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 -v Verbose"
35 //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
36 //usage: "\nexits only on I/O errors (link down etc)"
39 #include <netinet/ether.h>
41 #include <net/if_arp.h>
42 #include <linux/sockios.h>
46 /* We don't need more than 32 bits of the counter */
47 #define MONOTONIC_US() ((unsigned)monotonic_us())
50 struct ether_header eth;
56 LINKLOCAL_ADDR = 0xa9fe0000,
58 /* protocol timeout parameters, specified in seconds */
64 RATE_LIMIT_INTERVAL = 60,
67 ANNOUNCE_INTERVAL = 2,
71 /* States during the configuration process. */
80 #define VDBG(...) do { } while (0)
88 struct sockaddr saddr;
89 struct ether_addr eth_addr;
91 #define G (*(struct globals*)&bb_common_bufsiz1)
92 #define saddr (G.saddr )
93 #define eth_addr (G.eth_addr)
94 #define INIT_G() do { } while (0)
98 * Pick a random link local IP address on 169.254/16, except that
99 * the first and last 256 addresses are reserved.
101 static uint32_t pick(void)
106 tmp = rand() & IN_CLASSB_HOST;
107 } while (tmp > (IN_CLASSB_HOST - 0x0200));
108 return htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
112 * Broadcast an ARP packet.
115 /* int op, - always ARPOP_REQUEST */
116 /* const struct ether_addr *source_eth, - always ð_addr */
117 struct in_addr source_ip,
118 const struct ether_addr *target_eth, struct in_addr target_ip)
120 enum { op = ARPOP_REQUEST };
121 #define source_eth (ð_addr)
124 memset(&p, 0, sizeof(p));
127 p.eth.ether_type = htons(ETHERTYPE_ARP);
128 memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
129 memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
132 p.arp.arp_hrd = htons(ARPHRD_ETHER);
133 p.arp.arp_pro = htons(ETHERTYPE_IP);
134 p.arp.arp_hln = ETH_ALEN;
136 p.arp.arp_op = htons(op);
137 memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
138 memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
139 memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
140 memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
143 // Even though sock_fd is already bound to saddr, just send()
144 // won't work, because "socket is not connected"
145 // (and connect() won't fix that, "operation not supported").
146 // Thus we sendto() to saddr. I wonder which sockaddr
147 // (from bind() or from sendto()?) kernel actually uses
148 // to determine iface to emit the packet from...
149 xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr));
155 * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
157 static int run(char *argv[3], const char *param, struct in_addr *ip)
160 char *addr = addr; /* for gcc */
161 const char *fmt = "%s %s %s" + 3;
163 argv[2] = (char*)param;
165 VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
168 addr = inet_ntoa(*ip);
172 bb_info_msg(fmt, argv[2], argv[0], addr);
174 status = spawn_and_wait(argv + 1);
176 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
180 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
185 * Return milliseconds of random delay, up to "secs" seconds.
187 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
189 return rand() % (secs * 1000);
195 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
196 int zcip_main(int argc UNUSED_PARAM, char **argv)
202 // ugly trick, but I want these zeroed in one go
204 const struct in_addr null_ip;
205 const struct ether_addr null_addr;
208 int timeout_ms; /* must be signed */
215 #define null_ip (L.null_ip )
216 #define null_addr (L.null_addr )
219 #define timeout_ms (L.timeout_ms)
220 #define conflicts (L.conflicts )
221 #define nprobes (L.nprobes )
222 #define nclaims (L.nclaims )
223 #define ready (L.ready )
224 #define verbose (L.verbose )
226 memset(&L, 0, sizeof(L));
229 #define FOREGROUND (opts & 1)
230 #define QUIT (opts & 2)
231 // parse commandline: prog [options] ifname script
232 // exactly 2 args; -v accumulates and implies -f
233 opt_complementary = "=2:vv:vf";
234 opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
236 // on NOMMU reexec early (or else we will rerun things twice)
238 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
240 // open an ARP socket
241 // (need to do it before openlog to prevent openlog from taking
242 // fd 3 (sock_fd==3))
243 xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
245 // do it before all bb_xx_msg calls
246 openlog(applet_name, 0, LOG_DAEMON);
247 logmode |= LOGMODE_SYSLOG;
249 if (opts & 4) { // -r n.n.n.n
250 if (inet_aton(r_opt, &ip) == 0
251 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
253 bb_error_msg_and_die("invalid link address");
258 /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
259 /* We need to make space for script argument: */
262 /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
263 #define argv_intf (argv[0])
265 xsetenv("interface", argv_intf);
267 // initialize the interface (modprobe, ifup, etc)
268 if (run(argv, "init", NULL))
272 // saddr is: { u16 sa_family; u8 sa_data[14]; }
273 //memset(&saddr, 0, sizeof(saddr));
274 //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
275 safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data));
277 // bind to the interface's ARP socket
278 xbind(sock_fd, &saddr, sizeof(saddr));
280 // get the interface's ethernet address
281 //memset(&ifr, 0, sizeof(ifr));
282 strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
283 xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
284 memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
286 // start with some stable ip address, either a function of
287 // the hardware address or else the last address we used.
288 // we are taking low-order four bytes, as top-order ones
289 // aren't random enough.
290 // NOTE: the sequence of addresses we try changes only
291 // depending on when we detect conflicts.
294 move_from_unaligned32(t, ((char *)ð_addr + 2));
300 // FIXME cases to handle:
301 // - zcip already running!
302 // - link already has local address... just defend/update
304 // daemonize now; don't delay system startup
307 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
309 bb_info_msg("start, interface %s", argv_intf);
312 // run the dynamic address negotiation protocol,
313 // restarting after address conflicts:
314 // - start with some address we want to try
315 // - short random delay
316 // - arp probes to see if another host uses it
317 // - arp announcements that we're claiming it
319 // - defend it, within limits
321 // - address is successfully obtained and -q was given:
322 // run "<script> config", then exit with exitcode 0
323 // - poll error (when does this happen?)
324 // - read error (when does this happen?)
325 // - sendto error (in arp()) (when does this happen?)
326 // - revents & POLLERR (link down). run "<script> deconfig" first
329 struct pollfd fds[1];
330 unsigned deadline_us;
332 int source_ip_conflict;
333 int target_ip_conflict;
336 fds[0].events = POLLIN;
339 // poll, being ready to adjust current timeout
341 timeout_ms = random_delay_ms(PROBE_WAIT);
342 // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
343 // make the kernel filter out all packets except
344 // ones we'd care about.
346 // set deadline_us to the point in time when we timeout
347 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
349 VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
350 timeout_ms, argv_intf, nprobes, nclaims);
352 switch (safe_poll(fds, 1, timeout_ms)) {
355 //bb_perror_msg("poll"); - done in safe_poll
360 VDBG("state = %d\n", state);
363 // timeouts in the PROBE state mean no conflicting ARP packets
364 // have been received, so we can progress through the states
365 if (nprobes < PROBE_NUM) {
367 VDBG("probe/%u %s@%s\n",
368 nprobes, argv_intf, inet_ntoa(ip));
369 arp(/* ARPOP_REQUEST, */
370 /* ð_addr, */ null_ip,
372 timeout_ms = PROBE_MIN * 1000;
373 timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
376 // Switch to announce state.
379 VDBG("announce/%u %s@%s\n",
380 nclaims, argv_intf, inet_ntoa(ip));
381 arp(/* ARPOP_REQUEST, */
384 timeout_ms = ANNOUNCE_INTERVAL * 1000;
387 case RATE_LIMIT_PROBE:
388 // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
389 // have been received, so we can move immediately to the announce state
392 VDBG("announce/%u %s@%s\n",
393 nclaims, argv_intf, inet_ntoa(ip));
394 arp(/* ARPOP_REQUEST, */
397 timeout_ms = ANNOUNCE_INTERVAL * 1000;
400 // timeouts in the ANNOUNCE state mean no conflicting ARP packets
401 // have been received, so we can progress through the states
402 if (nclaims < ANNOUNCE_NUM) {
404 VDBG("announce/%u %s@%s\n",
405 nclaims, argv_intf, inet_ntoa(ip));
406 arp(/* ARPOP_REQUEST, */
409 timeout_ms = ANNOUNCE_INTERVAL * 1000;
412 // Switch to monitor state.
414 // link is ok to use earlier
415 // FIXME update filters
416 run(argv, "config", &ip);
419 timeout_ms = -1; // Never timeout in the monitor state.
421 // NOTE: all other exit paths
422 // should deconfig ...
428 // We won! No ARP replies, so just go back to monitor.
434 // Invalid, should never happen. Restart the whole protocol.
442 break; // case 0 (timeout)
444 // packets arriving, or link went down
446 // We need to adjust the timeout in case we didn't receive
447 // a conflicting packet.
448 if (timeout_ms > 0) {
449 unsigned diff = deadline_us - MONOTONIC_US();
450 if ((int)(diff) < 0) {
451 // Current time is greater than the expected timeout time.
452 // Should never happen.
453 VDBG("missed an expected timeout\n");
456 VDBG("adjusting timeout\n");
457 timeout_ms = (diff / 1000) | 1; /* never 0 */
461 if ((fds[0].revents & POLLIN) == 0) {
462 if (fds[0].revents & POLLERR) {
463 // FIXME: links routinely go down;
464 // this shouldn't necessarily exit.
465 bb_error_msg("iface %s is down", argv_intf);
467 run(argv, "deconfig", &ip);
475 if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
476 bb_perror_msg_and_die(bb_msg_read_error);
478 if (p.eth.ether_type != htons(ETHERTYPE_ARP))
482 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
483 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
484 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
485 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
486 VDBG("%s recv arp type=%d, op=%d,\n",
487 argv_intf, ntohs(p.eth.ether_type),
488 ntohs(p.arp.arp_op));
489 VDBG("\tsource=%s %s\n",
492 VDBG("\ttarget=%s %s\n",
497 if (p.arp.arp_op != htons(ARPOP_REQUEST)
498 && p.arp.arp_op != htons(ARPOP_REPLY))
501 source_ip_conflict = 0;
502 target_ip_conflict = 0;
504 if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0
505 && memcmp(&p.arp.arp_sha, ð_addr, ETH_ALEN) != 0
507 source_ip_conflict = 1;
509 if (p.arp.arp_op == htons(ARPOP_REQUEST)
510 && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0
511 && memcmp(&p.arp.arp_tha, ð_addr, ETH_ALEN) != 0
513 target_ip_conflict = 1;
516 VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
517 state, source_ip_conflict, target_ip_conflict);
521 // When probing or announcing, check for source IP conflicts
522 // and other hosts doing ARP probes (target IP conflicts).
523 if (source_ip_conflict || target_ip_conflict) {
525 if (conflicts >= MAX_CONFLICTS) {
526 VDBG("%s ratelimit\n", argv_intf);
527 timeout_ms = RATE_LIMIT_INTERVAL * 1000;
528 state = RATE_LIMIT_PROBE;
531 // restart the whole protocol
539 // If a conflict, we try to defend with a single ARP probe.
540 if (source_ip_conflict) {
541 VDBG("monitor conflict -- defending\n");
543 timeout_ms = DEFEND_INTERVAL * 1000;
544 arp(/* ARPOP_REQUEST, */
550 // Well, we tried. Start over (on conflict).
551 if (source_ip_conflict) {
553 VDBG("defend conflict -- starting over\n");
555 run(argv, "deconfig", &ip);
557 // restart the whole protocol
565 // Invalid, should never happen. Restart the whole protocol.
566 VDBG("invalid state -- starting over\n");
574 break; // case 1 (packets arriving)