaims, argv_intf, inet_ntoa(ip));
393 timeout_ms = ANNOUNCE_INTERVAL * 1000;
394 arp(/* ARPOP_REQUEST, */
399 case RATE_LIMIT_PROBE:
400 // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
401 // have been received, so we can move immediately to the announce state
404 VDBG("announce/%u %s@%s\n",
405 nclaims, argv_intf, inet_ntoa(ip));
406 timeout_ms = ANNOUNCE_INTERVAL * 1000;
407 arp(/* ARPOP_REQUEST, */
412 // timeouts in the ANNOUNCE state mean no conflicting ARP packets
413 // have been received, so we can progress through the states
414 if (nclaims < ANNOUNCE_NUM) {
416 VDBG("announce/%u %s@%s\n",
417 nclaims, argv_intf, inet_ntoa(ip));
418 timeout_ms = ANNOUNCE_INTERVAL * 1000;
419 arp(/* ARPOP_REQUEST, */
424 // Switch to monitor state.
426 // link is ok to use earlier
427 // FIXME update filters
428 run(argv, "config", &ip);
431 timeout_ms = -1; // Never timeout in the monitor state.
433 // NOTE: all other exit paths
434 // should deconfig ...
440 // We won! No ARP replies, so just go back to monitor.
446 // Invalid, should never happen. Restart the whole protocol.
448 ip.s_addr = pick_nip();
454 break; // case 0 (timeout)
456 // packets arriving, or link went down
458 // We need to adjust the timeout in case we didn't receive
459 // a conflicting packet.
460 if (timeout_ms > 0) {
461 unsigned diff = deadline_us - MONOTONIC_US();
462 if ((int)(diff) < 0) {
463 // Current time is greater than the expected timeout time.
464 // Should never happen.
465 VDBG("missed an expected timeout\n");
468 VDBG("adjusting timeout\n");
469 timeout_ms = (diff / 1000) | 1; /* never 0 */
473 if ((fds[0].revents & POLLIN) == 0) {
474 if (fds[0].revents & POLLERR) {
475 // FIXME: links routinely go down;
476 // this shouldn't necessarily exit.
477 bb_error_msg("iface %s is down", argv_intf);
479 run(argv, "deconfig", &ip);
487 if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
488 bb_perror_msg_and_die(bb_msg_read_error);
490 if (p.eth.ether_type != htons(ETHERTYPE_ARP))
494 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
495 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
496 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
497 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
498 VDBG("%s recv arp type=%d, op=%d,\n",
499 argv_intf, ntohs(p.eth.ether_type),
500 ntohs(p.arp.arp_op));
501 VDBG("\tsource=%s %s\n",
504 VDBG("\ttarget=%s %s\n",
509 if (p.arp.arp_op != htons(ARPOP_REQUEST)
510 && p.arp.arp_op != htons(ARPOP_REPLY)
515 source_ip_conflict = 0;
516 target_ip_conflict = 0;
518 if (memcmp(&p.arp.arp_sha, ð_addr, ETH_ALEN) != 0) {
519 if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr))) {
520 /* A probe or reply with source_ip == chosen ip */
521 source_ip_conflict = 1;
523 if (p.arp.arp_op == htons(ARPOP_REQUEST)
524 && memcmp(p.arp.arp_spa, &null_ip, sizeof(struct in_addr)) == 0
525 && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0
527 /* A probe with source_ip == 0.0.0.0, target_ip == chosen ip:
528 * another host trying to claim this ip!
530 target_ip_conflict = 1;
534 VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
535 state, source_ip_conflict, target_ip_conflict);
539 // When probing or announcing, check for source IP conflicts
540 // and other hosts doing ARP probes (target IP conflicts).
541 if (source_ip_conflict || target_ip_conflict) {
543 if (conflicts >= MAX_CONFLICTS) {
544 VDBG("%s ratelimit\n", argv_intf);
545 timeout_ms = RATE_LIMIT_INTERVAL * 1000;
546 state = RATE_LIMIT_PROBE;
549 // restart the whole protocol
550 ip.s_addr = pick_nip();
557 // If a conflict, we try to defend with a single ARP probe.
558 if (source_ip_conflict) {
559 VDBG("monitor conflict -- defending\n");
561 timeout_ms = DEFEND_INTERVAL * 1000;
562 arp(/* ARPOP_REQUEST, */
568 // Well, we tried. Start over (on conflict).
569 if (source_ip_conflict) {
571 VDBG("defend conflict -- starting over\n");
573 run(argv, "deconfig", &ip);
575 // restart the whole protocol
576 ip.s_addr = pick_nip();
583 // Invalid, should never happen. Restart the whole protocol.
584 VDBG("invalid state -- starting over\n");
586 ip.s_addr = pick_nip();
592 break; // case 1 (packets arriving)