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.
20 //config: select PLATFORM_LINUX
21 //config: select FEATURE_SYSLOG
23 //config: ZCIP provides ZeroConf IPv4 address selection, according to RFC 3927.
24 //config: It's a daemon that allocates and defends a dynamically assigned
25 //config: address on the 169.254/16 network, requiring no system administrator.
27 //config: See http://www.zeroconf.org for further details, and "zcip.script"
28 //config: in the busybox examples.
30 //applet:IF_ZCIP(APPLET(zcip, BB_DIR_SBIN, BB_SUID_DROP))
32 //kbuild:lib-$(CONFIG_ZCIP) += zcip.o
37 // - more real-world usage/testing, especially daemon mode
38 // - kernel packet filters to reduce scheduling noise
39 // - avoid silent script failures, especially under load...
40 // - link status monitoring (restart on link-up; stop on link-down)
42 //usage:#define zcip_trivial_usage
43 //usage: "[OPTIONS] IFACE SCRIPT"
44 //usage:#define zcip_full_usage "\n\n"
45 //usage: "Manage a ZeroConf IPv4 link-local address\n"
46 //usage: "\n -f Run in foreground"
47 //usage: "\n -q Quit after obtaining address"
48 //usage: "\n -r 169.254.x.x Request this address first"
49 //usage: "\n -l x.x.0.0 Use this range instead of 169.254"
50 //usage: "\n -v Verbose"
52 //usage: "\n$LOGGING=none Suppress logging"
53 //usage: "\n$LOGGING=syslog Log to syslog"
55 //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
56 //usage: "\nexits only on I/O errors (link down etc)"
59 #include "common_bufsiz.h"
60 #include <netinet/ether.h>
62 #include <net/if_arp.h>
63 #include <linux/sockios.h>
67 /* We don't need more than 32 bits of the counter */
68 #define MONOTONIC_US() ((unsigned)monotonic_us())
71 struct ether_header eth;
76 /* 0-1 seconds before sending 1st probe */
78 /* 1-2 seconds between probes */
81 PROBE_NUM = 3, /* total probes to send */
82 ANNOUNCE_INTERVAL = 2, /* 2 seconds between announces */
83 ANNOUNCE_NUM = 3, /* announces to send */
84 /* if probe/announce sees a conflict, multiply RANDOM(NUM_CONFLICT) by... */
85 CONFLICT_MULTIPLIER = 2,
86 /* if we monitor and see a conflict, how long is defend state? */
90 /* States during the configuration process. */
98 #define VDBG(...) do { } while (0)
106 struct sockaddr iface_sockaddr;
107 struct ether_addr our_ethaddr;
108 uint32_t localnet_ip;
110 #define G (*(struct globals*)bb_common_bufsiz1)
111 #define INIT_G() do { setup_common_bufsiz(); } while (0)
115 * Pick a random link local IP address on 169.254/16, except that
116 * the first and last 256 addresses are reserved.
118 static uint32_t pick_nip(void)
123 tmp = rand() & IN_CLASSB_HOST;
124 } while (tmp > (IN_CLASSB_HOST - 0x0200));
125 return htonl((G.localnet_ip + 0x0100) + tmp);
128 static const char *nip_to_a(uint32_t nip)
132 return inet_ntoa(in);
136 * Broadcast an ARP packet.
138 static void send_arp_request(
139 /* int op, - always ARPOP_REQUEST */
140 /* const struct ether_addr *source_eth, - always &G.our_ethaddr */
142 const struct ether_addr *target_eth, uint32_t target_nip)
144 enum { op = ARPOP_REQUEST };
145 #define source_eth (&G.our_ethaddr)
148 memset(&p, 0, sizeof(p));
151 p.eth.ether_type = htons(ETHERTYPE_ARP);
152 memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
153 memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
156 p.arp.arp_hrd = htons(ARPHRD_ETHER);
157 p.arp.arp_pro = htons(ETHERTYPE_IP);
158 p.arp.arp_hln = ETH_ALEN;
160 p.arp.arp_op = htons(op);
161 memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
162 memcpy(&p.arp.arp_spa, &source_nip, 4);
163 memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
164 memcpy(&p.arp.arp_tpa, &target_nip, 4);
167 // Even though sock_fd is already bound to G.iface_sockaddr, just send()
168 // won't work, because "socket is not connected"
169 // (and connect() won't fix that, "operation not supported").
170 // Thus we sendto() to G.iface_sockaddr. I wonder which sockaddr
171 // (from bind() or from sendto()?) kernel actually uses
172 // to determine iface to emit the packet from...
173 xsendto(sock_fd, &p, sizeof(p), &G.iface_sockaddr, sizeof(G.iface_sockaddr));
179 * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
181 static int run(char *argv[3], const char *param, uint32_t nip)
184 const char *addr = addr; /* for gcc */
185 const char *fmt = "%s %s %s" + 3;
187 argv[2] = (char*)param;
189 VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
192 addr = nip_to_a(nip);
196 bb_error_msg(fmt, argv[2], argv[0], addr);
198 status = spawn_and_wait(argv + 1);
200 bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
204 bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
209 * Return milliseconds of random delay, up to "secs" seconds.
211 static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
213 return (unsigned)rand() % (secs * 1000);
219 int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
220 int zcip_main(int argc UNUSED_PARAM, char **argv)
223 const char *l_opt = "169.254.0.0";
228 // Ugly trick, but I want these zeroed in one go
230 const struct ether_addr null_ethaddr;
234 int timeout_ms; // must be signed
237 #define null_ethaddr (L.null_ethaddr)
239 #define chosen_nip (L.chosen_nip )
240 #define conflicts (L.conflicts )
241 #define timeout_ms (L.timeout_ms )
242 #define verbose (L.verbose )
244 memset(&L, 0, sizeof(L));
247 #define FOREGROUND (opts & 1)
248 #define QUIT (opts & 2)
249 // Parse commandline: prog [options] ifname script
250 // exactly 2 args; -v accumulates and implies -f
251 opt_complementary = "=2:vv:vf";
252 opts = getopt32(argv, "fqr:l:v", &r_opt, &l_opt, &verbose);
254 // on NOMMU reexec early (or else we will rerun things twice)
256 bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
258 // Open an ARP socket
259 // (need to do it before openlog to prevent openlog from taking
260 // fd 3 (sock_fd==3))
261 xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
263 // do it before all bb_xx_msg calls
264 openlog(applet_name, 0, LOG_DAEMON);
265 logmode |= LOGMODE_SYSLOG;
267 bb_logenv_override();
271 if (inet_aton(l_opt, &net) == 0
272 || (net.s_addr & htonl(IN_CLASSB_NET)) != net.s_addr
274 bb_error_msg_and_die("invalid network address");
276 G.localnet_ip = ntohl(net.s_addr);
278 if (opts & 4) { // -r n.n.n.n
280 if (inet_aton(r_opt, &ip) == 0
281 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != G.localnet_ip
283 bb_error_msg_and_die("invalid link address");
285 chosen_nip = ip.s_addr;
289 /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
290 /* We need to make space for script argument: */
293 /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
294 #define argv_intf (argv[0])
296 xsetenv("interface", argv_intf);
298 // Initialize the interface (modprobe, ifup, etc)
299 if (run(argv, "init", 0))
302 // Initialize G.iface_sockaddr
303 // G.iface_sockaddr is: { u16 sa_family; u8 sa_data[14]; }
304 //memset(&G.iface_sockaddr, 0, sizeof(G.iface_sockaddr));
305 //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
306 safe_strncpy(G.iface_sockaddr.sa_data, argv_intf, sizeof(G.iface_sockaddr.sa_data));
308 // Bind to the interface's ARP socket
309 xbind(sock_fd, &G.iface_sockaddr, sizeof(G.iface_sockaddr));
311 // Get the interface's ethernet address
312 //memset(&ifr, 0, sizeof(ifr));
313 strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
314 xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
315 memcpy(&G.our_ethaddr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
317 // Start with some stable ip address, either a function of
318 // the hardware address or else the last address we used.
319 // we are taking low-order four bytes, as top-order ones
320 // aren't random enough.
321 // NOTE: the sequence of addresses we try changes only
322 // depending on when we detect conflicts.
325 move_from_unaligned32(t, ((char *)&G.our_ethaddr + 2));
328 // FIXME cases to handle:
329 // - zcip already running!
330 // - link already has local address... just defend/update
332 // Daemonize now; don't delay system startup
335 bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
337 bb_error_msg("start, interface %s", argv_intf);
340 // Run the dynamic address negotiation protocol,
341 // restarting after address conflicts:
342 // - start with some address we want to try
343 // - short random delay
344 // - arp probes to see if another host uses it
345 // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 tell 0.0.0.0
346 // - arp announcements that we're claiming it
347 // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 (00:04:e2:64:23:c2) tell 169.254.194.171
349 // - defend it, within limits
351 // - address is successfully obtained and -q was given:
352 // run "<script> config", then exit with exitcode 0
353 // - poll error (when does this happen?)
354 // - read error (when does this happen?)
355 // - sendto error (in send_arp_request()) (when does this happen?)
356 // - revents & POLLERR (link down). run "<script> deconfig" first
357 if (chosen_nip == 0) {
359 chosen_nip = pick_nip();
364 struct pollfd fds[1];
365 unsigned deadline_us = deadline_us;
371 fds[0].events = POLLIN;
374 // Poll, being ready to adjust current timeout
376 timeout_ms = random_delay_ms(PROBE_WAIT);
377 // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
378 // make the kernel filter out all packets except
379 // ones we'd care about.
381 if (timeout_ms >= 0) {
382 // Set deadline_us to the point in time when we timeout
383 deadline_us = MONOTONIC_US() + timeout_ms * 1000;
386 VDBG("...wait %d %s nsent=%u\n",
387 timeout_ms, argv_intf, nsent);
389 n = safe_poll(fds, 1, timeout_ms);
391 //bb_perror_msg("poll"); - done in safe_poll
394 if (n == 0) { // timed out?
395 VDBG("state:%d\n", state);
398 // No conflicting ARP packets were seen:
399 // we can progress through the states
400 if (nsent < PROBE_NUM) {
402 VDBG("probe/%u %s@%s\n",
403 nsent, argv_intf, nip_to_a(chosen_nip));
404 timeout_ms = PROBE_MIN * 1000;
405 timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
406 send_arp_request(0, &null_ethaddr, chosen_nip);
409 // Switch to announce state
414 // No conflicting ARP packets were seen:
415 // we can progress through the states
416 if (nsent < ANNOUNCE_NUM) {
419 VDBG("announce/%u %s@%s\n",
420 nsent, argv_intf, nip_to_a(chosen_nip));
421 timeout_ms = ANNOUNCE_INTERVAL * 1000;
422 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
425 // Switch to monitor state
426 // FIXME update filters
427 run(argv, "config", chosen_nip);
428 // NOTE: all other exit paths should deconfig...
431 // fall through: switch to MONITOR
434 // case MONITOR: (shouldn't happen, MONITOR timeout is infinite)
435 // Defend period ended with no ARP replies - we won
436 timeout_ms = -1; // never timeout in monitor state
442 // Packet arrived, or link went down.
443 // We need to adjust the timeout in case we didn't receive
444 // a conflicting packet.
445 if (timeout_ms > 0) {
446 unsigned diff = deadline_us - MONOTONIC_US();
447 if ((int)(diff) < 0) {
448 // Current time is greater than the expected timeout time.
451 VDBG("adjusting timeout\n");
452 timeout_ms = (diff / 1000) | 1; // never 0
455 if ((fds[0].revents & POLLIN) == 0) {
456 if (fds[0].revents & POLLERR) {
457 // FIXME: links routinely go down;
458 // this shouldn't necessarily exit.
459 bb_error_msg("iface %s is down", argv_intf);
460 if (state >= MONITOR) {
461 // Only if we are in MONITOR or DEFEND
462 run(argv, "deconfig", chosen_nip);
470 if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
471 bb_perror_msg_and_die(bb_msg_read_error);
474 if (p.eth.ether_type != htons(ETHERTYPE_ARP))
476 if (p.arp.arp_op != htons(ARPOP_REQUEST)
477 && p.arp.arp_op != htons(ARPOP_REPLY)
483 struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
484 struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
485 struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
486 struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
487 VDBG("source=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa));
488 VDBG("target=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa));
492 if (memcmp(&p.arp.arp_sha, &G.our_ethaddr, ETH_ALEN) != 0) {
493 if (memcmp(p.arp.arp_spa, &chosen_nip, 4) == 0) {
494 // A probe or reply with source_ip == chosen ip
497 if (p.arp.arp_op == htons(ARPOP_REQUEST)
498 && memcmp(p.arp.arp_spa, &const_int_0, 4) == 0
499 && memcmp(p.arp.arp_tpa, &chosen_nip, 4) == 0
501 // A probe with source_ip == 0.0.0.0, target_ip == chosen ip:
502 // another host trying to claim this ip!
506 VDBG("state:%d ip_conflict:%d\n", state, ip_conflict);
510 // Either src or target IP conflict exists
511 if (state <= ANNOUNCE) {
514 timeout_ms = PROBE_MIN * 1000
515 + CONFLICT_MULTIPLIER * random_delay_ms(conflicts);
516 goto new_nip_and_PROBE;
519 // MONITOR or DEFEND: only src IP conflict is a problem
520 if (ip_conflict & 1) {
521 if (state == MONITOR) {
522 // Src IP conflict, defend with a single ARP probe
523 VDBG("monitor conflict - defending\n");
524 timeout_ms = DEFEND_INTERVAL * 1000;
526 send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
530 // Another src IP conflict, start over
531 VDBG("defend conflict - starting over\n");
532 run(argv, "deconfig", chosen_nip);
535 goto new_nip_and_PROBE;
537 // Note: if we only have a target IP conflict here (ip_conflict & 2),
538 // IOW: if we just saw this sort of ARP packet:
539 // aa:bb:cc:dd:ee:ff > xx:xx:xx:xx:xx:xx arp who-has <chosen_nip> tell 0.0.0.0
540 // we expect _kernel_ to respond to that, because <chosen_nip>
541 // is (expected to be) configured on this iface.