1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * RFC3927 ZeroConf IPv4 Link-Local addressing
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4 | * (see <http://www.zeroconf.org/>)
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5 | *
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6 | * Copyright (C) 2003 by Arthur van Hoff (avh@strangeberry.com)
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7 | * Copyright (C) 2004 by David Brownell
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8 | *
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9 | * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
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10 | */
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11 |
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12 | /*
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13 | * ZCIP just manages the 169.254.*.* addresses. That network is not
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14 | * routed at the IP level, though various proxies or bridges can
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15 | * certainly be used. Its naming is built over multicast DNS.
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16 | */
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17 |
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18 | //#define DEBUG
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19 |
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20 | // TODO:
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21 | // - more real-world usage/testing, especially daemon mode
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22 | // - kernel packet filters to reduce scheduling noise
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23 | // - avoid silent script failures, especially under load...
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24 | // - link status monitoring (restart on link-up; stop on link-down)
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25 |
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26 | #include <syslog.h>
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27 | #include <poll.h>
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28 | #include <sys/wait.h>
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29 | #include <netinet/ether.h>
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30 | #include <net/ethernet.h>
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31 | #include <net/if.h>
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32 | #include <net/if_arp.h>
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33 | #include <linux/if_packet.h>
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34 | #include <linux/sockios.h>
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35 |
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36 | #include "libbb.h"
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37 |
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38 | /* We don't need more than 32 bits of the counter */
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39 | #define MONOTONIC_US() ((unsigned)monotonic_us())
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40 |
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41 | struct arp_packet {
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42 | struct ether_header hdr;
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43 | struct ether_arp arp;
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44 | } ATTRIBUTE_PACKED;
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45 |
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46 | enum {
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47 | /* 169.254.0.0 */
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48 | LINKLOCAL_ADDR = 0xa9fe0000,
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49 |
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50 | /* protocol timeout parameters, specified in seconds */
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51 | PROBE_WAIT = 1,
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52 | PROBE_MIN = 1,
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53 | PROBE_MAX = 2,
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54 | PROBE_NUM = 3,
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55 | MAX_CONFLICTS = 10,
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56 | RATE_LIMIT_INTERVAL = 60,
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57 | ANNOUNCE_WAIT = 2,
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58 | ANNOUNCE_NUM = 2,
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59 | ANNOUNCE_INTERVAL = 2,
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60 | DEFEND_INTERVAL = 10
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61 | };
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62 |
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63 | /* States during the configuration process. */
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64 | enum {
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65 | PROBE = 0,
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66 | RATE_LIMIT_PROBE,
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67 | ANNOUNCE,
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68 | MONITOR,
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69 | DEFEND
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70 | };
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71 |
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72 | #define VDBG(fmt,args...) \
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73 | do { } while (0)
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74 |
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75 | /**
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76 | * Pick a random link local IP address on 169.254/16, except that
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77 | * the first and last 256 addresses are reserved.
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78 | */
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79 | static void pick(struct in_addr *ip)
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80 | {
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81 | unsigned tmp;
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82 |
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83 | do {
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84 | tmp = rand() & IN_CLASSB_HOST;
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85 | } while (tmp > (IN_CLASSB_HOST - 0x0200));
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86 | ip->s_addr = htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
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87 | }
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88 |
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89 | /**
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90 | * Broadcast an ARP packet.
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91 | */
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92 | static void arp(int fd, struct sockaddr *saddr, int op,
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93 | const struct ether_addr *source_addr, struct in_addr source_ip,
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94 | const struct ether_addr *target_addr, struct in_addr target_ip)
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95 | {
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96 | struct arp_packet p;
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97 | memset(&p, 0, sizeof(p));
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98 |
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99 | // ether header
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100 | p.hdr.ether_type = htons(ETHERTYPE_ARP);
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101 | memcpy(p.hdr.ether_shost, source_addr, ETH_ALEN);
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102 | memset(p.hdr.ether_dhost, 0xff, ETH_ALEN);
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103 |
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104 | // arp request
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105 | p.arp.arp_hrd = htons(ARPHRD_ETHER);
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106 | p.arp.arp_pro = htons(ETHERTYPE_IP);
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107 | p.arp.arp_hln = ETH_ALEN;
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108 | p.arp.arp_pln = 4;
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109 | p.arp.arp_op = htons(op);
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110 | memcpy(&p.arp.arp_sha, source_addr, ETH_ALEN);
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111 | memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
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112 | memcpy(&p.arp.arp_tha, target_addr, ETH_ALEN);
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113 | memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
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114 |
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115 | // send it
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116 | xsendto(fd, &p, sizeof(p), saddr, sizeof(*saddr));
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117 |
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118 | // Currently all callers ignore errors, that's why returns are
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119 | // commented out...
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120 | //return 0;
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121 | }
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122 |
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123 | /**
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124 | * Run a script. argv[2] is already NULL.
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125 | */
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126 | static int run(char *argv[3], const char *intf, struct in_addr *ip)
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127 | {
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128 | int status;
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129 |
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130 | VDBG("%s run %s %s\n", intf, argv[0], argv[1]);
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131 |
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132 | if (ip) {
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133 | char *addr = inet_ntoa(*ip);
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134 | setenv("ip", addr, 1);
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135 | bb_info_msg("%s %s %s", argv[1], intf, addr);
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136 | }
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137 |
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138 | status = wait4pid(spawn(argv));
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139 | if (status < 0) {
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140 | bb_perror_msg("%s %s", argv[1], intf);
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141 | return -errno;
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142 | }
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143 | if (status != 0)
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144 | bb_error_msg("script %s %s failed, exitcode=%d", argv[0], argv[1], status);
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145 | return status;
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146 | }
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147 |
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148 | /**
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149 | * Return milliseconds of random delay, up to "secs" seconds.
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150 | */
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151 | static unsigned ALWAYS_INLINE ms_rdelay(unsigned secs)
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152 | {
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153 | return rand() % (secs * 1000);
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154 | }
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155 |
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156 | /**
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157 | * main program
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158 | */
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159 | int zcip_main(int argc, char **argv);
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160 | int zcip_main(int argc, char **argv)
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161 | {
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162 | int state = PROBE;
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163 | struct ether_addr eth_addr;
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164 | const char *why;
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165 | int fd;
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166 | char *r_opt;
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167 | unsigned opts;
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168 |
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169 | /* Ugly trick, but I want these zeroed in one go */
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170 | struct {
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171 | const struct in_addr null_ip;
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172 | const struct ether_addr null_addr;
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173 | struct sockaddr saddr;
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174 | struct in_addr ip;
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175 | struct ifreq ifr;
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176 | char *intf;
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177 | char *script_av[3];
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178 | int timeout_ms; /* must be signed */
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179 | unsigned conflicts;
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180 | unsigned nprobes;
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181 | unsigned nclaims;
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182 | int ready;
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183 | int verbose;
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184 | } L;
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185 | #define null_ip (L.null_ip )
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186 | #define null_addr (L.null_addr )
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187 | #define saddr (L.saddr )
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188 | #define ip (L.ip )
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189 | #define ifr (L.ifr )
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190 | #define intf (L.intf )
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191 | #define script_av (L.script_av )
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192 | #define timeout_ms (L.timeout_ms)
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193 | #define conflicts (L.conflicts )
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194 | #define nprobes (L.nprobes )
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195 | #define nclaims (L.nclaims )
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196 | #define ready (L.ready )
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197 | #define verbose (L.verbose )
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198 |
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199 | memset(&L, 0, sizeof(L));
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200 |
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201 | #define FOREGROUND (opts & 1)
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202 | #define QUIT (opts & 2)
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203 | // parse commandline: prog [options] ifname script
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204 | // exactly 2 args; -v accumulates and implies -f
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205 | opt_complementary = "=2:vv:vf";
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206 | opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
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207 | if (!FOREGROUND) {
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208 | /* Do it early, before all bb_xx_msg calls */
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209 | openlog(applet_name, 0, LOG_DAEMON);
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210 | logmode |= LOGMODE_SYSLOG;
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211 | }
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212 | if (opts & 4) { // -r n.n.n.n
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213 | if (inet_aton(r_opt, &ip) == 0
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214 | || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
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215 | ) {
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216 | bb_error_msg_and_die("invalid link address");
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217 | }
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218 | }
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219 | // On NOMMU reexec early (or else we will rerun things twice)
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220 | #if !BB_MMU
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221 | if (!FOREGROUND)
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222 | bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
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223 | #endif
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224 | argc -= optind;
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225 | argv += optind;
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226 |
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227 | intf = argv[0];
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228 | script_av[0] = argv[1];
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229 | setenv("interface", intf, 1);
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230 |
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231 | // initialize the interface (modprobe, ifup, etc)
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232 | script_av[1] = (char*)"init";
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233 | if (run(script_av, intf, NULL))
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234 | return EXIT_FAILURE;
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235 |
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236 | // initialize saddr
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237 | //memset(&saddr, 0, sizeof(saddr));
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238 | safe_strncpy(saddr.sa_data, intf, sizeof(saddr.sa_data));
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239 |
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240 | // open an ARP socket
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241 | fd = xsocket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
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242 | // bind to the interface's ARP socket
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243 | xbind(fd, &saddr, sizeof(saddr));
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244 |
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245 | // get the interface's ethernet address
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246 | //memset(&ifr, 0, sizeof(ifr));
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247 | strncpy(ifr.ifr_name, intf, sizeof(ifr.ifr_name));
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248 | xioctl(fd, SIOCGIFHWADDR, &ifr);
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249 | memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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250 |
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251 | // start with some stable ip address, either a function of
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252 | // the hardware address or else the last address we used.
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253 | // NOTE: the sequence of addresses we try changes only
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254 | // depending on when we detect conflicts.
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255 | srand(*(unsigned*)&ifr.ifr_hwaddr.sa_data);
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256 | if (ip.s_addr == 0)
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257 | pick(&ip);
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258 |
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259 | // FIXME cases to handle:
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260 | // - zcip already running!
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261 | // - link already has local address... just defend/update
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262 |
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263 | // daemonize now; don't delay system startup
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264 | if (!FOREGROUND) {
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265 | #if BB_MMU
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266 | bb_daemonize(DAEMON_CHDIR_ROOT);
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267 | #endif
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268 | bb_info_msg("start, interface %s", intf);
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269 | }
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270 |
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271 | // run the dynamic address negotiation protocol,
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272 | // restarting after address conflicts:
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273 | // - start with some address we want to try
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274 | // - short random delay
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275 | // - arp probes to see if another host else uses it
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276 | // - arp announcements that we're claiming it
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277 | // - use it
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278 | // - defend it, within limits
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279 | while (1) {
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280 | struct pollfd fds[1];
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281 | unsigned deadline_us;
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282 | struct arp_packet p;
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283 |
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284 | int source_ip_conflict = 0;
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285 | int target_ip_conflict = 0;
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286 |
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287 | fds[0].fd = fd;
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288 | fds[0].events = POLLIN;
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289 | fds[0].revents = 0;
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290 |
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291 | // poll, being ready to adjust current timeout
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292 | if (!timeout_ms) {
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293 | timeout_ms = ms_rdelay(PROBE_WAIT);
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294 | // FIXME setsockopt(fd, SO_ATTACH_FILTER, ...) to
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295 | // make the kernel filter out all packets except
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296 | // ones we'd care about.
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297 | }
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298 | // set deadline_us to the point in time when we timeout
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299 | deadline_us = MONOTONIC_US() + timeout_ms * 1000;
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300 |
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301 | VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
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302 | timeout_ms, intf, nprobes, nclaims);
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303 | switch (poll(fds, 1, timeout_ms)) {
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304 |
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305 | // timeout
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306 | case 0:
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307 | VDBG("state = %d\n", state);
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308 | switch (state) {
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309 | case PROBE:
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310 | // timeouts in the PROBE state mean no conflicting ARP packets
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311 | // have been received, so we can progress through the states
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312 | if (nprobes < PROBE_NUM) {
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313 | nprobes++;
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314 | VDBG("probe/%u %s@%s\n",
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315 | nprobes, intf, inet_ntoa(ip));
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316 | arp(fd, &saddr, ARPOP_REQUEST,
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317 | ð_addr, null_ip,
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318 | &null_addr, ip);
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319 | timeout_ms = PROBE_MIN * 1000;
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320 | timeout_ms += ms_rdelay(PROBE_MAX - PROBE_MIN);
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321 | }
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322 | else {
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323 | // Switch to announce state.
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324 | state = ANNOUNCE;
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325 | nclaims = 0;
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326 | VDBG("announce/%u %s@%s\n",
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327 | nclaims, intf, inet_ntoa(ip));
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328 | arp(fd, &saddr, ARPOP_REQUEST,
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329 | ð_addr, ip,
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330 | ð_addr, ip);
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331 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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332 | }
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333 | break;
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334 | case RATE_LIMIT_PROBE:
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335 | // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
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336 | // have been received, so we can move immediately to the announce state
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337 | state = ANNOUNCE;
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338 | nclaims = 0;
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339 | VDBG("announce/%u %s@%s\n",
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340 | nclaims, intf, inet_ntoa(ip));
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341 | arp(fd, &saddr, ARPOP_REQUEST,
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342 | ð_addr, ip,
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343 | ð_addr, ip);
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344 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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345 | break;
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346 | case ANNOUNCE:
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347 | // timeouts in the ANNOUNCE state mean no conflicting ARP packets
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348 | // have been received, so we can progress through the states
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349 | if (nclaims < ANNOUNCE_NUM) {
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350 | nclaims++;
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351 | VDBG("announce/%u %s@%s\n",
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352 | nclaims, intf, inet_ntoa(ip));
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353 | arp(fd, &saddr, ARPOP_REQUEST,
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354 | ð_addr, ip,
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355 | ð_addr, ip);
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356 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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357 | }
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358 | else {
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359 | // Switch to monitor state.
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360 | state = MONITOR;
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361 | // link is ok to use earlier
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362 | // FIXME update filters
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363 | script_av[1] = (char*)"config";
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364 | run(script_av, intf, &ip);
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365 | ready = 1;
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366 | conflicts = 0;
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367 | timeout_ms = -1; // Never timeout in the monitor state.
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368 |
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369 | // NOTE: all other exit paths
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370 | // should deconfig ...
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371 | if (QUIT)
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372 | return EXIT_SUCCESS;
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373 | }
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374 | break;
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375 | case DEFEND:
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376 | // We won! No ARP replies, so just go back to monitor.
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377 | state = MONITOR;
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378 | timeout_ms = -1;
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379 | conflicts = 0;
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380 | break;
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381 | default:
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382 | // Invalid, should never happen. Restart the whole protocol.
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383 | state = PROBE;
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384 | pick(&ip);
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385 | timeout_ms = 0;
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386 | nprobes = 0;
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387 | nclaims = 0;
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388 | break;
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389 | } // switch (state)
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390 | break; // case 0 (timeout)
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391 | // packets arriving
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392 | case 1:
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393 | // We need to adjust the timeout in case we didn't receive
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394 | // a conflicting packet.
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395 | if (timeout_ms > 0) {
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396 | unsigned diff = deadline_us - MONOTONIC_US();
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397 | if ((int)(diff) < 0) {
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398 | // Current time is greater than the expected timeout time.
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399 | // Should never happen.
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400 | VDBG("missed an expected timeout\n");
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401 | timeout_ms = 0;
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402 | } else {
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403 | VDBG("adjusting timeout\n");
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404 | timeout_ms = diff / 1000;
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405 | if (!timeout_ms) timeout_ms = 1;
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406 | }
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407 | }
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408 |
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409 | if ((fds[0].revents & POLLIN) == 0) {
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410 | if (fds[0].revents & POLLERR) {
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411 | // FIXME: links routinely go down;
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412 | // this shouldn't necessarily exit.
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413 | bb_error_msg("%s: poll error", intf);
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414 | if (ready) {
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415 | script_av[1] = (char*)"deconfig";
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416 | run(script_av, intf, &ip);
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417 | }
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418 | return EXIT_FAILURE;
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419 | }
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420 | continue;
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421 | }
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422 |
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423 | // read ARP packet
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424 | if (recv(fd, &p, sizeof(p), 0) < 0) {
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425 | why = "recv";
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426 | goto bad;
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427 | }
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428 | if (p.hdr.ether_type != htons(ETHERTYPE_ARP))
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429 | continue;
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430 |
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431 | #ifdef DEBUG
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432 | {
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433 | struct ether_addr * sha = (struct ether_addr *) p.arp.arp_sha;
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434 | struct ether_addr * tha = (struct ether_addr *) p.arp.arp_tha;
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435 | struct in_addr * spa = (struct in_addr *) p.arp.arp_spa;
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436 | struct in_addr * tpa = (struct in_addr *) p.arp.arp_tpa;
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437 | VDBG("%s recv arp type=%d, op=%d,\n",
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438 | intf, ntohs(p.hdr.ether_type),
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439 | ntohs(p.arp.arp_op));
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440 | VDBG("\tsource=%s %s\n",
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441 | ether_ntoa(sha),
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442 | inet_ntoa(*spa));
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443 | VDBG("\ttarget=%s %s\n",
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444 | ether_ntoa(tha),
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445 | inet_ntoa(*tpa));
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446 | }
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447 | #endif
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448 | if (p.arp.arp_op != htons(ARPOP_REQUEST)
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449 | && p.arp.arp_op != htons(ARPOP_REPLY))
|
---|
450 | continue;
|
---|
451 |
|
---|
452 | if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
|
---|
453 | memcmp(ð_addr, &p.arp.arp_sha, ETH_ALEN) != 0) {
|
---|
454 | source_ip_conflict = 1;
|
---|
455 | }
|
---|
456 | if (memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0 &&
|
---|
457 | p.arp.arp_op == htons(ARPOP_REQUEST) &&
|
---|
458 | memcmp(ð_addr, &p.arp.arp_tha, ETH_ALEN) != 0) {
|
---|
459 | target_ip_conflict = 1;
|
---|
460 | }
|
---|
461 |
|
---|
462 | VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
|
---|
463 | state, source_ip_conflict, target_ip_conflict);
|
---|
464 | switch (state) {
|
---|
465 | case PROBE:
|
---|
466 | case ANNOUNCE:
|
---|
467 | // When probing or announcing, check for source IP conflicts
|
---|
468 | // and other hosts doing ARP probes (target IP conflicts).
|
---|
469 | if (source_ip_conflict || target_ip_conflict) {
|
---|
470 | conflicts++;
|
---|
471 | if (conflicts >= MAX_CONFLICTS) {
|
---|
472 | VDBG("%s ratelimit\n", intf);
|
---|
473 | timeout_ms = RATE_LIMIT_INTERVAL * 1000;
|
---|
474 | state = RATE_LIMIT_PROBE;
|
---|
475 | }
|
---|
476 |
|
---|
477 | // restart the whole protocol
|
---|
478 | pick(&ip);
|
---|
479 | timeout_ms = 0;
|
---|
480 | nprobes = 0;
|
---|
481 | nclaims = 0;
|
---|
482 | }
|
---|
483 | break;
|
---|
484 | case MONITOR:
|
---|
485 | // If a conflict, we try to defend with a single ARP probe.
|
---|
486 | if (source_ip_conflict) {
|
---|
487 | VDBG("monitor conflict -- defending\n");
|
---|
488 | state = DEFEND;
|
---|
489 | timeout_ms = DEFEND_INTERVAL * 1000;
|
---|
490 | arp(fd, &saddr,
|
---|
491 | ARPOP_REQUEST,
|
---|
492 | ð_addr, ip,
|
---|
493 | ð_addr, ip);
|
---|
494 | }
|
---|
495 | break;
|
---|
496 | case DEFEND:
|
---|
497 | // Well, we tried. Start over (on conflict).
|
---|
498 | if (source_ip_conflict) {
|
---|
499 | state = PROBE;
|
---|
500 | VDBG("defend conflict -- starting over\n");
|
---|
501 | ready = 0;
|
---|
502 | script_av[1] = (char*)"deconfig";
|
---|
503 | run(script_av, intf, &ip);
|
---|
504 |
|
---|
505 | // restart the whole protocol
|
---|
506 | pick(&ip);
|
---|
507 | timeout_ms = 0;
|
---|
508 | nprobes = 0;
|
---|
509 | nclaims = 0;
|
---|
510 | }
|
---|
511 | break;
|
---|
512 | default:
|
---|
513 | // Invalid, should never happen. Restart the whole protocol.
|
---|
514 | VDBG("invalid state -- starting over\n");
|
---|
515 | state = PROBE;
|
---|
516 | pick(&ip);
|
---|
517 | timeout_ms = 0;
|
---|
518 | nprobes = 0;
|
---|
519 | nclaims = 0;
|
---|
520 | break;
|
---|
521 | } // switch state
|
---|
522 |
|
---|
523 | break; // case 1 (packets arriving)
|
---|
524 | default:
|
---|
525 | why = "poll";
|
---|
526 | goto bad;
|
---|
527 | } // switch poll
|
---|
528 | }
|
---|
529 | bad:
|
---|
530 | bb_perror_msg("%s, %s", intf, why);
|
---|
531 | return EXIT_FAILURE;
|
---|
532 | }
|
---|