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 <string.h>
  12 #include <sys/socket.h>
  13 #include <features.h>
  14 #if (__GLIBC__ >= 2 && __GLIBC_MINOR >= 1) || defined _NEWLIB_VERSION
  15 #include <netpacket/packet.h>
  16 #include <net/ethernet.h>
  17 #else
  18 #include <asm/types.h>
  19 #include <linux/if_packet.h>
  20 #include <linux/if_ether.h>
  21 #endif
  22 #include <stdlib.h>
  23 #include <time.h>
  24 #include <unistd.h>
  25 #include <netinet/in.h>
  26 #include <arpa/inet.h>
  27 #include <fcntl.h>
  28
  29
  30 #include "dhcpd.h"
  31 #include "clientpacket.h"
  32 #include "options.h"
  33 #include "dhcpc.h"
  34 #include "common.h"
  35
  36
  37 /* Create a random xid */
  38 unsigned long random_xid(void)
  39 {
  40         static int initialized;
  41         if (!initialized) {
  42                 unsigned long seed;
  43
  44                 if (open_read_close("/dev/urandom", &seed, sizeof(seed)) < 0) {
  45                         bb_info_msg("Cannot load seed "
  46                                 "from /dev/urandom: %s", strerror(errno));
  47                         seed = time(0);
  48                 }
  49                 srand(seed);
  50                 initialized++;
  51         }
  52         return rand();
  53 }
  54
  55
  56 /* initialize a packet with the proper defaults */
  57 static void init_packet(struct dhcpMessage *packet, char type)
  58 {
  59         udhcp_init_header(packet, type);
  60         memcpy(packet->chaddr, client_config.arp, 6);
  61         if (client_config.clientid)
  62             add_option_string(packet->options, client_config.clientid);
  63         if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
  64         if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
  65         add_option_string(packet->options, client_config.vendorclass);
  66 }
  67
  68
  69 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  70  * from the struct in options.c. Don't do bounds checking here because it
  71  * goes towards the head of the packet. */
  72 static void add_requests(struct dhcpMessage *packet)
  73 {
  74         int end = end_option(packet->options);
  75         int i, len = 0;
  76
  77         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  78         for (i = 0; dhcp_options[i].code; i++)
  79                 if (dhcp_options[i].flags & OPTION_REQ)
  80                         packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
  81         packet->options[end + OPT_LEN] = len;
  82         packet->options[end + OPT_DATA + len] = DHCP_END;
  83
  84 }
  85
  86
  87 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  88 int send_discover(unsigned long xid, unsigned long requested)
  89 {
  90         struct dhcpMessage packet;
  91
  92         init_packet(&packet, DHCPDISCOVER);
  93         packet.xid = xid;
  94         if (requested)
  95                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  96
  97         add_requests(&packet);
  98         bb_info_msg("Sending discover...");
  99         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 100                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 101 }
 102
 103
 104 /* Broadcasts a DHCP request message */
 105 int send_selecting(unsigned long xid, unsigned long server, unsigned long requested)
 106 {
 107         struct dhcpMessage packet;
 108         struct in_addr addr;
 109
 110         init_packet(&packet, DHCPREQUEST);
 111         packet.xid = xid;
 112
 113         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 114         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 115
 116         add_requests(&packet);
 117         addr.s_addr = requested;
 118         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 119         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 120                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 121 }
 122
 123
 124 /* Unicasts or broadcasts a DHCP renew message */
 125 int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr)
 126 {
 127         struct dhcpMessage packet;
 128         int ret = 0;
 129
 130         init_packet(&packet, DHCPREQUEST);
 131         packet.xid = xid;
 132         packet.ciaddr = ciaddr;
 133
 134         add_requests(&packet);
 135         bb_info_msg("Sending renew...");
 136         if (server)
 137                 ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 138         else ret = udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 139                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 140         return ret;
 141 }
 142
 143
 144 /* Unicasts a DHCP release message */
 145 int send_release(unsigned long server, unsigned long ciaddr)
 146 {
 147         struct dhcpMessage packet;
 148
 149         init_packet(&packet, DHCPRELEASE);
 150         packet.xid = random_xid();
 151         packet.ciaddr = ciaddr;
 152
 153         add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
 154         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 155
 156         bb_info_msg("Sending release...");
 157         return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 158 }
 159
 160
 161 /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
 162 int get_raw_packet(struct dhcpMessage *payload, int fd)
 163 {
 164         int bytes;
 165         struct udp_dhcp_packet packet;
 166         uint32_t source, dest;
 167         uint16_t check;
 168
 169         memset(&packet, 0, sizeof(struct udp_dhcp_packet));
 170         bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
 171         if (bytes < 0) {
 172                 DEBUG("Cannot read on raw listening socket - ignoring");
 173                 usleep(500000); /* possible down interface, looping condition */
 174                 return -1;
 175         }
 176
 177         if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
 178                 DEBUG("Message too short, ignoring");
 179                 return -2;
 180         }
 181
 182         if (bytes < ntohs(packet.ip.tot_len)) {
 183                 DEBUG("Truncated packet");
 184                 return -2;
 185         }
 186
 187         /* ignore any extra garbage bytes */
 188         bytes = ntohs(packet.ip.tot_len);
 189
 190         /* Make sure its the right packet for us, and that it passes sanity checks */
 191         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION ||
 192             packet.ip.ihl != sizeof(packet.ip) >> 2 || packet.udp.dest != htons(CLIENT_PORT) ||
 193             bytes > (int) sizeof(struct udp_dhcp_packet) ||
 194             ntohs(packet.udp.len) != (uint16_t) (bytes - sizeof(packet.ip))) {
 195                 DEBUG("Unrelated/bogus packet");
 196                 return -2;
 197         }
 198
 199         /* check IP checksum */
 200         check = packet.ip.check;
 201         packet.ip.check = 0;
 202         if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
 203                 DEBUG("bad IP header checksum, ignoring");
 204                 return -1;
 205         }
 206
 207         /* verify the UDP checksum by replacing the header with a psuedo header */
 208         source = packet.ip.saddr;
 209         dest = packet.ip.daddr;
 210         check = packet.udp.check;
 211         packet.udp.check = 0;
 212         memset(&packet.ip, 0, sizeof(packet.ip));
 213
 214         packet.ip.protocol = IPPROTO_UDP;
 215         packet.ip.saddr = source;
 216         packet.ip.daddr = dest;
 217         packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
 218         if (check && check != udhcp_checksum(&packet, bytes)) {
 219                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 220                 return -2;
 221         }
 222
 223         memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 224
 225         if (ntohl(payload->cookie) != DHCP_MAGIC) {
 226                 bb_error_msg("received bogus message (bad magic) - ignoring");
 227                 return -2;
 228         }
 229         DEBUG("oooooh!!! got some!");
 230         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 231
 232 }