Question

我在此网站上引用了C代码：https://gist.github.com/austinmarton/2862515

这是一张图片来解释：

我在两个部分编辑它，一个pat用于ethertype（将0x0800更改为自定义协议0x1234）另一部分是删除IP头处理的代码（因为原始代码基于IP，但我需要一个原始的以太网帧）。

我使用wireshark来检测数据包，我可以接收我发送的数据包（在图像的左侧），我可以看到send.out正好发送数据包（图像的右下角）。但是recv.out无法接收数据包！？（图片的右上角）。

但是，如果我使用0x0800作为协议，recv.out可以从外部接收数据包，但仍然无法接收我发送的数据包。

设置套接字是否有错误

这是我的代码：

send.c

#include <arpa/inet.h>
#include <linux/if_packet.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>

#define MY_DEST_MAC0    0xbc
#define MY_DEST_MAC1    0xee
#define MY_DEST_MAC2    0x7b
#define MY_DEST_MAC3    0x75
#define MY_DEST_MAC4    0x56
#define MY_DEST_MAC5    0x2a

#define DEFAULT_IF  "eth0"
#define BUF_SIZ     1024

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

    unsigned short proto = 0x1234;

    /* Get interface name *//*eth0*/
    if (argc > 1)
        strcpy(ifName, argv[1]);
    else
        strcpy(ifName, DEFAULT_IF);

    /* Open RAW socket to send on *//*IPv4*/
    if ((sockfd = socket(AF_PACKET, SOCK_RAW, htons(proto))) == -1) {
        perror("socket");
    }

    /* Get the index of the interface to send on *//*0*/
    memset(&if_idx, 0, sizeof(struct ifreq));
    strncpy(if_idx.ifr_name, ifName, IFNAMSIZ-1);
    if (ioctl(sockfd, SIOCGIFINDEX, &if_idx) < 0)/*save INDEX info into if_idx*/
        perror("SIOCGIFINDEX");
    /* Get the MAC address of the interface to send on *//*local*//*save MAC info into if_mac*/
    memset(&if_mac, 0, sizeof(struct ifreq));
    strncpy(if_mac.ifr_name, ifName, IFNAMSIZ-1);
    if (ioctl(sockfd, SIOCGIFHWADDR, &if_mac) < 0)
        perror("SIOCGIFHWADDR");

    /* Construct the Ethernet header */
    memset(sendbuf, 0, BUF_SIZ);
    /* Ethernet header */
    eh->ether_shost[0] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[0];
    eh->ether_shost[1] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[1];
    eh->ether_shost[2] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[2];
    eh->ether_shost[3] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[3];
    eh->ether_shost[4] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[4];
    eh->ether_shost[5] = ((uint8_t *)&if_mac.ifr_hwaddr.sa_data)[5];
    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 field */
    eh->ether_type = htons(proto);
    tx_len += sizeof(struct ether_header);

    /* Packet data */
    sendbuf[tx_len++] = "h";
    sendbuf[tx_len++] = "e";
    sendbuf[tx_len++] = "l";
    sendbuf[tx_len++] = "l";
    sendbuf[tx_len++] = "o";

    /* 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 */
int cnt=0;
while(cnt<5){
    if (sendto(sockfd, sendbuf, tx_len, 0, (struct sockaddr*)&socket_address, sizeof(struct sockaddr_ll)) < 0)
        printf("Send failed\n");
    else
        printf("success!\n");

    cnt++;
}
    return 0;

}

recv.c

#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>

#define DEST_MAC0   0xbc
#define DEST_MAC1   0xee
#define DEST_MAC2   0x7b
#define DEST_MAC3   0x75
#define DEST_MAC4   0x56
#define DEST_MAC5   0x2a

#define ETHER_TYPE  0x1234

#define DEFAULT_IF  "eth0"
#define BUF_SIZ     1024

int main(int argc, char *argv[])
{
    char sender[INET6_ADDRSTRLEN];
    int sockfd, ret, i;
    int sockopt;
    ssize_t numbytes;
    struct ifreq ifopts;    /* set promiscuous mode */
    struct sockaddr_storage their_addr;
    uint8_t buf[BUF_SIZ];
    char ifName[IFNAMSIZ];

    /* Get interface name *//*eth0*/
    if (argc > 1)
        strcpy(ifName, argv[1]);
    else
        strcpy(ifName, DEFAULT_IF);

    /* Header structures */
    struct ether_header *eh = (struct ether_header *) buf;

    /* Open PF_PACKET socket, listening for EtherType ETHER_TYPE *//*0x1234*/
    if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETHER_TYPE))) == -1) {
        perror("listener: socket"); 
        return -1;
    }

    /* Set interface to promiscuous mode - do we need to do this every time? *//*cpy ifname into ifr_name*/
    strncpy(ifopts.ifr_name, ifName, IFNAMSIZ-1);
    ioctl(sockfd, SIOCGIFFLAGS, &ifopts); /*set promisc mode*/
    ifopts.ifr_flags |= IFF_PROMISC;
    ioctl(sockfd, SIOCSIFFLAGS, &ifopts);
    /* Allow the socket to be reused - incase connection is closed prematurely */
    if (setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &sockopt, sizeof sockopt) == -1) {
        perror("setsockopt");
        close(sockfd);
        exit(EXIT_FAILURE);
    }
    /* Bind to device */
    if (setsockopt(sockfd, SOL_SOCKET, SO_BINDTODEVICE, ifName, IFNAMSIZ-1) == -1)  {
        perror("SO_BINDTODEVICE");
        close(sockfd);
        exit(EXIT_FAILURE);
    }

repeat: printf("listener: Waiting to recvfrom...\n");
    numbytes = recvfrom(sockfd, buf, BUF_SIZ, 0, NULL, NULL);
    printf("listener: got packet %lu bytes\n", numbytes);

    /* Check the packet is for me */
    if (eh->ether_dhost[0] == DEST_MAC0 &&
            eh->ether_dhost[1] == DEST_MAC1 &&
            eh->ether_dhost[2] == DEST_MAC2 &&
            eh->ether_dhost[3] == DEST_MAC3 &&
            eh->ether_dhost[4] == DEST_MAC4 &&
            eh->ether_dhost[5] == DEST_MAC5) {
        printf("Correct destination MAC address\n");
    } else {
        printf("Wrong destination MAC: %x:%x:%x:%x:%x:%x\n",
                        eh->ether_dhost[0],
                        eh->ether_dhost[1],
                        eh->ether_dhost[2],
                        eh->ether_dhost[3],
                        eh->ether_dhost[4],
                        eh->ether_dhost[5]);
        ret = -1;
        goto done;
    }

    /* Print packet */
    printf("\tData:");
    for (i=0; i<numbytes; i++) printf("%02x:", buf[i]);
    printf("\n");

done:   goto repeat;

    close(sockfd);
    return ret;
}

Answer 1

您可以通过接收代码中的以下更改获取目标中的所有帧：

请替换行： if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETHER_TYPE))) == -1) {

这一行： if ((sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) == -1) {

因为在您的原始代码中您更改了正常的以太网头类型，然后操作系统无法检测到其进程侦听器（您的程序）并将其发送给您，但是当您设置此行时，操作系统可以获取所有结果，以便您可以获得特殊答案。

Answer 2

我开始进行套接字编程，所以有人应该确认一下。

我很确定接口会丢弃数据包，因为源和目标mac是相同的...尝试使用另一台PC并更改每一侧的目标mac以确认这一点（虚拟机也能正常工作）

Answer 3

我还使用了类似的代码来传输以太网帧。这种类型的套接字在本地不起作用。由于@Goncalo建议使用不同的PC，或者如果您的PC上有两个NIC，您应该使用它们。这是我用来接收帧的代码。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>    
#include <linux/if.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <sys/ioctl.h>

union ethframe
{
  struct
  {
    struct ethhdr    header;
    unsigned char    data[ETH_DATA_LEN];
  } field;
  unsigned char    buffer[ETH_FRAME_LEN];
};

int main(int argc, char **argv) {
  char *iface = "eth1";
  unsigned char dest[ETH_ALEN]     
          = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
  unsigned short proto = 0x1234;
  int recv_result,i;
  char buff[ETH_FRAME_LEN];
  unsigned short data_len;

  int s;
  if ((s = socket(AF_PACKET, SOCK_RAW, htons(proto))) < 0) {
    printf("Error: could not open socket\n");
    return -1;
  }

  struct ifreq buffer;
  int ifindex;
  memset(&buffer, 0x00, sizeof(buffer));
  strncpy(buffer.ifr_name, iface, IFNAMSIZ);
  if (ioctl(s, SIOCGIFINDEX, &buffer) < 0) {
    printf("Error: could not get interface index\n");
    close(s);
    return -1;
  }
  ifindex = buffer.ifr_ifindex;

  unsigned char source[ETH_ALEN];
  if (ioctl(s, SIOCGIFHWADDR, &buffer) < 0) {
    printf("Error: could not get interface address\n");
    close(s);
    return -1;
  }
  memcpy((void*)source, (void*)(buffer.ifr_hwaddr.sa_data),
         ETH_ALEN);


  struct sockaddr_ll saddrll;
  memset((void*)&saddrll, 0, sizeof(saddrll));
  saddrll.sll_family = PF_PACKET;   
  saddrll.sll_ifindex = ifindex;
  saddrll.sll_halen = ETH_ALEN;
  memcpy((void*)(saddrll.sll_addr), (void*)dest, ETH_ALEN);

  socklen_t sll_len = (socklen_t)sizeof(saddrll);  

  if (recv_result = recvfrom(s, buff, ETH_FRAME_LEN, 0,
    (struct sockaddr *)&saddrll, &sll_len) > 0)
    printf("Success!\n");
  else
    printf("Error, could not send\n");

  data_len=sizeof(buff);
  printf("\tData:");
    for (i=0; i<data_len; i++) printf("%c", buff[i]);


  printf("\tDone: \n");
  close(s);

  return 0;
}

无法接收我刚刚发送的原始以太网帧数据包

3 个答案: