1 | /* vi: set sw=4 ts=4: */
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2 | /* Port to Busybox Copyright (C) 2006 Jesse Dutton <jessedutton@gmail.com>
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3 | *
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4 | * Licensed under GPLv2, see file LICENSE in this source tree.
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5 | *
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6 | * DHCP Relay for 'DHCPv4 Configuration of IPSec Tunnel Mode' support
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7 | * Copyright (C) 2002 Mario Strasser <mast@gmx.net>,
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8 | * Zuercher Hochschule Winterthur,
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9 | * Netbeat AG
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10 | * Upstream has GPL v2 or later
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11 | */
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12 |
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13 | //usage:#define dhcprelay_trivial_usage
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14 | //usage: "CLIENT_IFACE[,CLIENT_IFACE2]... SERVER_IFACE [SERVER_IP]"
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15 | //usage:#define dhcprelay_full_usage "\n\n"
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16 | //usage: "Relay DHCP requests between clients and server"
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17 |
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18 | #include "common.h"
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19 |
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20 | #define SERVER_PORT 67
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21 |
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22 | /* lifetime of an xid entry in sec. */
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23 | #define MAX_LIFETIME 2*60
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24 | /* select timeout in sec. */
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25 | #define SELECT_TIMEOUT (MAX_LIFETIME / 8)
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26 |
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27 | /* This list holds information about clients. The xid_* functions manipulate this list. */
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28 | struct xid_item {
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29 | unsigned timestamp;
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30 | int client;
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31 | uint32_t xid;
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32 | struct sockaddr_in ip;
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33 | struct xid_item *next;
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34 | } FIX_ALIASING;
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35 |
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36 | #define dhcprelay_xid_list (*(struct xid_item*)&bb_common_bufsiz1)
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37 |
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38 | static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client)
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39 | {
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40 | struct xid_item *item;
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41 |
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42 | /* create new xid entry */
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43 | item = xmalloc(sizeof(struct xid_item));
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44 |
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45 | /* add xid entry */
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46 | item->ip = *ip;
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47 | item->xid = xid;
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48 | item->client = client;
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49 | item->timestamp = monotonic_sec();
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50 | item->next = dhcprelay_xid_list.next;
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51 | dhcprelay_xid_list.next = item;
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52 |
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53 | return item;
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54 | }
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55 |
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56 | static void xid_expire(void)
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57 | {
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58 | struct xid_item *item = dhcprelay_xid_list.next;
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59 | struct xid_item *last = &dhcprelay_xid_list;
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60 | unsigned current_time = monotonic_sec();
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61 |
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62 | while (item != NULL) {
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63 | if ((current_time - item->timestamp) > MAX_LIFETIME) {
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64 | last->next = item->next;
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65 | free(item);
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66 | item = last->next;
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67 | } else {
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68 | last = item;
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69 | item = item->next;
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70 | }
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71 | }
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72 | }
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73 |
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74 | static struct xid_item *xid_find(uint32_t xid)
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75 | {
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76 | struct xid_item *item = dhcprelay_xid_list.next;
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77 | while (item != NULL) {
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78 | if (item->xid == xid) {
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79 | break;
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80 | }
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81 | item = item->next;
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82 | }
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83 | return item;
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84 | }
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85 |
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86 | static void xid_del(uint32_t xid)
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87 | {
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88 | struct xid_item *item = dhcprelay_xid_list.next;
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89 | struct xid_item *last = &dhcprelay_xid_list;
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90 | while (item != NULL) {
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91 | if (item->xid == xid) {
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92 | last->next = item->next;
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93 | free(item);
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94 | item = last->next;
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95 | } else {
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96 | last = item;
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97 | item = item->next;
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98 | }
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99 | }
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100 | }
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101 |
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102 | /**
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103 | * get_dhcp_packet_type - gets the message type of a dhcp packet
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104 | * p - pointer to the dhcp packet
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105 | * returns the message type on success, -1 otherwise
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106 | */
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107 | static int get_dhcp_packet_type(struct dhcp_packet *p)
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108 | {
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109 | uint8_t *op;
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110 |
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111 | /* it must be either a BOOTREQUEST or a BOOTREPLY */
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112 | if (p->op != BOOTREQUEST && p->op != BOOTREPLY)
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113 | return -1;
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114 | /* get message type option */
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115 | op = udhcp_get_option(p, DHCP_MESSAGE_TYPE);
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116 | if (op != NULL)
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117 | return op[0];
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118 | return -1;
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119 | }
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120 |
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121 | /**
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122 | * make_iface_list - parses client/server interface names
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123 | * returns array
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124 | */
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125 | static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
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126 | {
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127 | char *s, **iface_list;
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128 | int i, cn;
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129 |
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130 | /* get number of items */
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131 | cn = 2; /* 1 server iface + at least 1 client one */
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132 | s = client_and_server_ifaces[0]; /* list of client ifaces */
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133 | while (*s) {
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134 | if (*s == ',')
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135 | cn++;
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136 | s++;
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137 | }
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138 | *client_number = cn;
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139 |
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140 | /* create vector of pointers */
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141 | iface_list = xzalloc(cn * sizeof(iface_list[0]));
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142 |
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143 | iface_list[0] = client_and_server_ifaces[1]; /* server iface */
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144 |
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145 | i = 1;
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146 | s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */
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147 | goto store_client_iface_name;
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148 |
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149 | while (i < cn) {
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150 | if (*s++ == ',') {
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151 | s[-1] = '\0';
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152 | store_client_iface_name:
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153 | iface_list[i++] = s;
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154 | }
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155 | }
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156 |
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157 | return iface_list;
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158 | }
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159 |
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160 | /* Creates listen sockets (in fds) bound to client and server ifaces,
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161 | * and returns numerically max fd.
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162 | */
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163 | static int init_sockets(char **iface_list, int num_clients, int *fds)
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164 | {
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165 | int i, n;
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166 |
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167 | n = 0;
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168 | for (i = 0; i < num_clients; i++) {
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169 | fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]);
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170 | if (n < fds[i])
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171 | n = fds[i];
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172 | }
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173 | return n;
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174 | }
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175 |
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176 | static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to)
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177 | {
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178 | int err;
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179 |
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180 | errno = 0;
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181 | err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to));
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182 | err -= msg_len;
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183 | if (err)
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184 | bb_perror_msg("sendto");
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185 | return err;
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186 | }
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187 |
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188 | /**
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189 | * pass_to_server() - forwards dhcp packets from client to server
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190 | * p - packet to send
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191 | * client - number of the client
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192 | */
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193 | static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
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194 | struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
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195 | {
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196 | int type;
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197 |
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198 | /* check packet_type */
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199 | type = get_dhcp_packet_type(p);
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200 | if (type != DHCPDISCOVER && type != DHCPREQUEST
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201 | && type != DHCPDECLINE && type != DHCPRELEASE
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202 | && type != DHCPINFORM
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203 | ) {
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204 | return;
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205 | }
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206 |
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207 | /* create new xid entry */
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208 | xid_add(p->xid, client_addr, client);
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209 |
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210 | /* forward request to server */
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211 | /* note that we send from fds[0] which is bound to SERVER_PORT (67).
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212 | * IOW: we send _from_ SERVER_PORT! Although this may look strange,
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213 | * RFC 1542 not only allows, but prescribes this for BOOTP relays.
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214 | */
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215 | sendto_ip4(fds[0], p, packet_len, server_addr);
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216 | }
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217 |
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218 | /**
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219 | * pass_to_client() - forwards dhcp packets from server to client
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220 | * p - packet to send
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221 | */
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222 | static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
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223 | {
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224 | int type;
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225 | struct xid_item *item;
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226 |
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227 | /* check xid */
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228 | item = xid_find(p->xid);
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229 | if (!item) {
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230 | return;
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231 | }
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232 |
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233 | /* check packet type */
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234 | type = get_dhcp_packet_type(p);
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235 | if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
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236 | return;
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237 | }
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238 |
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239 | //TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set!
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240 | if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
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241 | item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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242 |
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243 | if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
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244 | return; /* send error occurred */
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245 | }
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246 |
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247 | /* remove xid entry */
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248 | xid_del(p->xid);
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249 | }
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250 |
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251 | int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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252 | int dhcprelay_main(int argc, char **argv)
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253 | {
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254 | struct sockaddr_in server_addr;
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255 | char **iface_list;
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256 | int *fds;
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257 | int num_sockets, max_socket;
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258 | uint32_t our_nip;
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259 |
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260 | server_addr.sin_family = AF_INET;
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261 | server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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262 | server_addr.sin_port = htons(SERVER_PORT);
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263 |
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264 | /* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
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265 | if (argc == 4) {
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266 | if (!inet_aton(argv[3], &server_addr.sin_addr))
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267 | bb_perror_msg_and_die("bad server IP");
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268 | } else if (argc != 3) {
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269 | bb_show_usage();
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270 | }
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271 |
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272 | iface_list = make_iface_list(argv + 1, &num_sockets);
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273 |
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274 | fds = xmalloc(num_sockets * sizeof(fds[0]));
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275 |
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276 | /* Create sockets and bind one to every iface */
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277 | max_socket = init_sockets(iface_list, num_sockets, fds);
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278 |
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279 | /* Get our IP on server_iface */
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280 | if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
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281 | return 1;
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282 |
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283 | /* Main loop */
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284 | while (1) {
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285 | // reinit stuff from time to time? go back to make_iface_list
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286 | // every N minutes?
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287 | fd_set rfds;
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288 | struct timeval tv;
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289 | int i;
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290 |
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291 | FD_ZERO(&rfds);
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292 | for (i = 0; i < num_sockets; i++)
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293 | FD_SET(fds[i], &rfds);
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294 | tv.tv_sec = SELECT_TIMEOUT;
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295 | tv.tv_usec = 0;
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296 | if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
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297 | int packlen;
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298 | struct dhcp_packet dhcp_msg;
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299 |
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300 | /* server */
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301 | if (FD_ISSET(fds[0], &rfds)) {
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302 | packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
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303 | if (packlen > 0) {
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304 | pass_to_client(&dhcp_msg, packlen, fds);
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305 | }
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306 | }
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307 |
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308 | /* clients */
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309 | for (i = 1; i < num_sockets; i++) {
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310 | struct sockaddr_in client_addr;
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311 | socklen_t addr_size;
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312 |
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313 | if (!FD_ISSET(fds[i], &rfds))
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314 | continue;
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315 |
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316 | addr_size = sizeof(client_addr);
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317 | packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
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318 | (struct sockaddr *)(&client_addr), &addr_size);
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319 | if (packlen <= 0)
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320 | continue;
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321 |
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322 | /* Get our IP on corresponding client_iface */
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323 | // RFC 1542
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324 | // 4.1 General BOOTP Processing for Relay Agents
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325 | // 4.1.1 BOOTREQUEST Messages
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326 | // If the relay agent does decide to relay the request, it MUST examine
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327 | // the 'giaddr' ("gateway" IP address) field. If this field is zero,
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328 | // the relay agent MUST fill this field with the IP address of the
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329 | // interface on which the request was received. If the interface has
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330 | // more than one IP address logically associated with it, the relay
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331 | // agent SHOULD choose one IP address associated with that interface and
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332 | // use it consistently for all BOOTP messages it relays. If the
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333 | // 'giaddr' field contains some non-zero value, the 'giaddr' field MUST
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334 | // NOT be modified. The relay agent MUST NOT, under any circumstances,
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335 | // fill the 'giaddr' field with a broadcast address as is suggested in
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336 | // [1] (Section 8, sixth paragraph).
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337 |
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338 | // but why? what if server can't route such IP? Client ifaces may be, say, NATed!
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339 |
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340 | // 4.1.2 BOOTREPLY Messages
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341 | // BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
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342 | // It is the responsibility of BOOTP servers to send BOOTREPLY messages
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343 | // directly to the relay agent identified in the 'giaddr' field.
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344 | // (yeah right, unless it is impossible... see comment above)
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345 | // Therefore, a relay agent may assume that all BOOTREPLY messages it
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346 | // receives are intended for BOOTP clients on its directly-connected
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347 | // networks.
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348 | //
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349 | // When a relay agent receives a BOOTREPLY message, it should examine
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350 | // the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
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351 | // These fields should provide adequate information for the relay agent
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352 | // to deliver the BOOTREPLY message to the client.
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353 | //
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354 | // The 'giaddr' field can be used to identify the logical interface from
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355 | // which the reply must be sent (i.e., the host or router interface
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356 | // connected to the same network as the BOOTP client). If the content
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357 | // of the 'giaddr' field does not match one of the relay agent's
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358 | // directly-connected logical interfaces, the BOOTREPLY messsage MUST be
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359 | // silently discarded.
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360 | if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) {
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361 | /* Fall back to our IP on server iface */
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362 | // this makes more sense!
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363 | dhcp_msg.gateway_nip = our_nip;
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364 | }
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365 | // maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
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366 | pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
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367 | }
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368 | }
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369 | xid_expire();
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370 | } /* while (1) */
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371 |
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372 | /* return 0; - not reached */
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373 | }
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