1 | /* vi: set sw=4 ts=4: */
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2 | /* clientpacket.c
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3 | *
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4 | * Packet generation and dispatching functions for the DHCP client.
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5 | *
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6 | * Russ Dill <Russ.Dill@asu.edu> July 2001
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7 | *
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8 | * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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9 | */
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10 |
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11 | #include <features.h>
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12 | #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
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13 | #include <netpacket/packet.h>
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14 | #include <net/ethernet.h>
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15 | #else
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16 | #include <asm/types.h>
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17 | #include <linux/if_packet.h>
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18 | #include <linux/if_ether.h>
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19 | #endif
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20 |
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21 | #include "common.h"
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22 | #include "dhcpd.h"
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23 | #include "dhcpc.h"
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24 | #include "options.h"
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25 |
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26 |
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27 | /* Create a random xid */
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28 | uint32_t random_xid(void)
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29 | {
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30 | static smallint initialized;
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31 |
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32 | if (!initialized) {
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33 | srand(monotonic_us());
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34 | initialized = 1;
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35 | }
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36 | return rand();
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37 | }
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38 |
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39 |
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40 | /* initialize a packet with the proper defaults */
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41 | static void init_packet(struct dhcpMessage *packet, char type)
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42 | {
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43 | udhcp_init_header(packet, type);
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44 | memcpy(packet->chaddr, client_config.arp, 6);
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45 | if (client_config.clientid)
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46 | add_option_string(packet->options, client_config.clientid);
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47 | if (client_config.hostname)
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48 | add_option_string(packet->options, client_config.hostname);
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49 | if (client_config.fqdn)
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50 | add_option_string(packet->options, client_config.fqdn);
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51 | add_option_string(packet->options, client_config.vendorclass);
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52 | }
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53 |
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54 |
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55 | /* Add a parameter request list for stubborn DHCP servers. Pull the data
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56 | * from the struct in options.c. Don't do bounds checking here because it
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57 | * goes towards the head of the packet. */
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58 | static void add_requests(struct dhcpMessage *packet)
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59 | {
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60 | int end = end_option(packet->options);
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61 | int i, len = 0;
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62 |
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63 | packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
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64 | for (i = 0; dhcp_options[i].code; i++)
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65 | if (dhcp_options[i].flags & OPTION_REQ)
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66 | packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
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67 | packet->options[end + OPT_LEN] = len;
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68 | packet->options[end + OPT_DATA + len] = DHCP_END;
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69 |
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70 | }
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71 |
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72 |
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73 | /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
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74 | int send_discover(uint32_t xid, uint32_t requested)
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75 | {
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76 | struct dhcpMessage packet;
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77 |
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78 | init_packet(&packet, DHCPDISCOVER);
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79 | packet.xid = xid;
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80 | if (requested)
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81 | add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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82 |
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83 | add_requests(&packet);
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84 | bb_info_msg("Sending discover...");
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85 | return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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86 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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87 | }
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88 |
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89 |
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90 | /* Broadcasts a DHCP request message */
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91 | int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
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92 | {
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93 | struct dhcpMessage packet;
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94 | struct in_addr addr;
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95 |
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96 | init_packet(&packet, DHCPREQUEST);
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97 | packet.xid = xid;
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98 |
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99 | add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
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100 | add_simple_option(packet.options, DHCP_SERVER_ID, server);
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101 |
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102 | add_requests(&packet);
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103 | addr.s_addr = requested;
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104 | bb_info_msg("Sending select for %s...", inet_ntoa(addr));
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105 | return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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106 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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107 | }
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108 |
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109 |
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110 | /* Unicasts or broadcasts a DHCP renew message */
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111 | int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
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112 | {
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113 | struct dhcpMessage packet;
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114 |
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115 | init_packet(&packet, DHCPREQUEST);
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116 | packet.xid = xid;
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117 | packet.ciaddr = ciaddr;
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118 |
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119 | add_requests(&packet);
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120 | bb_info_msg("Sending renew...");
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121 | if (server)
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122 | return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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123 |
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124 | return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
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125 | SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
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126 | }
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127 |
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128 |
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129 | /* Unicasts a DHCP release message */
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130 | int send_release(uint32_t server, uint32_t ciaddr)
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131 | {
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132 | struct dhcpMessage packet;
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133 |
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134 | init_packet(&packet, DHCPRELEASE);
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135 | packet.xid = random_xid();
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136 | packet.ciaddr = ciaddr;
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137 |
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138 | add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
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139 | add_simple_option(packet.options, DHCP_SERVER_ID, server);
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140 |
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141 | bb_info_msg("Sending release...");
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142 | return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
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143 | }
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144 |
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145 |
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146 | /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
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147 | int get_raw_packet(struct dhcpMessage *payload, int fd)
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148 | {
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149 | int bytes;
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150 | struct udp_dhcp_packet packet;
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151 | uint32_t source, dest;
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152 | uint16_t check;
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153 |
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154 | memset(&packet, 0, sizeof(struct udp_dhcp_packet));
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155 | bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
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156 | if (bytes < 0) {
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157 | DEBUG("Cannot read on raw listening socket - ignoring");
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158 | usleep(500000); /* possible down interface, looping condition */
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159 | return -1;
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160 | }
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161 |
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162 | if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
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163 | DEBUG("Message too short, ignoring");
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164 | return -2;
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165 | }
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166 |
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167 | if (bytes < ntohs(packet.ip.tot_len)) {
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168 | DEBUG("Truncated packet");
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169 | return -2;
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170 | }
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171 |
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172 | /* ignore any extra garbage bytes */
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173 | bytes = ntohs(packet.ip.tot_len);
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174 |
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175 | /* Make sure its the right packet for us, and that it passes sanity checks */
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176 | if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
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177 | || packet.ip.ihl != sizeof(packet.ip) >> 2
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178 | || packet.udp.dest != htons(CLIENT_PORT)
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179 | || bytes > (int) sizeof(struct udp_dhcp_packet)
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180 | || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
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181 | ) {
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182 | DEBUG("Unrelated/bogus packet");
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183 | return -2;
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184 | }
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185 |
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186 | /* check IP checksum */
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187 | check = packet.ip.check;
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188 | packet.ip.check = 0;
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189 | if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
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190 | DEBUG("bad IP header checksum, ignoring");
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191 | return -1;
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192 | }
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193 |
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194 | /* verify the UDP checksum by replacing the header with a psuedo header */
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195 | source = packet.ip.saddr;
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196 | dest = packet.ip.daddr;
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197 | check = packet.udp.check;
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198 | packet.udp.check = 0;
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199 | memset(&packet.ip, 0, sizeof(packet.ip));
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200 |
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201 | packet.ip.protocol = IPPROTO_UDP;
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202 | packet.ip.saddr = source;
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203 | packet.ip.daddr = dest;
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204 | packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
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205 | if (check && check != udhcp_checksum(&packet, bytes)) {
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206 | bb_error_msg("packet with bad UDP checksum received, ignoring");
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207 | return -2;
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208 | }
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209 |
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210 | memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
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211 |
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212 | if (ntohl(payload->cookie) != DHCP_MAGIC) {
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213 | bb_error_msg("received bogus message (bad magic) - ignoring");
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214 | return -2;
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215 | }
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216 | DEBUG("oooooh!!! got some!");
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217 | return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
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218 | }
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