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         if ((type != DHCPDECLINE) && (type != DHCPRELEASE))
  52                 add_option_string(packet->options, client_config.vendorclass);
  53 }
  54
  55
  56 /* Add a parameter request list for stubborn DHCP servers. Pull the data
  57  * from the struct in options.c. Don't do bounds checking here because it
  58  * goes towards the head of the packet. */
  59 static void add_param_req_option(struct dhcpMessage *packet)
  60 {
  61         uint8_t c;
  62         int end = end_option(packet->options);
  63         int i, len = 0;
  64
  65         for (i = 0; (c = dhcp_options[i].code) != 0; i++) {
  66                 if (((dhcp_options[i].flags & OPTION_REQ)
  67                      && !client_config.no_default_options)
  68                  || (client_config.opt_mask[c >> 3] & (1 << (c & 7)))
  69                 ) {
  70                         packet->options[end + OPT_DATA + len] = c;
  71                         len++;
  72                 }
  73         }
  74         if (len) {
  75                 packet->options[end + OPT_CODE] = DHCP_PARAM_REQ;
  76                 packet->options[end + OPT_LEN] = len;
  77                 packet->options[end + OPT_DATA + len] = DHCP_END;
  78         }
  79 }
  80
  81
  82 #if ENABLE_FEATURE_UDHCPC_ARPING
  83 /* Unicast a DHCP decline message */
  84 int send_decline(uint32_t xid, uint32_t server, uint32_t requested)
  85 {
  86         struct dhcpMessage packet;
  87
  88         init_packet(&packet, DHCPDECLINE);
  89         packet.xid = xid;
  90         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
  91         add_simple_option(packet.options, DHCP_SERVER_ID, server);
  92
  93         bb_info_msg("Sending decline...");
  94
  95         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
  96                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
  97 }
  98 #endif
  99
 100 /* Broadcast a DHCP discover packet to the network, with an optionally requested IP */
 101 int send_discover(uint32_t xid, uint32_t requested)
 102 {
 103         struct dhcpMessage packet;
 104
 105         init_packet(&packet, DHCPDISCOVER);
 106         packet.xid = xid;
 107         if (requested)
 108                 add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 109
 110         /* Explicitly saying that we want RFC-compliant packets helps
 111          * some buggy DHCP servers to NOT send bigger packets */
 112         add_simple_option(packet.options, DHCP_MAX_SIZE, htons(576));
 113
 114         add_param_req_option(&packet);
 115
 116         bb_info_msg("Sending discover...");
 117         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 118                         SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 119 }
 120
 121
 122 /* Broadcasts a DHCP request message */
 123 int send_selecting(uint32_t xid, uint32_t server, uint32_t requested)
 124 {
 125         struct dhcpMessage packet;
 126         struct in_addr addr;
 127
 128         init_packet(&packet, DHCPREQUEST);
 129         packet.xid = xid;
 130
 131         add_simple_option(packet.options, DHCP_REQUESTED_IP, requested);
 132         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 133         add_param_req_option(&packet);
 134
 135         addr.s_addr = requested;
 136         bb_info_msg("Sending select for %s...", inet_ntoa(addr));
 137         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 138                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 139 }
 140
 141
 142 /* Unicasts or broadcasts a DHCP renew message */
 143 int send_renew(uint32_t xid, uint32_t server, uint32_t ciaddr)
 144 {
 145         struct dhcpMessage packet;
 146
 147         init_packet(&packet, DHCPREQUEST);
 148         packet.xid = xid;
 149         packet.ciaddr = ciaddr;
 150
 151         add_param_req_option(&packet);
 152         bb_info_msg("Sending renew...");
 153         if (server)
 154                 return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 155
 156         return udhcp_send_raw_packet(&packet, INADDR_ANY, CLIENT_PORT, INADDR_BROADCAST,
 157                                 SERVER_PORT, MAC_BCAST_ADDR, client_config.ifindex);
 158 }
 159
 160
 161 /* Unicasts a DHCP release message */
 162 int send_release(uint32_t server, uint32_t ciaddr)
 163 {
 164         struct dhcpMessage packet;
 165
 166         init_packet(&packet, DHCPRELEASE);
 167         packet.xid = random_xid();
 168         packet.ciaddr = ciaddr;
 169
 170         add_simple_option(packet.options, DHCP_SERVER_ID, server);
 171
 172         bb_info_msg("Sending release...");
 173         return udhcp_send_kernel_packet(&packet, ciaddr, CLIENT_PORT, server, SERVER_PORT);
 174 }
 175
 176
 177 /* Returns -1 on errors that are fatal for the socket, -2 for those that aren't */
 178 int udhcp_recv_raw_packet(struct dhcpMessage *payload, int fd)
 179 {
 180         int bytes;
 181         struct udp_dhcp_packet packet;
 182         uint16_t check;
 183
 184         memset(&packet, 0, sizeof(packet));
 185         bytes = safe_read(fd, &packet, sizeof(packet));
 186         if (bytes < 0) {
 187                 DEBUG("Cannot read on raw listening socket - ignoring");
 188                 /* NB: possible down interface, etc. Caller should pause. */
 189                 return bytes; /* returns -1 */
 190         }
 191
 192         if (bytes < (int) (sizeof(packet.ip) + sizeof(packet.udp))) {
 193                 DEBUG("Packet is too short, ignoring");
 194                 return -2;
 195         }
 196
 197         if (bytes < ntohs(packet.ip.tot_len)) {
 198                 /* packet is bigger than sizeof(packet), we did partial read */
 199                 DEBUG("Oversized packet, ignoring");
 200                 return -2;
 201         }
 202
 203         /* ignore any extra garbage bytes */
 204         bytes = ntohs(packet.ip.tot_len);
 205
 206         /* make sure its the right packet for us, and that it passes sanity checks */
 207         if (packet.ip.protocol != IPPROTO_UDP || packet.ip.version != IPVERSION
 208          || packet.ip.ihl != (sizeof(packet.ip) >> 2)
 209          || packet.udp.dest != htons(CLIENT_PORT)
 210         /* || bytes > (int) sizeof(packet) - can't happen */
 211          || ntohs(packet.udp.len) != (uint16_t)(bytes - sizeof(packet.ip))
 212         ) {
 213                 DEBUG("Unrelated/bogus packet");
 214                 return -2;
 215         }
 216
 217         /* verify IP checksum */
 218         check = packet.ip.check;
 219         packet.ip.check = 0;
 220         if (check != udhcp_checksum(&packet.ip, sizeof(packet.ip))) {
 221                 DEBUG("Bad IP header checksum, ignoring");
 222                 return -2;
 223         }
 224
 225         /* verify UDP checksum. IP header has to be modified for this */
 226         memset(&packet.ip, 0, offsetof(struct iphdr, protocol));
 227         /* ip.xx fields which are not memset: protocol, check, saddr, daddr */
 228         packet.ip.tot_len = packet.udp.len; /* yes, this is needed */
 229         check = packet.udp.check;
 230         packet.udp.check = 0;
 231         if (check && check != udhcp_checksum(&packet, bytes)) {
 232                 bb_error_msg("packet with bad UDP checksum received, ignoring");
 233                 return -2;
 234         }
 235
 236         memcpy(payload, &packet.data, bytes - (sizeof(packet.ip) + sizeof(packet.udp)));
 237
 238         if (payload->cookie != htonl(DHCP_MAGIC)) {
 239                 bb_error_msg("received bogus message (bad magic), ignoring");
 240                 return -2;
 241         }
 242         DEBUG("Got valid DHCP packet");
 243         return bytes - (sizeof(packet.ip) + sizeof(packet.udp));
 244 }