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 FAST_FUNC 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         if ((type != DHCPDECLINE) && (type != DHCPRELEASE))
  52                 add_option_string(packet->options, client_config.vendorclass);
  53 }
  54
  55
  56 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  57  * from the struct in options.c. Don't do bounds checking here because it
  58  * goes towards the head of the packet. */
  59 static void add_param_req_option(struct dhcpMessage *packet)
  60 {
  61         uint8_t c;
  62         int end = end_option(packet->options);
  63         int i, len = 0;
  64
  65         for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
  66                 if (((dhcp_options[i].flags & OPTION_REQ)
  67                      && !client_config.no_default_options)
  68                  || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
  69                 ) {
  70                         packet->options[end + OPT_DATA + len] = c;
  71                         len++;
  72                 }
  73         }
  74         if (len) {
  75                 packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  76                 packet->options[end + OPT_LEN] = len;
  77                 packet->options[end + OPT_DATA + len] = DHCP_END;
  78         }
  79 }
  80
  81 /* RFC 2131
  82  * 4.4.4 Use of broadcast and unicast
  83  *
  84  * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
  85  * messages, unless the client knows the address of a DHCP server.
  86  * The client unicasts DHCPRELEASE messages to the server. Because
  87  * the client is declining the use of the IP address supplied by the server,
  88  * the client broadcasts DHCPDECLINE messages.
  89  *
  90  * When the DHCP client knows the address of a DHCP server, in either
  91  * INIT or REBOOTING state, the client may use that address
  92  * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
  93  * The client may also use unicast to send DHCPINFORM messages
  94  * to a known DHCP server. If the client receives no response to DHCP
  95  * messages sent to the IP address of a known DHCP server, the DHCP
  96  * client reverts to using the IP broadcast address.
  97  */
  98
  99 static int raw_bcast_from_client_config_ifindex(struct dhcpMessage *packet)
 100 {
 101         return udhcp_send_raw_packet(packet,
 102                 /*src*/ INADDR_ANY, CLIENT_PORT,
 103                 /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
 104                 client_config.ifindex);
 105 }
 106
 107
 108 #if ENABLE_FEATURE_UDHCPC_ARPING
 109 /* Broadcast a DHCP decline message */
 110 int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested)
 111 {
 112         struct dhcpMessage packet;
 113
 114         init_packet(&packet, DHCPDECLINE);
 115         packet.xid = xid;
 116         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 117         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 118
 119         bb_info_msg("Sending decline...");
 120
 121         return raw_bcast_from_client_config_ifindex(&packet);
 122 }
 123 #endif
 124
 125 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
 126 int FAST_FUNC send_discover(uint32_t xid, uint32_t requested)
 127 {
 128         struct dhcpMessage packet;
 129
 130         init_packet(&packet, DHCPDISCOVER);
 131         packet.xid = xid;
 132         if (requested)
 133                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 134
 135         /* Explicitly saying that we want RFC-compliant packets helps
 136          * some buggy DHCP servers to NOT send bigger packets */
 137         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 138
 139         add_param_req_option(&packet);
 140
 141         bb_info_msg("Sending discover...");
 142         return raw_bcast_from_client_config_ifindex(&packet);
 143 }
 144
 145
 146 /* Broadcasts a DHCP request message */
 147 /* RFC 2131 3.1 paragraph 3:
 148  * "The client _broadcasts_ a DHCPREQUEST message..."
 149  */
 150 int FAST_FUNC send_select(uint32_t xid, uint32_t server, uint32_t requested)
 151 {
 152         struct dhcpMessage packet;
 153         struct in_addr addr;
 154
 155         init_packet(&packet, DHCPREQUEST);
 156         packet.xid = xid;
 157
 158         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 159         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 160         add_param_req_option(&packet);
 161
 162         addr.s_addr = requested;
 163         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 164         return raw_bcast_from_client_config_ifindex(&packet);
 165 }
 166
 167
 168 /* Unicasts or broadcasts a DHCP renew message */
 169 int FAST_FUNC send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 170 {
 171         struct dhcpMessage packet;
 172
 173         init_packet(&packet, DHCPREQUEST);
 174         packet.xid = xid;
 175         packet.ciaddr = ciaddr;
 176
 177         add_param_req_option(&packet);
 178         bb_info_msg("Sending renew...");
 179         if (server)
 180                 return udhcp_send_kernel_packet(&packet,
 181                         ciaddr, CLIENT_PORT,
 182                         server, SERVER_PORT);
 183
 184         return raw_bcast_from_client_config_ifindex(&packet);
 185 }
 186
 187
 188 /* Unicasts a DHCP release message */
 189 int FAST_FUNC send_release(uint32_t server, uint32_t ciaddr)
 190 {
 191         struct dhcpMessage packet;
 192
 193         init_packet(&packet, DHCPRELEASE);
 194         packet.xid = random_xid();
 195         packet.ciaddr = ciaddr;
 196
 197         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 198
 199         bb_info_msg("Sending release...");
 200         return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 201 }
 202
 203
 204 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
 205 int FAST_FUNC udhcp_recv_raw_packet(struct dhcpMessage *payload, int fd)
 206 {
 207         int bytes;
 208         struct udp_dhcp_packet packet;
 209         uint16_t check;
 210
 211         memset(&packet, 0, sizeof(packet));
 212         bytes = safe_read(fd, &packet, sizeof(packet));
 213         if (bytes < 0) {
 214                 DEBUG("Cannot read on raw listening socket - ignoring");
 215                 /* NB: possible down interface, etc. Caller should pause. */
 216                 return bytes; /* returns -1 */
 217         }
 218
 219         if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 220                 DEBUG("Packet is too short, ignoring");
 221                 return -2;
 222         }
 223
 224         if (bytes < ntohs(packet.ip.tot_len)) {
 225                 /* packet is bigger than sizeof(packet), we did partial read */
 226                 DEBUG("Oversized packet, ignoring");
 227                 return -2;
 228         }
 229
 230         /* ignore any extra garbage bytes */
 231         bytes = ntohs(packet.ip.tot_len);
 232
 233         /* make sure its the right packet for us, and that it passes sanity checks */
 234         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 235          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 236          || packet.udp.dest != htons(CLIENT_PORT)
 237         /* || bytes > (int) sizeof(packet) - can't happen */
 238          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 239         ) {
 240                 DEBUG("Unrelated/bogus packet");
 241                 return -2;
 242         }
 243
 244         /* verify IP checksum */
 245         check = packet.ip.check;
 246         packet.ip.check = 0;
 247         if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
 248                 DEBUG("Bad IP header checksum, ignoring");
 249                 return -2;
 250         }
 251
 252         /* verify UDP checksum. IP header has to be modified for this */
 253         memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
 254         /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
 255         packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 256         check = packet.udp.check;
 257         packet.udp.check = 0;
 258         if (check && check != udhcp_checksum(&packet, bytes)) {
 259                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 260                 return -2;
 261         }
 262
 263         memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 264
 265         if (payload->cookie != htonl(DHCP_MAGIC)) {
 266                 bb_error_msg("received bogus message (bad magic), ignoring");
 267                 return -2;
 268         }
 269         DEBUG("Got valid DHCP packet");
 270         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 271 }