1 | /*
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2 | * RFC3927 ZeroConf IPv4 Link-Local addressing
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3 | * (see <http://www.zeroconf.org/>)
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4 | *
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5 | * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
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6 | * Copyright (C) 2004 by David Brownell
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7 | *
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8 | * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
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9 | */
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10 |
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11 | /*
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12 | * ZCIP just manages the 169.254.*.* addresses. That network is not
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13 | * routed at the IP level, though various proxies or bridges can
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14 | * certainly be used. Its naming is built over multicast DNS.
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15 | */
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16 |
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17 | // #define DEBUG
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18 |
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19 | // TODO:
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20 | // - more real-world usage/testing, especially daemon mode
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21 | // - kernel packet filters to reduce scheduling noise
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22 | // - avoid silent script failures, especially under load...
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23 | // - link status monitoring (restart on link-up; stop on link-down)
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24 |
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25 | #include "busybox.h"
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26 | #include <errno.h>
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27 | #include <string.h>
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28 | #include <syslog.h>
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29 | #include <poll.h>
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30 | #include <time.h>
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31 |
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32 | #include <sys/wait.h>
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33 |
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34 | #include <netinet/ether.h>
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35 | #include <net/ethernet.h>
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36 | #include <net/if.h>
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37 | #include <net/if_arp.h>
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38 |
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39 | #include <linux/if_packet.h>
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40 | #include <linux/sockios.h>
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41 |
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42 |
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43 | struct arp_packet {
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44 | struct ether_header hdr;
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45 | // FIXME this part is netinet/if_ether.h "struct ether_arp"
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46 | struct arphdr arp;
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47 | struct ether_addr source_addr;
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48 | struct in_addr source_ip;
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49 | struct ether_addr target_addr;
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50 | struct in_addr target_ip;
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51 | } ATTRIBUTE_PACKED;
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52 |
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53 | enum {
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54 | /* 169.254.0.0 */
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55 | LINKLOCAL_ADDR = 0xa9fe0000,
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56 |
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57 | /* protocol timeout parameters, specified in seconds */
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58 | PROBE_WAIT = 1,
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59 | PROBE_MIN = 1,
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60 | PROBE_MAX = 2,
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61 | PROBE_NUM = 3,
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62 | MAX_CONFLICTS = 10,
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63 | RATE_LIMIT_INTERVAL = 60,
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64 | ANNOUNCE_WAIT = 2,
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65 | ANNOUNCE_NUM = 2,
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66 | ANNOUNCE_INTERVAL = 2,
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67 | DEFEND_INTERVAL = 10
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68 | };
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69 |
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70 | static const struct in_addr null_ip = { 0 };
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71 | static const struct ether_addr null_addr = { {0, 0, 0, 0, 0, 0} };
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72 |
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73 | static int verbose = 0;
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74 |
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75 | #define DBG(fmt,args...) \
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76 | do { } while (0)
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77 | #define VDBG DBG
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78 |
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79 | /**
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80 | * Pick a random link local IP address on 169.254/16, except that
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81 | * the first and last 256 addresses are reserved.
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82 | */
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83 | static void pick(struct in_addr *ip)
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84 | {
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85 | unsigned tmp;
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86 |
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87 | /* use cheaper math than lrand48() mod N */
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88 | do {
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89 | tmp = (lrand48() >> 16) & IN_CLASSB_HOST;
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90 | } while (tmp > (IN_CLASSB_HOST - 0x0200));
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91 | ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
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92 | }
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93 |
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94 | /**
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95 | * Broadcast an ARP packet.
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96 | */
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97 | static int arp(int fd, struct sockaddr *saddr, int op,
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98 | const struct ether_addr *source_addr, struct in_addr source_ip,
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99 | const struct ether_addr *target_addr, struct in_addr target_ip)
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100 | {
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101 | struct arp_packet p;
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102 |
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103 | // ether header
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104 | p.hdr.ether_type = htons(ETHERTYPE_ARP);
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105 | memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
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106 | memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
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107 |
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108 | // arp request
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109 | p.arp.ar_hrd = htons(ARPHRD_ETHER);
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110 | p.arp.ar_pro = htons(ETHERTYPE_IP);
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111 | p.arp.ar_hln = ETH_ALEN;
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112 | p.arp.ar_pln = 4;
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113 | p.arp.ar_op = htons(op);
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114 | memcpy(&p.source_addr, source_addr, ETH_ALEN);
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115 | memcpy(&p.source_ip, &source_ip, sizeof (p.source_ip));
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116 | memcpy(&p.target_addr, target_addr, ETH_ALEN);
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117 | memcpy(&p.target_ip, &target_ip, sizeof (p.target_ip));
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118 |
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119 | // send it
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120 | if (sendto(fd, &p, sizeof (p), 0, saddr, sizeof (*saddr)) < 0) {
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121 | perror("sendto");
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122 | return -errno;
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123 | }
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124 | return 0;
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125 | }
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126 |
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127 | /**
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128 | * Run a script.
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129 | */
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130 | static int run(char *script, char *arg, char *intf, struct in_addr *ip)
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131 | {
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132 | int pid, status;
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133 | char *why;
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134 |
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135 | if (script != NULL) {
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136 | VDBG("%s run %s %s\n", intf, script, arg);
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137 | if (ip != NULL) {
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138 | char *addr = inet_ntoa(*ip);
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139 | setenv("ip", addr, 1);
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140 | syslog(LOG_INFO, "%s %s %s", arg, intf, addr);
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141 | }
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142 |
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143 | pid = vfork();
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144 | if (pid < 0) { // error
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145 | why = "vfork";
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146 | goto bad;
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147 | } else if (pid == 0) { // child
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148 | execl(script, script, arg, NULL);
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149 | perror("execl");
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150 | _exit(EXIT_FAILURE);
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151 | }
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152 |
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153 | if (waitpid(pid, &status, 0) <= 0) {
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154 | why = "waitpid";
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155 | goto bad;
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156 | }
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157 | if (WEXITSTATUS(status) != 0) {
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158 | bb_error_msg("script %s failed, exit=%d\n",
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159 | script, WEXITSTATUS(status));
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160 | return -errno;
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161 | }
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162 | }
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163 | return 0;
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164 | bad:
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165 | status = -errno;
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166 | syslog(LOG_ERR, "%s %s, %s error: %s",
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167 | arg, intf, why, strerror(errno));
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168 | return status;
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169 | }
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170 |
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171 |
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172 | /**
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173 | * Return milliseconds of random delay, up to "secs" seconds.
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174 | */
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175 | static inline unsigned ms_rdelay(unsigned secs)
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176 | {
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177 | return lrand48() % (secs * 1000);
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178 | }
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179 |
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180 | /**
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181 | * main program
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182 | */
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183 |
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184 | int zcip_main(int argc, char *argv[])
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185 | {
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186 | char *intf = NULL;
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187 | char *script = NULL;
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188 | int quit = 0;
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189 | int foreground = 0;
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190 |
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191 | char *why;
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192 | struct sockaddr saddr;
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193 | struct ether_addr addr;
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194 | struct in_addr ip = { 0 };
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195 | int fd;
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196 | int ready = 0;
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197 | suseconds_t timeout = 0; // milliseconds
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198 | time_t defend = 0;
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199 | unsigned conflicts = 0;
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200 | unsigned nprobes = 0;
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201 | unsigned nclaims = 0;
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202 | int t;
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203 |
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204 | // parse commandline: prog [options] ifname script
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205 | while ((t = getopt(argc, argv, "fqr:v")) != EOF) {
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206 | switch (t) {
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207 | case 'f':
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208 | foreground = 1;
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209 | continue;
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210 | case 'q':
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211 | quit = 1;
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212 | continue;
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213 | case 'r':
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214 | if (inet_aton(optarg, &ip) == 0
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215 | || (ntohl(ip.s_addr) & IN_CLASSB_NET)
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216 | != LINKLOCAL_ADDR) {
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217 | bb_error_msg_and_die("invalid link address");
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218 | }
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219 | continue;
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220 | case 'v':
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221 | verbose++;
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222 | foreground = 1;
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223 | continue;
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224 | default:
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225 | bb_error_msg_and_die("bad option");
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226 | }
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227 | }
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228 | if (optind < argc - 1) {
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229 | intf = argv[optind++];
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230 | setenv("interface", intf, 1);
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231 | script = argv[optind++];
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232 | }
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233 | if (optind != argc || !intf)
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234 | bb_show_usage();
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235 | openlog(bb_applet_name, 0, LOG_DAEMON);
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236 |
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237 | // initialize the interface (modprobe, ifup, etc)
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238 | if (run(script, "init", intf, NULL) < 0)
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239 | return EXIT_FAILURE;
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240 |
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241 | // initialize saddr
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242 | memset(&saddr, 0, sizeof (saddr));
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243 | safe_strncpy(saddr.sa_data, intf, sizeof (saddr.sa_data));
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244 |
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245 | // open an ARP socket
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246 | if ((fd = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP))) < 0) {
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247 | why = "open";
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248 | fail:
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249 | foreground = 1;
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250 | goto bad;
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251 | }
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252 | // bind to the interface's ARP socket
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253 | if (bind(fd, &saddr, sizeof (saddr)) < 0) {
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254 | why = "bind";
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255 | goto fail;
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256 | } else {
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257 | struct ifreq ifr;
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258 | unsigned short seed[3];
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259 |
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260 | // get the interface's ethernet address
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261 | memset(&ifr, 0, sizeof (ifr));
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262 | strncpy(ifr.ifr_name, intf, sizeof (ifr.ifr_name));
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263 | if (ioctl(fd, SIOCGIFHWADDR, &ifr) < 0) {
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264 | why = "get ethernet address";
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265 | goto fail;
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266 | }
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267 | memcpy(&addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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268 |
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269 | // start with some stable ip address, either a function of
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270 | // the hardware address or else the last address we used.
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271 | // NOTE: the sequence of addresses we try changes only
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272 | // depending on when we detect conflicts.
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273 | memcpy(seed, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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274 | seed48(seed);
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275 | if (ip.s_addr == 0)
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276 | pick(&ip);
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277 | }
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278 |
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279 | // FIXME cases to handle:
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280 | // - zcip already running!
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281 | // - link already has local address... just defend/update
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282 |
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283 | // daemonize now; don't delay system startup
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284 | if (!foreground) {
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285 | if (daemon(0, verbose) < 0) {
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286 | why = "daemon";
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287 | goto bad;
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288 | }
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289 | syslog(LOG_INFO, "start, interface %s", intf);
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290 | }
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291 |
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292 | // run the dynamic address negotiation protocol,
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293 | // restarting after address conflicts:
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294 | // - start with some address we want to try
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295 | // - short random delay
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296 | // - arp probes to see if another host else uses it
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297 | // - arp announcements that we're claiming it
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298 | // - use it
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299 | // - defend it, within limits
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300 | while (1) {
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301 | struct pollfd fds[1];
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302 | struct timeval tv1;
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303 | struct arp_packet p;
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304 |
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305 | fds[0].fd = fd;
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306 | fds[0].events = POLLIN;
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307 | fds[0].revents = 0;
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308 |
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309 | // poll, being ready to adjust current timeout
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310 | if (!timeout) {
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311 | timeout = ms_rdelay(PROBE_WAIT);
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312 | // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
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313 | // make the kernel filter out all packets except
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314 | // ones we'd care about.
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315 | }
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316 | gettimeofday(&tv1, NULL);
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317 | tv1.tv_usec += (timeout % 1000) * 1000;
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318 | while (tv1.tv_usec > 1000000) {
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319 | tv1.tv_usec -= 1000000;
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320 | tv1.tv_sec++;
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321 | }
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322 | tv1.tv_sec += timeout / 1000;
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323 |
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324 | VDBG("...wait %ld %s nprobes=%d, nclaims=%d\n",
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325 | timeout, intf, nprobes, nclaims);
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326 | switch (poll(fds, 1, timeout)) {
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327 |
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328 | // timeouts trigger protocol transitions
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329 | case 0:
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330 | // probes
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331 | if (nprobes < PROBE_NUM) {
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332 | nprobes++;
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333 | VDBG("probe/%d %s@%s\n",
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334 | nprobes, intf, inet_ntoa(ip));
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335 | (void)arp(fd, &saddr, ARPOP_REQUEST,
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336 | &addr, null_ip,
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337 | &null_addr, ip);
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338 | if (nprobes < PROBE_NUM) {
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339 | timeout = PROBE_MIN * 1000;
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340 | timeout += ms_rdelay(PROBE_MAX
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341 | - PROBE_MIN);
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342 | } else
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343 | timeout = ANNOUNCE_WAIT * 1000;
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344 | }
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345 | // then announcements
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346 | else if (nclaims < ANNOUNCE_NUM) {
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347 | nclaims++;
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348 | VDBG("announce/%d %s@%s\n",
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349 | nclaims, intf, inet_ntoa(ip));
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350 | (void)arp(fd, &saddr, ARPOP_REQUEST,
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351 | &addr, ip,
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352 | &addr, ip);
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353 | if (nclaims < ANNOUNCE_NUM) {
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354 | timeout = ANNOUNCE_INTERVAL * 1000;
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355 | } else {
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356 | // link is ok to use earlier
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357 | run(script, "config", intf, &ip);
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358 | ready = 1;
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359 | conflicts = 0;
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360 | timeout = -1;
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361 |
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362 | // NOTE: all other exit paths
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363 | // should deconfig ...
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364 | if (quit)
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365 | return EXIT_SUCCESS;
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366 | // FIXME update filters
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367 | }
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368 | }
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369 | break;
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370 |
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371 | // packets arriving
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372 | case 1:
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373 | // maybe adjust timeout
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374 | if (timeout > 0) {
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375 | struct timeval tv2;
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376 |
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377 | gettimeofday(&tv2, NULL);
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378 | if (timercmp(&tv1, &tv2, <)) {
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379 | timeout = 0;
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380 | } else {
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381 | timersub(&tv1, &tv2, &tv1);
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382 | timeout = 1000 * tv1.tv_sec
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383 | + tv1.tv_usec / 1000;
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384 | }
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385 | }
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386 | if ((fds[0].revents & POLLIN) == 0) {
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387 | if (fds[0].revents & POLLERR) {
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388 | // FIXME: links routinely go down;
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389 | // this shouldn't necessarily exit.
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390 | bb_error_msg("%s: poll error\n", intf);
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391 | if (ready) {
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392 | run(script, "deconfig",
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393 | intf, &ip);
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394 | }
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395 | return EXIT_FAILURE;
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396 | }
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397 | continue;
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398 | }
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399 | // read ARP packet
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400 | if (recv(fd, &p, sizeof (p), 0) < 0) {
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401 | why = "recv";
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402 | goto bad;
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403 | }
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404 | if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
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405 | continue;
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406 |
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407 | VDBG("%s recv arp type=%d, op=%d,\n",
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408 | intf, ntohs(p.hdr.ether_type),
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409 | ntohs(p.arp.ar_op));
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410 | VDBG("\tsource=%s %s\n",
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411 | ether_ntoa(&p.source_addr),
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412 | inet_ntoa(p.source_ip));
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413 | VDBG("\ttarget=%s %s\n",
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414 | ether_ntoa(&p.target_addr),
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415 | inet_ntoa(p.target_ip));
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416 | if (p.arp.ar_op != htons(ARPOP_REQUEST)
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417 | && p.arp.ar_op != htons(ARPOP_REPLY))
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418 | continue;
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419 |
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420 | // some cases are always conflicts
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421 | if ((p.source_ip.s_addr == ip.s_addr)
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422 | && (memcmp(&addr, &p.source_addr,
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423 | ETH_ALEN) != 0)) {
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424 | collision:
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425 | VDBG("%s ARP conflict from %s\n", intf,
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426 | ether_ntoa(&p.source_addr));
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427 | if (ready) {
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428 | time_t now = time(0);
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429 |
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430 | if ((defend + DEFEND_INTERVAL)
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431 | < now) {
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432 | defend = now;
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433 | (void)arp(fd, &saddr,
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434 | ARPOP_REQUEST,
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435 | &addr, ip,
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436 | &addr, ip);
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437 | VDBG("%s defend\n", intf);
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438 | timeout = -1;
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439 | continue;
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440 | }
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441 | defend = now;
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442 | ready = 0;
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443 | run(script, "deconfig", intf, &ip);
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444 | // FIXME rm filters: setsockopt(fd,
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445 | // SO_DETACH_FILTER, ...)
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446 | }
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447 | conflicts++;
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448 | if (conflicts >= MAX_CONFLICTS) {
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449 | VDBG("%s ratelimit\n", intf);
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450 | sleep(RATE_LIMIT_INTERVAL);
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451 | }
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452 | // restart the whole protocol
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453 | pick(&ip);
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454 | timeout = 0;
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455 | nprobes = 0;
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456 | nclaims = 0;
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457 | }
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458 | // two hosts probing one address is a collision too
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459 | else if (p.target_ip.s_addr == ip.s_addr
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460 | && nclaims == 0
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461 | && p.arp.ar_op == htons(ARPOP_REQUEST)
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462 | && memcmp(&addr, &p.target_addr,
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463 | ETH_ALEN) != 0) {
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464 | goto collision;
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465 | }
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466 | break;
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467 |
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468 | default:
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469 | why = "poll";
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470 | goto bad;
|
---|
471 | }
|
---|
472 | }
|
---|
473 | bad:
|
---|
474 | if (foreground)
|
---|
475 | perror(why);
|
---|
476 | else
|
---|
477 | syslog(LOG_ERR, "%s %s, %s error: %s",
|
---|
478 | bb_applet_name, intf, why, strerror(errno));
|
---|
479 | return EXIT_FAILURE;
|
---|
480 | }
|
---|