int main(int argc, char* argv[]) {
srandomdev();
if (argc != 2) {
errx(EX_USAGE, "Usage: %s <device>", argv[0]);
}
char* dev = argv[1];
char errbuf[LIBNET_ERRBUF_SIZE];
libnet_t* context = libnet_init(LIBNET_LINK, dev, errbuf);
if (context == NULL) {
errx(EX_UNAVAILABLE, "libnet_init: %s", errbuf);
}
uint8_t buf[MAX_DHCP_SIZE];
uint16_t size = MAX_DHCP_SIZE;
build_dhcp_discover(source_mac, "lozenge", buf, &size);
libnet_ptag_t ether_tag = LIBNET_PTAG_INITIALIZER;
libnet_ptag_t ip_tag = LIBNET_PTAG_INITIALIZER;
libnet_ptag_t udp_tag = LIBNET_PTAG_INITIALIZER;
udp_tag = libnet_build_udp(68, 67, LIBNET_UDP_H + size,
0, buf, size,
context, udp_tag);
u_short ipid = random() & 0xffff;
ip_tag = libnet_build_ipv4(
LIBNET_IPV4_H + LIBNET_UDP_H + size,
0, ipid, 0, 0xff,
IPPROTO_UDP, 0, 0, 0xffffffff,
NULL, 0, context, ip_tag);
ether_tag = libnet_build_ethernet(broadcast_mac, source_mac,
ETHERTYPE_IP, NULL, 0, context, ether_tag);
if (libnet_write(context) == -1) {
libnet_destroy(context);
errx(EX_UNAVAILABLE, "libnet_write");
}
printf("Wrote\n");
libnet_destroy(context);
return 0;
}
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);
}