Hello all,
For a school assignment we need to make a program in C that does a correct DHCP discover (and if that works, we need to catch the answer etc). However, we've been trying to get the program to work, but there are several problems:
1. packetsize gets increased by 2 bytes (probably from allignment problems?) (should be 1500 but is 1502, the 2 extra bytes seem to come from the dhcp_packet struct).
2. The IP header checksum is incorrect (in Wireshark)
3. The UDP header checksum is incorrect (in Wireshark)
4. We don't know how to set the options for the request.
We're using a dhcp header file from ISC (dhcpd). The code we have so far is in dhcpreq.c.
dhcp.h
Code:
/* dhcp.h
Protocol structures... */
/*
* Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
* Copyright (c) 1995-2003 by Internet Software Consortium
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
* OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
* Internet Systems Consortium, Inc.
* 950 Charter Street
* Redwood City, CA 94063
* <[email protected]>
* http://www.isc.org/
*
* This software has been written for Internet Systems Consortium
* by Ted Lemon in cooperation with Vixie Enterprises. To learn more
* about Internet Systems Consortium, see ``http://www.isc.org''.
* To learn more about Vixie Enterprises, see ``http://www.vix.com''.
*/
#define DHCP_UDP_OVERHEAD (14 + /* Ethernet header */ \
20 + /* IP header */ \
8) /* UDP header */
#define DHCP_SNAME_LEN 64
#define DHCP_FILE_LEN 128
#define DHCP_FIXED_NON_UDP 236
#define DHCP_FIXED_LEN (DHCP_FIXED_NON_UDP + DHCP_UDP_OVERHEAD)
/* Everything but options. */
#define DHCP_MTU_MAX 1500
#define DHCP_OPTION_LEN (DHCP_MTU_MAX - DHCP_FIXED_LEN)
#define BOOTP_MIN_LEN 300
#define DHCP_MIN_LEN 548
struct dhcp_packet {
u_int8_t op; /* 0: Message opcode/type */
u_int8_t htype; /* 1: Hardware addr type (net/if_types.h) */
u_int8_t hlen; /* 2: Hardware addr length */
u_int8_t hops; /* 3: Number of relay agent hops from client */
u_int32_t xid; /* 4: Transaction ID */
u_int16_t secs; /* 8: Seconds since client started looking */
u_int16_t flags; /* 10: Flag bits */
struct in_addr ciaddr; /* 12: Client IP address (if already in use) */
struct in_addr yiaddr; /* 16: Client IP address */
struct in_addr siaddr; /* 18: IP address of next server to talk to */
struct in_addr giaddr; /* 20: DHCP relay agent IP address */
unsigned char chaddr [16]; /* 24: Client hardware address */
char sname [DHCP_SNAME_LEN]; /* 40: Server name */
char file [DHCP_FILE_LEN]; /* 104: Boot filename */
unsigned char options [DHCP_OPTION_LEN];
/* 212: Optional parameters
(actual length dependent on MTU). */
};
/* BOOTP (rfc951) message types */
#define BOOTREQUEST 1
#define BOOTREPLY 2
/* Possible values for flags field... */
#define BOOTP_BROADCAST 32768L
/* Possible values for hardware type (htype) field... */
#define HTYPE_ETHER 1 /* Ethernet 10Mbps */
#define HTYPE_IEEE802 6 /* IEEE 802.2 Token Ring... */
#define HTYPE_FDDI 8 /* FDDI... */
/* Magic cookie validating dhcp options field (and bootp vendor
extensions field). */
#define DHCP_OPTIONS_COOKIE "\143\202\123\143"
/* DHCP Option codes: */
#define DHO_PAD 0
#define DHO_SUBNET_MASK 1
#define DHO_TIME_OFFSET 2
#define DHO_ROUTERS 3
#define DHO_TIME_SERVERS 4
#define DHO_NAME_SERVERS 5
#define DHO_DOMAIN_NAME_SERVERS 6
#define DHO_LOG_SERVERS 7
#define DHO_COOKIE_SERVERS 8
#define DHO_LPR_SERVERS 9
#define DHO_IMPRESS_SERVERS 10
#define DHO_RESOURCE_LOCATION_SERVERS 11
#define DHO_HOST_NAME 12
#define DHO_BOOT_SIZE 13
#define DHO_MERIT_DUMP 14
#define DHO_DOMAIN_NAME 15
#define DHO_SWAP_SERVER 16
#define DHO_ROOT_PATH 17
#define DHO_EXTENSIONS_PATH 18
#define DHO_IP_FORWARDING 19
#define DHO_NON_LOCAL_SOURCE_ROUTING 20
#define DHO_POLICY_FILTER 21
#define DHO_MAX_DGRAM_REASSEMBLY 22
#define DHO_DEFAULT_IP_TTL 23
#define DHO_PATH_MTU_AGING_TIMEOUT 24
#define DHO_PATH_MTU_PLATEAU_TABLE 25
#define DHO_INTERFACE_MTU 26
#define DHO_ALL_SUBNETS_LOCAL 27
#define DHO_BROADCAST_ADDRESS 28
#define DHO_PERFORM_MASK_DISCOVERY 29
#define DHO_MASK_SUPPLIER 30
#define DHO_ROUTER_DISCOVERY 31
#define DHO_ROUTER_SOLICITATION_ADDRESS 32
#define DHO_STATIC_ROUTES 33
#define DHO_TRAILER_ENCAPSULATION 34
#define DHO_ARP_CACHE_TIMEOUT 35
#define DHO_IEEE802_3_ENCAPSULATION 36
#define DHO_DEFAULT_TCP_TTL 37
#define DHO_TCP_KEEPALIVE_INTERVAL 38
#define DHO_TCP_KEEPALIVE_GARBAGE 39
#define DHO_NIS_DOMAIN 40
#define DHO_NIS_SERVERS 41
#define DHO_NTP_SERVERS 42
#define DHO_VENDOR_ENCAPSULATED_OPTIONS 43
#define DHO_NETBIOS_NAME_SERVERS 44
#define DHO_NETBIOS_DD_SERVER 45
#define DHO_NETBIOS_NODE_TYPE 46
#define DHO_NETBIOS_SCOPE 47
#define DHO_FONT_SERVERS 48
#define DHO_X_DISPLAY_MANAGER 49
#define DHO_DHCP_REQUESTED_ADDRESS 50
#define DHO_DHCP_LEASE_TIME 51
#define DHO_DHCP_OPTION_OVERLOAD 52
#define DHO_DHCP_MESSAGE_TYPE 53
#define DHO_DHCP_SERVER_IDENTIFIER 54
#define DHO_DHCP_PARAMETER_REQUEST_LIST 55
#define DHO_DHCP_MESSAGE 56
#define DHO_DHCP_MAX_MESSAGE_SIZE 57
#define DHO_DHCP_RENEWAL_TIME 58
#define DHO_DHCP_REBINDING_TIME 59
#define DHO_VENDOR_CLASS_IDENTIFIER 60
#define DHO_DHCP_CLIENT_IDENTIFIER 61
#define DHO_NWIP_DOMAIN_NAME 62
#define DHO_NWIP_SUBOPTIONS 63
#define DHO_USER_CLASS 77
#define DHO_FQDN 81
#define DHO_DHCP_AGENT_OPTIONS 82
#define DHO_SUBNET_SELECTION 118 /* RFC3011! */
/* The DHO_AUTHENTICATE option is not a standard yet, so I've
allocated an option out of the "local" option space for it on a
temporary basis. Once an option code number is assigned, I will
immediately and shamelessly break this, so don't count on it
continuing to work. */
#define DHO_AUTHENTICATE 210
#define DHO_END 255
/* DHCP message types. */
#define DHCPDISCOVER 1
#define DHCPOFFER 2
#define DHCPREQUEST 3
#define DHCPDECLINE 4
#define DHCPACK 5
#define DHCPNAK 6
#define DHCPRELEASE 7
#define DHCPINFORM 8
/* Relay Agent Information option subtypes: */
#define RAI_CIRCUIT_ID 1
#define RAI_REMOTE_ID 2
#define RAI_AGENT_ID 3
/* FQDN suboptions: */
#define FQDN_NO_CLIENT_UPDATE 1
#define FQDN_SERVER_UPDATE 2
#define FQDN_ENCODED 3
#define FQDN_RCODE1 4
#define FQDN_RCODE2 5
#define FQDN_HOSTNAME 6
#define FQDN_DOMAINNAME 7
#define FQDN_FQDN 8
#define FQDN_SUBOPTION_COUNT 8
dhcpreq.c
Code:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <linux/if.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#include <netinet/in.h>
#include <netinet/ether.h>
#include <netinet/ip.h>
#include <netinet/udp.h>
#include <arpa/inet.h>
#include "dhcp.h"
int main(int argc, char *argv[])
{
int sock;
unsigned int packetsize = (sizeof(struct ether_header) + sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dhcp_packet));
unsigned char packet[packetsize];
printf("Packetsize %d\n", packetsize);
printf("DHCP_OPTION_LEN %d\n", DHCP_OPTION_LEN);
printf("DHCP_FIXED_LEN %d\n", DHCP_FIXED_LEN);
printf("Packet size min dhcp %d\n", (sizeof(struct ether_header) + sizeof(struct iphdr) + sizeof(struct udphdr)));
struct sockaddr_ll addr;
struct ether_header *eth = (struct ether_header *) (packet);
struct iphdr *ip = (struct iphdr *) (packet + sizeof(struct ether_header));
struct udphdr *udp = (struct udphdr *) (packet + sizeof(struct iphdr) + sizeof(struct ether_header));
struct dhcp_packet *dhcp = (struct dhcp_packet *) (packet + sizeof(struct udphdr) + sizeof(struct iphdr) + sizeof(struct ether_header));
struct ifreq ifreq;
char SourceHwaddr[17];
//If other than one argument is giving error!
if (argc != 2)
{
fprintf(stderr, "Usages: dhcpreq <INTERFACE>\n");
exit(1);
}
//Create a UDP Socket with IP Protocol
if ((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP))) == -1)
//if ((sock = socket(PF_PACKET, SOCK_DGRAM, IPPROTO_IP)) == -1)
{
perror("creating socket");
exit(0);
}
//Set the interface name to argv[1] to define what interface we have
strcpy(ifreq.ifr_name, argv[1]);
//Get the hardware address
if (ioctl(sock, SIOCGIFHWADDR, &ifreq) != 0)
{
perror("ioctl get hwaddr");
exit(0);
}
//Put the hardware address in a chararray
sprintf(SourceHwaddr, "%02x:%02x:%02x:%02x:%02x:%02x", (unsigned char) ifreq.ifr_hwaddr.sa_data[0], (unsigned char) ifreq.ifr_hwaddr.sa_data[1],
(unsigned char) ifreq.ifr_hwaddr.sa_data[2], (unsigned char) ifreq.ifr_hwaddr.sa_data[3], (unsigned char) ifreq.ifr_hwaddr.sa_data[4],
(unsigned char) ifreq.ifr_hwaddr.sa_data[5]);
/*
* Begin Ethernet Header
*/
//Destination ethernet address
memcpy(eth->ether_dhost, ether_aton("ff:ff:ff:ff:ff:ff"), ETH_ALEN);
//Source ethernet address
memcpy(eth->ether_shost, ether_aton(SourceHwaddr), ETH_ALEN);
//Ethernet type
eth->ether_type = htons(ETH_P_IP);
/*
* End Ethernet Header
*/
/*
* Begin IP Header
*/
//Set the type of service
ip->tos = 0;
//Set the IP version
ip->version = 4;
//Set the IP header length
ip->ihl = sizeof(struct iphdr) >> 2;
//Set the total length
ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr) + sizeof(struct dhcp_packet));
//Set the id
ip->id = htons((int) (rand() / (((double) RAND_MAX + 1) / 14095)));
//Set the fragment offset
ip->frag_off = 0;
//Set the TTL
ip->ttl = 128;
//Set the protocol
ip->protocol = IPPROTO_UDP;
//Let IP set the checksum
//Set the source IP
ip->saddr = inet_addr("0.0.0.0");
//Set the destenations IP
ip->daddr = inet_addr("255.255.255.255");
/*
* End IP Header
*/
/*
* Begin UDP Header
*/
//Set the source port
udp->source = htons(67);
//Set the desentation port
udp->dest = htons(68);
//Set the UDP length (incl dhcp packet)
udp->len = htons(sizeof(struct udphdr) + sizeof(struct dhcp_packet));
/*
* End UDP Header
*/
/*
* Begin DHCP Packet
*/
dhcp->op = BOOTREQUEST;
dhcp->htype = HTYPE_ETHER;
dhcp->hlen = ETH_ALEN;
dhcp->hops = 0;
dhcp->secs = 0;
dhcp->flags = htons(BOOTP_BROADCAST);
inet_aton("0.0.0.0", (struct in_addr *) &dhcp->ciaddr);
inet_aton("0.0.0.0", (struct in_addr *) &dhcp->yiaddr);
inet_aton("0.0.0.0", (struct in_addr *) &dhcp->siaddr);
inet_aton("0.0.0.0", (struct in_addr *) &dhcp->giaddr);
//Copy the MAC address from ifreq
memcpy(dhcp->chaddr, &ifreq.ifr_addr, ETHER_ADDR_LEN);
//Servername must be null
bzero(dhcp->sname, sizeof(dhcp->sname));
//Filename must be null
bzero(dhcp->file, sizeof(dhcp->file));
//Must bu filled in
bzero(dhcp->options, sizeof(dhcp->options));
/*
* End DHCP Packet
*/
//clear the addr and set the data in it
memset(&addr, 0, sizeof(struct sockaddr_ll));
addr.sll_family = PF_PACKET;
addr.sll_protocol = htons(ETH_P_ARP);
if (ioctl(sock, SIOCGIFINDEX, &ifreq) != 0)
{
perror("ioctl get index");
exit(0);
}
addr.sll_ifindex = ifreq.ifr_ifindex;
printf("Interface index: %d\n", ifreq.ifr_ifindex);
//Try to bind the socket on a address
if (bind(sock, (struct sockaddr *) &addr, sizeof(struct sockaddr_ll)) != 0)
{
perror("Socket Binding error");
exit(0);
}
//Write the packet to the socket
int n = 0;
if ((n = write(sock, packet, packetsize)) <= 0)
{
perror("Packet sending error");
exit(0);
}
printf("%d bytes sent\n", n);
close(sock);
return 0;
}
The main problem is that our teachers have no idea how to do this either because they haven't even made the program them selfs yet. There also is no information available on the internet that can help us any further (google has no results when you search for the things we want).
So if anyone can point us into the right direction with one of the problems it would be great.
Thanks in advance.