networking/udhcp/clientpacket.c

   1 /* clientpacket.c
   2  *
   3  * Packet generation and dispatching functions for the DHCP client.
   4  *
   5  * Russ Dill <Russ.Dill@asu.edu> July 2001
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
   8  */
   9
  10 #include <string.h>
  11 #include <sys/socket.h>
  12 #include <features.h>
  13 #if (__GLIBC__ >= 2 && __GLIBC_MINOR >= 1) || defined _NEWLIB_VERSION
  14 #include <netpacket/packet.h>
  15 #include <net/ethernet.h>
  16 #else
  17 #include <asm/types.h>
  18 #include <linux/if_packet.h>
  19 #include <linux/if_ether.h>
  20 #endif
  21 #include <stdlib.h>
  22 #include <time.h>
  23 #include <unistd.h>
  24 #include <netinet/in.h>
  25 #include <arpa/inet.h>
  26 #include <fcntl.h>
  27
  28
  29 #include "dhcpd.h"
  30 #include "clientpacket.h"
  31 #include "options.h"
  32 #include "dhcpc.h"
  33 #include "common.h"
  34
  35
  36 /* Create a random xid */
  37 unsigned long random_xid(void)
  38 {
  39         static int initialized;
  40         if (!initialized) {
  41                 int fd;
  42                 unsigned long seed;
  43
  44                 fd = open("/dev/urandom", 0);
  45                 if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
  46                         LOG(LOG_WARNING, "Could not load seed from /dev/urandom: %m");
  47                         seed = time(0);
  48                 }
  49                 if (fd >= 0) close(fd);
  50                 srand(seed);
  51                 initialized++;
  52         }
  53         return rand();
  54 }
  55
  56
  57 /* initialize a packet with the proper defaults */
  58 static void init_packet(struct dhcpMessage *packet, char type)
  59 {
  60         udhcp_init_header(packet, type);
  61         memcpy(packet->chaddr, client_config.arp, 6);
  62         if (client_config.clientid)
  63             add_option_string(packet->options, client_config.clientid);
  64         if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
  65         if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
  66         add_option_string(packet->options, client_config.vendorclass);
  67 }
  68
  69
  70 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  71  * from the struct in options.c. Don't do bounds checking here because it
  72  * goes towards the head of the packet. */
  73 static void add_requests(struct dhcpMessage *packet)
  74 {
  75         int end = end_option(packet->options);
  76         int i, len = 0;
  77
  78         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  79         for (i = 0; dhcp_options[i].code; i++)
  80                 if (dhcp_options[i].flags & OPTION_REQ)
  81                         packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
  82         packet->options[end + OPT_LEN] = len;
  83         packet->options[end + OPT_DATA + len] = DHCP_END;
  84
  85 }
  86
  87
  88 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  89 int send_discover(unsigned long xid, unsigned long requested)
  90 {
  91         struct dhcpMessage packet;
  92
  93         init_packet(&packet, DHCPDISCOVER);
  94         packet.xid = xid;
  95         if (requested)
  96                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  97
  98         add_requests(&packet);
  99         LOG(LOG_DEBUG, "Sending discover...");
 100         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 101                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 102 }
 103
 104
 105 /* Broadcasts a DHCP request message */
 106 int send_selecting(unsigned long xid, unsigned long server, unsigned long requested)
 107 {
 108         struct dhcpMessage packet;
 109         struct in_addr addr;
 110
 111         init_packet(&packet, DHCPREQUEST);
 112         packet.xid = xid;
 113
 114         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 115         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 116
 117         add_requests(&packet);
 118         addr.s_addr = requested;
 119         LOG(LOG_DEBUG, "Sending select for %s...", inet_ntoa(addr));
 120         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 121                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 122 }
 123
 124
 125 /* Unicasts or broadcasts a DHCP renew message */
 126 int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr)
 127 {
 128         struct dhcpMessage packet;
 129         int ret = 0;
 130
 131         init_packet(&packet, DHCPREQUEST);
 132         packet.xid = xid;
 133         packet.ciaddr = ciaddr;
 134
 135         add_requests(&packet);
 136         LOG(LOG_DEBUG, "Sending renew...");
 137         if (server)
 138                 ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 139         else ret = udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 140                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 141         return ret;
 142 }
 143
 144
 145 /* Unicasts a DHCP release message */
 146 int send_release(unsigned long server, unsigned long ciaddr)
 147 {
 148         struct dhcpMessage packet;
 149
 150         init_packet(&packet, DHCPRELEASE);
 151         packet.xid = random_xid();
 152         packet.ciaddr = ciaddr;
 153
 154         add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
 155         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 156
 157         LOG(LOG_DEBUG, "Sending release...");
 158         return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 159 }
 160
 161
 162 /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
 163 int get_raw_packet(struct dhcpMessage *payload, int fd)
 164 {
 165         int bytes;
 166         struct udp_dhcp_packet packet;
 167         uint32_t source, dest;
 168         uint16_t check;
 169
 170         memset(&packet, 0, sizeof(struct udp_dhcp_packet));
 171         bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
 172         if (bytes < 0) {
 173                 DEBUG(LOG_INFO, "couldn't read on raw listening socket -- ignoring");
 174                 usleep(500000); /* possible down interface, looping condition */
 175                 return -1;
 176         }
 177
 178         if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
 179                 DEBUG(LOG_INFO, "message too short, ignoring");
 180                 return -2;
 181         }
 182
 183         if (bytes < ntohs(packet.ip.tot_len)) {
 184                 DEBUG(LOG_INFO, "Truncated packet");
 185                 return -2;
 186         }
 187
 188         /* ignore any extra garbage bytes */
 189         bytes = ntohs(packet.ip.tot_len);
 190
 191         /* Make sure its the right packet for us, and that it passes sanity checks */
 192         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION ||
 193             packet.ip.ihl != sizeof(packet.ip) >> 2 || packet.udp.dest != htons(CLIENT_PORT) ||
 194             bytes > (int) sizeof(struct udp_dhcp_packet) ||
 195             ntohs(packet.udp.len) != (uint16_t) (bytes - sizeof(packet.ip))) {
 196                 DEBUG(LOG_INFO, "unrelated/bogus packet");
 197                 return -2;
 198         }
 199
 200         /* check IP checksum */
 201         check = packet.ip.check;
 202         packet.ip.check = 0;
 203         if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
 204                 DEBUG(LOG_INFO, "bad IP header checksum, ignoring");
 205                 return -1;
 206         }
 207
 208         /* verify the UDP checksum by replacing the header with a psuedo header */
 209         source = packet.ip.saddr;
 210         dest = packet.ip.daddr;
 211         check = packet.udp.check;
 212         packet.udp.check = 0;
 213         memset(&packet.ip, 0, sizeof(packet.ip));
 214
 215         packet.ip.protocol = IPPROTO_UDP;
 216         packet.ip.saddr = source;
 217         packet.ip.daddr = dest;
 218         packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
 219         if (check && check != udhcp_checksum(&packet, bytes)) {
 220                 DEBUG(LOG_ERR, "packet with bad UDP checksum received, ignoring");
 221                 return -2;
 222         }
 223
 224         memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 225
 226         if (ntohl(payload->cookie) != DHCP_MAGIC) {
 227                 LOG(LOG_ERR, "received bogus message (bad magic) -- ignoring");
 228                 return -2;
 229         }
 230         DEBUG(LOG_INFO, "oooooh!!! got some!");
 231         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 232
 233 }