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/*
* OpenVPN -- An application to securely tunnel IP networks
* over a single TCP/UDP port, with support for SSL/TLS-based
* session authentication and key exchange,
* packet encryption, packet authentication, and
* packet compression.
*
* Copyright (C) 2002-2010 OpenVPN Technologies, Inc. <sales@openvpn.net>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2
* as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program (see the file COPYING included with this
* distribution); if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "syshead.h"
#include "dhcp.h"
#include "socket.h"
#include "error.h"
#include "memdbg.h"
static int
get_dhcp_message_type (const struct dhcp *dhcp, const int optlen)
{
const uint8_t *p = (uint8_t *) (dhcp + 1);
int i;
for (i = 0; i < optlen; ++i)
{
const uint8_t type = p[i];
const int room = optlen - i;
if (type == DHCP_END) /* didn't find what we were looking for */
return -1;
else if (type == DHCP_PAD) /* no-operation */
;
else if (type == DHCP_MSG_TYPE) /* what we are looking for */
{
if (room >= 3)
{
if (p[i+1] == 1) /* option length should be 1 */
return p[i+2]; /* return message type */
}
return -1;
}
else /* some other option */
{
if (room >= 2)
{
const int len = p[i+1]; /* get option length */
i += (len + 1); /* advance to next option */
}
}
}
return -1;
}
static in_addr_t
do_extract (struct dhcp *dhcp, const int optlen)
{
uint8_t *p = (uint8_t *) (dhcp + 1);
int i;
in_addr_t ret = 0;
for (i = 0; i < optlen; ++i)
{
const uint8_t type = p[i];
const int room = optlen - i;
if (type == DHCP_END)
break;
else if (type == DHCP_PAD)
;
else if (type == DHCP_ROUTER)
{
if (room >= 2)
{
const int len = p[i+1]; /* get option length */
if (len <= (room-2))
{
if (!ret && len >= 4 && (len & 3) == 0)
{
memcpy (&ret, p+i+2, 4); /* get router IP address */
ret = ntohl (ret);
}
memset (p+i, DHCP_PAD, len+2); /* delete the router option by padding it out */
}
i += (len + 1); /* advance to next option */
}
}
else /* some other option */
{
if (room >= 2)
{
const int len = p[i+1]; /* get option length */
i += (len + 1); /* advance to next option */
}
}
}
return ret;
}
static uint16_t
udp_checksum (const uint8_t *buf,
const int len_udp,
const uint8_t *src_addr,
const uint8_t *dest_addr)
{
uint16_t word16;
uint32_t sum = 0;
int i;
/* make 16 bit words out of every two adjacent 8 bit words and */
/* calculate the sum of all 16 bit words */
for (i = 0; i < len_udp; i += 2){
word16 = ((buf[i] << 8) & 0xFF00) + ((i + 1 < len_udp) ? (buf[i+1] & 0xFF) : 0);
sum += word16;
}
/* add the UDP pseudo header which contains the IP source and destination addresses */
for (i = 0; i < 4; i += 2){
word16 =((src_addr[i] << 8) & 0xFF00) + (src_addr[i+1] & 0xFF);
sum += word16;
}
for (i = 0; i < 4; i += 2){
word16 =((dest_addr[i] << 8) & 0xFF00) + (dest_addr[i+1] & 0xFF);
sum += word16;
}
/* the protocol number and the length of the UDP packet */
sum += (uint16_t) OPENVPN_IPPROTO_UDP + (uint16_t) len_udp;
/* keep only the last 16 bits of the 32 bit calculated sum and add the carries */
while (sum >> 16)
sum = (sum & 0xFFFF) + (sum >> 16);
/* Take the one's complement of sum */
return ((uint16_t) ~sum);
}
in_addr_t
dhcp_extract_router_msg (struct buffer *ipbuf)
{
struct dhcp_full *df = (struct dhcp_full *) BPTR (ipbuf);
const int optlen = BLEN (ipbuf) - (sizeof (struct openvpn_iphdr) + sizeof (struct openvpn_udphdr) + sizeof (struct dhcp));
if (optlen >= 0
&& df->ip.protocol == OPENVPN_IPPROTO_UDP
&& df->udp.source == htons (BOOTPS_PORT)
&& df->udp.dest == htons (BOOTPC_PORT)
&& df->dhcp.op == BOOTREPLY
&& get_dhcp_message_type (&df->dhcp, optlen) == DHCPACK)
{
/* get the router IP address while padding out all DHCP router options */
const in_addr_t ret = do_extract (&df->dhcp, optlen);
/* recompute the UDP checksum */
df->udp.check = htons (udp_checksum ((uint8_t *) &df->udp,
sizeof (struct openvpn_udphdr) + sizeof (struct dhcp) + optlen,
(uint8_t *)&df->ip.saddr,
(uint8_t *)&df->ip.daddr));
if (ret)
{
struct gc_arena gc = gc_new ();
msg (D_ROUTE, "Extracted DHCP router address: %s", print_in_addr_t (ret, 0, &gc));
gc_free (&gc);
}
return ret;
}
else
return 0;
}
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