一：linux下的网络设备

linux的网络设备信息都在/proc/net/dev，从这里我们可以得到所有网卡的名字，如eth0， eth1等等

root@dlrc-desktop:/home/dlrc/dlsp-ep9302/work/mystar-v0.4# cat /proc/net/dev

Inter-| Receive | Transmit

face |bytes packets errs drop fifo frame compressed multicast|bytes packets errs drop

lo: 472252 1696 0 0 0 0 0 0 472252 1696 0 0 0 0 0 0

eth1:20826443 20156 0 0 0 0 0 0 926357 14613 0 0 0 0 0 0

上面的lo和eth1便是我的网卡名字。ifconfig就是读取/proc/net/dev这个文件来取得设备名列表的。

二：读取网卡mac地址

可以通过ioctl(sock, SIOCGIFHWADDR, &ifr)读取mac地址，对任意类型的socket都适用，只需指定第三参数struct ifreq ifr的ifr.ifr_name, 这个ifr_name就是网络设备的名字，如eth0, eth1, lo等，在/proc/net/dev可找到。ioctl通过ifr_name获取设备信息。

struct ifreq ifr;

strncpy(ifr.ifr_name, name, 6);

if (ioctl(sock, SIOCGIFHWADDR, &ifr) < 0){

perror("get_hwaddr ioctl:");

close(sock);

return -1;

}

以下是一个实现：

/**

* get_hwaddr - get netdevice mac addr

* @name: device name, e.g: eth0

* @hwaddr: where to save mac, 6 byte hwaddr[6]

* @return: 0 on success, -1 on failure

*/

int get_hwaddr(char *name, unsigned char *hwaddr)

{

struct ifreq ifr;

unsigned char memzero[6];

int sock;

if(name == NULL || hwaddr == NULL){

printf("get_hwaddr: NULL para\n");

return -1;

}

sock = socket(AF_INET, SOCK_STREAM, 0);

if(sock < 0){

printf("get_hwaddr: socket error\n");

//return -1;

}

//get eth1 mac addr

memset(hwaddr, 0, 6);

memset(&ifr, 0, sizeof(ifr));

strncpy(ifr.ifr_name, name, 6);

if (ioctl(sock, SIOCGIFHWADDR, &ifr) < 0){

perror("get_hwaddr ioctl:");

close(sock);

return -1;

} else {

memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);

//printf("hwaddr: %2x : %2x : %2x : %2x : %2x : %2x\n", hwaddr[0], hwaddr[1],hwaddr[2], hwaddr[3],hwaddr[4], hwaddr[5]);

}

memset(memzero, 0, 6);

if(memcmp(memzero, hwaddr, 6) == 0){

printf("no mac\n");

return -1;

}

close(sock);

return 0;

}

三：发送底层网络数据包

绕过TCP，UDP等传输协议，自己维护协议首部，发送原始数据包，在自定义的协议方面很方便。

SOCK_RAW提供了一个数据包接口直接访问底层网络。使用这个socket需要root权限。

创建 socket，用于发送自定义数据报：

int sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

if(sock < 0){

perror("sock");

return -1;

}

第三个参数htons(ETH_P_ALL)只对recvfrom有意义。用这个socket发送的数据，都需要自己维护数据包协议首部，包括网络数据包中的mac地址。

发送数据包：

struct sockaddr_ll sll;

memset(&sll, 0, sizeof(sll));

sll.sll_ifindex = 2; // 指定网卡

if (sendto(sock, packet_start, sizeof packet_start, 0, &sll, sizeof(sll)) < 0){

perror("sendto");

return 1;

}

sendto发送原始数据包，只需用struct sockaddr_ll的sll_ifindex指定网卡。

接收这类的数据包：

ret = recvfrom(sock, buf, 1024, 0, NULL, NULL);

以下是一个简单的实现，运行两个实例，一个带参数，用于发送数据包。一个不带参数，用于接收数据包。完整的源码在最下面：

在wireshark可以看到，发送的数据包就是原始的网络数据包。

完整的源码：

/*

* socket.c

*

* Copyright (C) 2011 crazyleen

*

*/

#include

#include

#include

#include

#include /* for the glibc version number */

#if __GLIBC__ >= 2 && __GLIBC_MINOR >= 1

#include

#include /* the L2 protocols */

#else

#include

#include

#include /* The L2 protocols */

#endif

#include

#include

#include

#include

#include

#define _PATH_PROCNET_DEV "/proc/net/dev"

static char *get_name(char *name, char *p)

{

while (isspace(*p))

p++;

while (*p) {

if (isspace(*p))

break;

if (*p == ':') {/* could be an alias */

char *dot = p, *dotname = name;

*name++ = *p++;

while (isdigit(*p))

*name++ = *p++;

if (*p != ':') {/* it wasn't, backup */

p = dot;

name = dotname;

}

if (*p == '\0')

return NULL;

p++;

break;

}

*name++ = *p++;

}

*name++ = '\0';

return p;

}

/**

* read_netdev_proc - read net dev names form proc/net/dev

* @devname: where to store dev names, devname[num][len]

*/

static int read_netdev_proc(void *devname, const int num, const int len)

{

FILE *fh;

char buf[512];

int cnt = 0;

char *dev = (char *)devname;

if(devname == NULL || num < 1 || len < 4){

printf("read_netdev_proc: para error\n");

return -1;

}

memset(devname, 0, len * num);

fh = fopen(_PATH_PROCNET_DEV, "r");

if (!fh) {

fprintf(stderr, "Warning: cannot open %s (%s). Limited output.\n",

_PATH_PROCNET_DEV, strerror(errno));

return -1;

}

fgets(buf, sizeof buf, fh);/* eat two line */

fgets(buf, sizeof buf, fh);

cnt = 0;

while (fgets(buf, sizeof buf, fh) && cnt < num) {

char *s, name[IFNAMSIZ];

s = get_name(name, buf);

strncpy(devname, name, len);

devname += len;

printf("get_name: %s\n", name);

}

if (ferror(fh)) {

perror(_PATH_PROCNET_DEV);

}

fclose(fh);

return 0;

}

/**

* get_hwaddr - get netdevice mac addr

* @name: device name, e.g: eth0

* @hwaddr: where to save mac, 6 byte hwaddr[6]

* @return: 0 on success, -1 on failure

*/

int get_hwaddr(char *name, unsigned char *hwaddr)

{

struct ifreq ifr;

unsigned char memzero[6];

int sock;

if(name == NULL || hwaddr == NULL){

printf("get_hwaddr: NULL para\n");

return -1;

}

sock = socket(AF_INET, SOCK_STREAM, 0);

if(sock < 0){

printf("get_hwaddr: socket error\n");

//return -1;

}

//get eth1 mac addr

memset(hwaddr, 0, 6);

memset(&ifr, 0, sizeof(ifr));

strncpy(ifr.ifr_name, name, 6);

if (ioctl(sock, SIOCGIFHWADDR, &ifr) < 0){

perror("get_hwaddr ioctl:");

close(sock);

return -1;

} else {

memcpy(hwaddr, ifr.ifr_hwaddr.sa_data, 6);

//printf("hwaddr: %2x : %2x : %2x : %2x : %2x : %2x\n", hwaddr[0], hwaddr[1],hwaddr[2], hwaddr[3],hwaddr[4], hwaddr[5]);

}

memset(memzero, 0, 6);

if(memcmp(memzero, hwaddr, 6) == 0){

printf("no mac\n");

return -1;

}

close(sock);

return 0;

}

unsigned char packet_start[]={

0xff, 0xff, 0xff, 0xff, 0xff, 0xff,//dst mac

0x00, 0x23, 0x54, 0x0e, 0xe5, 0xd8,//src mac

0x88, 0x8e, //Type: 802.1x authentication

0x01, //Version:v1

0x01, //Type: Start (1)

0x00, 0x00//Length 0

};

void printhex(void *hex, int len, char *tag)

{

int i;

unsigned char *p = (unsigned char *)hex;

if(len < 1)

return;

for(i = 0; i < len - 1; i++){

if(*p < 0x10)

printf("0%x%s", *p++, tag);

else

printf("%2x%s", *p++, tag);

}

if(*p < 0x10)

printf("0%x\n", *p++);

else

printf("%2x\n", *p++);

}

int main(int argc, char **argv)

{

int i;

unsigned char hwaddr[6];

char devname[3][7];

unsigned char buf[1024]; // for revevied packet

int ret;

read_netdev_proc(devname, 3, 7);

for(i = 0; i < 3 && get_hwaddr(devname[i], hwaddr) != 0; i++){

//empty

}

printf("devname: [ %s ]\t", devname[i]);

printhex(hwaddr, 6, ":");

int sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));

if(sock < 0){

perror("sock");

return -1;

}

struct sockaddr_ll sll;

memset(&sll, 0, sizeof(sll));

sll.sll_ifindex = 2; // It seems only need this to specify which NIC to use

memcpy(packet_start + 6, hwaddr, 6);

//memcpy(packet_start, hwaddr, 6);

while(argc == 1){

if (sendto(sock, packet_start, sizeof packet_start, 0, &sll, sizeof(sll)) < 0){

perror("sendto");

return 1;

}

printf("Sendto Success!\n");

sleep(1);

}

while(argc == 2){

ret = recvfrom(sock, buf, 1024, 0, NULL, NULL);

printf("recv: ");

printhex(buf, ret, " ");

}

return 0;

}