Linux网络接口操作之ioctl-2_ARP条目 - 快车库

相关定义

ARP条目相关操作的定义

/* include/linux/sockios.h */

/* ARP cache control calls. */
            /*  0x8950 - 0x8952  * obsolete calls, don't re-use */
#define SIOCDARP    0x8953      /* delete ARP table entry   */
#define SIOCGARP    0x8954      /* get ARP table entry      */
#define SIOCSARP    0x8955      /* set ARP table entry      */

ARP条目操作的结构与相关标志

/* include/linux/if_arp.h */

/* ARP ioctl request. */
struct arpreq {
  struct sockaddr   arp_pa;     /* protocol address     */
  struct sockaddr   arp_ha;     /* hardware address     */
  int               arp_flags;  /* flags            */
  struct sockaddr   arp_netmask;    /* netmask (only for proxy arps) */
  char              arp_dev[16];
};


/* ARP Flag values. */
#define ATF_COM         0x02        /* completed entry (ha valid)   */
#define ATF_PERM        0x04        /* permanent entry      */
#define ATF_PUBL        0x08        /* publish entry        */
#define ATF_USETRAILERS 0x10        /* has requested trailers   */
#define ATF_NETMASK     0x20        /* want to use a netmask (only
                                       for proxy entries) */
#define ATF_DONTPUB     0x40        /* don't answer this addresses  */

SIOCDARP/SIOCGARP/SIOCSARP作为ioctl(2)的第2个参数，分别用于在ARP表中删除/获取/添加单个条目

struct arpreq结构地址作为ioctl(2)的第3个参数；执行操作时，arp_pa被转换为IPv4套接字地址结构(struct sockaddr_in)，表示目的端的IP地址；arp_ha为通用套接字地址结构，sa_family为AF_UNSPEC，sa_data中包含网络接口的2层地址，如以太网mac地址，表示目的端的2层地址；arp_flags用于指定ARP操作的标志；arp_netmask用于代理ARP；arp_dev用于指定本地网络接口的名称

获取ARP条目时，需要初始化arp_pa，arp_dev，然后调用ioctl(SIOCGARP)，成功返回后arp_pa中包含的IP地址对应的mac地址保存在arp_ha.sa_data中；若指定的网络接口不存在，或存在但与指定的目标主机IP地址不对应，则ioctl以"(ENXIO)No such device or address"错误调用失败
无法通过ioctl操作获取整个ARP表，arp(8)命令的-a选项是通过读取系统中的/proc/net/arp文件内容实现该目的

添加ARP条目时，需要同时初始化arp_pa，arp_dev，arp_ha.sa_data以及arp_flags，然后调用ioctl(SIOCSARP)

删除ARP条目时，需要初始化arp_pa，arp_dev，然后调用ioctl(SIOCDARP)，成功返回后，指定目标地址对应的ARP条目被删除；若指定的网络接口不存在，或存在但与指定的目标主机IP地址不对应，则ioctl以"(ENXIO)No such device or address"错误调用失败

示例程序

系统双网卡，名称分别为eth0与eth1
初始的ARP表内容为：

# arp -n
Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.56.254           ether   00:50:56:f8:57:2f   C                     eth0
192.168.56.2             ether   00:50:56:f4:a3:a0   C                     eth0
192.168.56.1             ether   00:50:56:c0:00:08   C                     eth0

1 . 指定本地网络接口名称与目标主机IP地址作为参数，获取对应的mac地址

/* get_arp_entry_ioctl.c */

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if_arp.h>

static void get_arp_entry(const char *, const char *);

int main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr,
        "Usage: %s [local interface name] [dst ip addres]\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    char ifname[IFNAMSIZ] = {'\0'};
    strncpy(ifname, argv[1], IFNAMSIZ-1);

    char ipaddr[INET_ADDRSTRLEN] = {'\0'};
    strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);

    get_arp_entry(ifname, ipaddr);

    return 0;
}

static void get_arp_entry(const char *dev, const char *ip)
{
    int sfd, saved_errno, ret;
    unsigned char *mac;
    struct arpreq arp_req;
    struct sockaddr_in *sin;

    sin = (struct sockaddr_in *)&(arp_req.arp_pa);

    memset(&arp_req, 0, sizeof(arp_req));
    sin->sin_family = AF_INET;
    inet_pton(AF_INET, ip, &(sin->sin_addr));
    strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);

    sfd = socket(AF_INET, SOCK_DGRAM, 0);

    saved_errno = errno;
    ret = ioctl(sfd, SIOCGARP, &arp_req);
    if (ret < 0) {
        fprintf(stderr, "Get ARP entry failed : %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    errno = saved_errno;

    if (arp_req.arp_flags & ATF_COM) {
        mac = (unsigned char *)arp_req.arp_ha.sa_data;
        printf("MAC: %02x:%02x:%02x:%02x:%02x:%02x\n",
                mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
    } else {
        printf("MAC: Not in the ARP cache.\n");
    }
}

编译并运行

# gcc get_arp_entry_ioctl.c -g3 -DC=-5 -o get_arp_entry_ioctl
#
# ./get_arp_entry_ioctl eth0 192.168.56.1
MAC: 00:50:56:c0:00:08
#
# ./get_arp_entry_ioctl eth1 192.168.56.1
Get ARP entry failed : No such device or address
#
# ./get_arp_entry_ioctl eth1 192.168.56.100
Get ARP entry failed : No such device or address

2 . 指定本地网络接口名称，目标主机IP地址与mac地址作为参数，添加ARP条目

/* set_arp_entry_ioctl.c */

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/if_ether.h>
#include <net/if_arp.h>

static void set_arp_entry(char *, char *, char *);
static int parse_mac(char *, char *);

int main(int argc, char *argv[])
{
    if (argc != 4) {
        fprintf(stderr,
        "Usage: %s [local interface name] [dst ip addres] [dst mac address]\n",
        argv[0]);
        exit(EXIT_FAILURE);
    }

    char ifname[IFNAMSIZ] = {'\0'};
    strncpy(ifname, argv[1], IFNAMSIZ-1);

    char ipaddr[INET_ADDRSTRLEN] = {'\0'};
    strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);

    int mac_size = strlen(argv[3]);
    unsigned char *macaddr = (unsigned char *)malloc(mac_size);
    memcpy(macaddr, argv[3], mac_size);

    set_arp_entry(ifname, ipaddr, macaddr);
    printf("Adding an arp entry done.\n");

    return 0;
}

static void set_arp_entry(char *dev, char *ip, char *mac)
{
    int sfd, saved_errno, ret;
    struct arpreq arp_req;
    struct sockaddr_in *sin;

    sfd = socket(AF_INET, SOCK_DGRAM, 0);

    sin = (struct sockaddr_in *)&(arp_req.arp_pa);

    memset(&arp_req, 0, sizeof(arp_req));
    sin->sin_family = AF_INET;
    inet_pton(AF_INET, ip, &(sin->sin_addr));
    strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);
    parse_mac(mac, arp_req.arp_ha.sa_data);
    arp_req.arp_flags = ATF_PERM | ATF_COM;

    saved_errno = errno;
    ret = ioctl(sfd, SIOCSARP, &arp_req);
    if (ret < 0) {
        fprintf(stderr, "Set ARP entry failed : %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    errno = saved_errno;
}

static int parse_mac(char *mac, char *dst)
{
    int i;
    unsigned byte;
    char *s;

    i = 0;
    while ((s = strsep(&mac, ":")) != NULL) {
        if (sscanf(s, "%x", &byte) != 1 || byte > 0xff)
            return -1;
        *(dst+i) = byte;
        i++;
    }

    if (i != ETH_ALEN) {
        fprintf(stderr, "Invalid mac address\n");
        exit(EXIT_FAILURE);
    }

    return 0;
}

编译并运行

# gcc set_arp_entry_ioctl.c -g3 -DC=-5 -o set_arp_entry_ioctl
#
# ./set_arp_entry_ioctl eth0 192.168.56.100 aa:bb:cc:dd:ee:ff
Adding an arp entry done.
#
# ./get_arp_entry_ioctl eth0 192.168.56.100
MAC: aa:bb:cc:dd:ee:ff
#
# arp -n
Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.56.1             ether   00:50:56:c0:00:08   C                     eth0
192.168.56.254           ether   00:50:56:f8:57:2f   C                     eth0
192.168.56.100           ether   aa:bb:cc:dd:ee:ff   CM                    eth0
192.168.56.2             ether   00:50:56:f4:a3:a0   C                     eth0

3 . 指定本地网络接口名称与目标主机IP地址作为参数，删除对应的ARP条目

/* del_arp_entry_ioctl.c */

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if_arp.h>

static void del_arp_entry(char *, char *);

int main(int argc, char *argv[])
{
    if (argc != 3) {
        fprintf(stderr,
        "Usage: %s [local interface name] [dst ip addres]\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    char ifname[IFNAMSIZ] = {'\0'};
    strncpy(ifname, argv[1], IFNAMSIZ-1);

    char ipaddr[INET_ADDRSTRLEN] = {'\0'};
    strncpy(ipaddr, argv[2], INET_ADDRSTRLEN);

    del_arp_entry(ifname, ipaddr);
    printf("Deleting an arp entry done.\n");
}

static void del_arp_entry(char *dev, char *ip)
{
    int sfd, saved_errno, ret;
    struct arpreq arp_req;
    struct sockaddr_in *sin;

    sfd = socket(AF_INET, SOCK_DGRAM, 0);

    sin = (struct sockaddr_in *)&(arp_req.arp_pa);
    memset(&arp_req, 0, sizeof(arp_req));
    sin->sin_family = AF_INET;
    strncpy(arp_req.arp_dev, dev, IFNAMSIZ-1);
    inet_pton(AF_INET, ip, &(sin->sin_addr));


    saved_errno = errno;
    ret = ioctl(sfd, SIOCDARP, &arp_req);
    if (ret < 0) {
        fprintf(stderr, "Delete ARP entry failed : %s\n", strerror(errno));
        exit(EXIT_FAILURE);
    }
    errno = saved_errno;
}

编译并运行

# gcc del_arp_entry_ioctl.c -g3 -DC=-5 -o del_arp_entry_ioctl
#
# ./del_arp_entry_ioctl eth0 192.168.56.100
Deleting an arp entry done.
#
# ./del_arp_entry_ioctl eth0 192.168.56.200
Delete ARP entry failed : No such device or address
#
# ./del_arp_entry_ioctl eth1 192.168.56.100
Delete ARP entry failed : No such device or address
#
# arp -n
Address                  HWtype  HWaddress           Flags Mask            Iface
192.168.56.1             ether   00:50:56:c0:00:08   C                     eth0
192.168.56.254           ether   00:50:56:f8:57:2f   C                     eth0
192.168.56.100                   (incomplete)                              eth0
192.168.56.2             ether   00:50:56:f4:a3:a0   C                     eth0
#
# cat /proc/net/arp 
IP address       HW type     Flags       HW address            Mask     Device
192.168.56.1     0x1         0x2         00:50:56:c0:00:08     *        eth0
192.168.56.254   0x1         0x2         00:50:56:f8:57:2f     *        eth0
192.168.56.100   0x1         0x0         aa:bb:cc:dd:ee:ff     *        eth0
192.168.56.2     0x1         0x2         00:50:56:f4:a3:a0     *        eth0
#
# ./get_arp_entry_ioctl eth0 192.168.56.100
MAC: Not in the ARP cache.