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