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 <errno.h>
  22 #include <net/ethernet.h>
  23 #include <net/if_arp.h>
  24 #include <string.h>
  25
  26 #include "dhcp-internal.h"
  27 #include "dhcp-protocol.h"
  28
  29 #define DHCP_CLIENT_MIN_OPTIONS_SIZE            312
  30
  31 int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
  32                       uint8_t type, uint16_t arp_type, size_t optlen,
  33                       size_t *optoffset) {
  34         size_t offset = 0;
  35         int r;
  36
  37         assert(op == BOOTREQUEST || op == BOOTREPLY);
  38         assert(arp_type == ARPHRD_ETHER || arp_type == ARPHRD_INFINIBAND);
  39
  40         message->op = op;
  41         message->htype = arp_type;
  42         message->hlen = (arp_type == ARPHRD_ETHER) ? ETHER_ADDR_LEN : 0;
  43         message->xid = htobe32(xid);
  44         message->magic = htobe32(DHCP_MAGIC_COOKIE);
  45
  46         r = dhcp_option_append(message, optlen, &offset, 0,
  47                                SD_DHCP_OPTION_MESSAGE_TYPE, 1, &type);
  48         if (r < 0)
  49                 return r;
  50
  51         *optoffset = offset;
  52
  53         return 0;
  54 }
  55
  56 uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len) {
  57         uint64_t *buf_64 = (uint64_t*)buf;
  58         uint64_t *end_64 = buf_64 + (len / sizeof(uint64_t));
  59         uint64_t sum = 0;
  60
  61         /* See RFC1071 */
  62
  63         while (buf_64 < end_64) {
  64                 sum += *buf_64;
  65                 if (sum < *buf_64)
  66                         /* wrap around in one's complement */
  67                         sum++;
  68
  69                 buf_64++;
  70         }
  71
  72         if (len % sizeof(uint64_t)) {
  73                 /* If the buffer is not aligned to 64-bit, we need
  74                    to zero-pad the last few bytes and add them in */
  75                 uint64_t buf_tail = 0;
  76
  77                 memcpy(&buf_tail, buf_64, len % sizeof(uint64_t));
  78
  79                 sum += buf_tail;
  80                 if (sum < buf_tail)
  81                         /* wrap around */
  82                         sum++;
  83         }
  84
  85         while (sum >> 16)
  86                 sum = (sum & 0xffff) + (sum >> 16);
  87
  88         return ~sum;
  89 }
  90
  91 void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
  92                                    uint16_t source_port, be32_t destination_addr,
  93                                    uint16_t destination_port, uint16_t len) {
  94         packet->ip.version = IPVERSION;
  95         packet->ip.ihl = DHCP_IP_SIZE / 4;
  96         packet->ip.tot_len = htobe16(len);
  97
  98         packet->ip.tos = IPTOS_CLASS_CS6;
  99
 100         packet->ip.protocol = IPPROTO_UDP;
 101         packet->ip.saddr = source_addr;
 102         packet->ip.daddr = destination_addr;
 103
 104         packet->udp.source = htobe16(source_port);
 105         packet->udp.dest = htobe16(destination_port);
 106
 107         packet->udp.len = htobe16(len - DHCP_IP_SIZE);
 108
 109         packet->ip.check = packet->udp.len;
 110         packet->udp.check = dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, len - 8);
 111
 112         packet->ip.ttl = IPDEFTTL;
 113         packet->ip.check = 0;
 114         packet->ip.check = dhcp_packet_checksum((uint8_t*)&packet->ip, DHCP_IP_SIZE);
 115 }
 116
 117 int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
 118         size_t hdrlen;
 119
 120         assert(packet);
 121
 122         /* IP */
 123
 124         if (packet->ip.version != IPVERSION) {
 125                 log_debug("ignoring packet: not IPv4");
 126                 return -EINVAL;
 127         }
 128
 129         if (packet->ip.ihl < 5) {
 130                 log_debug("ignoring packet: IPv4 IHL (%u words) invalid",
 131                           packet->ip.ihl);
 132                 return -EINVAL;
 133         }
 134
 135         hdrlen = packet->ip.ihl * 4;
 136         if (hdrlen < 20) {
 137                 log_debug("ignoring packet: IPv4 IHL (%zu bytes) "
 138                           "smaller than minimum (20 bytes)", hdrlen);
 139                 return -EINVAL;
 140         }
 141
 142         if (len < hdrlen) {
 143                 log_debug("ignoring packet: packet (%zu bytes) "
 144                           "smaller than expected (%zu) by IP header", len,
 145                           hdrlen);
 146                 return -EINVAL;
 147         }
 148
 149         /* UDP */
 150
 151         if (packet->ip.protocol != IPPROTO_UDP) {
 152                 log_debug("ignoring packet: not UDP");
 153                 return -EINVAL;
 154         }
 155
 156         if (len < hdrlen + be16toh(packet->udp.len)) {
 157                 log_debug("ignoring packet: packet (%zu bytes) "
 158                           "smaller than expected (%zu) by UDP header", len,
 159                           hdrlen + be16toh(packet->udp.len));
 160                 return -EINVAL;
 161         }
 162
 163         if (be16toh(packet->udp.dest) != DHCP_PORT_CLIENT) {
 164                 log_debug("ignoring packet: to port %u, which "
 165                           "is not the DHCP client port (%u)",
 166                           be16toh(packet->udp.dest), DHCP_PORT_CLIENT);
 167                 return -EINVAL;
 168         }
 169
 170         /* checksums - computing these is relatively expensive, so only do it
 171            if all the other checks have passed
 172          */
 173
 174         if (dhcp_packet_checksum((uint8_t*)&packet->ip, hdrlen)) {
 175                 log_debug("ignoring packet: invalid IP checksum");
 176                 return -EINVAL;
 177         }
 178
 179         if (checksum && packet->udp.check) {
 180                 packet->ip.check = packet->udp.len;
 181                 packet->ip.ttl = 0;
 182
 183                 if (dhcp_packet_checksum((uint8_t*)&packet->ip.ttl,
 184                                   be16toh(packet->udp.len) + 12)) {
 185                         log_debug("ignoring packet: invalid UDP checksum");
 186                         return -EINVAL;
 187                 }
 188         }
 189
 190         return 0;
 191 }