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 #include "common.h"
  11 #include "dhcpd.h"
  12 #include "dhcpc.h"
  13 #include "options.h"
  14
  15 //#include <features.h>
  16 #if (defined(__GLIBC__) && __GLIBC__ >= 2 && __GLIBC_MINOR__ >= 1) || defined _NEWLIB_VERSION
  17 #include <netpacket/packet.h>
  18 #include <net/ethernet.h>
  19 #else
  20 #include <asm/types.h>
  21 #include <linux/if_packet.h>
  22 #include <linux/if_ether.h>
  23 #endif
  24
  25
  26 /* Create a random xid */
  27 uint32_t FAST_FUNC random_xid(void)
  28 {
  29         static smallint initialized;
  30
  31         if (!initialized) {
  32                 srand(monotonic_us());
  33                 initialized = 1;
  34         }
  35         return rand();
  36 }
  37
  38
  39 /* Initialize the packet with the proper defaults */
  40 static void init_packet(struct dhcp_packet *packet, char type)
  41 {
  42         udhcp_init_header(packet, type);
  43         memcpy(packet->chaddr, client_config.client_mac, 6);
  44         if (client_config.clientid)
  45                 add_option_string(packet->options, client_config.clientid);
  46         if (client_config.hostname)
  47                 add_option_string(packet->options, client_config.hostname);
  48         if (client_config.fqdn)
  49                 add_option_string(packet->options, client_config.fqdn);
  50         if ((type != DHCPDECLINE) && (type != DHCPRELEASE))
  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_param_req_option(struct dhcp_packet *packet)
  59 {
  60         uint8_t c;
  61         int end = end_option(packet->options);
  62         int i, len = 0;
  63
  64         for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
  65                 if (((dhcp_options[i].flags & OPTION_REQ)
  66                      && !client_config.no_default_options)
  67                  || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
  68                 ) {
  69                         packet->options[end + OPT_DATA + len] = c;
  70                         len++;
  71                 }
  72         }
  73         if (len) {
  74                 packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  75                 packet->options[end + OPT_LEN] = len;
  76                 packet->options[end + OPT_DATA + len] = DHCP_END;
  77         }
  78 }
  79
  80 /* RFC 2131
  81  * 4.4.4 Use of broadcast and unicast
  82  *
  83  * The DHCP client broadcasts DHCPDISCOVER, DHCPREQUEST and DHCPINFORM
  84  * messages, unless the client knows the address of a DHCP server.
  85  * The client unicasts DHCPRELEASE messages to the server. Because
  86  * the client is declining the use of the IP address supplied by the server,
  87  * the client broadcasts DHCPDECLINE messages.
  88  *
  89  * When the DHCP client knows the address of a DHCP server, in either
  90  * INIT or REBOOTING state, the client may use that address
  91  * in the DHCPDISCOVER or DHCPREQUEST rather than the IP broadcast address.
  92  * The client may also use unicast to send DHCPINFORM messages
  93  * to a known DHCP server. If the client receives no response to DHCP
  94  * messages sent to the IP address of a known DHCP server, the DHCP
  95  * client reverts to using the IP broadcast address.
  96  */
  97
  98 static int raw_bcast_from_client_config_ifindex(struct dhcp_packet *packet)
  99 {
 100         return udhcp_send_raw_packet(packet,
 101                 /*src*/ INADDR_ANY, CLIENT_PORT,
 102                 /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
 103                 client_config.ifindex);
 104 }
 105
 106
 107 #if ENABLE_FEATURE_UDHCPC_ARPING
 108 /* Broadcast a DHCP decline message */
 109 int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested)
 110 {
 111         struct dhcp_packet packet;
 112
 113         init_packet(&packet, DHCPDECLINE);
 114         packet.xid = xid;
 115         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 116         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 117
 118         bb_info_msg("Sending decline...");
 119
 120         return raw_bcast_from_client_config_ifindex(&packet);
 121 }
 122 #endif
 123
 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 dhcp_packet 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 /* Broadcast 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 dhcp_packet 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 /* Unicast or broadcast a DHCP renew message */
 169 int FAST_FUNC send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 170 {
 171         struct dhcp_packet 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 /* Unicast a DHCP release message */
 189 int FAST_FUNC send_release(uint32_t server, uint32_t ciaddr)
 190 {
 191         struct dhcp_packet 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 dhcp_packet *dhcp_pkt, int fd)
 206 {
 207         int bytes;
 208         struct ip_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                 log1("Packet read error, 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                 log1("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                 log1("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                 log1("Unrelated/bogus packet, ignoring");
 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                 log1("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                 log1("Packet with bad UDP checksum received, ignoring");
 260                 return -2;
 261         }
 262
 263         memcpy(dhcp_pkt, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 264
 265         if (dhcp_pkt->cookie != htonl(DHCP_MAGIC)) {
 266                 bb_info_msg("Packet with bad magic, ignoring");
 267                 return -2;
 268         }
 269         log1("Got valid DHCP packet");
 270         udhcp_dump_packet(dhcp_pkt);
 271         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 272 }