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-rw-r--r--src/openvpn/dhcp.c212
1 files changed, 212 insertions, 0 deletions
diff --git a/src/openvpn/dhcp.c b/src/openvpn/dhcp.c
new file mode 100644
index 0000000..8d0b18a
--- /dev/null
+++ b/src/openvpn/dhcp.c
@@ -0,0 +1,212 @@
+/*
+ * 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
+ */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#elif defined(_MSC_VER)
+#include "config-msvc.h"
+#endif
+
+#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, int optlen)
+{
+ uint8_t *p = (uint8_t *) (dhcp + 1);
+ int i;
+ in_addr_t ret = 0;
+
+ for (i = 0; i < optlen; )
+ {
+ const uint8_t type = p[i];
+ const int room = optlen - i;
+ if (type == DHCP_END)
+ break;
+ else if (type == DHCP_PAD)
+ ++i;
+ else if (type == DHCP_ROUTER)
+ {
+ if (room >= 2)
+ {
+ const int len = p[i+1]; /* get option length */
+ if (len <= (room-2))
+ {
+ /* get router IP address */
+ if (!ret && len >= 4 && (len & 3) == 0)
+ {
+ memcpy (&ret, p+i+2, 4);
+ ret = ntohl (ret);
+ }
+ {
+ /* delete the router option */
+ uint8_t *dest = p + i;
+ const int owlen = len + 2; /* len of data to overwrite */
+ uint8_t *src = dest + owlen;
+ uint8_t *end = p + optlen;
+ const int movlen = end - src;
+ if (movlen > 0)
+ memmove(dest, src, movlen); /* overwrite router option */
+ memset(end - owlen, DHCP_PAD, owlen); /* pad tail */
+ }
+ }
+ else
+ break;
+ }
+ else
+ break;
+ }
+ else /* some other option */
+ {
+ if (room >= 2)
+ {
+ const int len = p[i+1]; /* get option length */
+ i += (len + 2); /* advance to next option */
+ }
+ else
+ break;
+ }
+ }
+ 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)
+ {
+ const int message_type = get_dhcp_message_type (&df->dhcp, optlen);
+ if (message_type == DHCPACK || message_type == DHCPOFFER)
+ {
+ /* 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 = 0;
+ 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));
+
+ /* only return the extracted Router address if DHCPACK */
+ if (message_type == DHCPACK)
+ {
+ 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;
+ }
+ }
+ }
+ return 0;
+}