diff options
Diffstat (limited to 'dhcp.c')
| -rw-r--r-- | dhcp.c | 183 |
1 files changed, 183 insertions, 0 deletions
@@ -0,0 +1,183 @@ +/* + * 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) 2002-2008 Telethra, 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; +} |