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, size_t len) {
  63         uint64_t *buf_64 = buf;
  64         uint64_t *end_64 = (uint64_t*)buf + (len / sizeof(uint64_t));
  65         uint32_t *buf_32;
  66         uint16_t *buf_16;
  67         uint8_t *buf_8;
  68         uint64_t sum = 0;
  69
  70         while (buf_64 < end_64) {
  71                 sum += *buf_64;
  72                 if (sum < *buf_64)
  73                         sum++;
  74
  75                 buf_64 ++;
  76         }
  77
  78         buf_32 = (uint32_t*)buf_64;
  79
  80         if (len & sizeof(uint32_t)) {
  81                 sum += *buf_32;
  82                 if (sum < *buf_32)
  83                         sum++;
  84
  85                 buf_32 ++;
  86         }
  87
  88         buf_16 = (uint16_t*)buf_32;
  89
  90         if (len & sizeof(uint16_t)) {
  91                 sum += *buf_16;
  92                 if (sum < *buf_16)
  93                         sum ++;
  94
  95                 buf_16 ++;
  96         }
  97
  98         buf_8 = (uint8_t*)buf_16;
  99
 100         if (len & sizeof(uint8_t)) {
 101                 sum += *buf_8;
 102                 if (sum < *buf_8)
 103                         sum++;
 104         }
 105
 106         while (sum >> 16)
 107                 sum = (sum & 0xffff) + (sum >> 16);
 108
 109         return ~sum;
 110 }
 111
 112 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
 113                                    uint16_t source_port, be32_t destination_addr,
 114                                    uint16_t destination_port, uint16_t len) {
 115         packet->ip.version = IPVERSION;
 116         packet->ip.ihl = DHCP_IP_SIZE / 4;
 117         packet->ip.tot_len = htobe16(len);
 118
 119         packet->ip.tos = IPTOS_CLASS_CS6;
 120
 121         packet->ip.protocol = IPPROTO_UDP;
 122         packet->ip.saddr = source_addr;
 123         packet->ip.daddr = destination_addr;
 124
 125         packet->udp.source = htobe16(source_port);
 126         packet->udp.dest = htobe16(destination_port);
 127
 128         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 129
 130         packet->ip.check = packet->udp.len;
 131         packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
 132
 133         packet->ip.ttl = IPDEFTTL;
 134         packet->ip.check = 0;
 135         packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
 136 }
 137
 138 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 139         size_t hdrlen;
 140
 141         assert(packet);
 142
 143         /* IP */
 144
 145         if (packet->ip.version != IPVERSION) {
 146                 log_debug("ignoring packet: not IPv4");
 147                 return -EINVAL;
 148         }
 149
 150         if (packet->ip.ihl < 5) {
 151                 log_debug("ignoring packet: IPv4 IHL (%u words) invalid",
 152                           packet->ip.ihl);
 153                 return -EINVAL;
 154         }
 155
 156         hdrlen = packet->ip.ihl * 4;
 157         if (hdrlen < 20) {
 158                 log_debug("ignoring packet: IPv4 IHL (%zu bytes) "
 159                           "smaller than minimum (20 bytes)", hdrlen);
 160                 return -EINVAL;
 161         }
 162
 163         if (len < hdrlen) {
 164                 log_debug("ignoring packet: packet (%zu bytes) "
 165                           "smaller than expected (%zu) by IP header", len,
 166                           hdrlen);
 167                 return -EINVAL;
 168         }
 169
 170         /* UDP */
 171
 172         if (packet->ip.protocol != IPPROTO_UDP) {
 173                 log_debug("ignoring packet: not UDP");
 174                 return -EINVAL;
 175         }
 176
 177         if (len < hdrlen + be16toh(packet->udp.len)) {
 178                 log_debug("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 (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 185                 log_debug("ignoring packet: to port %u, which "
 186                           "is not the DHCP client port (%u)",
 187                           be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 188                 return -EINVAL;
 189         }
 190
 191         /* checksums - computing these is relatively expensive, so only do it
 192            if all the other checks have passed
 193          */
 194
 195         if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
 196                 log_debug("ignoring packet: invalid IP checksum");
 197                 return -EINVAL;
 198         }
 199
 200         if (checksum && packet->udp.check) {
 201                 packet->ip.check = packet->udp.len;
 202                 packet->ip.ttl = 0;
 203
 204                 if (dhcp_packet_checksum(&packet->ip.ttl,
 205                                   be16toh(packet->udp.len) + 12)) {
 206                         log_debug("ignoring packet: invalid UDP checksum");
 207                         return -EINVAL;
 208                 }
 209         }
 210
 211         return 0;
 212 }