src/libsystemd-network/dhcp-packet.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright (C) 2013 Intel Corporation. All rights reserved.
   5   Copyright (C) 2014 Tom Gundersen
   6
   7   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <stdlib.h>
  22 #include <errno.h>
  23 #include <string.h>
  24 #include <stdio.h>
  25 #include <net/ethernet.h>
  26 #include <net/if_arp.h>
  27 #include <sys/param.h>
  28
  29 #include "util.h"
  30 #include "list.h"
  31
  32 #include "dhcp-protocol.h"
  33 #include "dhcp-lease-internal.h"
  34 #include "dhcp-internal.h"
  35 #include "sd-dhcp-lease.h"
  36 #include "sd-dhcp-client.h"
  37
  38 #define DHCP_CLIENT_MIN_OPTIONS_SIZE            312
  39
  40 int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
  41                       uint8_t type, uint8_t **opt, size_t *optlen) {
  42         int err;
  43
  44         assert(op == BOOTREQUEST || op == BOOTREPLY);
  45
  46         *opt = (uint8_t *)(message + 1);
  47
  48         if (*optlen < 4)
  49                 return -ENOBUFS;
  50         *optlen -= 4;
  51
  52         message->op = op;
  53         message->htype = ARPHRD_ETHER;
  54         message->hlen = ETHER_ADDR_LEN;
  55         message->xid = htobe32(xid);
  56
  57         (*opt)[0] = 0x63;
  58         (*opt)[1] = 0x82;
  59         (*opt)[2] = 0x53;
  60         (*opt)[3] = 0x63;
  61
  62         *opt += 4;
  63
  64         err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
  65                                  &type);
  66         if (err < 0)
  67                 return err;
  68
  69         return 0;
  70 }
  71
  72 uint16_t dhcp_packet_checksum(void *buf, int len) {
  73         uint32_t sum;
  74         uint16_t *check;
  75         int i;
  76         uint8_t *odd;
  77
  78         sum = 0;
  79         check = buf;
  80
  81         for (i = 0; i < len / 2 ; i++)
  82                 sum += check[i];
  83
  84         if (len & 0x01) {
  85                 odd = buf;
  86                 sum += odd[len - 1];
  87         }
  88
  89         while (sum >> 16)
  90                 sum = (sum & 0xffff) + (sum >> 16);
  91
  92         return ~sum;
  93 }
  94
  95 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
  96                                    uint16_t source_port, be32_t destination_addr,
  97                                    uint16_t destination_port, uint16_t len) {
  98         packet->ip.version = IPVERSION;
  99         packet->ip.ihl = DHCP_IP_SIZE / 4;
 100         packet->ip.tot_len = htobe16(len);
 101
 102         packet->ip.protocol = IPPROTO_UDP;
 103         packet->ip.saddr = source_addr;
 104         packet->ip.daddr = destination_addr;
 105
 106         packet->udp.source = htobe16(source_port);
 107         packet->udp.dest = htobe16(destination_port);
 108
 109         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 110
 111         packet->ip.check = packet->udp.len;
 112         packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
 113
 114         packet->ip.ttl = IPDEFTTL;
 115         packet->ip.check = 0;
 116         packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
 117 }
 118
 119 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 120         size_t hdrlen;
 121
 122         assert(packet);
 123
 124         /* IP */
 125
 126         if (len < DHCP_IP_SIZE) {
 127                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 128                                 " smaller than IP header (%u bytes)", len,
 129                                 DHCP_IP_SIZE);
 130                 return -EINVAL;
 131         }
 132
 133         if (packet->ip.version != IPVERSION) {
 134                 log_dhcp_client(client, "ignoring packet: not IPv4");
 135                 return -EINVAL;
 136         }
 137
 138         if (packet->ip.ihl < 5) {
 139                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
 140                                 packet->ip.ihl);
 141                 return -EINVAL;
 142         }
 143
 144         hdrlen = packet->ip.ihl * 4;
 145         if (hdrlen < 20) {
 146                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
 147                                 "smaller than minimum (20 bytes)", hdrlen);
 148                 return -EINVAL;
 149         }
 150
 151         if (len < hdrlen) {
 152                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 153                                 "smaller than expected (%zu) by IP header", len,
 154                                 hdrlen);
 155                 return -EINVAL;
 156         }
 157
 158         if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
 159                 log_dhcp_client(client, "ignoring packet: invalid IP checksum");
 160                 return -EINVAL;
 161         }
 162
 163         /* UDP */
 164
 165         if (packet->ip.protocol != IPPROTO_UDP) {
 166                 log_dhcp_client(client, "ignoring packet: not UDP");
 167                 return -EINVAL;
 168         }
 169
 170         if (len < DHCP_IP_UDP_SIZE) {
 171                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 172                                 " smaller than IP+UDP header (%u bytes)", len,
 173                                 DHCP_IP_UDP_SIZE);
 174                 return -EINVAL;
 175         }
 176
 177         if (len < hdrlen + be16toh(packet->udp.len)) {
 178                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 179                                 "smaller than expected (%zu) by UDP header", len,
 180                                 hdrlen + be16toh(packet->udp.len));
 181                 return -EINVAL;
 182         }
 183
 184         if (checksum && packet->udp.check) {
 185                 packet->ip.check = packet->udp.len;
 186                 packet->ip.ttl = 0;
 187
 188                 if (dhcp_packet_checksum(&packet->ip.ttl,
 189                                   be16toh(packet->udp.len) + 12)) {
 190                         log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
 191                         return -EINVAL;
 192                 }
 193         }
 194
 195         if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 196                 log_dhcp_client(client, "ignoring packet: to port %u, which "
 197                                 "is not the DHCP client port (%u)",
 198                                 be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 199                 return -EINVAL;
 200         }
 201
 202         return 0;
 203 }