/* vi: set sw=4 ts=4: */ /* * RFC3927 ZeroConf IPv4 Link-Local addressing * (see ) * * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com) * Copyright (C) 2004 by David Brownell * * Licensed under the GPL v2 or later, see the file LICENSE in this tarball. */ /* * ZCIP just manages the 169.254.*.* addresses. That network is not * routed at the IP level, though various proxies or bridges can * certainly be used. Its naming is built over multicast DNS. */ //#define DEBUG // TODO: // - more real-world usage/testing, especially daemon mode // - kernel packet filters to reduce scheduling noise // - avoid silent script failures, especially under load... // - link status monitoring (restart on link-up; stop on link-down) #include "busybox.h" #include #include #include #include #include #include #include #include #include #include #include #include struct arp_packet { struct ether_header hdr; struct ether_arp arp; } ATTRIBUTE_PACKED; enum { /* 169.254.0.0 */ LINKLOCAL_ADDR = 0xa9fe0000, /* protocol timeout parameters, specified in seconds */ PROBE_WAIT = 1, PROBE_MIN = 1, PROBE_MAX = 2, PROBE_NUM = 3, MAX_CONFLICTS = 10, RATE_LIMIT_INTERVAL = 60, ANNOUNCE_WAIT = 2, ANNOUNCE_NUM = 2, ANNOUNCE_INTERVAL = 2, DEFEND_INTERVAL = 10 }; /* States during the configuration process. */ enum { PROBE = 0, RATE_LIMIT_PROBE, ANNOUNCE, MONITOR, DEFEND }; /* Implicitly zero-initialized */ static const struct in_addr null_ip; static const struct ether_addr null_addr; static int verbose; #define DBG(fmt,args...) \ do { } while (0) #define VDBG DBG /** * Pick a random link local IP address on 169.254/16, except that * the first and last 256 addresses are reserved. */ static void pick(struct in_addr *ip) { unsigned tmp; /* use cheaper math than lrand48() mod N */ do { tmp = (lrand48() >> 16) & IN_CLASSB_HOST; } while (tmp > (IN_CLASSB_HOST - 0x0200)); ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp); } /** * Broadcast an ARP packet. */ static int arp(int fd, struct sockaddr *saddr, int op, const struct ether_addr *source_addr, struct in_addr source_ip, const struct ether_addr *target_addr, struct in_addr target_ip) { struct arp_packet p; memset(&p, 0, sizeof(p)); // ether header p.hdr.ether_type = htons(ETHERTYPE_ARP); memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN); memset(p.hdr.ether_dhost, 0xff, ETH_ALEN); // arp request p.arp.arp_hrd = htons(ARPHRD_ETHER); p.arp.arp_pro = htons(ETHERTYPE_IP); p.arp.arp_hln = ETH_ALEN; p.arp.arp_pln = 4; p.arp.arp_op = htons(op); memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN); memcpy(&p.arp.arp_spa, &source_ip, sizeof (p.arp.arp_spa)); memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN); memcpy(&p.arp.arp_tpa, &target_ip, sizeof (p.arp.arp_tpa)); // send it if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) { perror("sendto"); return -errno; } return 0; } /** * Run a script. */ static int run(char *script, char *arg, char *intf, struct in_addr *ip) { int pid, status; char *why; if (script != NULL) { VDBG("%s run %s %s\n", intf, script, arg); if (ip != NULL) { char *addr = inet_ntoa(*ip); setenv("ip", addr, 1); syslog(LOG_INFO, "%s %s %s", arg, intf, addr); } pid = vfork(); if (pid < 0) { // error why = "vfork"; goto bad; } else if (pid == 0) { // child execl(script, script, arg, NULL); perror("execl"); _exit(EXIT_FAILURE); } if (waitpid(pid, &status, 0) <= 0) { why = "waitpid"; goto bad; } if (WEXITSTATUS(status) != 0) { bb_error_msg("script %s failed, exit=%d\n", script, WEXITSTATUS(status)); return -errno; } } return 0; bad: status = -errno; syslog(LOG_ERR, "%s %s, %s error: %s", arg, intf, why, strerror(errno)); return status; } /** * Return milliseconds of random delay, up to "secs" seconds. */ static unsigned ATTRIBUTE_ALWAYS_INLINE ms_rdelay(unsigned secs) { return lrand48() % (secs * 1000); } /** * main program */ int zcip_main(int argc, char *argv[]) { char *intf = NULL; char *script = NULL; int quit = 0; int foreground = 0; char *why; struct sockaddr saddr; struct ether_addr addr; struct in_addr ip = { 0 }; int fd; int ready = 0; suseconds_t timeout = 0; // milliseconds unsigned conflicts = 0; unsigned nprobes = 0; unsigned nclaims = 0; int t; int state = PROBE; // parse commandline: prog [options] ifname script while ((t = getopt(argc, argv, "fqr:v")) != EOF) { switch (t) { case 'f': foreground = 1; continue; case 'q': quit = 1; continue; case 'r': if (inet_aton(optarg, &ip) == 0 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR) { bb_error_msg_and_die("invalid link address"); } continue; case 'v': verbose++; foreground = 1; continue; default: bb_error_msg_and_die("bad option"); } } if (optind < argc - 1) { intf = argv[optind++]; setenv("interface", intf, 1); script = argv[optind++]; } if (optind != argc || !intf) bb_show_usage(); openlog(bb_applet_name, 0, LOG_DAEMON); // initialize the interface (modprobe, ifup, etc) if (run(script, "init", intf, NULL) < 0) return EXIT_FAILURE; // initialize saddr memset(&saddr, 0, sizeof (saddr)); safe_strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data)); // open an ARP socket if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) { why = "open"; fail: foreground = 1; goto bad; } // bind to the interface's ARP socket if (bind(fd, &saddr, sizeof (saddr)) < 0) { why = "bind"; goto fail; } else { struct ifreq ifr; unsigned short seed[3]; // get the interface's ethernet address memset(&ifr, 0, sizeof (ifr)); strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name)); if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) { why = "get ethernet address"; goto fail; } memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN); // start with some stable ip address, either a function of // the hardware address or else the last address we used. // NOTE: the sequence of addresses we try changes only // depending on when we detect conflicts. memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN); seed48(seed); if (ip.s_addr == 0) pick(&ip); } // FIXME cases to handle: // - zcip already running! // - link already has local address... just defend/update // daemonize now; don't delay system startup if (!foreground) { xdaemon(0, verbose); syslog(LOG_INFO, "start, interface %s", intf); } // run the dynamic address negotiation protocol, // restarting after address conflicts: // - start with some address we want to try // - short random delay // - arp probes to see if another host else uses it // - arp announcements that we're claiming it // - use it // - defend it, within limits while (1) { struct pollfd fds[1]; struct timeval tv1; struct arp_packet p; fds[0].fd = fd; fds[0].events = POLLIN; fds[0].revents = 0; int source_ip_conflict = 0; int target_ip_conflict = 0; // poll, being ready to adjust current timeout if (!timeout) { timeout = ms_rdelay(PROBE_WAIT); // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to // make the kernel filter out all packets except // ones we'd care about. } // set tv1 to the point in time when we timeout gettimeofday(&tv1, NULL); tv1.tv_usec += (timeout % 1000) * 1000; while (tv1.tv_usec > 1000000) { tv1.tv_usec -= 1000000; tv1.tv_sec++; } tv1.tv_sec += timeout / 1000; VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n", timeout, intf, nprobes, nclaims); switch (poll(fds, 1, timeout)) { // timeout case 0: VDBG("state = %d\n", state); switch (state) { case PROBE: // timeouts in the PROBE state means no conflicting ARP packets // have been received, so we can progress through the states if (nprobes < PROBE_NUM) { nprobes++; VDBG("probe/%d %s@%s\n", nprobes, intf, inet_ntoa(ip)); (void)arp(fd, &saddr, ARPOP_REQUEST, &addr, null_ip, &null_addr, ip); timeout = PROBE_MIN * 1000; timeout += ms_rdelay(PROBE_MAX - PROBE_MIN); } else { // Switch to announce state. state = ANNOUNCE; nclaims = 0; VDBG("announce/%d %s@%s\n", nclaims, intf, inet_ntoa(ip)); (void)arp(fd, &saddr, ARPOP_REQUEST, &addr, ip, &addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; } break; case RATE_LIMIT_PROBE: // timeouts in the RATE_LIMIT_PROBE state means no conflicting ARP packets // have been received, so we can move immediately to the announce state state = ANNOUNCE; nclaims = 0; VDBG("announce/%d %s@%s\n", nclaims, intf, inet_ntoa(ip)); (void)arp(fd, &saddr, ARPOP_REQUEST, &addr, ip, &addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; break; case ANNOUNCE: // timeouts in the ANNOUNCE state means no conflicting ARP packets // have been received, so we can progress through the states if (nclaims < ANNOUNCE_NUM) { nclaims++; VDBG("announce/%d %s@%s\n", nclaims, intf, inet_ntoa(ip)); (void)arp(fd, &saddr, ARPOP_REQUEST, &addr, ip, &addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; } else { // Switch to monitor state. state = MONITOR; // link is ok to use earlier // FIXME update filters run(script, "config", intf, &ip); ready = 1; conflicts = 0; timeout = -1; // Never timeout in the monitor state. // NOTE: all other exit paths // should deconfig ... if (quit) return EXIT_SUCCESS; } break; case DEFEND: // We won! No ARP replies, so just go back to monitor. state = MONITOR; timeout = -1; conflicts = 0; break; default: // Invalid, should never happen. Restart the whole protocol. state = PROBE; pick(&ip); timeout = 0; nprobes = 0; nclaims = 0; break; } // switch (state) break; // case 0 (timeout) // packets arriving case 1: // We need to adjust the timeout in case we didn't receive // a conflicting packet. if (timeout > 0) { struct timeval tv2; gettimeofday(&tv2, NULL); if (timercmp(&tv1, &tv2, <)) { // Current time is greater than the expected timeout time. // Should never happen. VDBG("missed an expected timeout\n"); timeout = 0; } else { VDBG("adjusting timeout\n"); timersub(&tv1, &tv2, &tv1); timeout = 1000 * tv1.tv_sec + tv1.tv_usec / 1000; } } if ((fds[0].revents & POLLIN) == 0) { if (fds[0].revents & POLLERR) { // FIXME: links routinely go down; // this shouldn't necessarily exit. bb_error_msg("%s: poll error\n", intf); if (ready) { run(script, "deconfig", intf, &ip); } return EXIT_FAILURE; } continue; } // read ARP packet if (recv(fd, &p, sizeof (p), 0) < 0) { why = "recv"; goto bad; } if (p.hdr.ether_type != htons(ETHERTYPE_ARP)) continue; #ifdef DEBUG { struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha; struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha; struct in_addr * spa = (struct in_addr *) p.arp.arp_spa; struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa; VDBG("%s recv arp type=%d, op=%d,\n", intf, ntohs(p.hdr.ether_type), ntohs(p.arp.arp_op)); VDBG("\tsource=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa)); VDBG("\ttarget=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa)); } #endif if (p.arp.arp_op != htons(ARPOP_REQUEST) && p.arp.arp_op != htons(ARPOP_REPLY)) continue; if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 && memcmp(&addr, &p.arp.arp_sha, ETH_ALEN) != 0) { source_ip_conflict = 1; } if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 && p.arp.arp_op == htons(ARPOP_REQUEST) && memcmp(&addr, &p.arp.arp_tha, ETH_ALEN) != 0) { target_ip_conflict = 1; } VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n", state, source_ip_conflict, target_ip_conflict); switch (state) { case PROBE: case ANNOUNCE: // When probing or announcing, check for source IP conflicts // and other hosts doing ARP probes (target IP conflicts). if (source_ip_conflict || target_ip_conflict) { conflicts++; if (conflicts >= MAX_CONFLICTS) { VDBG("%s ratelimit\n", intf); timeout = RATE_LIMIT_INTERVAL * 1000; state = RATE_LIMIT_PROBE; } // restart the whole protocol pick(&ip); timeout = 0; nprobes = 0; nclaims = 0; } break; case MONITOR: // If a conflict, we try to defend with a single ARP probe. if (source_ip_conflict) { VDBG("monitor conflict -- defending\n"); state = DEFEND; timeout = DEFEND_INTERVAL * 1000; (void)arp(fd, &saddr, ARPOP_REQUEST, &addr, ip, &addr, ip); } break; case DEFEND: // Well, we tried. Start over (on conflict). if (source_ip_conflict) { state = PROBE; VDBG("defend conflict -- starting over\n"); ready = 0; run(script, "deconfig", intf, &ip); // restart the whole protocol pick(&ip); timeout = 0; nprobes = 0; nclaims = 0; } break; default: // Invalid, should never happen. Restart the whole protocol. VDBG("invalid state -- starting over\n"); state = PROBE; pick(&ip); timeout = 0; nprobes = 0; nclaims = 0; break; } // switch state break; // case 1 (packets arriving) default: why = "poll"; goto bad; } // switch poll } bad: if (foreground) perror(why); else syslog(LOG_ERR, "%s %s, %s error: %s", bb_applet_name, intf, why, strerror(errno)); return EXIT_FAILURE; }