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
  82 static int raw_bcast_from_client_config_ifindex(struct dhcpMessage *packet)
  83 {
  84         return udhcp_send_raw_packet(packet,
  85                 /*src*/ INADDR_ANY, CLIENT_PORT,
  86                 /*dst*/ INADDR_BROADCAST, SERVER_PORT, MAC_BCAST_ADDR,
  87                 client_config.ifindex);
  88 }
  89
  90
  91 #if ENABLE_FEATURE_UDHCPC_ARPING
  92 /* Broadcast a DHCP decline message */
  93 //FIXME: maybe it should be unicast?
  94 int FAST_FUNC send_decline(uint32_t xid, uint32_t server, uint32_t requested)
  95 {
  96         struct dhcpMessage packet;
  97
  98         init_packet(&packet, DHCPDECLINE);
  99         packet.xid = xid;
 100         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 101         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 102
 103         bb_info_msg("Sending decline...");
 104
 105         return raw_bcast_from_client_config_ifindex(&packet);
 106 }
 107 #endif
 108
 109 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
 110 int FAST_FUNC send_discover(uint32_t xid, uint32_t requested)
 111 {
 112         struct dhcpMessage packet;
 113
 114         init_packet(&packet, DHCPDISCOVER);
 115         packet.xid = xid;
 116         if (requested)
 117                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 118
 119         /* Explicitly saying that we want RFC-compliant packets helps
 120          * some buggy DHCP servers to NOT send bigger packets */
 121         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 122
 123         add_param_req_option(&packet);
 124
 125         bb_info_msg("Sending discover...");
 126         return raw_bcast_from_client_config_ifindex(&packet);
 127 }
 128
 129
 130 /* Broadcasts a DHCP request message */
 131 //FIXME: maybe it should be unicast?
 132 int FAST_FUNC send_select(uint32_t xid, uint32_t server, uint32_t requested)
 133 {
 134         struct dhcpMessage packet;
 135         struct in_addr addr;
 136
 137         init_packet(&packet, DHCPREQUEST);
 138         packet.xid = xid;
 139
 140         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 141         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 142         add_param_req_option(&packet);
 143
 144         addr.s_addr = requested;
 145         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 146         return raw_bcast_from_client_config_ifindex(&packet);
 147 }
 148
 149
 150 /* Unicasts or broadcasts a DHCP renew message */
 151 int FAST_FUNC send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 152 {
 153         struct dhcpMessage packet;
 154
 155         init_packet(&packet, DHCPREQUEST);
 156         packet.xid = xid;
 157         packet.ciaddr = ciaddr;
 158
 159         add_param_req_option(&packet);
 160         bb_info_msg("Sending renew...");
 161         if (server)
 162                 return udhcp_send_kernel_packet(&packet,
 163                         ciaddr, CLIENT_PORT,
 164                         server, SERVER_PORT);
 165
 166         return raw_bcast_from_client_config_ifindex(&packet);
 167 }
 168
 169
 170 /* Unicasts a DHCP release message */
 171 int FAST_FUNC send_release(uint32_t server, uint32_t ciaddr)
 172 {
 173         struct dhcpMessage packet;
 174
 175         init_packet(&packet, DHCPRELEASE);
 176         packet.xid = random_xid();
 177         packet.ciaddr = ciaddr;
 178
 179         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 180
 181         bb_info_msg("Sending release...");
 182         return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 183 }
 184
 185
 186 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
 187 int FAST_FUNC udhcp_recv_raw_packet(struct dhcpMessage *payload, int fd)
 188 {
 189         int bytes;
 190         struct udp_dhcp_packet packet;
 191         uint16_t check;
 192
 193         memset(&packet, 0, sizeof(packet));
 194         bytes = safe_read(fd, &packet, sizeof(packet));
 195         if (bytes < 0) {
 196                 DEBUG("Cannot read on raw listening socket - ignoring");
 197                 /* NB: possible down interface, etc. Caller should pause. */
 198                 return bytes; /* returns -1 */
 199         }
 200
 201         if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 202                 DEBUG("Packet is too short, ignoring");
 203                 return -2;
 204         }
 205
 206         if (bytes < ntohs(packet.ip.tot_len)) {
 207                 /* packet is bigger than sizeof(packet), we did partial read */
 208                 DEBUG("Oversized packet, ignoring");
 209                 return -2;
 210         }
 211
 212         /* ignore any extra garbage bytes */
 213         bytes = ntohs(packet.ip.tot_len);
 214
 215         /* make sure its the right packet for us, and that it passes sanity checks */
 216         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 217          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 218          || packet.udp.dest != htons(CLIENT_PORT)
 219         /* || bytes > (int) sizeof(packet) - can't happen */
 220          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 221         ) {
 222                 DEBUG("Unrelated/bogus packet");
 223                 return -2;
 224         }
 225
 226         /* verify IP checksum */
 227         check = packet.ip.check;
 228         packet.ip.check = 0;
 229         if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
 230                 DEBUG("Bad IP header checksum, ignoring");
 231                 return -2;
 232         }
 233
 234         /* verify UDP checksum. IP header has to be modified for this */
 235         memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
 236         /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
 237         packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 238         check = packet.udp.check;
 239         packet.udp.check = 0;
 240         if (check && check != udhcp_checksum(&packet, bytes)) {
 241                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 242                 return -2;
 243         }
 244
 245         memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 246
 247         if (payload->cookie != htonl(DHCP_MAGIC)) {
 248                 bb_error_msg("received bogus message (bad magic), ignoring");
 249                 return -2;
 250         }
 251         DEBUG("Got valid DHCP packet");
 252         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 253 }