C 数据链路套接字读取传出数据包？

我编写了一个简单的程序，使用原始数据链路套接字读取通过本地以太网接口（比如eth0）的数据包。这是我的程序的循环结构。完整的源代码附在本文末尾。该计划基于。我在CentOS 7上编译了源代码

while(1)
{

    if ((bytes = recvfrom(recvsd, recv_ether_frame, IP_MAXPACKET, 0, (struct sockaddr *)&from, &fromlen)) < 0) {
        perror ("recvfrom() failed ");
    }

    if ( (0==memcmp(recv_ether_frame, dst_mac, 6)) && (0==memcmp(recv_ether_frame+6, src_mac, 6)))
    {
        printf("Outgoing >>>>>>>>>>>>>>>>>>>>\n");

        dumpMemory(recv_ether_frame, bytes, 16);
    }

    if ((0==memcmp(recv_ether_frame, src_mac, 6)) && (0==memcmp(recv_ether_frame+6, dst_mac, 6)) )
    {

        printf("Incoming >>>>>>>>>>>>>>>>>>>>\n");

        dumpMemory(recv_ether_frame, bytes, 16);
    }
}

一个简短的回答是——是的。

---

但为什么你会感到惊讶呢？

我以前用L3套接字编程，据我所知，recvfrom（sock…）应该只返回sock上传入的数据包。我希望L2套接字也有同样的行为。这就是为什么一开始我很惊讶。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <net/ethernet.h>
#include <netinet/udp.h>
#include <netinet/tcp.h>
#include <errno.h>




// Define some constants.
#define ETH_HDRLEN 14  // Ethernet header length
#define IP4_HDRLEN 20  // IPv4 header length
#define ICMP_HDRLEN 8  // ICMP header length for echo request, excludes data

using namespace std;


void dumpMemory(void* data, size_t len, int bytes_per_row)
{
    size_t i;
    for (i=0; i<len; i++) {
        printf("%02X ", ((unsigned char*)data)[i] );
        if (0==(i+1)%bytes_per_row) {
            printf("\n");
        }
    }
    printf("\n");
}


int
main (int argc, char **argv)
{
    int i, status, datalen, send_frame_length, tmpsd, recvsd, bytes, timeout, trycount, trylim, done;
    char *interface, *src_ip, *dst_ip, *rec_ip;
    struct iphdr *send_iphdr, *recv_iphdr;
    struct icmp send_icmphdr, *recv_icmphdr;
    unsigned char *src_mac, *dst_mac, *recv_ether_frame;
    struct sockaddr_ll device;
    struct ifreq ifr;
    struct sockaddr from;
    socklen_t fromlen;


    if (argc != 6) {
        printf("Example usage: ./a.out <dev_name>  <src_mac> <src_ip> <dst_mac> <dst_ip>\n");
        return -1;
    }

    // Allocate memory for various arrays.
    src_mac = (unsigned char*)malloc (6);
    dst_mac = (unsigned char*)malloc (6);
    recv_ether_frame = (unsigned char*)malloc (IP_MAXPACKET);
    interface = (char*)malloc (40);


    strcpy (interface, argv[1]);
    sscanf(argv[2], "%x:%x:%x:%x:%x:%x", &src_mac[0], &src_mac[1], &src_mac[2], &src_mac[3], &src_mac[4], &src_mac[5]);
    src_ip = argv[3];
    struct in_addr src_in_addr;
    if (inet_pton(PF_INET, src_ip, &src_in_addr) <=0 ) {
        perror("inet_pton failed ");
        exit (1);
    }

    sscanf(argv[4], "%x:%x:%x:%x:%x:%x", &dst_mac[0], &dst_mac[1], &dst_mac[2], &dst_mac[3], &dst_mac[4], &dst_mac[5]);
    struct in_addr dst_in_addr;
    dst_ip = argv[5];
    if (inet_pton(PF_INET, dst_ip, &dst_in_addr) <=0 ) {
        perror("inet_pton failed ");
        exit (1);
    }

    // Submit request for a socket descriptor to look up interface.
    // We'll use it to send packets as well, so we leave it open.
    if ((tmpsd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
        perror ("socket() failed to get socket descriptor for using ioctl() ");
        exit (EXIT_FAILURE);
    }

    // Use ioctl() to look up interface name and get its MAC address.
    // memset (&ifr, 0, sizeof (ifr));
    // snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
    // if (ioctl (tmpsd, SIOCGIFHWADDR, &ifr) < 0) {
    //   perror ("ioctl() failed to get source MAC address ");
    //   return (EXIT_FAILURE);
    // }

    // Copy source MAC address.
    //memcpy (src_mac, ifr.ifr_hwaddr.sa_data, 6);

    snprintf (ifr.ifr_name, sizeof (ifr.ifr_name), "%s", interface);
    if ((ifr.ifr_ifindex = if_nametoindex (interface)) == 0) {
        perror ("if_nametoindex() failed to obtain interface index ");
        exit (EXIT_FAILURE);
    }

    /* Get the current flags that the device might have */
    if (ioctl (tmpsd, SIOCGIFFLAGS, &ifr) == -1)
    {
        perror ("Error: Could not retrive the flags from the device.\n");
        exit (1);
    }

    /* Set the old flags plus the IFF_PROMISC flag */
//    ifr.ifr_flags |= IFF_PROMISC;
//    if (ioctl (tmpsd, SIOCSIFFLAGS, &ifr) == -1)
//    {
//        perror ("Error: Could not set flag IFF_PROMISC");
//        exit (1);
//    }
//    printf ("Entering promiscuous mode\n");
    close(tmpsd);

    if ((recvsd = socket (PF_PACKET, SOCK_RAW, htons (ETH_P_ALL))) < 0) {
        perror ("socket() failed to obtain a receive socket descriptor ");
        exit (EXIT_FAILURE);
    }

    if (setsockopt (recvsd, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof (ifr)) < 0) {
        printf("setsockopt(...SOL_SOCKET, SO_BINDTODEVICE,...) failed: %s\n", strerror(errno));
    }

    while(1)
    {
        memset (recv_ether_frame, 0, IP_MAXPACKET * sizeof (uint8_t));
        memset (&from, 0, sizeof (from));
        fromlen = sizeof (from);

        if ((bytes = recvfrom(recvsd, recv_ether_frame, IP_MAXPACKET, 0, (struct sockaddr *)&from, &fromlen)) < 0) {
            perror ("recvfrom() failed ");
        }

        if ( (0==memcmp(recv_ether_frame, dst_mac, 6)) && (0==memcmp(recv_ether_frame+6, src_mac, 6)))
        {
            printf("Outgoing >>>>>>>>>>>>>>>>>>>>\n");

            dumpMemory(recv_ether_frame, bytes, 16);
        }

        if ((0==memcmp(recv_ether_frame, src_mac, 6)) && (0==memcmp(recv_ether_frame+6, dst_mac, 6)) )
        {

            printf("Incoming >>>>>>>>>>>>>>>>>>>>\n");

            dumpMemory(recv_ether_frame, bytes, 16);
        }
    }

    // Close socket descriptors.
    close (recvsd);


    // Free allocated memory.
    free (src_mac);
    free (dst_mac);
    free (recv_ether_frame);
    free (interface);

    return (EXIT_SUCCESS);
}