/* 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 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 }; #define VDBG(fmt,args...) \ do { } while (0) /** * 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); } /* TODO: we need a flag to direct bb_[p]error_msg output to stderr. */ /** * Broadcast an ARP packet. */ static void 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) { bb_perror_msg("sendto"); //return -errno; } // Currently all callers ignore errors, that's why returns are // commented out... //return 0; } /** * Run a script. argv[2] is already NULL. */ static int run(char *argv[3], const char *intf, struct in_addr *ip) { int status; VDBG("%s run %s %s\n", intf, argv[0], argv[1]); if (ip) { char *addr = inet_ntoa(*ip); setenv("ip", addr, 1); bb_info_msg("%s %s %s", argv[1], intf, addr); } status = wait4pid(spawn(argv)); if (status < 0) { bb_perror_msg("%s %s", argv[1], intf); return -errno; } if (status != 0) bb_error_msg("script %s %s failed, exitcode=%d", argv[0], argv[1], status); 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); int zcip_main(int argc, char **argv) { int state = PROBE; struct ether_addr eth_addr; const char *why; int fd; char *r_opt; unsigned opts; /* Ugly trick, but I want these zeroed in one go */ struct { const struct in_addr null_ip; const struct ether_addr null_addr; struct sockaddr saddr; struct in_addr ip; struct ifreq ifr; char *intf; char *script_av[3]; suseconds_t timeout; // milliseconds unsigned conflicts; unsigned nprobes; unsigned nclaims; int ready; int verbose; } L; #define null_ip (L.null_ip ) #define null_addr (L.null_addr) #define saddr (L.saddr ) #define ip (L.ip ) #define ifr (L.ifr ) #define intf (L.intf ) #define script_av (L.script_av) #define timeout (L.timeout ) #define conflicts (L.conflicts) #define nprobes (L.nprobes ) #define nclaims (L.nclaims ) #define ready (L.ready ) #define verbose (L.verbose ) memset(&L, 0, sizeof(L)); #define FOREGROUND (opts & 1) #define QUIT (opts & 2) // parse commandline: prog [options] ifname script // exactly 2 args; -v accumulates and implies -f opt_complementary = "=2:vv:vf"; opts = getopt32(argc, argv, "fqr:v", &r_opt, &verbose); if (!FOREGROUND) { /* Do it early, before all bb_xx_msg calls */ openlog(applet_name, 0, LOG_DAEMON); logmode |= LOGMODE_SYSLOG; } if (opts & 4) { // -r n.n.n.n if (inet_aton(r_opt, &ip) == 0 || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR ) { bb_error_msg_and_die("invalid link address"); } } // On NOMMU reexec early (or else we will rerun things twice) #if !BB_MMU if (!FOREGROUND) bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv); #endif argc -= optind; argv += optind; intf = argv[0]; script_av[0] = argv[1]; setenv("interface", intf, 1); // initialize the interface (modprobe, ifup, etc) script_av[1] = (char*)"init"; if (run(script_av, intf, NULL)) return EXIT_FAILURE; // initialize saddr //memset(&saddr, 0, sizeof(saddr)); safe_strncpy(saddr.sa_data, intf, sizeof(saddr.sa_data)); // open an ARP socket fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)); // bind to the interface's ARP socket xbind(fd, &saddr, sizeof(saddr)); // 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) { bb_perror_msg_and_die("get ethernet address"); } memcpy(ð_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. // (SVID 3 bogon: who says that "short" is always 16 bits?) seed48( (unsigned short*)&ifr.ifr_hwaddr.sa_data ); 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) { #if BB_MMU bb_daemonize(DAEMON_CHDIR_ROOT); #endif bb_info_msg("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; int source_ip_conflict = 0; int target_ip_conflict = 0; fds[0].fd = fd; fds[0].events = POLLIN; fds[0].revents = 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 mean 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)); arp(fd, &saddr, ARPOP_REQUEST, ð_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)); arp(fd, &saddr, ARPOP_REQUEST, ð_addr, ip, ð_addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; } break; case RATE_LIMIT_PROBE: // timeouts in the RATE_LIMIT_PROBE state mean 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)); arp(fd, &saddr, ARPOP_REQUEST, ð_addr, ip, ð_addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; break; case ANNOUNCE: // timeouts in the ANNOUNCE state mean 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)); arp(fd, &saddr, ARPOP_REQUEST, ð_addr, ip, ð_addr, ip); timeout = ANNOUNCE_INTERVAL * 1000; } else { // Switch to monitor state. state = MONITOR; // link is ok to use earlier // FIXME update filters script_av[1] = (char*)"config"; run(script_av, 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", intf); if (ready) { script_av[1] = (char*)"deconfig"; run(script_av, 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(ð_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(ð_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; arp(fd, &saddr, ARPOP_REQUEST, ð_addr, ip, ð_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; script_av[1] = (char*)"deconfig"; run(script_av, 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: bb_perror_msg("%s, %s", intf, why); return EXIT_FAILURE; }