networking/udhcp/clientpacket.c

   1 /* vi: set sw=4 ts=4: */
   2 /* clientpacket.c
   3  *
   4  * Packet generation and dispatching functions for the DHCP client.
   5  *
   6  * Russ Dill <Russ.Dill@asu.edu> July 2001
   7  *
   8  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
   9  */
  10
  11 #include <features.h>
  12 #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
  13 #include <netpacket/packet.h>
  14 #include <net/ethernet.h>
  15 #else
  16 #include <asm/types.h>
  17 #include <linux/if_packet.h>
  18 #include <linux/if_ether.h>
  19 #endif
  20
  21 #include "common.h"
  22 #include "dhcpd.h"
  23 #include "dhcpc.h"
  24 #include "options.h"
  25
  26
  27 /* Create a random xid */
  28 uint32_t random_xid(void)
  29 {
  30         static smallint initialized;
  31
  32         if (!initialized) {
  33                 srand(monotonic_us());
  34                 initialized = 1;
  35         }
  36         return rand();
  37 }
  38
  39
  40 /* initialize a packet with the proper defaults */
  41 static void init_packet(struct dhcpMessage *packet, char type)
  42 {
  43         udhcp_init_header(packet, type);
  44         memcpy(packet->chaddr, client_config.arp, 6);
  45         if (client_config.clientid)
  46                 add_option_string(packet->options, client_config.clientid);
  47         if (client_config.hostname)
  48                 add_option_string(packet->options, client_config.hostname);
  49         if (client_config.fqdn)
  50                 add_option_string(packet->options, client_config.fqdn);
  51         add_option_string(packet->options, client_config.vendorclass);
  52 }
  53
  54
  55 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  56  * from the struct in options.c. Don't do bounds checking here because it
  57  * goes towards the head of the packet. */
  58 static void add_requests(struct dhcpMessage *packet)
  59 {
  60         int end = end_option(packet->options);
  61         int i, len = 0;
  62
  63         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  64         for (i = 0; dhcp_options[i].code; i++)
  65                 if (dhcp_options[i].flags & OPTION_REQ)
  66                         packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
  67         packet->options[end + OPT_LEN] = len;
  68         packet->options[end + OPT_DATA + len] = DHCP_END;
  69
  70 }
  71
  72 #if ENABLE_FEATURE_UDHCPC_ARPING
  73 /* Unicast a DHCP decline message */
  74 int send_decline(uint32_t xid, uint32_t server)
  75 {
  76         struct dhcpMessage packet;
  77
  78         init_packet(&packet, DHCPDECLINE);
  79         packet.xid = xid;
  80         add_requests(&packet);
  81
  82         bb_info_msg("Sending decline...");
  83
  84         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
  85                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
  86 }
  87 #endif
  88
  89 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  90 int send_discover(uint32_t xid, uint32_t requested)
  91 {
  92         struct dhcpMessage packet;
  93
  94         init_packet(&packet, DHCPDISCOVER);
  95         packet.xid = xid;
  96         if (requested)
  97                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  98
  99         /* Explicitly saying that we want RFC-compliant packets helps
 100          * some buggy DHCP servers to NOT send bigger packets */
 101         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 102         add_requests(&packet);
 103         bb_info_msg("Sending discover...");
 104         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 105                         SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 106 }
 107
 108
 109 /* Broadcasts a DHCP request message */
 110 int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
 111 {
 112         struct dhcpMessage packet;
 113         struct in_addr addr;
 114
 115         init_packet(&packet, DHCPREQUEST);
 116         packet.xid = xid;
 117
 118         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 119         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 120
 121         add_requests(&packet);
 122         addr.s_addr = requested;
 123         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 124         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 125                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 126 }
 127
 128
 129 /* Unicasts or broadcasts a DHCP renew message */
 130 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 131 {
 132         struct dhcpMessage packet;
 133
 134         init_packet(&packet, DHCPREQUEST);
 135         packet.xid = xid;
 136         packet.ciaddr = ciaddr;
 137
 138         add_requests(&packet);
 139         bb_info_msg("Sending renew...");
 140         if (server)
 141                 return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 142
 143         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 144                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 145 }
 146
 147
 148 /* Unicasts a DHCP release message */
 149 int send_release(uint32_t server, uint32_t ciaddr)
 150 {
 151         struct dhcpMessage packet;
 152
 153         init_packet(&packet, DHCPRELEASE);
 154         packet.xid = random_xid();
 155         packet.ciaddr = ciaddr;
 156
 157         add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
 158         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 159
 160         bb_info_msg("Sending release...");
 161         return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 162 }
 163
 164
 165 /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
 166 int get_raw_packet(struct dhcpMessage *payload, int fd)
 167 {
 168         int bytes;
 169         struct udp_dhcp_packet packet;
 170         uint32_t source, dest;
 171         uint16_t check;
 172
 173         memset(&packet, 0, sizeof(struct udp_dhcp_packet));
 174         bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
 175         if (bytes < 0) {
 176                 DEBUG("Cannot read on raw listening socket - ignoring");
 177                 sleep(1); /* possible down interface, looping condition */
 178                 return -1;
 179         }
 180
 181         if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
 182                 DEBUG("Message too short, ignoring");
 183                 return -2;
 184         }
 185
 186         if (bytes < ntohs(packet.ip.tot_len)) {
 187                 DEBUG("Truncated packet");
 188                 return -2;
 189         }
 190
 191         /* ignore any extra garbage bytes */
 192         bytes = ntohs(packet.ip.tot_len);
 193
 194         /* Make sure its the right packet for us, and that it passes sanity checks */
 195         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 196          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 197          || packet.udp.dest != htons(CLIENT_PORT)
 198          || bytes > (int) sizeof(struct udp_dhcp_packet)
 199          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 200         ) {
 201                 DEBUG("Unrelated/bogus packet");
 202                 return -2;
 203         }
 204
 205         /* check IP checksum */
 206         check = packet.ip.check;
 207         packet.ip.check = 0;
 208         if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
 209                 DEBUG("bad IP header checksum, ignoring");
 210                 return -1;
 211         }
 212
 213         /* verify the UDP checksum by replacing the header with a pseudo header */
 214         source = packet.ip.saddr;
 215         dest = packet.ip.daddr;
 216         check = packet.udp.check;
 217         packet.udp.check = 0;
 218         memset(&packet.ip, 0, sizeof(packet.ip));
 219
 220         packet.ip.protocol = IPPROTO_UDP;
 221         packet.ip.saddr = source;
 222         packet.ip.daddr = dest;
 223         packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
 224         if (check && check != udhcp_checksum(&packet, bytes)) {
 225                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 226                 return -2;
 227         }
 228
 229         memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 230
 231         if (payload->cookie != htonl(DHCP_MAGIC)) {
 232                 bb_error_msg("received bogus message (bad magic) - ignoring");
 233                 return -2;
 234         }
 235         DEBUG("oooooh!!! got some!");
 236         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 237 }