Sending ICMP request using C program

/**********************************************************************************
* AUTHOR : Chaitanya bhargav M
* Date : 14/10/2009
* description : To send an icmp request to specified host via specified
* Interface.
* License : Never mind to do any thing with this code.But, it might be unreliable
* *********************************************************************************
* CopyLeft(c) Chaitanya bhargav M 2009
***********************************************************************************/
#include
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#include
#include

typedef unsigned long int uint32;
typedef unsigned short int uint16;
typedef unsigned char uint8;

#define ETHER_TYPE_FOR_IP 0x0800
#define PROTOCOL_ICMP 0x01

// For proper memory allocation for each packet
#pragma pack(1)
// Ethernet header
typedef struct eth_hdr
{
uint8 dest_mac[6];
uint8 src_mac[6];
uint16 ether_type;
}ETH_HDR;
// 802.1Q Header
typedef struct vlan_hdr
{
uint16 type;
uint16 vlanID;
}VLAN_HDR;
// IP Header without options
typedef struct ip_hdr
{
uint8 version_headerlen;
uint8 diffserv;
uint16 total_len;
uint16 ident;
uint8 flags;
uint8 frag_offset;
uint8 ttl;
uint8 protocol;
uint16 checksum;
uint32 src_addr;
uint32 dest_addr;
}IP_HDR;
// ICMP Header
typedef struct icmp_hdr
{
uint8 type;
uint8 code;
uint16 checksum;
uint16 ident;
uint16 seq_no;
}ICMP_HDR;
// My own ICMP packet
typedef struct icmp_packet
{
ETH_HDR eth;
IP_HDR ip;
ICMP_HDR icmp;
uint8 data[32];
}ICMP_PKT;

// Function prototypes to calculate checksum and to print packet
unsigned short int header_checksum(char *, unsigned short int );
int print_pkt( char *, unsigned short int );

int main(int argc, char *argv[])
{
struct sockaddr_in *sin;
struct ifreq ifr;
struct sockaddr_ll sa;
int if_fd,icmp_fd,retVal,arp_flagg = 1;
unsigned long int ipAddr,IfIndex;
unsigned char IfMac[6];
ICMP_PKT pkt;
// It's my gateway. So, i am hardcoding
unsigned char gateway[7] = { 0x00,0x1A,0x6D,0x2B,0x89,0x29 };

if(argc != 3)
{
printf("Usage:\n ./icmp_req \n");
exit(1);
}

if(getuid() && geteuid())
{
printf("Oops!\n No Super user right\n");
exit(1);
}

// Check for default gateway
if(!strcmp(argv[1],"eth0"))
{
arp_flagg = 0;
}

if_fd = socket(AF_INET, SOCK_DGRAM, 0);
if( if_fd < 0 )
{
perror("If Socket");
exit(1);
}

//==============================Interface related data======================
// provide Interface name
strcpy(ifr.ifr_name,argv[1]);

// IP address
retVal = ioctl( if_fd, SIOCGIFADDR, &ifr, sizeof(ifr));
if( retVal < 0 )
{
perror("IFADDR IOCTL");
close(if_fd);
exit(1);
}
sin = (struct sockaddr_in *)&ifr.ifr_addr;
ipAddr = ntohl(sin->sin_addr.s_addr);

#ifdef DBG_ICMP
printf("IpAddr = %s\n",inet_ntoa(sin->sin_addr));
#endif

// MAC address
retVal = ioctl(if_fd, SIOCGIFHWADDR, &ifr, sizeof(ifr));
if( retVal < 0)
{
perror("IFHWADDR IOCTL");
close(if_fd);
exit(1);
}
memcpy(IfMac, ifr.ifr_hwaddr.sa_data, 6 * sizeof(unsigned char));

#ifdef DBG_ICMP
printf("MAC = %02x:%02x:%02x:%02x:%02x:%02x\n", IfMac[0],IfMac[1],IfMac[2],IfMac[3],IfMac[4],IfMac[5]);
#endif

// Interface index
retVal = ioctl(if_fd, SIOCGIFINDEX, &ifr, sizeof(ifr));
if( retVal < 0)
{
perror("IFINDEX");
close(if_fd);
exit(1);
}

#ifdef DBG_ICMP
printf("IfIndex = %d\n",ifr.ifr_ifindex);
#endif

IfIndex = ifr.ifr_ifindex;
//==============================Interface related data=====================

//==============================Packet socket==============================

icmp_fd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP));
if(icmp_fd < 0 )
{
perror("ICMP Socket");
close(if_fd);
exit(1);
}

//=============================Frame the packet============================
// Ethernet header
if(!arp_flagg) // If sending via gateway
{
memcpy(pkt.eth.dest_mac, gateway, 6 * sizeof(unsigned char));
}
else // If sending via private interface
{
memset(pkt.eth.dest_mac, 0xFF, 6 * sizeof(unsigned char));
}
memcpy(pkt.eth.src_mac, IfMac, 6 * sizeof(unsigned char));
pkt.eth.ether_type = htons(ETHER_TYPE_FOR_IP);

// IP header
pkt.ip.version_headerlen = 0x45; // version = IPv4, len = 5 (x 32 = 160)
pkt.ip.diffserv = 0x00; // Best effort
pkt.ip.total_len = htons(0x003C); // 20 IP header + 8 UDP header + 32 data
pkt.ip.ident = htons(0xa9b1); // just to identify reply
pkt.ip.flags = 0x00; // no fragmentation
pkt.ip.frag_offset = htons(0x0000); // no fragmentaion
pkt.ip.ttl = 0x80; // let's give 128
pkt.ip.protocol = PROTOCOL_ICMP; // ICMP protocol inside IP
pkt.ip.checksum = htons(0x0000); // Will be found out after framing full header
pkt.ip.src_addr = htonl(ipAddr); // inet address of given Interface
pkt.ip.dest_addr = inet_addr(argv[2]);// to whom shall we send

pkt.ip.checksum = htons(header_checksum( (char *)&pkt.ip.version_headerlen, 20));

// ICMP header
pkt.icmp.type = 0x08; // ICMP request
pkt.icmp.code = 0x00; // Code for ICMP request
pkt.icmp.checksum = htons(0x0000); // Will be filled after framing full header
pkt.icmp.ident = htons(0x0300); // anything
pkt.icmp.seq_no = htons(0xC000); // anything

pkt.icmp.checksum = htons(header_checksum( (char *)&pkt.icmp.type, 8));

// Data padding
memset(pkt.data, 0, 32 * sizeof(unsigned char));// Windows(R) Style

#ifndef DBG_ICMP
print_pkt((char *)&pkt, sizeof(pkt));
#endif

//======================Ok, Now send it!================

// We need this to send the packet
sa.sll_family = AF_PACKET; // AF_PACKET is a must
sa.sll_ifindex = ifr.ifr_ifindex; // chosen if. index number
sa.sll_protocol = htons(ETH_P_IP); // protocol of interest

// Now send it!
retVal = sendto(icmp_fd, &pkt, sizeof(pkt), 0, (struct sockaddr *)&sa, sizeof(sa));
if(retVal < 0 )
{
perror("send to");
close(icmp_fd);
close(if_fd);
exit(1);
}

return 0;
}

/***********************************************************
* To find the checksum of any header
* Description:
* - add two bytes at a time till the end
* - add the overflow till you come up with a 2-byte result
* - take a 1's compliment
***********************************************************/
unsigned short int header_checksum(char *buf, unsigned short int len)
{
unsigned char *header;

unsigned short int low16 = 0,i = 0;
unsigned long int checksum_32 =0;

// add 2 bytes at a time
for(i = 0; i < len; i+=2 )
{
low16 = (buf[i] << 8)&0xFF00 | buf[i+1]&0xFF ;
checksum_32 = checksum_32 + low16;
}

// Append the overflow -- 2 times for safety
if(checksum_32 >> 16)
{
checksum_32 = (checksum_32 & 0xFFFF) + (checksum_32 >> 16);
}
if(checksum_32 >> 16)
{
checksum_32 = (checksum_32 & 0xFFFF) + (checksum_32 >> 16);
}
// One's compliment
checksum_32 = ~checksum_32;

return (checksum_32&0xFFFF);
}

/**********************************************
* To Print the packet *
**********************************************/
int print_pkt( char *buf, unsigned short int len)
{
int i = 0;

printf("Size of packet = %d\n",len);
for( i = 0; i < len ; i++)
{
if(i%16 == 0)
printf("\n");

printf("%02x ",buf[i]&0xff);
}
printf("\n");
return 0;
}

Reading routing table using C program

#include"sys/socket.h"
#include"sys/types.h"
#include"unistd.h"
#include"stdio.h"
#include"stdlib.h"
#include"string.h"
#include"asm/types.h"
#include"linux/netlink.h"
#include"linux/rtnetlink.h"
#include"sys/ioctl.h"
#include"net/if.h"
#include"net/route.h"

#pragma pack(2)
// Structure for sending the request
typedef struct
{
struct nlmsghdr nlMsgHdr;
struct rtmsg rtMsg;
char buf[1024];
}route_request;

// Structure for storing routes
struct RouteInfo
{
unsigned long dstAddr;
unsigned long mask;
unsigned long gateWay;
unsigned long flags;
unsigned long srcAddr;
unsigned char proto;
char ifName[IF_NAMESIZE];
};

// Function for accessing interface name
int ifname(int ,char *);

int main(int argc, char *argv[])
{
int route_sock,i,j;
route_request *request = (route_request *)malloc(sizeof(route_request));
int retValue = -1,nbytes = 0,reply_len = 0;
char reply_ptr[1024];
ssize_t counter = 1024;
int count =0;
struct rtmsg *rtp;
struct rtattr *rtap;
struct nlmsghdr *nlp;
int rtl;
struct RouteInfo route[24];
char* buf = reply_ptr;
unsigned long bufsize ;

if( argc > 1)
{
if(getuid() && geteuid())
{
printf("Oops!\n Need SuperUser rights!\n");
}
exit(1);
}

route_sock = socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE);

bzero(request,sizeof(route_request));

// Fill in the NETLINK header
request->nlMsgHdr.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
request->nlMsgHdr.nlmsg_type = RTM_GETROUTE;
request->nlMsgHdr.nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;

// set the routing message header
request->rtMsg.rtm_family = AF_INET;
request->rtMsg.rtm_table = 254;

// Send routing request
if ((retValue = send(route_sock, request, sizeof(route_request), 0)) < 0)
{
perror("send");
exit(1);
}

for(;;)
{
if( counter < sizeof( struct nlmsghdr))
{
printf("Routing table is bigger than 1024\n");
exit(1);
}

nbytes = recv(route_sock, &reply_ptr[reply_len], counter, 0);

if(nbytes < 0 )
{
printf("Error in recv\n");
break;
}

if(nbytes == 0)
printf("EOF in netlink\n");

nlp = (struct nlmsghdr*)(&reply_ptr[reply_len]);

if (nlp->nlmsg_type == NLMSG_DONE)
{
// All data has been received.
// Truncate the reply to exclude this message,
// i.e. do not increase reply_len.
break;
}

if (nlp->nlmsg_type == NLMSG_ERROR)
{
printf("Error in msg\n");
exit(1);
}

reply_len += nbytes;
counter -= nbytes;
}

/*======================================================*/
bufsize = reply_len;
// string to hold content of the route
// table (i.e. one entry)
unsigned int flags;

// outer loop: loops thru all the NETLINK
// headers that also include the route entry
// header
nlp = (struct nlmsghdr *) buf;

for(i= -1; NLMSG_OK(nlp, bufsize); nlp=NLMSG_NEXT(nlp, bufsize))
{
// get route entry header
rtp = (struct rtmsg *) NLMSG_DATA(nlp);
// we are only concerned about the
// tableId route table
if(rtp->rtm_table != 254)
continue;
i++;
// init all the strings
bzero(&route[i], sizeof(struct RouteInfo));
flags = rtp->rtm_flags;
route[i].proto = rtp->rtm_protocol;

// inner loop: loop thru all the attributes of
// one route entry
rtap = (struct rtattr *) RTM_RTA(rtp);
rtl = RTM_PAYLOAD(nlp);
for( ; RTA_OK(rtap, rtl); rtap = RTA_NEXT(rtap, rtl))
{
switch(rtap->rta_type)
{
// destination IPv4 address
case RTA_DST:
count = 32 - rtp->rtm_dst_len;

route[i].dstAddr = *(unsigned long *) RTA_DATA(rtap);

route[i].mask = 0xffffffff;
for (; count!=0 ;count--)
route[i].mask = route[i].mask << 1;

//printf("dst:%s \tmask:0x%x \t",inet_ntoa(route[i].dstAddr), route[i].mask);
break;
case RTA_GATEWAY:
route[i].gateWay = *(unsigned long *) RTA_DATA(rtap);
//printf("gw:%s\t",inet_ntoa(route[i].gateWay));
break;
case RTA_PREFSRC:
route[i].srcAddr = *(unsigned long *) RTA_DATA(rtap);
//printf("src:%s\t", inet_ntoa(route[i].srcAddr));
break;
// unique ID associated with the network
// interface
case RTA_OIF:
ifname(*((int *) RTA_DATA(rtap)),route[i].ifName);
//printf( "ifname %s\n", route[i].ifName);
break;
default:
break;
}

}
//set Flags

//[TODO]: UP hardcoded?!
route[i].flags|=RTF_UP;
if (route[i].gateWay != 0)
route[i].flags|=RTF_GATEWAY;
if (route[i].mask == 0xFFFFFFFF)
route[i].flags|=RTF_HOST;
}

// Print the route records
printf("Destination\tGateway \tNetmask \tflags \tIfname \n");
printf("-----------\t------- \t--------\t------\t------ \n");
for( j = 0; j<= i; j++)
{
printf("%s \t0x%08x\t0x%08x \t%d \t%s\n",
inet_ntoa(route[j].dstAddr),
ntohl(route[j].gateWay),
route[j].mask,
route[j].flags,
route[j].ifName);
}
return 0;
}

/*--------------------------------------------------------------
* To get the name of the interface provided the interface index
*--------------------------------------------------------------*/
int ifname(int if_index,char *ifName)
{
int fd,retVal = -1;
struct sockaddr_in *sin;
struct ifreq ifr;


fd = socket(AF_INET, SOCK_DGRAM, 0);
if(fd == -1)
{
perror("socket");
exit(1);
}

ifr.ifr_ifindex = if_index;

if(ioctl(fd, SIOCGIFNAME, &ifr, sizeof(ifr)))
{
perror("ioctl");
exit(1);
}

strcpy(ifName, ifr.ifr_name);
return ;
}