vcs.maemo.org Git - busybox4maemo/blob - 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         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         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  66         for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
  67                 if ((dhcp_options[i].flags & OPTION_REQ)
  68                  || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
  69                 ) {
  70                         packet->options[end + OPT_DATA + len] = c;
  71                         len++;
  72                 }
  73         }
  74         packet->options[end + OPT_LEN] = len;
  75         packet->options[end + OPT_DATA + len] = DHCP_END;
  76 }
  77
  78
  79 #if ENABLE_FEATURE_UDHCPC_ARPING
  80 /* Unicast a DHCP decline message */
  81 int send_decline(uint32_t xid, uint32_t server, uint32_t requested)
  82 {
  83         struct dhcpMessage packet;
  84
  85         init_packet(&packet, DHCPDECLINE);
  86         packet.xid = xid;
  87         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  88         add_simple_option(packet.options, DHCP_SERVER_ID, server);
  89
  90         bb_info_msg("Sending decline...");
  91
  92         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
  93                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
  94 }
  95 #endif
  96
  97 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  98 int send_discover(uint32_t xid, uint32_t requested)
  99 {
 100         struct dhcpMessage packet;
 101
 102         init_packet(&packet, DHCPDISCOVER);
 103         packet.xid = xid;
 104         if (requested)
 105                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 106
 107         /* Explicitly saying that we want RFC-compliant packets helps
 108          * some buggy DHCP servers to NOT send bigger packets */
 109         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 110         add_param_req_option(&packet);
 111         bb_info_msg("Sending discover...");
 112         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 113                         SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 114 }
 115
 116
 117 /* Broadcasts a DHCP request message */
 118 int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
 119 {
 120         struct dhcpMessage packet;
 121         struct in_addr addr;
 122
 123         init_packet(&packet, DHCPREQUEST);
 124         packet.xid = xid;
 125
 126         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 127         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 128
 129         add_param_req_option(&packet);
 130         addr.s_addr = requested;
 131         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 132         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 133                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 134 }
 135
 136
 137 /* Unicasts or broadcasts a DHCP renew message */
 138 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 139 {
 140         struct dhcpMessage packet;
 141
 142         init_packet(&packet, DHCPREQUEST);
 143         packet.xid = xid;
 144         packet.ciaddr = ciaddr;
 145
 146         add_param_req_option(&packet);
 147         bb_info_msg("Sending renew...");
 148         if (server)
 149                 return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 150
 151         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 152                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 153 }
 154
 155
 156 /* Unicasts a DHCP release message */
 157 int send_release(uint32_t server, uint32_t ciaddr)
 158 {
 159         struct dhcpMessage packet;
 160
 161         init_packet(&packet, DHCPRELEASE);
 162         packet.xid = random_xid();
 163         packet.ciaddr = ciaddr;
 164
 165         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 166
 167         bb_info_msg("Sending release...");
 168         return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 169 }
 170
 171
 172 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
 173 int get_raw_packet(struct dhcpMessage *payload, int fd)
 174 {
 175         int bytes;
 176         struct udp_dhcp_packet packet;
 177         uint16_t check;
 178
 179         memset(&packet, 0, sizeof(packet));
 180         bytes = safe_read(fd, &packet, sizeof(packet));
 181         if (bytes < 0) {
 182                 DEBUG("Cannot read on raw listening socket - ignoring");
 183                 sleep(1); /* possible down interface, looping condition */
 184                 return bytes; /* returns -1 */
 185         }
 186
 187         if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 188                 DEBUG("Packet is too short, ignoring");
 189                 return -2;
 190         }
 191
 192         if (bytes < ntohs(packet.ip.tot_len)) {
 193                 /* packet is bigger than sizeof(packet), we did partial read */
 194                 DEBUG("Oversized packet, ignoring");
 195                 return -2;
 196         }
 197
 198         /* ignore any extra garbage bytes */
 199         bytes = ntohs(packet.ip.tot_len);
 200
 201         /* make sure its the right packet for us, and that it passes sanity checks */
 202         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 203          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 204          || packet.udp.dest != htons(CLIENT_PORT)
 205         /* || bytes > (int) sizeof(packet) - can't happen */
 206          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 207         ) {
 208                 DEBUG("Unrelated/bogus packet");
 209                 return -2;
 210         }
 211
 212         /* verify IP checksum */
 213         check = packet.ip.check;
 214         packet.ip.check = 0;
 215         if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
 216                 DEBUG("Bad IP header checksum, ignoring");
 217                 return -2;
 218         }
 219
 220         /* verify UDP checksum. IP header has to be modified for this */
 221         memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
 222         /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
 223         packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 224         check = packet.udp.check;
 225         packet.udp.check = 0;
 226         if (check && check != udhcp_checksum(&packet, bytes)) {
 227                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 228                 return -2;
 229         }
 230
 231         memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 232
 233         if (payload->cookie != htonl(DHCP_MAGIC)) {
 234                 bb_error_msg("received bogus message (bad magic), ignoring");
 235                 return -2;
 236         }
 237         DEBUG("Got valid DHCP packet");
 238         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 239 }