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         message->op = op;
  47         message->htype = ARPHRD_ETHER;
  48         message->hlen = ETHER_ADDR_LEN;
  49         message->xid = htobe32(xid);
  50         message->magic = htobe32(DHCP_MAGIC_COOKIE);
  51
  52         *opt = (uint8_t *)(message + 1);
  53
  54         err = dhcp_option_append(opt, optlen, DHCP_OPTION_MESSAGE_TYPE, 1,
  55                                  &type);
  56         if (err < 0)
  57                 return err;
  58
  59         return 0;
  60 }
  61
  62 uint16_t dhcp_packet_checksum(void *buf, int len) {
  63         uint32_t sum;
  64         uint16_t *check;
  65         int i;
  66         uint8_t *odd;
  67
  68         sum = 0;
  69         check = buf;
  70
  71         for (i = 0; i < len / 2 ; i++)
  72                 sum += check[i];
  73
  74         if (len & 0x01) {
  75                 odd = buf;
  76                 sum += odd[len - 1];
  77         }
  78
  79         while (sum >> 16)
  80                 sum = (sum & 0xffff) + (sum >> 16);
  81
  82         return ~sum;
  83 }
  84
  85 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
  86                                    uint16_t source_port, be32_t destination_addr,
  87                                    uint16_t destination_port, uint16_t len) {
  88         packet->ip.version = IPVERSION;
  89         packet->ip.ihl = DHCP_IP_SIZE / 4;
  90         packet->ip.tot_len = htobe16(len);
  91
  92         packet->ip.protocol = IPPROTO_UDP;
  93         packet->ip.saddr = source_addr;
  94         packet->ip.daddr = destination_addr;
  95
  96         packet->udp.source = htobe16(source_port);
  97         packet->udp.dest = htobe16(destination_port);
  98
  99         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 100
 101         packet->ip.check = packet->udp.len;
 102         packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
 103
 104         packet->ip.ttl = IPDEFTTL;
 105         packet->ip.check = 0;
 106         packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
 107 }
 108
 109 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 110         size_t hdrlen;
 111
 112         assert(packet);
 113
 114         /* IP */
 115
 116         if (len < DHCP_IP_SIZE) {
 117                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 118                                 " smaller than IP header (%u bytes)", len,
 119                                 DHCP_IP_SIZE);
 120                 return -EINVAL;
 121         }
 122
 123         if (packet->ip.version != IPVERSION) {
 124                 log_dhcp_client(client, "ignoring packet: not IPv4");
 125                 return -EINVAL;
 126         }
 127
 128         if (packet->ip.ihl < 5) {
 129                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%u words) invalid",
 130                                 packet->ip.ihl);
 131                 return -EINVAL;
 132         }
 133
 134         hdrlen = packet->ip.ihl * 4;
 135         if (hdrlen < 20) {
 136                 log_dhcp_client(client, "ignoring packet: IPv4 IHL (%zu bytes) "
 137                                 "smaller than minimum (20 bytes)", hdrlen);
 138                 return -EINVAL;
 139         }
 140
 141         if (len < hdrlen) {
 142                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 143                                 "smaller than expected (%zu) by IP header", len,
 144                                 hdrlen);
 145                 return -EINVAL;
 146         }
 147
 148         /* UDP */
 149
 150         if (packet->ip.protocol != IPPROTO_UDP) {
 151                 log_dhcp_client(client, "ignoring packet: not UDP");
 152                 return -EINVAL;
 153         }
 154
 155         if (len < DHCP_IP_UDP_SIZE) {
 156                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 157                                 " smaller than IP+UDP header (%u bytes)", len,
 158                                 DHCP_IP_UDP_SIZE);
 159                 return -EINVAL;
 160         }
 161
 162         if (len < hdrlen + be16toh(packet->udp.len)) {
 163                 log_dhcp_client(client, "ignoring packet: packet (%zu bytes) "
 164                                 "smaller than expected (%zu) by UDP header", len,
 165                                 hdrlen + be16toh(packet->udp.len));
 166                 return -EINVAL;
 167         }
 168
 169         if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 170                 log_dhcp_client(client, "ignoring packet: to port %u, which "
 171                                 "is not the DHCP client port (%u)",
 172                                 be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 173                 return -EINVAL;
 174         }
 175
 176         /* checksums - computing these is relatively expensive, so only do it
 177            if all the other checks have passed
 178          */
 179
 180         if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
 181                 log_dhcp_client(client, "ignoring packet: invalid IP checksum");
 182                 return -EINVAL;
 183         }
 184
 185         if (checksum && packet->udp.check) {
 186                 packet->ip.check = packet->udp.len;
 187                 packet->ip.ttl = 0;
 188
 189                 if (dhcp_packet_checksum(&packet->ip.ttl,
 190                                   be16toh(packet->udp.len) + 12)) {
 191                         log_dhcp_client(client, "ignoring packet: invalid UDP checksum");
 192                         return -EINVAL;
 193                 }
 194         }
 195
 196         return 0;
 197 }