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 GPLv2 or later, see file LICENSE in this source tree.
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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 | //usage:#define zcip_trivial_usage
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27 | //usage: "[OPTIONS] IFACE SCRIPT"
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28 | //usage:#define zcip_full_usage "\n\n"
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29 | //usage: "Manage a ZeroConf IPv4 link-local address\n"
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30 | //usage: "\n -f Run in foreground"
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31 | //usage: "\n -q Quit after obtaining address"
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32 | //usage: "\n -r 169.254.x.x Request this address first"
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33 | //usage: "\n -v Verbose"
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34 | //usage: "\n"
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35 | //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
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36 | //usage: "\nexits only on I/O errors (link down etc)"
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37 |
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38 | #include "libbb.h"
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39 | #include <netinet/ether.h>
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40 | #include <net/if.h>
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41 | #include <net/if_arp.h>
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42 | #include <linux/sockios.h>
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43 |
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44 | #include <syslog.h>
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45 |
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46 | /* We don't need more than 32 bits of the counter */
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47 | #define MONOTONIC_US() ((unsigned)monotonic_us())
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48 |
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49 | struct arp_packet {
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50 | struct ether_header eth;
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51 | struct ether_arp arp;
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52 | } PACKED;
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53 |
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54 | enum {
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55 | /* 169.254.0.0 */
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56 | LINKLOCAL_ADDR = 0xa9fe0000,
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57 |
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58 | /* protocol timeout parameters, specified in seconds */
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59 | PROBE_WAIT = 1,
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60 | PROBE_MIN = 1,
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61 | PROBE_MAX = 2,
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62 | PROBE_NUM = 3,
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63 | MAX_CONFLICTS = 10,
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64 | RATE_LIMIT_INTERVAL = 60,
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65 | ANNOUNCE_WAIT = 2,
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66 | ANNOUNCE_NUM = 2,
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67 | ANNOUNCE_INTERVAL = 2,
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68 | DEFEND_INTERVAL = 10
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69 | };
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70 |
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71 | /* States during the configuration process. */
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72 | enum {
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73 | PROBE = 0,
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74 | RATE_LIMIT_PROBE,
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75 | ANNOUNCE,
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76 | MONITOR,
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77 | DEFEND
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78 | };
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79 |
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80 | #define VDBG(...) do { } while (0)
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81 |
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82 |
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83 | enum {
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84 | sock_fd = 3
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85 | };
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86 |
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87 | struct globals {
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88 | struct sockaddr saddr;
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89 | struct ether_addr eth_addr;
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90 | } FIX_ALIASING;
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91 | #define G (*(struct globals*)&bb_common_bufsiz1)
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92 | #define saddr (G.saddr )
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93 | #define eth_addr (G.eth_addr)
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94 | #define INIT_G() do { } while (0)
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95 |
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96 |
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97 | /**
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98 | * Pick a random link local IP address on 169.254/16, except that
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99 | * the first and last 256 addresses are reserved.
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100 | */
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101 | static uint32_t pick(void)
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102 | {
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103 | unsigned tmp;
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104 |
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105 | do {
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106 | tmp = rand() & IN_CLASSB_HOST;
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107 | } while (tmp > (IN_CLASSB_HOST - 0x0200));
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108 | return htonl((LINKLOCAL_ADDR + 0x0100) + tmp);
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109 | }
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110 |
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111 | /**
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112 | * Broadcast an ARP packet.
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113 | */
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114 | static void arp(
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115 | /* int op, - always ARPOP_REQUEST */
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116 | /* const struct ether_addr *source_eth, - always ð_addr */
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117 | struct in_addr source_ip,
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118 | const struct ether_addr *target_eth, struct in_addr target_ip)
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119 | {
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120 | enum { op = ARPOP_REQUEST };
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121 | #define source_eth (ð_addr)
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122 |
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123 | struct arp_packet p;
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124 | memset(&p, 0, sizeof(p));
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125 |
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126 | // ether header
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127 | p.eth.ether_type = htons(ETHERTYPE_ARP);
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128 | memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
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129 | memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
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130 |
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131 | // arp request
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132 | p.arp.arp_hrd = htons(ARPHRD_ETHER);
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133 | p.arp.arp_pro = htons(ETHERTYPE_IP);
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134 | p.arp.arp_hln = ETH_ALEN;
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135 | p.arp.arp_pln = 4;
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136 | p.arp.arp_op = htons(op);
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137 | memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
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138 | memcpy(&p.arp.arp_spa, &source_ip, sizeof(p.arp.arp_spa));
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139 | memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
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140 | memcpy(&p.arp.arp_tpa, &target_ip, sizeof(p.arp.arp_tpa));
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141 |
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142 | // send it
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143 | // Even though sock_fd is already bound to saddr, just send()
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144 | // won't work, because "socket is not connected"
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145 | // (and connect() won't fix that, "operation not supported").
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146 | // Thus we sendto() to saddr. I wonder which sockaddr
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147 | // (from bind() or from sendto()?) kernel actually uses
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148 | // to determine iface to emit the packet from...
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149 | xsendto(sock_fd, &p, sizeof(p), &saddr, sizeof(saddr));
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150 | #undef source_eth
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151 | }
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152 |
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153 | /**
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154 | * Run a script.
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155 | * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
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156 | */
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157 | static int run(char *argv[3], const char *param, struct in_addr *ip)
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158 | {
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159 | int status;
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160 | char *addr = addr; /* for gcc */
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161 | const char *fmt = "%s %s %s" + 3;
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162 |
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163 | argv[2] = (char*)param;
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164 |
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165 | VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
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166 |
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167 | if (ip) {
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168 | addr = inet_ntoa(*ip);
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169 | xsetenv("ip", addr);
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170 | fmt -= 3;
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171 | }
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172 | bb_info_msg(fmt, argv[2], argv[0], addr);
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173 |
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174 | status = spawn_and_wait(argv + 1);
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175 | if (status < 0) {
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176 | bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
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177 | return -errno;
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178 | }
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179 | if (status != 0)
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180 | bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
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181 | return status;
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182 | }
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183 |
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184 | /**
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185 | * Return milliseconds of random delay, up to "secs" seconds.
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186 | */
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187 | static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
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188 | {
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189 | return rand() % (secs * 1000);
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190 | }
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191 |
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192 | /**
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193 | * main program
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194 | */
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195 | int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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196 | int zcip_main(int argc UNUSED_PARAM, char **argv)
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197 | {
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198 | int state;
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199 | char *r_opt;
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200 | unsigned opts;
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201 |
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202 | // ugly trick, but I want these zeroed in one go
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203 | struct {
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204 | const struct in_addr null_ip;
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205 | const struct ether_addr null_addr;
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206 | struct in_addr ip;
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207 | struct ifreq ifr;
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208 | int timeout_ms; /* must be signed */
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209 | unsigned conflicts;
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210 | unsigned nprobes;
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211 | unsigned nclaims;
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212 | int ready;
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213 | int verbose;
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214 | } L;
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215 | #define null_ip (L.null_ip )
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216 | #define null_addr (L.null_addr )
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217 | #define ip (L.ip )
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218 | #define ifr (L.ifr )
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219 | #define timeout_ms (L.timeout_ms)
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220 | #define conflicts (L.conflicts )
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221 | #define nprobes (L.nprobes )
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222 | #define nclaims (L.nclaims )
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223 | #define ready (L.ready )
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224 | #define verbose (L.verbose )
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225 |
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226 | memset(&L, 0, sizeof(L));
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227 | INIT_G();
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228 |
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229 | #define FOREGROUND (opts & 1)
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230 | #define QUIT (opts & 2)
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231 | // parse commandline: prog [options] ifname script
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232 | // exactly 2 args; -v accumulates and implies -f
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233 | opt_complementary = "=2:vv:vf";
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234 | opts = getopt32(argv, "fqr:v", &r_opt, &verbose);
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235 | #if !BB_MMU
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236 | // on NOMMU reexec early (or else we will rerun things twice)
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237 | if (!FOREGROUND)
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238 | bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
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239 | #endif
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240 | // open an ARP socket
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241 | // (need to do it before openlog to prevent openlog from taking
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242 | // fd 3 (sock_fd==3))
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243 | xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
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244 | if (!FOREGROUND) {
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245 | // do it before all bb_xx_msg calls
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246 | openlog(applet_name, 0, LOG_DAEMON);
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247 | logmode |= LOGMODE_SYSLOG;
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248 | }
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249 | if (opts & 4) { // -r n.n.n.n
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250 | if (inet_aton(r_opt, &ip) == 0
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251 | || (ntohl(ip.s_addr) & IN_CLASSB_NET) != LINKLOCAL_ADDR
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252 | ) {
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253 | bb_error_msg_and_die("invalid link address");
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254 | }
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255 | }
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256 | argv += optind - 1;
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257 |
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258 | /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
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259 | /* We need to make space for script argument: */
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260 | argv[0] = argv[1];
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261 | argv[1] = argv[2];
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262 | /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
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263 | #define argv_intf (argv[0])
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264 |
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265 | xsetenv("interface", argv_intf);
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266 |
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267 | // initialize the interface (modprobe, ifup, etc)
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268 | if (run(argv, "init", NULL))
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269 | return EXIT_FAILURE;
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270 |
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271 | // initialize saddr
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272 | // saddr is: { u16 sa_family; u8 sa_data[14]; }
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273 | //memset(&saddr, 0, sizeof(saddr));
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274 | //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
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275 | safe_strncpy(saddr.sa_data, argv_intf, sizeof(saddr.sa_data));
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276 |
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277 | // bind to the interface's ARP socket
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278 | xbind(sock_fd, &saddr, sizeof(saddr));
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279 |
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280 | // get the interface's ethernet address
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281 | //memset(&ifr, 0, sizeof(ifr));
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282 | strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
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283 | xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
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284 | memcpy(ð_addr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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285 |
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286 | // start with some stable ip address, either a function of
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287 | // the hardware address or else the last address we used.
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288 | // we are taking low-order four bytes, as top-order ones
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289 | // aren't random enough.
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290 | // NOTE: the sequence of addresses we try changes only
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291 | // depending on when we detect conflicts.
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292 | {
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293 | uint32_t t;
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294 | move_from_unaligned32(t, ((char *)ð_addr + 2));
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295 | srand(t);
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296 | }
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297 | if (ip.s_addr == 0)
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298 | ip.s_addr = pick();
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299 |
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300 | // FIXME cases to handle:
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301 | // - zcip already running!
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302 | // - link already has local address... just defend/update
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303 |
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304 | // daemonize now; don't delay system startup
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305 | if (!FOREGROUND) {
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306 | #if BB_MMU
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307 | bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
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308 | #endif
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309 | bb_info_msg("start, interface %s", argv_intf);
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310 | }
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311 |
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312 | // run the dynamic address negotiation protocol,
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313 | // restarting after address conflicts:
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314 | // - start with some address we want to try
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315 | // - short random delay
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316 | // - arp probes to see if another host uses it
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317 | // - arp announcements that we're claiming it
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318 | // - use it
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319 | // - defend it, within limits
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320 | // exit if:
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321 | // - address is successfully obtained and -q was given:
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322 | // run "<script> config", then exit with exitcode 0
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323 | // - poll error (when does this happen?)
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324 | // - read error (when does this happen?)
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325 | // - sendto error (in arp()) (when does this happen?)
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326 | // - revents & POLLERR (link down). run "<script> deconfig" first
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327 | state = PROBE;
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328 | while (1) {
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329 | struct pollfd fds[1];
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330 | unsigned deadline_us;
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331 | struct arp_packet p;
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332 | int source_ip_conflict;
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333 | int target_ip_conflict;
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334 |
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335 | fds[0].fd = sock_fd;
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336 | fds[0].events = POLLIN;
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337 | fds[0].revents = 0;
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338 |
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339 | // poll, being ready to adjust current timeout
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340 | if (!timeout_ms) {
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341 | timeout_ms = random_delay_ms(PROBE_WAIT);
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342 | // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
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343 | // make the kernel filter out all packets except
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344 | // ones we'd care about.
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345 | }
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346 | // set deadline_us to the point in time when we timeout
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347 | deadline_us = MONOTONIC_US() + timeout_ms * 1000;
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348 |
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349 | VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
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350 | timeout_ms, argv_intf, nprobes, nclaims);
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351 |
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352 | switch (safe_poll(fds, 1, timeout_ms)) {
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353 |
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354 | default:
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355 | //bb_perror_msg("poll"); - done in safe_poll
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356 | return EXIT_FAILURE;
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357 |
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358 | // timeout
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359 | case 0:
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360 | VDBG("state = %d\n", state);
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361 | switch (state) {
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362 | case PROBE:
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363 | // timeouts in the PROBE state mean no conflicting ARP packets
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364 | // have been received, so we can progress through the states
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365 | if (nprobes < PROBE_NUM) {
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366 | nprobes++;
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367 | VDBG("probe/%u %s@%s\n",
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368 | nprobes, argv_intf, inet_ntoa(ip));
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369 | arp(/* ARPOP_REQUEST, */
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370 | /* ð_addr, */ null_ip,
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371 | &null_addr, ip);
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372 | timeout_ms = PROBE_MIN * 1000;
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373 | timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
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374 | }
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375 | else {
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376 | // Switch to announce state.
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377 | state = ANNOUNCE;
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378 | nclaims = 0;
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379 | VDBG("announce/%u %s@%s\n",
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380 | nclaims, argv_intf, inet_ntoa(ip));
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381 | arp(/* ARPOP_REQUEST, */
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382 | /* ð_addr, */ ip,
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383 | ð_addr, ip);
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384 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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385 | }
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386 | break;
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387 | case RATE_LIMIT_PROBE:
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388 | // timeouts in the RATE_LIMIT_PROBE state mean no conflicting ARP packets
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389 | // have been received, so we can move immediately to the announce state
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390 | state = ANNOUNCE;
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391 | nclaims = 0;
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392 | VDBG("announce/%u %s@%s\n",
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393 | nclaims, argv_intf, inet_ntoa(ip));
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394 | arp(/* ARPOP_REQUEST, */
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395 | /* ð_addr, */ ip,
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396 | ð_addr, ip);
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397 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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398 | break;
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399 | case ANNOUNCE:
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400 | // timeouts in the ANNOUNCE state mean no conflicting ARP packets
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401 | // have been received, so we can progress through the states
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402 | if (nclaims < ANNOUNCE_NUM) {
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403 | nclaims++;
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404 | VDBG("announce/%u %s@%s\n",
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405 | nclaims, argv_intf, inet_ntoa(ip));
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406 | arp(/* ARPOP_REQUEST, */
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407 | /* ð_addr, */ ip,
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408 | ð_addr, ip);
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409 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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410 | }
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411 | else {
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412 | // Switch to monitor state.
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413 | state = MONITOR;
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414 | // link is ok to use earlier
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415 | // FIXME update filters
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416 | run(argv, "config", &ip);
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417 | ready = 1;
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418 | conflicts = 0;
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419 | timeout_ms = -1; // Never timeout in the monitor state.
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420 |
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421 | // NOTE: all other exit paths
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422 | // should deconfig ...
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423 | if (QUIT)
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424 | return EXIT_SUCCESS;
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425 | }
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426 | break;
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427 | case DEFEND:
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428 | // We won! No ARP replies, so just go back to monitor.
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429 | state = MONITOR;
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430 | timeout_ms = -1;
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431 | conflicts = 0;
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432 | break;
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433 | default:
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434 | // Invalid, should never happen. Restart the whole protocol.
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435 | state = PROBE;
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436 | ip.s_addr = pick();
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437 | timeout_ms = 0;
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438 | nprobes = 0;
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439 | nclaims = 0;
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440 | break;
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441 | } // switch (state)
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442 | break; // case 0 (timeout)
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443 |
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444 | // packets arriving, or link went down
|
---|
445 | case 1:
|
---|
446 | // We need to adjust the timeout in case we didn't receive
|
---|
447 | // a conflicting packet.
|
---|
448 | if (timeout_ms > 0) {
|
---|
449 | unsigned diff = deadline_us - MONOTONIC_US();
|
---|
450 | if ((int)(diff) < 0) {
|
---|
451 | // Current time is greater than the expected timeout time.
|
---|
452 | // Should never happen.
|
---|
453 | VDBG("missed an expected timeout\n");
|
---|
454 | timeout_ms = 0;
|
---|
455 | } else {
|
---|
456 | VDBG("adjusting timeout\n");
|
---|
457 | timeout_ms = (diff / 1000) | 1; /* never 0 */
|
---|
458 | }
|
---|
459 | }
|
---|
460 |
|
---|
461 | if ((fds[0].revents & POLLIN) == 0) {
|
---|
462 | if (fds[0].revents & POLLERR) {
|
---|
463 | // FIXME: links routinely go down;
|
---|
464 | // this shouldn't necessarily exit.
|
---|
465 | bb_error_msg("iface %s is down", argv_intf);
|
---|
466 | if (ready) {
|
---|
467 | run(argv, "deconfig", &ip);
|
---|
468 | }
|
---|
469 | return EXIT_FAILURE;
|
---|
470 | }
|
---|
471 | continue;
|
---|
472 | }
|
---|
473 |
|
---|
474 | // read ARP packet
|
---|
475 | if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
|
---|
476 | bb_perror_msg_and_die(bb_msg_read_error);
|
---|
477 | }
|
---|
478 | if (p.eth.ether_type != htons(ETHERTYPE_ARP))
|
---|
479 | continue;
|
---|
480 | #ifdef DEBUG
|
---|
481 | {
|
---|
482 | struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
|
---|
483 | struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
|
---|
484 | struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
|
---|
485 | struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
|
---|
486 | VDBG("%s recv arp type=%d, op=%d,\n",
|
---|
487 | argv_intf, ntohs(p.eth.ether_type),
|
---|
488 | ntohs(p.arp.arp_op));
|
---|
489 | VDBG("\tsource=%s %s\n",
|
---|
490 | ether_ntoa(sha),
|
---|
491 | inet_ntoa(*spa));
|
---|
492 | VDBG("\ttarget=%s %s\n",
|
---|
493 | ether_ntoa(tha),
|
---|
494 | inet_ntoa(*tpa));
|
---|
495 | }
|
---|
496 | #endif
|
---|
497 | if (p.arp.arp_op != htons(ARPOP_REQUEST)
|
---|
498 | && p.arp.arp_op != htons(ARPOP_REPLY))
|
---|
499 | continue;
|
---|
500 |
|
---|
501 | source_ip_conflict = 0;
|
---|
502 | target_ip_conflict = 0;
|
---|
503 |
|
---|
504 | if (memcmp(p.arp.arp_spa, &ip.s_addr, sizeof(struct in_addr)) == 0
|
---|
505 | && memcmp(&p.arp.arp_sha, ð_addr, ETH_ALEN) != 0
|
---|
506 | ) {
|
---|
507 | source_ip_conflict = 1;
|
---|
508 | }
|
---|
509 | if (p.arp.arp_op == htons(ARPOP_REQUEST)
|
---|
510 | && memcmp(p.arp.arp_tpa, &ip.s_addr, sizeof(struct in_addr)) == 0
|
---|
511 | && memcmp(&p.arp.arp_tha, ð_addr, ETH_ALEN) != 0
|
---|
512 | ) {
|
---|
513 | target_ip_conflict = 1;
|
---|
514 | }
|
---|
515 |
|
---|
516 | VDBG("state = %d, source ip conflict = %d, target ip conflict = %d\n",
|
---|
517 | state, source_ip_conflict, target_ip_conflict);
|
---|
518 | switch (state) {
|
---|
519 | case PROBE:
|
---|
520 | case ANNOUNCE:
|
---|
521 | // When probing or announcing, check for source IP conflicts
|
---|
522 | // and other hosts doing ARP probes (target IP conflicts).
|
---|
523 | if (source_ip_conflict || target_ip_conflict) {
|
---|
524 | conflicts++;
|
---|
525 | if (conflicts >= MAX_CONFLICTS) {
|
---|
526 | VDBG("%s ratelimit\n", argv_intf);
|
---|
527 | timeout_ms = RATE_LIMIT_INTERVAL * 1000;
|
---|
528 | state = RATE_LIMIT_PROBE;
|
---|
529 | }
|
---|
530 |
|
---|
531 | // restart the whole protocol
|
---|
532 | ip.s_addr = pick();
|
---|
533 | timeout_ms = 0;
|
---|
534 | nprobes = 0;
|
---|
535 | nclaims = 0;
|
---|
536 | }
|
---|
537 | break;
|
---|
538 | case MONITOR:
|
---|
539 | // If a conflict, we try to defend with a single ARP probe.
|
---|
540 | if (source_ip_conflict) {
|
---|
541 | VDBG("monitor conflict -- defending\n");
|
---|
542 | state = DEFEND;
|
---|
543 | timeout_ms = DEFEND_INTERVAL * 1000;
|
---|
544 | arp(/* ARPOP_REQUEST, */
|
---|
545 | /* ð_addr, */ ip,
|
---|
546 | ð_addr, ip);
|
---|
547 | }
|
---|
548 | break;
|
---|
549 | case DEFEND:
|
---|
550 | // Well, we tried. Start over (on conflict).
|
---|
551 | if (source_ip_conflict) {
|
---|
552 | state = PROBE;
|
---|
553 | VDBG("defend conflict -- starting over\n");
|
---|
554 | ready = 0;
|
---|
555 | run(argv, "deconfig", &ip);
|
---|
556 |
|
---|
557 | // restart the whole protocol
|
---|
558 | ip.s_addr = pick();
|
---|
559 | timeout_ms = 0;
|
---|
560 | nprobes = 0;
|
---|
561 | nclaims = 0;
|
---|
562 | }
|
---|
563 | break;
|
---|
564 | default:
|
---|
565 | // Invalid, should never happen. Restart the whole protocol.
|
---|
566 | VDBG("invalid state -- starting over\n");
|
---|
567 | state = PROBE;
|
---|
568 | ip.s_addr = pick();
|
---|
569 | timeout_ms = 0;
|
---|
570 | nprobes = 0;
|
---|
571 | nclaims = 0;
|
---|
572 | break;
|
---|
573 | } // switch state
|
---|
574 | break; // case 1 (packets arriving)
|
---|
575 | } // switch poll
|
---|
576 | } // while (1)
|
---|
577 | #undef argv_intf
|
---|
578 | }
|
---|