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-rw-r--r--networking/zcip.c546
1 files changed, 546 insertions, 0 deletions
diff --git a/networking/zcip.c b/networking/zcip.c
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1/* vi: set sw=4 ts=4: */
2/*
3 * RFC3927 ZeroConf IPv4 Link-Local addressing
4 * (see <http://www.zeroconf.org/>)
5 *
6 * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
7 * Copyright (C) 2004 by David Brownell
8 *
9 * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
10 */
11
12/*
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.
16 */
17
18//#define DEBUG
19
20// TODO:
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)
25
26#include "busybox.h"
27#include <syslog.h>
28#include <poll.h>
29#include <sys/wait.h>
30#include <netinet/ether.h>
31#include <net/ethernet.h>
32#include <net/if.h>
33#include <net/if_arp.h>
34
35#include <linux/if_packet.h>
36#include <linux/sockios.h>
37
38
39struct arp_packet {
40 struct ether_header hdr;
41 struct ether_arp arp;
42} ATTRIBUTE_PACKED;
43
44enum {
45/* 169.254.0.0 */
46 LINKLOCAL_ADDR = 0xa9fe0000,
47
48/* protocol timeout parameters, specified in seconds */
49 PROBE_WAIT = 1,
50 PROBE_MIN = 1,
51 PROBE_MAX = 2,
52 PROBE_NUM = 3,
53 MAX_CONFLICTS = 10,
54 RATE_LIMIT_INTERVAL = 60,
55 ANNOUNCE_WAIT = 2,
56 ANNOUNCE_NUM = 2,
57 ANNOUNCE_INTERVAL = 2,
58 DEFEND_INTERVAL = 10
59};
60
61/* States during the configuration process. */
62enum {
63 PROBE = 0,
64 RATE_LIMIT_PROBE,
65 ANNOUNCE,
66 MONITOR,
67 DEFEND
68};
69
70#define VDBG(fmt,args...) \
71 do { } while (0)
72
73static unsigned opts;
74#define FOREGROUND (opts & 1)
75#define QUIT (opts & 2)
76
77/**
78 * Pick a random link local IP address on 169.254/16, except that
79 * the first and last 256 addresses are reserved.
80 */
81static void pick(struct in_addr *ip)
82{
83 unsigned tmp;
84
85 /* use cheaper math than lrand48() mod N */
86 do {
87 tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
88 } while (tmp > (IN_CLASSB_HOST - 0x0200));
89 ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
90}
91
92/* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */
93
94/**
95 * Broadcast an ARP packet.
96 */
97static void arp(int fd, struct sockaddr *saddr, int op,
98 const struct ether_addr *source_addr, struct in_addr source_ip,
99 const struct ether_addr *target_addr, struct in_addr target_ip)
100{
101 struct arp_packet p;
102 memset(&p, 0, sizeof(p));
103
104 // ether header
105 p.hdr.ether_type = htons(ETHERTYPE_ARP);
106 memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
107 memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
108
109 // arp request
110 p.arp.arp_hrd = htons(ARPHRD_ETHER);
111 p.arp.arp_pro = htons(ETHERTYPE_IP);
112 p.arp.arp_hln = ETH_ALEN;
113 p.arp.arp_pln = 4;
114 p.arp.arp_op = htons(op);
115 memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
116 memcpy(&p.arp.arp_spa, &source_ip, sizeof (p.arp.arp_spa));
117 memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
118 memcpy(&p.arp.arp_tpa, &target_ip, sizeof (p.arp.arp_tpa));
119
120 // send it
121 if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
122 bb_perror_msg("sendto");
123 //return -errno;
124 }
125 // Currently all callers ignore errors, that's why returns are
126 // commented out...
127 //return 0;
128}
129
130/**
131 * Run a script.
132 */
133static int run(char *script, char *arg, char *intf, struct in_addr *ip)
134{
135 int pid, status;
136 char *why;
137
138 if(1) { //always true: if (script != NULL)
139 VDBG("%s run %s %s\n", intf, script, arg);
140 if (ip != NULL) {
141 char *addr = inet_ntoa(*ip);
142 setenv("ip", addr, 1);
143 bb_info_msg("%s %s %s", arg, intf, addr);
144 }
145
146 pid = vfork();
147 if (pid < 0) { // error
148 why = "vfork";
149 goto bad;
150 } else if (pid == 0) { // child
151 execl(script, script, arg, NULL);
152 bb_perror_msg("execl");
153 _exit(EXIT_FAILURE);
154 }
155
156 if (waitpid(pid, &status, 0) <= 0) {
157 why = "waitpid";
158 goto bad;
159 }
160 if (WEXITSTATUS(status) != 0) {
161 bb_error_msg("script %s failed, exit=%d",
162 script, WEXITSTATUS(status));
163 return -errno;
164 }
165 }
166 return 0;
167bad:
168 status = -errno;
169 bb_perror_msg("%s %s, %s", arg, intf, why);
170 return status;
171}
172
173
174/**
175 * Return milliseconds of random delay, up to "secs" seconds.
176 */
177static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs)
178{
179 return lrand48() % (secs * 1000);
180}
181
182/**
183 * main program
184 */
185
186/* Used to be auto variables on main() stack, but
187 * most of them were zero-inited. Moving them to bss
188 * is more space-efficient.
189 */
190static const struct in_addr null_ip; // = { 0 };
191static const struct ether_addr null_addr; // = { {0, 0, 0, 0, 0, 0} };
192
193static struct sockaddr saddr; // memset(0);
194static struct in_addr ip; // = { 0 };
195static struct ifreq ifr; //memset(0);
196
197static char *intf; // = NULL;
198static char *script; // = NULL;
199static suseconds_t timeout; // = 0; // milliseconds
200static unsigned conflicts; // = 0;
201static unsigned nprobes; // = 0;
202static unsigned nclaims; // = 0;
203static int ready; // = 0;
204static int verbose; // = 0;
205static int state = PROBE;
206
207int zcip_main(int argc, char *argv[])
208{
209 struct ether_addr eth_addr;
210 char *why;
211 int fd;
212
213 // parse commandline: prog [options] ifname script
214 char *r_opt;
215 opt_complementary = "vv:vf"; // -v accumulates and implies -f
216 opts = getopt32(argc, argv, "fqr:v", &r_opt, &verbose);
217 if (!FOREGROUND) {
218 /* Do it early, before all bb_xx_msg calls */
219 logmode = LOGMODE_SYSLOG;
220 openlog(applet_name, 0, LOG_DAEMON);
221 }
222 if (opts & 4) { // -r n.n.n.n
223 if (inet_aton(r_opt, &ip) == 0
224 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR) {
225 bb_error_msg_and_die("invalid link address");
226 }
227 }
228 argc -= optind;
229 argv += optind;
230 if (argc != 2)
231 bb_show_usage();
232 intf = argv[0];
233 script = argv[1];
234 setenv("interface", intf, 1);
235
236 // initialize the interface (modprobe, ifup, etc)
237 if (run(script, "init", intf, NULL) < 0)
238 return EXIT_FAILURE;
239
240 // initialize saddr
241 //memset(&saddr, 0, sizeof (saddr));
242 safe_strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
243
244 // open an ARP socket
245 fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
246 // bind to the interface's ARP socket
247 xbind(fd, &saddr, sizeof (saddr));
248
249 // get the interface's ethernet address
250 //memset(&ifr, 0, sizeof (ifr));
251 strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
252 if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
253 bb_perror_msg_and_die("get ethernet address");
254 }
255 memcpy(&eth_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
256
257 // start with some stable ip address, either a function of
258 // the hardware address or else the last address we used.
259 // NOTE: the sequence of addresses we try changes only
260 // depending on when we detect conflicts.
261 // (SVID 3 bogon: who says that "short" is always 16 bits?)
262 seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data );
263 if (ip.s_addr == 0)
264 pick(&ip);
265
266 // FIXME cases to handle:
267 // - zcip already running!
268 // - link already has local address... just defend/update
269
270 // daemonize now; don't delay system startup
271 if (!FOREGROUND) {
272 setsid();
273 xdaemon(0, 0);
274 bb_info_msg("start, interface %s", intf);
275 }
276
277 // run the dynamic address negotiation protocol,
278 // restarting after address conflicts:
279 // - start with some address we want to try
280 // - short random delay
281 // - arp probes to see if another host else uses it
282 // - arp announcements that we're claiming it
283 // - use it
284 // - defend it, within limits
285 while (1) {
286 struct pollfd fds[1];
287 struct timeval tv1;
288 struct arp_packet p;
289
290 int source_ip_conflict = 0;
291 int target_ip_conflict = 0;
292
293 fds[0].fd = fd;
294 fds[0].events = POLLIN;
295 fds[0].revents = 0;
296
297 // poll, being ready to adjust current timeout
298 if (!timeout) {
299 timeout = ms_rdelay(PROBE_WAIT);
300 // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
301 // make the kernel filter out all packets except
302 // ones we'd care about.
303 }
304 // set tv1 to the point in time when we timeout
305 gettimeofday(&tv1, NULL);
306 tv1.tv_usec += (timeout % 1000) * 1000;
307 while (tv1.tv_usec > 1000000) {
308 tv1.tv_usec -= 1000000;
309 tv1.tv_sec++;
310 }
311 tv1.tv_sec += timeout / 1000;
312
313 VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
314 timeout, intf, nprobes, nclaims);
315 switch (poll(fds, 1, timeout)) {
316
317 // timeout
318 case 0:
319 VDBG("state = %d\n", state);
320 switch (state) {
321 case PROBE:
322 // timeouts in the PROBE state mean no conflicting ARP packets
323 // have been received, so we can progress through the states
324 if (nprobes < PROBE_NUM) {
325 nprobes++;
326 VDBG("probe/%d %s@%s\n",
327 nprobes, intf, inet_ntoa(ip));
328 arp(fd, &saddr, ARPOP_REQUEST,
329 &eth_addr, null_ip,
330 &null_addr, ip);
331 timeout = PROBE_MIN * 1000;
332 timeout += ms_rdelay(PROBE_MAX
333 - PROBE_MIN);
334 }
335 else {
336 // Switch to announce state.
337 state = ANNOUNCE;
338 nclaims = 0;
339 VDBG("announce/%d %s@%s\n",
340 nclaims, intf, inet_ntoa(ip));
341 arp(fd, &saddr, ARPOP_REQUEST,
342 &eth_addr, ip,
343 &eth_addr, ip);
344 timeout = ANNOUNCE_INTERVAL * 1000;
345 }
346 break;
347 case RATE_LIMIT_PROBE:
348 // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
349 // have been received, so we can move immediately to the announce state
350 state = ANNOUNCE;
351 nclaims = 0;
352 VDBG("announce/%d %s@%s\n",
353 nclaims, intf, inet_ntoa(ip));
354 arp(fd, &saddr, ARPOP_REQUEST,
355 &eth_addr, ip,
356 &eth_addr, ip);
357 timeout = ANNOUNCE_INTERVAL * 1000;
358 break;
359 case ANNOUNCE:
360 // timeouts in the ANNOUNCE state mean no conflicting ARP packets
361 // have been received, so we can progress through the states
362 if (nclaims < ANNOUNCE_NUM) {
363 nclaims++;
364 VDBG("announce/%d %s@%s\n",
365 nclaims, intf, inet_ntoa(ip));
366 arp(fd, &saddr, ARPOP_REQUEST,
367 &eth_addr, ip,
368 &eth_addr, ip);
369 timeout = ANNOUNCE_INTERVAL * 1000;
370 }
371 else {
372 // Switch to monitor state.
373 state = MONITOR;
374 // link is ok to use earlier
375 // FIXME update filters
376 run(script, "config", intf, &ip);
377 ready = 1;
378 conflicts = 0;
379 timeout = -1; // Never timeout in the monitor state.
380
381 // NOTE: all other exit paths
382 // should deconfig ...
383 if (QUIT)
384 return EXIT_SUCCESS;
385 }
386 break;
387 case DEFEND:
388 // We won! No ARP replies, so just go back to monitor.
389 state = MONITOR;
390 timeout = -1;
391 conflicts = 0;
392 break;
393 default:
394 // Invalid, should never happen. Restart the whole protocol.
395 state = PROBE;
396 pick(&ip);
397 timeout = 0;
398 nprobes = 0;
399 nclaims = 0;
400 break;
401 } // switch (state)
402 break; // case 0 (timeout)
403 // packets arriving
404 case 1:
405 // We need to adjust the timeout in case we didn't receive
406 // a conflicting packet.
407 if (timeout > 0) {
408 struct timeval tv2;
409
410 gettimeofday(&tv2, NULL);
411 if (timercmp(&tv1, &tv2, <)) {
412 // Current time is greater than the expected timeout time.
413 // Should never happen.
414 VDBG("missed an expected timeout\n");
415 timeout = 0;
416 } else {
417 VDBG("adjusting timeout\n");
418 timersub(&tv1, &tv2, &tv1);
419 timeout = 1000 * tv1.tv_sec
420 + tv1.tv_usec / 1000;
421 }
422 }
423
424 if ((fds[0].revents & POLLIN) == 0) {
425 if (fds[0].revents & POLLERR) {
426 // FIXME: links routinely go down;
427 // this shouldn't necessarily exit.
428 bb_error_msg("%s: poll error", intf);
429 if (ready) {
430 run(script, "deconfig",
431 intf, &ip);
432 }
433 return EXIT_FAILURE;
434 }
435 continue;
436 }
437
438 // read ARP packet
439 if (recv(fd, &p, sizeof (p), 0) < 0) {
440 why = "recv";
441 goto bad;
442 }
443 if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
444 continue;
445
446#ifdef DEBUG
447 {
448 struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
449 struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
450 struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
451 struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
452 VDBG("%s recv arp type=%d, op=%d,\n",
453 intf, ntohs(p.hdr.ether_type),
454 ntohs(p.arp.arp_op));
455 VDBG("\tsource=%s %s\n",
456 ether_ntoa(sha),
457 inet_ntoa(*spa));
458 VDBG("\ttarget=%s %s\n",
459 ether_ntoa(tha),
460 inet_ntoa(*tpa));
461 }
462#endif
463 if (p.arp.arp_op != htons(ARPOP_REQUEST)
464 && p.arp.arp_op != htons(ARPOP_REPLY))
465 continue;
466
467 if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
468 memcmp(&eth_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
469 source_ip_conflict = 1;
470 }
471 if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
472 p.arp.arp_op == htons(ARPOP_REQUEST) &&
473 memcmp(&eth_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
474 target_ip_conflict = 1;
475 }
476
477 VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
478 state, source_ip_conflict, target_ip_conflict);
479 switch (state) {
480 case PROBE:
481 case ANNOUNCE:
482 // When probing or announcing, check for source IP conflicts
483 // and other hosts doing ARP probes (target IP conflicts).
484 if (source_ip_conflict || target_ip_conflict) {
485 conflicts++;
486 if (conflicts >= MAX_CONFLICTS) {
487 VDBG("%s ratelimit\n", intf);
488 timeout = RATE_LIMIT_INTERVAL * 1000;
489 state = RATE_LIMIT_PROBE;
490 }
491
492 // restart the whole protocol
493 pick(&ip);
494 timeout = 0;
495 nprobes = 0;
496 nclaims = 0;
497 }
498 break;
499 case MONITOR:
500 // If a conflict, we try to defend with a single ARP probe.
501 if (source_ip_conflict) {
502 VDBG("monitor conflict -- defending\n");
503 state = DEFEND;
504 timeout = DEFEND_INTERVAL * 1000;
505 arp(fd, &saddr,
506 ARPOP_REQUEST,
507 &eth_addr, ip,
508 &eth_addr, ip);
509 }
510 break;
511 case DEFEND:
512 // Well, we tried. Start over (on conflict).
513 if (source_ip_conflict) {
514 state = PROBE;
515 VDBG("defend conflict -- starting over\n");
516 ready = 0;
517 run(script, "deconfig", intf, &ip);
518
519 // restart the whole protocol
520 pick(&ip);
521 timeout = 0;
522 nprobes = 0;
523 nclaims = 0;
524 }
525 break;
526 default:
527 // Invalid, should never happen. Restart the whole protocol.
528 VDBG("invalid state -- starting over\n");
529 state = PROBE;
530 pick(&ip);
531 timeout = 0;
532 nprobes = 0;
533 nclaims = 0;
534 break;
535 } // switch state
536
537 break; // case 1 (packets arriving)
538 default:
539 why = "poll";
540 goto bad;
541 } // switch poll
542 }
543bad:
544 bb_perror_msg("%s, %s", intf, why);
545 return EXIT_FAILURE;
546}