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 -l x.x.0.0 Use this range instead of 169.254"
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34 | //usage: "\n -v Verbose"
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35 | //usage: "\n"
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36 | //usage: "\n$LOGGING=none Suppress logging"
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37 | //usage: "\n$LOGGING=syslog Log to syslog"
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38 | //usage: "\n"
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39 | //usage: "\nWith no -q, runs continuously monitoring for ARP conflicts,"
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40 | //usage: "\nexits only on I/O errors (link down etc)"
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41 |
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42 | #include "libbb.h"
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43 | #include "common_bufsiz.h"
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44 | #include <netinet/ether.h>
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45 | #include <net/if.h>
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46 | #include <net/if_arp.h>
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47 | #include <linux/sockios.h>
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48 |
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49 | #include <syslog.h>
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50 |
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51 | /* We don't need more than 32 bits of the counter */
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52 | #define MONOTONIC_US() ((unsigned)monotonic_us())
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53 |
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54 | struct arp_packet {
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55 | struct ether_header eth;
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56 | struct ether_arp arp;
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57 | } PACKED;
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58 |
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59 | enum {
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60 | /* 0-1 seconds before sending 1st probe */
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61 | PROBE_WAIT = 1,
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62 | /* 1-2 seconds between probes */
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63 | PROBE_MIN = 1,
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64 | PROBE_MAX = 2,
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65 | PROBE_NUM = 3, /* total probes to send */
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66 | ANNOUNCE_INTERVAL = 2, /* 2 seconds between announces */
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67 | ANNOUNCE_NUM = 3, /* announces to send */
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68 | /* if probe/announce sees a conflict, multiply RANDOM(NUM_CONFLICT) by... */
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69 | CONFLICT_MULTIPLIER = 2,
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70 | /* if we monitor and see a conflict, how long is defend state? */
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71 | DEFEND_INTERVAL = 10,
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72 | };
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73 |
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74 | /* States during the configuration process. */
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75 | enum {
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76 | PROBE = 0,
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77 | ANNOUNCE,
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78 | MONITOR,
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79 | DEFEND
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80 | };
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81 |
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82 | #define VDBG(...) do { } while (0)
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83 |
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84 |
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85 | enum {
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86 | sock_fd = 3
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87 | };
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88 |
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89 | struct globals {
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90 | struct sockaddr iface_sockaddr;
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91 | struct ether_addr our_ethaddr;
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92 | uint32_t localnet_ip;
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93 | } FIX_ALIASING;
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94 | #define G (*(struct globals*)bb_common_bufsiz1)
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95 | #define INIT_G() do { setup_common_bufsiz(); } while (0)
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96 |
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97 |
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98 | /**
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99 | * Pick a random link local IP address on 169.254/16, except that
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100 | * the first and last 256 addresses are reserved.
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101 | */
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102 | static uint32_t pick_nip(void)
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103 | {
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104 | unsigned tmp;
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105 |
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106 | do {
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107 | tmp = rand() & IN_CLASSB_HOST;
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108 | } while (tmp > (IN_CLASSB_HOST - 0x0200));
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109 | return htonl((G.localnet_ip + 0x0100) + tmp);
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110 | }
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111 |
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112 | static const char *nip_to_a(uint32_t nip)
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113 | {
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114 | struct in_addr in;
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115 | in.s_addr = nip;
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116 | return inet_ntoa(in);
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117 | }
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118 |
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119 | /**
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120 | * Broadcast an ARP packet.
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121 | */
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122 | static void send_arp_request(
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123 | /* int op, - always ARPOP_REQUEST */
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124 | /* const struct ether_addr *source_eth, - always &G.our_ethaddr */
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125 | uint32_t source_nip,
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126 | const struct ether_addr *target_eth, uint32_t target_nip)
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127 | {
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128 | enum { op = ARPOP_REQUEST };
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129 | #define source_eth (&G.our_ethaddr)
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130 |
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131 | struct arp_packet p;
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132 | memset(&p, 0, sizeof(p));
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133 |
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134 | // ether header
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135 | p.eth.ether_type = htons(ETHERTYPE_ARP);
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136 | memcpy(p.eth.ether_shost, source_eth, ETH_ALEN);
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137 | memset(p.eth.ether_dhost, 0xff, ETH_ALEN);
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138 |
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139 | // arp request
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140 | p.arp.arp_hrd = htons(ARPHRD_ETHER);
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141 | p.arp.arp_pro = htons(ETHERTYPE_IP);
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142 | p.arp.arp_hln = ETH_ALEN;
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143 | p.arp.arp_pln = 4;
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144 | p.arp.arp_op = htons(op);
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145 | memcpy(&p.arp.arp_sha, source_eth, ETH_ALEN);
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146 | memcpy(&p.arp.arp_spa, &source_nip, 4);
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147 | memcpy(&p.arp.arp_tha, target_eth, ETH_ALEN);
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148 | memcpy(&p.arp.arp_tpa, &target_nip, 4);
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149 |
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150 | // send it
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151 | // Even though sock_fd is already bound to G.iface_sockaddr, just send()
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152 | // won't work, because "socket is not connected"
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153 | // (and connect() won't fix that, "operation not supported").
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154 | // Thus we sendto() to G.iface_sockaddr. I wonder which sockaddr
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155 | // (from bind() or from sendto()?) kernel actually uses
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156 | // to determine iface to emit the packet from...
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157 | xsendto(sock_fd, &p, sizeof(p), &G.iface_sockaddr, sizeof(G.iface_sockaddr));
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158 | #undef source_eth
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159 | }
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160 |
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161 | /**
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162 | * Run a script.
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163 | * argv[0]:intf argv[1]:script_name argv[2]:junk argv[3]:NULL
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164 | */
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165 | static int run(char *argv[3], const char *param, uint32_t nip)
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166 | {
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167 | int status;
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168 | const char *addr = addr; /* for gcc */
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169 | const char *fmt = "%s %s %s" + 3;
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170 |
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171 | argv[2] = (char*)param;
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172 |
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173 | VDBG("%s run %s %s\n", argv[0], argv[1], argv[2]);
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174 |
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175 | if (nip != 0) {
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176 | addr = nip_to_a(nip);
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177 | xsetenv("ip", addr);
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178 | fmt -= 3;
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179 | }
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180 | bb_error_msg(fmt, argv[2], argv[0], addr);
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181 |
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182 | status = spawn_and_wait(argv + 1);
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183 | if (status < 0) {
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184 | bb_perror_msg("%s %s %s" + 3, argv[2], argv[0]);
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185 | return -errno;
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186 | }
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187 | if (status != 0)
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188 | bb_error_msg("script %s %s failed, exitcode=%d", argv[1], argv[2], status & 0xff);
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189 | return status;
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190 | }
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191 |
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192 | /**
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193 | * Return milliseconds of random delay, up to "secs" seconds.
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194 | */
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195 | static ALWAYS_INLINE unsigned random_delay_ms(unsigned secs)
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196 | {
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197 | return (unsigned)rand() % (secs * 1000);
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198 | }
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199 |
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200 | /**
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201 | * main program
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202 | */
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203 | int zcip_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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204 | int zcip_main(int argc UNUSED_PARAM, char **argv)
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205 | {
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206 | char *r_opt;
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207 | const char *l_opt = "169.254.0.0";
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208 | int state;
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209 | int nsent;
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210 | unsigned opts;
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211 |
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212 | // Ugly trick, but I want these zeroed in one go
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213 | struct {
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214 | const struct ether_addr null_ethaddr;
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215 | struct ifreq ifr;
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216 | uint32_t chosen_nip;
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217 | int conflicts;
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218 | int timeout_ms; // must be signed
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219 | int verbose;
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220 | } L;
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221 | #define null_ethaddr (L.null_ethaddr)
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222 | #define ifr (L.ifr )
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223 | #define chosen_nip (L.chosen_nip )
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224 | #define conflicts (L.conflicts )
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225 | #define timeout_ms (L.timeout_ms )
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226 | #define verbose (L.verbose )
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227 |
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228 | memset(&L, 0, sizeof(L));
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229 | INIT_G();
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230 |
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231 | #define FOREGROUND (opts & 1)
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232 | #define QUIT (opts & 2)
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233 | // Parse commandline: prog [options] ifname script
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234 | // exactly 2 args; -v accumulates and implies -f
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235 | opt_complementary = "=2:vv:vf";
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236 | opts = getopt32(argv, "fqr:l:v", &r_opt, &l_opt, &verbose);
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237 | #if !BB_MMU
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238 | // on NOMMU reexec early (or else we will rerun things twice)
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239 | if (!FOREGROUND)
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240 | bb_daemonize_or_rexec(0 /*was: DAEMON_CHDIR_ROOT*/, argv);
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241 | #endif
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242 | // Open an ARP socket
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243 | // (need to do it before openlog to prevent openlog from taking
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244 | // fd 3 (sock_fd==3))
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245 | xmove_fd(xsocket(AF_PACKET, SOCK_PACKET, htons(ETH_P_ARP)), sock_fd);
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246 | if (!FOREGROUND) {
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247 | // do it before all bb_xx_msg calls
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248 | openlog(applet_name, 0, LOG_DAEMON);
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249 | logmode |= LOGMODE_SYSLOG;
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250 | }
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251 | bb_logenv_override();
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252 |
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253 | { // -l n.n.n.n
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254 | struct in_addr net;
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255 | if (inet_aton(l_opt, &net) == 0
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256 | || (net.s_addr & htonl(IN_CLASSB_NET)) != net.s_addr
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257 | ) {
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258 | bb_error_msg_and_die("invalid network address");
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259 | }
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260 | G.localnet_ip = ntohl(net.s_addr);
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261 | }
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262 | if (opts & 4) { // -r n.n.n.n
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263 | struct in_addr ip;
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264 | if (inet_aton(r_opt, &ip) == 0
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265 | || (ntohl(ip.s_addr) & IN_CLASSB_NET) != G.localnet_ip
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266 | ) {
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267 | bb_error_msg_and_die("invalid link address");
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268 | }
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269 | chosen_nip = ip.s_addr;
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270 | }
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271 | argv += optind - 1;
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272 |
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273 | /* Now: argv[0]:junk argv[1]:intf argv[2]:script argv[3]:NULL */
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274 | /* We need to make space for script argument: */
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275 | argv[0] = argv[1];
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276 | argv[1] = argv[2];
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277 | /* Now: argv[0]:intf argv[1]:script argv[2]:junk argv[3]:NULL */
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278 | #define argv_intf (argv[0])
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279 |
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280 | xsetenv("interface", argv_intf);
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281 |
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282 | // Initialize the interface (modprobe, ifup, etc)
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283 | if (run(argv, "init", 0))
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284 | return EXIT_FAILURE;
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285 |
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286 | // Initialize G.iface_sockaddr
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287 | // G.iface_sockaddr is: { u16 sa_family; u8 sa_data[14]; }
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288 | //memset(&G.iface_sockaddr, 0, sizeof(G.iface_sockaddr));
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289 | //TODO: are we leaving sa_family == 0 (AF_UNSPEC)?!
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290 | safe_strncpy(G.iface_sockaddr.sa_data, argv_intf, sizeof(G.iface_sockaddr.sa_data));
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291 |
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292 | // Bind to the interface's ARP socket
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293 | xbind(sock_fd, &G.iface_sockaddr, sizeof(G.iface_sockaddr));
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294 |
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295 | // Get the interface's ethernet address
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296 | //memset(&ifr, 0, sizeof(ifr));
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297 | strncpy_IFNAMSIZ(ifr.ifr_name, argv_intf);
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298 | xioctl(sock_fd, SIOCGIFHWADDR, &ifr);
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299 | memcpy(&G.our_ethaddr, &ifr.ifr_hwaddr.sa_data, ETH_ALEN);
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300 |
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301 | // Start with some stable ip address, either a function of
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302 | // the hardware address or else the last address we used.
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303 | // we are taking low-order four bytes, as top-order ones
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304 | // aren't random enough.
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305 | // NOTE: the sequence of addresses we try changes only
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306 | // depending on when we detect conflicts.
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307 | {
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308 | uint32_t t;
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309 | move_from_unaligned32(t, ((char *)&G.our_ethaddr + 2));
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310 | srand(t);
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311 | }
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312 | // FIXME cases to handle:
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313 | // - zcip already running!
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314 | // - link already has local address... just defend/update
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315 |
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316 | // Daemonize now; don't delay system startup
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317 | if (!FOREGROUND) {
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318 | #if BB_MMU
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319 | bb_daemonize(0 /*was: DAEMON_CHDIR_ROOT*/);
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320 | #endif
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321 | bb_error_msg("start, interface %s", argv_intf);
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322 | }
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323 |
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324 | // Run the dynamic address negotiation protocol,
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325 | // restarting after address conflicts:
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326 | // - start with some address we want to try
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327 | // - short random delay
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328 | // - arp probes to see if another host uses it
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329 | // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 tell 0.0.0.0
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330 | // - arp announcements that we're claiming it
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331 | // 00:04:e2:64:23:c2 > ff:ff:ff:ff:ff:ff arp who-has 169.254.194.171 (00:04:e2:64:23:c2) tell 169.254.194.171
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332 | // - use it
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333 | // - defend it, within limits
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334 | // exit if:
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335 | // - address is successfully obtained and -q was given:
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336 | // run "<script> config", then exit with exitcode 0
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337 | // - poll error (when does this happen?)
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338 | // - read error (when does this happen?)
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339 | // - sendto error (in send_arp_request()) (when does this happen?)
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340 | // - revents & POLLERR (link down). run "<script> deconfig" first
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341 | if (chosen_nip == 0) {
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342 | new_nip_and_PROBE:
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343 | chosen_nip = pick_nip();
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344 | }
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345 | nsent = 0;
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346 | state = PROBE;
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347 | while (1) {
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348 | struct pollfd fds[1];
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349 | unsigned deadline_us = deadline_us;
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350 | struct arp_packet p;
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351 | int ip_conflict;
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352 | int n;
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353 |
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354 | fds[0].fd = sock_fd;
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355 | fds[0].events = POLLIN;
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356 | fds[0].revents = 0;
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357 |
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358 | // Poll, being ready to adjust current timeout
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359 | if (!timeout_ms) {
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360 | timeout_ms = random_delay_ms(PROBE_WAIT);
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361 | // FIXME setsockopt(sock_fd, SO_ATTACH_FILTER, ...) to
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362 | // make the kernel filter out all packets except
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363 | // ones we'd care about.
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364 | }
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365 | if (timeout_ms >= 0) {
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366 | // Set deadline_us to the point in time when we timeout
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367 | deadline_us = MONOTONIC_US() + timeout_ms * 1000;
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368 | }
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369 |
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370 | VDBG("...wait %d %s nsent=%u\n",
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371 | timeout_ms, argv_intf, nsent);
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372 |
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373 | n = safe_poll(fds, 1, timeout_ms);
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374 | if (n < 0) {
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375 | //bb_perror_msg("poll"); - done in safe_poll
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376 | return EXIT_FAILURE;
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377 | }
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378 | if (n == 0) { // timed out?
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379 | VDBG("state:%d\n", state);
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380 | switch (state) {
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381 | case PROBE:
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382 | // No conflicting ARP packets were seen:
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383 | // we can progress through the states
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384 | if (nsent < PROBE_NUM) {
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385 | nsent++;
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386 | VDBG("probe/%u %s@%s\n",
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387 | nsent, argv_intf, nip_to_a(chosen_nip));
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388 | timeout_ms = PROBE_MIN * 1000;
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389 | timeout_ms += random_delay_ms(PROBE_MAX - PROBE_MIN);
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390 | send_arp_request(0, &null_ethaddr, chosen_nip);
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391 | continue;
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392 | }
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393 | // Switch to announce state
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394 | nsent = 0;
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395 | state = ANNOUNCE;
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396 | goto send_announce;
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397 | case ANNOUNCE:
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398 | // No conflicting ARP packets were seen:
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399 | // we can progress through the states
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400 | if (nsent < ANNOUNCE_NUM) {
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401 | send_announce:
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402 | nsent++;
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403 | VDBG("announce/%u %s@%s\n",
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404 | nsent, argv_intf, nip_to_a(chosen_nip));
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405 | timeout_ms = ANNOUNCE_INTERVAL * 1000;
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406 | send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
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407 | continue;
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408 | }
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409 | // Switch to monitor state
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410 | // FIXME update filters
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411 | run(argv, "config", chosen_nip);
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412 | // NOTE: all other exit paths should deconfig...
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413 | if (QUIT)
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414 | return EXIT_SUCCESS;
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415 | // fall through: switch to MONITOR
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416 | default:
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417 | // case DEFEND:
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418 | // case MONITOR: (shouldn't happen, MONITOR timeout is infinite)
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419 | // Defend period ended with no ARP replies - we won
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420 | timeout_ms = -1; // never timeout in monitor state
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421 | state = MONITOR;
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422 | continue;
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423 | }
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424 | }
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425 |
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426 | // Packet arrived, or link went down.
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427 | // We need to adjust the timeout in case we didn't receive
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428 | // a conflicting packet.
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---|
429 | if (timeout_ms > 0) {
|
---|
430 | unsigned diff = deadline_us - MONOTONIC_US();
|
---|
431 | if ((int)(diff) < 0) {
|
---|
432 | // Current time is greater than the expected timeout time.
|
---|
433 | diff = 0;
|
---|
434 | }
|
---|
435 | VDBG("adjusting timeout\n");
|
---|
436 | timeout_ms = (diff / 1000) | 1; // never 0
|
---|
437 | }
|
---|
438 |
|
---|
439 | if ((fds[0].revents & POLLIN) == 0) {
|
---|
440 | if (fds[0].revents & POLLERR) {
|
---|
441 | // FIXME: links routinely go down;
|
---|
442 | // this shouldn't necessarily exit.
|
---|
443 | bb_error_msg("iface %s is down", argv_intf);
|
---|
444 | if (state >= MONITOR) {
|
---|
445 | // Only if we are in MONITOR or DEFEND
|
---|
446 | run(argv, "deconfig", chosen_nip);
|
---|
447 | }
|
---|
448 | return EXIT_FAILURE;
|
---|
449 | }
|
---|
450 | continue;
|
---|
451 | }
|
---|
452 |
|
---|
453 | // Read ARP packet
|
---|
454 | if (safe_read(sock_fd, &p, sizeof(p)) < 0) {
|
---|
455 | bb_perror_msg_and_die(bb_msg_read_error);
|
---|
456 | }
|
---|
457 |
|
---|
458 | if (p.eth.ether_type != htons(ETHERTYPE_ARP))
|
---|
459 | continue;
|
---|
460 | if (p.arp.arp_op != htons(ARPOP_REQUEST)
|
---|
461 | && p.arp.arp_op != htons(ARPOP_REPLY)
|
---|
462 | ) {
|
---|
463 | continue;
|
---|
464 | }
|
---|
465 | #ifdef DEBUG
|
---|
466 | {
|
---|
467 | struct ether_addr *sha = (struct ether_addr *) p.arp.arp_sha;
|
---|
468 | struct ether_addr *tha = (struct ether_addr *) p.arp.arp_tha;
|
---|
469 | struct in_addr *spa = (struct in_addr *) p.arp.arp_spa;
|
---|
470 | struct in_addr *tpa = (struct in_addr *) p.arp.arp_tpa;
|
---|
471 | VDBG("source=%s %s\n", ether_ntoa(sha), inet_ntoa(*spa));
|
---|
472 | VDBG("target=%s %s\n", ether_ntoa(tha), inet_ntoa(*tpa));
|
---|
473 | }
|
---|
474 | #endif
|
---|
475 | ip_conflict = 0;
|
---|
476 | if (memcmp(&p.arp.arp_sha, &G.our_ethaddr, ETH_ALEN) != 0) {
|
---|
477 | if (memcmp(p.arp.arp_spa, &chosen_nip, 4) == 0) {
|
---|
478 | // A probe or reply with source_ip == chosen ip
|
---|
479 | ip_conflict = 1;
|
---|
480 | }
|
---|
481 | if (p.arp.arp_op == htons(ARPOP_REQUEST)
|
---|
482 | && memcmp(p.arp.arp_spa, &const_int_0, 4) == 0
|
---|
483 | && memcmp(p.arp.arp_tpa, &chosen_nip, 4) == 0
|
---|
484 | ) {
|
---|
485 | // A probe with source_ip == 0.0.0.0, target_ip == chosen ip:
|
---|
486 | // another host trying to claim this ip!
|
---|
487 | ip_conflict |= 2;
|
---|
488 | }
|
---|
489 | }
|
---|
490 | VDBG("state:%d ip_conflict:%d\n", state, ip_conflict);
|
---|
491 | if (!ip_conflict)
|
---|
492 | continue;
|
---|
493 |
|
---|
494 | // Either src or target IP conflict exists
|
---|
495 | if (state <= ANNOUNCE) {
|
---|
496 | // PROBE or ANNOUNCE
|
---|
497 | conflicts++;
|
---|
498 | timeout_ms = PROBE_MIN * 1000
|
---|
499 | + CONFLICT_MULTIPLIER * random_delay_ms(conflicts);
|
---|
500 | goto new_nip_and_PROBE;
|
---|
501 | }
|
---|
502 |
|
---|
503 | // MONITOR or DEFEND: only src IP conflict is a problem
|
---|
504 | if (ip_conflict & 1) {
|
---|
505 | if (state == MONITOR) {
|
---|
506 | // Src IP conflict, defend with a single ARP probe
|
---|
507 | VDBG("monitor conflict - defending\n");
|
---|
508 | timeout_ms = DEFEND_INTERVAL * 1000;
|
---|
509 | state = DEFEND;
|
---|
510 | send_arp_request(chosen_nip, &G.our_ethaddr, chosen_nip);
|
---|
511 | continue;
|
---|
512 | }
|
---|
513 | // state == DEFEND
|
---|
514 | // Another src IP conflict, start over
|
---|
515 | VDBG("defend conflict - starting over\n");
|
---|
516 | run(argv, "deconfig", chosen_nip);
|
---|
517 | conflicts = 0;
|
---|
518 | timeout_ms = 0;
|
---|
519 | goto new_nip_and_PROBE;
|
---|
520 | }
|
---|
521 | // Note: if we only have a target IP conflict here (ip_conflict & 2),
|
---|
522 | // IOW: if we just saw this sort of ARP packet:
|
---|
523 | // aa:bb:cc:dd:ee:ff > xx:xx:xx:xx:xx:xx arp who-has <chosen_nip> tell 0.0.0.0
|
---|
524 | // we expect _kernel_ to respond to that, because <chosen_nip>
|
---|
525 | // is (expected to be) configured on this iface.
|
---|
526 | } // while (1)
|
---|
527 | #undef argv_intf
|
---|
528 | }
|
---|