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 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         add_option_string(packet->options, client_config.vendorclass);
  52 }
  53
  54
  55 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  56  * from the struct in options.c. Don't do bounds checking here because it
  57  * goes towards the head of the packet. */
  58 static void add_requests(struct dhcpMessage *packet)
  59 {
  60         uint8_t c;
  61         int end = end_option(packet->options);
  62         int i, len = 0;
  63
  64         packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  65         for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
  66                 if (dhcp_options[i].flags & OPTION_REQ
  67                  || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
  68                 ) {
  69                         packet->options[end + OPT_DATA + len++] = c;
  70                 }
  71         }
  72         packet->options[end + OPT_LEN] = len;
  73         packet->options[end + OPT_DATA + len] = DHCP_END;
  74
  75 }
  76
  77 #if ENABLE_FEATURE_UDHCPC_ARPING
  78 /* Unicast a DHCP decline message */
  79 int send_decline(uint32_t xid, uint32_t server)
  80 {
  81         struct dhcpMessage packet;
  82
  83         init_packet(&packet, DHCPDECLINE);
  84         packet.xid = xid;
  85         add_requests(&packet);
  86
  87         bb_info_msg("Sending decline...");
  88
  89         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
  90                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
  91 }
  92 #endif
  93
  94 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
  95 int send_discover(uint32_t xid, uint32_t requested)
  96 {
  97         struct dhcpMessage packet;
  98
  99         init_packet(&packet, DHCPDISCOVER);
 100         packet.xid = xid;
 101         if (requested)
 102                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 103
 104         /* Explicitly saying that we want RFC-compliant packets helps
 105          * some buggy DHCP servers to NOT send bigger packets */
 106         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 107         add_requests(&packet);
 108         bb_info_msg("Sending discover...");
 109         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 110                         SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 111 }
 112
 113
 114 /* Broadcasts a DHCP request message */
 115 int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
 116 {
 117         struct dhcpMessage packet;
 118         struct in_addr addr;
 119
 120         init_packet(&packet, DHCPREQUEST);
 121         packet.xid = xid;
 122
 123         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 124         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 125
 126         add_requests(&packet);
 127         addr.s_addr = requested;
 128         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 129         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 130                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 131 }
 132
 133
 134 /* Unicasts or broadcasts a DHCP renew message */
 135 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 136 {
 137         struct dhcpMessage packet;
 138
 139         init_packet(&packet, DHCPREQUEST);
 140         packet.xid = xid;
 141         packet.ciaddr = ciaddr;
 142
 143         add_requests(&packet);
 144         bb_info_msg("Sending renew...");
 145         if (server)
 146                 return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 147
 148         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 149                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 150 }
 151
 152
 153 /* Unicasts a DHCP release message */
 154 int send_release(uint32_t server, uint32_t ciaddr)
 155 {
 156         struct dhcpMessage packet;
 157
 158         init_packet(&packet, DHCPRELEASE);
 159         packet.xid = random_xid();
 160         packet.ciaddr = ciaddr;
 161
 162         add_simple_option(packet.options, DHCP_REQUESTED_IP, ciaddr);
 163         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 164
 165         bb_info_msg("Sending release...");
 166         return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 167 }
 168
 169
 170 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
 171 int get_raw_packet(struct dhcpMessage *payload, int fd)
 172 {
 173         int bytes;
 174         struct udp_dhcp_packet packet;
 175         uint16_t check;
 176
 177         memset(&packet, 0, sizeof(packet));
 178         bytes = safe_read(fd, &packet, sizeof(packet));
 179         if (bytes < 0) {
 180                 DEBUG("Cannot read on raw listening socket - ignoring");
 181                 sleep(1); /* possible down interface, looping condition */
 182                 return bytes; /* returns -1 */
 183         }
 184
 185         if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 186                 DEBUG("Packet is too short, ignoring");
 187                 return -2;
 188         }
 189
 190         if (bytes < ntohs(packet.ip.tot_len)) {
 191                 /* packet is bigger than sizeof(packet), we did partial read */
 192                 DEBUG("Oversized packet, ignoring");
 193                 return -2;
 194         }
 195
 196         /* ignore any extra garbage bytes */
 197         bytes = ntohs(packet.ip.tot_len);
 198
 199         /* make sure its the right packet for us, and that it passes sanity checks */
 200         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 201          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 202          || packet.udp.dest != htons(CLIENT_PORT)
 203         /* || bytes > (int) sizeof(packet) - can't happen */
 204          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 205         ) {
 206                 DEBUG("Unrelated/bogus packet");
 207                 return -2;
 208         }
 209
 210         /* verify IP checksum */
 211         check = packet.ip.check;
 212         packet.ip.check = 0;
 213         if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
 214                 DEBUG("Bad IP header checksum, ignoring");
 215                 return -2;
 216         }
 217
 218         /* verify UDP checksum. IP header has to be modified for this */
 219         memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
 220         /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
 221         packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 222         check = packet.udp.check;
 223         packet.udp.check = 0;
 224         if (check && check != udhcp_checksum(&packet, bytes)) {
 225                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 226                 return -2;
 227         }
 228
 229         memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 230
 231         if (payload->cookie != htonl(DHCP_MAGIC)) {
 232                 bb_error_msg("received bogus message (bad magic), ignoring");
 233                 return -2;
 234         }
 235         DEBUG("Got valid DHCP packet");
 236         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 237 }