Initial Import

Makefile

@@ -0,0 +1,22 @@
+Cflag=
+LDflag=
+
+all:		dhclient
+
+dhclient:	dhclient.o dhcp.o net.o
+			gcc $(LDflag) dhclient.o dhcp.o net.o -o dhclient
+
+dhclient.o:	dhclient.c
+			gcc $(Cflag) -c dhclient.c
+
+dhcp.o:		dhcp.c dhcp.h
+			gcc $(Cflag) -c dhcp.c
+
+net.o:		net.c net.h
+			gcc $(Cflag) -c net.c
+
+clean:
+			rm -f *.o
+
+cleanall:   clean
+			rm -f dhclient

dhclient.c

@@ -0,0 +1,157 @@
+#include "dhcp.h"
+#include "net.h"
+
+#include <sys/socket.h>
+#include <netinet/udp.h>
+#include <arpa/inet.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <net/ethernet.h>
+
+#include <linux/if_arp.h>
+
+#define BUFF_SIZE 1024
+
+//http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch01s03.html
+
+void main(int argc, char** argv)
+{
+    if(geteuid() != 0)
+    {
+        fprintf(stderr, "You need root permissions\n");
+        exit(1);
+    }
+
+    //TODO : Add a debug mode
+    char* interface;
+    if(argc > 1)
+        interface = argv[1];
+    else
+    {
+        fprintf(stderr, "Please specify network interface to use\n");
+        exit(1);
+    }
+
+//    printf("Interface = %s\n", interface);
+
+    int sock = socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_IP));
+
+	//Set receive timeout
+	struct timeval tv;
+	tv.tv_usec = 0;
+	tv.tv_sec = 10; //10 seconds in case of latency on the network
+	setsockopt(sock, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
+
+    //retrieve ethernet NIC index and HW address
+    struct hw_eth_iface iface = find_iface(sock, interface); // TODO : Check interface existency, and print a list of possible NIC
+
+    struct sockaddr_ll target;
+    memset(&target, 0, sizeof(target));
+    target.sll_family   = PF_PACKET;
+    target.sll_protocol = htons(ETH_P_IP);
+    target.sll_ifindex  = iface.index;
+    target.sll_hatype   = ARPHRD_ETHER;
+    target.sll_pkttype  = PACKET_HOST;
+    target.sll_halen    = ETH_ALEN;
+
+    memset(target.sll_addr, 0xff, 6);
+
+    char buffer[BUFF_SIZE];
+
+//    struct dhcp_pkt *dhcp = (struct dhcp_pkt*)(buffer + sizeof(struct udpheader) + sizeof(struct ipheader));
+    struct dhcp_pkt dhcp;
+    int dhcp_len = build_dhcp_discover(&dhcp, iface.hw_addr, iface.addr_len);
+
+    int len = build_ip4_udp_pkt(buffer, BUFF_SIZE, (unsigned char*)&dhcp, dhcp_len, "0.0.0.0", "255.255.255.255", 68, 67, IPPROTO_UDP);
+
+	//Send the packet over the network
+    if(sendto(sock, buffer, len, 0, (struct sockaddr *)&target, sizeof(target)) < 0)
+    {
+        perror("Error while writing to socket");
+        exit(1);
+    }
+
+	//Now, wait for the server response, and read it
+
+receive:
+    memset(buffer, 0, BUFF_SIZE);
+
+	//Read a packet
+    int read_len = recvfrom(sock, buffer, BUFF_SIZE, 0, NULL, NULL);
+    if(read_len <= 0)
+    {
+        perror("Cannot read");
+        exit(1);
+    }
+
+    struct ipheader *rip   = (struct ipheader*) buffer;
+    struct udpheader *rudp = (struct udpheader*)(buffer + sizeof(struct ipheader));
+    struct dhcp_pkt *rdhcp = (struct dhcp_pkt*)(buffer + sizeof(struct udpheader) + sizeof(struct ipheader));
+
+    //Check packet validity
+	// if dest port isn't our or packet is not a dhcp one, drop the packet
+    if(rip->iph_protocol != IPPROTO_UDP || rudp->udph_destport != htons(68) || !is_dhcp(rdhcp) || rdhcp->op != OP_BOOT_REPLY)
+        goto receive;
+
+//    printf("Data Recieved, length = %d\n", read_len);
+
+	//Find the IP attributed to us by the server
+    struct in_addr raddr;
+    raddr.s_addr = rdhcp->yi_addr;
+
+    printf("IPADDR=%s\n", inet_ntoa(raddr));
+
+	//Now check DHCP options, and process them
+    struct dhcp_opt *opt = NULL;
+    int offs = 0;
+    opt = get_dhcp_option(rdhcp, &offs);
+    while(opt != NULL)
+    {
+//        printf("OPT FOUND offset = %d\n", offs);
+        switch(opt->id)
+        {
+            case OPTION_ROUTER: // If the option is the gateway address
+				if(opt->len == 4)
+				{
+					raddr.s_addr = char_to_ip(opt->values);
+					printf("GATEWAY=%s\n", inet_ntoa(raddr));
+				}
+                break;
+
+            case OPTION_SUBNET_MASK: // If the option is the netwmask
+				if(opt->len == 4)
+				{
+					raddr.s_addr = char_to_ip(opt->values);
+					printf("NETMASK=%s\n", inet_ntoa(raddr));
+				}
+                break;
+
+            case OPTION_DNS: // If option is the DNS addresses
+				if(opt->len % 4 == 0)
+				{
+					int i = 0;
+					printf("NAMESERVER=");
+					int max = opt->len / 4;
+					for(i = 0; i < max; i++)
+					{
+						raddr.s_addr = char_to_ip(opt->values + 4*i);
+						printf("%s", inet_ntoa(raddr));
+						if(i < max - 1)
+							printf(",");
+					}
+					printf("\n");
+				}
+                break;
+
+            default:
+                break;
+        }
+        opt = get_dhcp_option(rdhcp, &offs);
+    }
+
+    close(sock);
+    exit(0);
+}

dhcp.c

@@ -0,0 +1,72 @@
+#include "dhcp.h"
+
+#include <stdlib.h>
+#include <string.h>
+
+int build_dhcp_discover(struct dhcp_pkt* pkt, unsigned char* src_mac, int mac_len)
+{
+    memset(pkt, 0, sizeof(struct dhcp_pkt));
+    pkt->op      = OP_BOOT_REQUEST;
+    pkt->htype   = HW_TYPE_ETHERNET;
+    pkt->hlen    = HW_LENGTH_ETHERNET;
+    pkt->hops    = 0x00;
+    pkt->xid     = 0x3903f326; //TODO: Random transaction ID
+    pkt->secs    = 0x0000;
+    pkt->flags   = 0x0000;
+    pkt->ci_addr = 0x00000000;
+    pkt->yi_addr = 0x00000000;
+    pkt->si_addr = 0x00000000;
+    pkt->gi_addr = 0x00000000;
+
+    // memcpy(pkt->cm_addr, src_mac, mac_len); // LINK problem
+	int i;
+	for(i = 0; i < mac_len; i++)
+		pkt->cm_addr[i] = src_mac[i];
+
+    pkt->magic = DHCP_MAGIC;
+
+    //Add DHCP options
+    pkt->opt[0] = OPTION_DHCP_MESSAGE_TYPE;
+    pkt->opt[1] = 0x01;
+    pkt->opt[2] = VALUE_MESSAGE_DISCOVER;
+
+    pkt->opt[3] = OPTION_PARAMETER_REQUEST_LIST;
+    pkt->opt[4] = 0x03;
+    pkt->opt[5] = OPTION_ROUTER; // Ask for gateway address
+    pkt->opt[6] = OPTION_SUBNET_MASK; // Ask for the netmask
+    pkt->opt[7] = OPTION_DNS; // ASK for DNS address
+
+    pkt->opt[8] = DHCP_END;
+
+
+    //TODO : Use the same procedure to write options, than the one used to read options
+//    pkt->opt[0].id = 53;
+//    pkt->opt[0].len = 0x01;
+//    pkt->opt[0].values[0] = 0x01;
+//
+//    pkt->opt[1].id = DHCP_END;
+
+    return sizeof(struct dhcp_pkt);
+}
+
+int is_dhcp(struct dhcp_pkt* pkt)
+{
+	// It's a DHCP packet if dhcp magic number is good
+	//TODO: check the packet length ?
+    return pkt->magic == DHCP_MAGIC;
+}
+
+struct dhcp_opt* get_dhcp_option(struct dhcp_pkt *pkt, int *offset)
+{
+    if(pkt->opt[*offset] == 0x00 || pkt->opt[*offset] == DHCP_END)
+        return NULL;
+	// If the opt != end or != empty, cast the memory zone into a option struct, and return it
+	struct dhcp_opt* opt = (struct dhcp_opt*)&(pkt->opt[*offset]);
+	*offset += sizeof(struct dhcp_opt) + opt->len;
+    return opt;
+}
+
+unsigned int char_to_ip(unsigned char* ip)
+{
+	return htonl(ip[0] << 24 | ip[1] << 16 | ip[2] << 8 | ip[3]);
+}

dhcp.h

@@ -0,0 +1,96 @@
+#ifndef _DHCP_H
+#define _DHCP_H
+
+#define DHCP_MAGIC 			htonl(0x63825363)
+
+#define DHCP_MIN_PACK_SIZE 	240
+
+#define OP_BOOT_REQUEST 	0x01
+#define OP_BOOT_REPLY 		0x02
+
+#define HW_TYPE_ETHERNET 	0x01
+#define HW_LENGTH_ETHERNET 	0x06
+
+//DHCP options
+
+#define DHCP_END 	0xff
+
+#define OPTION_DHCP_MESSAGE_TYPE 	53
+#define VALUE_MESSAGE_DISCOVER 		0x01
+#define VALUE_MESSAGE_OFFER 		0x02
+#define VALUE_MESSAGE_REQUEST 		0x01
+#define VALUE_MESSAGE_ACK 			0x05
+#define VALUE_MESSAGE_NAK 			0x06
+#define VALUE_MESSAGE_INFORM 		0x08
+
+#define OPTION_SERVER_IP 			54
+#define OPTION_LEASE_TIME 			51
+#define OPTION_REQUESTED_IP 		50
+
+#define OPTION_PARAMETER_REQUEST_LIST 	55
+
+#define OPTION_SUBNET_MASK 		1
+#define OPTION_ROUTER 			3
+#define OPTION_BROADCAST_ADDR 	28
+#define OPTION_DNS 				6
+#define OPTION_DOMAIN_NAME 		15
+#define OPTION_HOST_NAME 		12
+
+//These should not really be usefull for what we do
+#define OPTION_TIME_OFFSET 		2
+#define OPTION_STATIC_ROUTE 	121
+#define OPTION_NIS_DOMAIN 		40
+#define OPTION_NIS_SERVERS 		41
+#define OPTION_NTP_SERVERS 		42
+#define OPTION_MTU 				26
+#define OPTION_DOMAIN_SEARCH 	119
+
+//DHCP options
+struct dhcp_opt {
+    unsigned char id;       // Option ID
+    unsigned char len;      // Option value length
+    unsigned char values[]; // Option value(s)
+};
+
+//DHCP packet structure
+struct dhcp_pkt
+{
+    unsigned char   op;     // Message type
+    unsigned char   htype;  // HW type
+    unsigned char   hlen;   // HW addr length
+    unsigned char   hops;   // Hops
+
+    unsigned int    xid;    // Transaction ID
+
+    unsigned short  secs;   // seconds elapsed
+    unsigned short  flags;  // Bootp flags
+
+    unsigned int    ci_addr; // Client address
+    unsigned int    yi_addr; // Your address
+    unsigned int    si_addr; // Next Server IP address
+    unsigned int    gi_addr; // Relay agent IP address
+    unsigned char   cm_addr[6];   // Client MAC address
+    unsigned char   ch_addr[10];  // Client hardware address padding
+
+    unsigned char   unused[192];
+
+    unsigned int    magic;      // DHCP magic number
+
+    unsigned char   opt[128];   // Options padding
+//    struct dhcp_opt opt [64];
+};
+
+//Build a discover DHCP packet, return packet size
+int build_dhcp_discover(struct dhcp_pkt* pkt, unsigned char* src_mac, int mac_len);
+
+//Check if the packet is a DHCP one
+int is_dhcp(struct dhcp_pkt* pkt);
+
+//Find an option in the DHCP packet. offset is the position of the option in the packet.
+// After the call, offset is updated to the offset of the next option (if any)
+struct dhcp_opt* get_dhcp_option(struct dhcp_pkt *pkt, int *offset);
+
+//Read an IP in a 4 bytes data array
+unsigned int char_to_ip(unsigned char* ip);
+
+#endif