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                 int fd;
  43                 unsigned long seed;
  44
  45                 fd = open("/dev/urandom", 0);
  46                 if (fd < 0 || read(fd, &seed, sizeof(seed)) < 0) {
  47                         bb_info_msg("Could not load seed "
  48                                 "from /dev/urandom: %s", strerror(errno));
  49                         seed = time(0);
  50                 }
  51                 if (fd >= 0) close(fd);
  52                 srand(seed);
  53                 initialized++;
  54         }
  55         return rand();
  56 }
  57
  58
  59 /* initialize a packet with the proper defaults */
  60 static void init_packet(struct dhcpMessage *packet, char type)
  61 {
  62         udhcp_init_header(packet, type);
  63         memcpy(packet->chaddr, client_config.arp, 6);
  64         if (client_config.clientid)
  65             add_option_string(packet->options, client_config.clientid);
  66         if (client_config.hostname) add_option_string(packet->options, client_config.hostname);
  67         if (client_config.fqdn) add_option_string(packet->options, client_config.fqdn);
  68         add_option_string(packet->options, client_config.vendorclass);
  69 }
  70
  71
  72 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  73  * from the struct in options.c. Don't do bounds checking here because it
  74  * goes towards the head of the packet. */
  75 static void add_requests(struct dhcpMessage *packet)
  76 {
  77         int end = end_option(packet->options);
  78         int i, len = 0;
  79
  80         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  81         for (i = 0; dhcp_options[i].code; i++)
  82                 if (dhcp_options[i].flags & OPTION_REQ)
  83                         packet->options[end + OPT_DATA + len++] = dhcp_options[i].code;
  84         packet->options[end + OPT_LEN] = len;
  85         packet->options[end + OPT_DATA + len] = DHCP_END;
  86
  87 }
  88
  89
  90 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  91 int send_discover(unsigned long xid, unsigned long requested)
  92 {
  93         struct dhcpMessage packet;
  94
  95         init_packet(&packet, DHCPDISCOVER);
  96         packet.xid = xid;
  97         if (requested)
  98                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  99
 100         add_requests(&packet);
 101         bb_info_msg("Sending discover...");
 102         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 103                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 104 }
 105
 106
 107 /* Broadcasts a DHCP request message */
 108 int send_selecting(unsigned long xid, unsigned long server, unsigned long requested)
 109 {
 110         struct dhcpMessage packet;
 111         struct in_addr addr;
 112
 113         init_packet(&packet, DHCPREQUEST);
 114         packet.xid = xid;
 115
 116         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 117         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 118
 119         add_requests(&packet);
 120         addr.s_addr = requested;
 121         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 122         return udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 123                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 124 }
 125
 126
 127 /* Unicasts or broadcasts a DHCP renew message */
 128 int send_renew(unsigned long xid, unsigned long server, unsigned long ciaddr)
 129 {
 130         struct dhcpMessage packet;
 131         int ret = 0;
 132
 133         init_packet(&packet, DHCPREQUEST);
 134         packet.xid = xid;
 135         packet.ciaddr = ciaddr;
 136
 137         add_requests(&packet);
 138         bb_info_msg("Sending renew...");
 139         if (server)
 140                 ret = udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 141         else ret = udhcp_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 142                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 143         return ret;
 144 }
 145
 146
 147 /* Unicasts a DHCP release message */
 148 int send_release(unsigned long server, unsigned long ciaddr)
 149 {
 150         struct dhcpMessage packet;
 151
 152         init_packet(&packet, DHCPRELEASE);
 153         packet.xid = random_xid();
 154         packet.ciaddr = ciaddr;
 155
 156         add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
 157         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 158
 159         bb_info_msg("Sending release...");
 160         return udhcp_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 161 }
 162
 163
 164 /* return -1 on errors that are fatal for the socket, -2 for those that aren't */
 165 int get_raw_packet(struct dhcpMessage *payload, int fd)
 166 {
 167         int bytes;
 168         struct udp_dhcp_packet packet;
 169         uint32_t source, dest;
 170         uint16_t check;
 171
 172         memset(&packet, 0, sizeof(struct udp_dhcp_packet));
 173         bytes = read(fd, &packet, sizeof(struct udp_dhcp_packet));
 174         if (bytes < 0) {
 175                 DEBUG("Couldn't read on raw listening socket - ignoring");
 176                 usleep(500000); /* possible down interface, looping condition */
 177                 return -1;
 178         }
 179
 180         if (bytes < (int) (sizeof(struct iphdr) + sizeof(struct udphdr))) {
 181                 DEBUG("Message too short, ignoring");
 182                 return -2;
 183         }
 184
 185         if (bytes < ntohs(packet.ip.tot_len)) {
 186                 DEBUG("Truncated packet");
 187                 return -2;
 188         }
 189
 190         /* ignore any extra garbage bytes */
 191         bytes = ntohs(packet.ip.tot_len);
 192
 193         /* Make sure its the right packet for us, and that it passes sanity checks */
 194         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION ||
 195             packet.ip.ihl != sizeof(packet.ip) >> 2 || packet.udp.dest != htons(CLIENT_PORT) ||
 196             bytes > (int) sizeof(struct udp_dhcp_packet) ||
 197             ntohs(packet.udp.len) != (uint16_t) (bytes - sizeof(packet.ip))) {
 198                 DEBUG("Unrelated/bogus packet");
 199                 return -2;
 200         }
 201
 202         /* check IP checksum */
 203         check = packet.ip.check;
 204         packet.ip.check = 0;
 205         if (check != udhcp_checksum(&(packet.ip), sizeof(packet.ip))) {
 206                 DEBUG("bad IP header checksum, ignoring");
 207                 return -1;
 208         }
 209
 210         /* verify the UDP checksum by replacing the header with a psuedo header */
 211         source = packet.ip.saddr;
 212         dest = packet.ip.daddr;
 213         check = packet.udp.check;
 214         packet.udp.check = 0;
 215         memset(&packet.ip, 0, sizeof(packet.ip));
 216
 217         packet.ip.protocol = IPPROTO_UDP;
 218         packet.ip.saddr = source;
 219         packet.ip.daddr = dest;
 220         packet.ip.tot_len = packet.udp.len; /* cheat on the psuedo-header */
 221         if (check && check != udhcp_checksum(&packet, bytes)) {
 222                 bb_error_msg("Packet with bad UDP checksum received, ignoring");
 223                 return -2;
 224         }
 225
 226         memcpy(payload, &(packet.data), bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 227
 228         if (ntohl(payload->cookie) != DHCP_MAGIC) {
 229                 bb_error_msg("Received bogus message (bad magic) - ignoring");
 230                 return -2;
 231         }
 232         DEBUG("oooooh!!! got some!");
 233         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 234
 235 }