Raw Ethernet Packet - Example Source Code

 

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작성일: 2023년 10월 10일

 

패킷 보내기 (Send a packet)

예제 코드

/**
 * How to build
 *  $  gcc send-raw-packet.c -o send-raw-packet
 *
 * How to run
 *  $ ./send-raw-packet
 *    or
 *  $ ./send-raw-packet  eth0
 */

#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>
#include <errno.h>


// FIXME: MY_DEST_MACX 값은 각자 테스트 환경이 맞게 수정해서 사용.
#define MY_DEST_MAC0	0x52
#define MY_DEST_MAC1	0x54
#define MY_DEST_MAC2	0x00
#define MY_DEST_MAC3	0xcf
#define MY_DEST_MAC4	0xab
#define MY_DEST_MAC5	0x76

// FIXME: DEFAULT_IF 값은 각자 테스트 환경이 맞게 수정해서 사용.
#define DEFAULT_IF	"enp7s0"

#define BUF_SIZ		1024


int main(int argc, char *argv[])
{
	int                  sockfd;
	int                  tx_len = 0;
	char                 sendbuf[BUF_SIZ];
	char                 ifName[IFNAMSIZ];
	struct ifreq         if_idx;
	struct ifreq         if_mac;
	struct ether_header  *eh = (struct ether_header *) sendbuf;
	struct iphdr         *iph = (struct iphdr *) (sendbuf + sizeof(struct ether_header));
	struct sockaddr_ll   socket_address;

	// Network interface name 지정하기 (예: eth0)
	if (argc > 1)
	{
		strcpy(ifName, argv[1]);
	}
	else
	{
		strcpy(ifName, DEFAULT_IF);
	}

	// RAW socket 사용을 위한 File descriptor 생성하기
	if ((sockfd = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW)) == -1)
	{
		printf("socket() error: %d (%s)\n", errno, strerror(errno));
		return 0;
	}

	// Network interface의 index 값 구하기
	memset(&if_idx, 0, sizeof(struct ifreq));
	strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
	if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0)
	{
		printf("ioctl(SIOCGIFINDEX, %s) error: %d (%s)\n", ifName, errno, strerror(errno));
		return 0;
	}

	// Network interface의 MAC address 구하기
	memset(&if_mac, 0, sizeof(struct ifreq));
	strncpy(if_mac.ifr_name, ifName, IFNAMSIZ-1);
	if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0)
	{
		printf("ioctl(SIOCGIFHWADDR, %s) error: %d (%s)\n", ifName, errno, strerror(errno));
		return 0;
	}

	// Ehternet header 구성하기 (참고: sendbuf pointer가 eh 주소를 pointing)
	memset(sendbuf, 0, BUF_SIZ);
	/*
	 * ioctl() 함수를 이용해서 얻은 'enp7s0' NIC에 대한 MAC Address 값을
	 * ethernet header 구조체의 ether_shost 변수에 복사한다.
	 */
	printf("( %s )  MAC address = ", ifName);
	for (int idx = 0; idx < 6; idx++)
	{
		eh->ether_shost[idx] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[idx];
		printf("%02x", eh->ether_shost[idx]);
		if (idx < 5)
		{
			printf(":");
		}
	}
	printf("\n");

	/*
	 * 일반적으로 NIC port의 MAC address를 ethernet frame의 source address로 사용하지만
	 * Ethernet packet 전송 테스트를 위해서 가짜 Source MAC address를 만들었다.
	 */
	eh->ether_shost[3] = 0x01;
	eh->ether_shost[4] = 0x02;
	eh->ether_shost[5] = 0x03;

	// Ethernet frame - Destination host MAC address
	eh->ether_dhost[0] = MY_DEST_MAC0;
	eh->ether_dhost[1] = MY_DEST_MAC1;
	eh->ether_dhost[2] = MY_DEST_MAC2;
	eh->ether_dhost[3] = MY_DEST_MAC3;
	eh->ether_dhost[4] = MY_DEST_MAC4;
	eh->ether_dhost[5] = MY_DEST_MAC5;

	// Ethertype:  Internet Protocol (0x0800)
	eh->ether_type = htons(ETH_P_IP);
	tx_len += sizeof(struct ether_header);

	// FIXME: IP Header
	//   각자 테스트 환경에 맞게 iph 변수를 수정하여 사용하기
  	iph->ihl = 20 >> 2;  // NOTE: (20 >> 2) * 4 = 20 bytes (IHL은 4 byte 단위로 해석되기 때문)
	iph->version = 4;
	iph->protocol = IPPROTO_IP;
	iph->saddr = inet_addr("10.1.1.10");
	iph->daddr = inet_addr("10.1.1.11");
	iph->tot_len = 46 + 32;

	tx_len += sizeof(struct iphdr);

	/* Payload (Packet data) */
	for (char idx = 0; idx < 32; idx++)
	{
		sendbuf[tx_len++] = idx;
	}

	/* Index of the network device */
	socket_address.sll_ifindex = if_idx.ifr_ifindex;
	/* Address length*/
	socket_address.sll_halen = ETH_ALEN;
	/* Destination MAC */
	socket_address.sll_addr[0] = MY_DEST_MAC0;
	socket_address.sll_addr[1] = MY_DEST_MAC1;
	socket_address.sll_addr[2] = MY_DEST_MAC2;
	socket_address.sll_addr[3] = MY_DEST_MAC3;
	socket_address.sll_addr[4] = MY_DEST_MAC4;
	socket_address.sll_addr[5] = MY_DEST_MAC5;

	/* Send packet */
	if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
	    printf("Send failed\n");

	return 0;
}

 

 

패킷 받기 (Receive a packet)

예제 코드

/**
 * How to build
 *  $  gcc recv-raw-packet.c -o recv-raw-packet
 *
 * How to run
 *  $ ./recv-raw-packet
 *    or
 *  $ ./recv-raw-packet  eth0
 */

#include <unistd.h>
#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <net/if.h>
#include <netinet/ether.h>
#include <errno.h>

#define ETHER_TYPE	0x0800

#define DEFAULT_IF	"enp7s0"
#define BUF_SIZ		1024

int main(int argc, char *argv[])
{
	char sender[INET6_ADDRSTRLEN];
	int sockfd, ret;
	int sockopt;
	ssize_t pktbytes;
	struct ifreq ifopts;	// To set promiscuous mode
	struct ifreq if_ip;	    // To get IP address of this host NIC
	struct sockaddr_storage peer_addr;
	uint8_t buf[BUF_SIZ];
	char ifName[IFNAMSIZ];

	// Network interface name 지정하기 (예: eth0)
	if (argc > 1)
	{
		strcpy(ifName, argv[1]);
	}
	else
	{
		strcpy(ifName, DEFAULT_IF);
	}

	// Ethernet + IP + UDP header
	struct ether_header *eh = (struct ether_header *) buf;
	struct iphdr *iph = (struct iphdr *) (buf + sizeof(struct ether_header));
	struct udphdr *udph = (struct udphdr *) (buf + sizeof(struct iphdr) + sizeof(struct ether_header));

	if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETHER_TYPE))) == -1)
	{
		printf("socket(PF_PACKET, SOCK_RAW, ETHER_TYPE) error: %d (%s)\n", errno, strerror(errno));
		return -1;
	}

	// Set interface to promiscuous mode
	strncpy(ifopts.ifr_name, ifName, IFNAMSIZ-1);
	ioctl(sockfd, SIOCGIFFLAGS, &ifopts);
	ifopts.ifr_flags |= IFF_PROMISC;
	ioctl(sockfd, SIOCSIFFLAGS, &ifopts);
	if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &sockopt, sizeof sockopt) == -1) {
		printf("setsockopt(SO_REUSEADDR) error: %d (%s)\n", errno, strerror(errno));
		close(sockfd);
		exit(0);
	}

	// Bind to device
	if (setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, ifName, IFNAMSIZ-1) == -1)	{
		printf("setsockopt(SO_BINDTODEVICE, %s) error: %d (%s)\n", ifName, errno, strerror(errno));
		close(sockfd);
		exit(0);
	}

repeat:
	printf("\nWaiting to recvfrom...\n");
	pktbytes = recvfrom(sockfd, buf, BUF_SIZ, 0, NULL, NULL);
	printf("  Got packet %lu bytes\n", pktbytes);

	printf("Destination  MAC address = ");
	for (int idx = 0; idx < 6; idx++)
	{
		printf("%02x", eh->ether_dhost[idx]);
		if (idx < 5)
		{
			printf(":");
		}
	}
	printf("\n");

	// Get source IP
	((struct sockaddr_in *)&peer_addr)->sin_addr.s_addr = iph->saddr;
	inet_ntop(AF_INET, &((struct sockaddr_in*)&peer_addr)->sin_addr, sender, sizeof sender);

	// Look up my device IP addr
	memset(&if_ip, 0, sizeof(struct ifreq));
	strncpy(if_ip.ifr_name, ifName, IFNAMSIZ-1);
	if (ioctl(sockfd, SIOCGIFADDR, &if_ip) >= 0) {
		printf("Source IP: %s\n My IP: %s\n", sender,
				inet_ntoa(((struct sockaddr_in *)&if_ip.ifr_addr)->sin_addr));
		// Ignore if I sent it
		if (strcmp(sender, inet_ntoa(((struct sockaddr_in *)&if_ip.ifr_addr)->sin_addr)) == 0)	{
			printf("but I sent it :(\n");
			ret = -1;
			goto done;
		}
	}

	/* UDP payload length */
	ret = ntohs(udph->len) - sizeof(struct udphdr);

	/* Print packet */
	printf("\tData:");
	for (int idx = 0; idx < pktbytes; idx++)
	{
		printf("%02x ", buf[idx]);
	}
	printf("\n");

done:
	goto repeat;

	close(sockfd);
	return ret;
}

 

 

 

 

 

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