linux sock_raw原始套接字编程

sock_raw原始套接字编程可以接收到本机网卡上的数据帧或者数据包,对与监听网络的流量和分析是很有作用的.一共可以有3种方式创建这种socket

 

1.socket(AF_INET, SOCK_RAW, IPPROTO_TCP|IPPROTO_UDP|IPPROTO_ICMP)发送接收ip数据包

2.socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP|ETH_P_ARP|ETH_P_ALL))发送接收以太网数据帧

3.socket(AF_INET, SOCK_PACKET, htons(ETH_P_IP|ETH_P_ARP|ETH_P_ALL))过时了,不要用啊

 

理解一下SOCK_RAW的原理, 比如网卡收到了一个 14+20+8+100+4 的udp的以太网数据帧.

 

首先,网卡对该数据帧进行硬过滤(根据网卡的模式不同会有不同的动作,如果设置了promisc混杂模式的话,则不做任何过滤直接交给下一层输入例程,否则非本机mac或者广播mac会被直接丢弃).按照上面的例子,如果成功的话,会进入ip输入例程.但是在进入ip输入例程之前,系统会检查系统中是否有通过socket(AF_PACKET, SOCK_RAW, ..)创建的套接字.如果有的话并且协议相符,在这个例子中就是需要ETH_P_IP或者ETH_P_ALL类型.系统就给每个这样的socket接收缓冲区发送一个数据帧拷贝.然后进入下一步.

 

其次,进入了ip输入例程(ip层会对该数据包进行软过滤,就是检查校验或者丢弃非本机ip或者广播ip的数据包等,具体要参考源代码),例子中就是如果成功的话会进入udp输入例程.但是在交给udp输入例程之前,系统会检查系统中是否有通过socket(AF_INET, SOCK_RAW, ..)创建的套接字.如果有的话并且协议相符,在这个例子中就是需要IPPROTO_UDP类型.系统就给每个这样的socket接收缓冲区发送一个数据帧拷贝.然后进入下一步.

 

最后,进入udp输入例程 ...

 

ps:如果校验和出错的话,内核会直接丢弃该数据包的.而不会拷贝给sock_raw的套接字,因为校验和都出错了,数据肯定有问题的包括所有信息都没有意义了.

 

进一步分析他们的能力.

1. socket(AF_INET, SOCK_RAW, IPPROTO_UDP);

能:该套接字可以接收协议类型为(tcp udp icmp等)发往本机的ip数据包,从上面看的就是20+8+100.

不能:不能收到非发往本地ip的数据包(ip软过滤会丢弃这些不是发往本机ip的数据包).

不能:不能收到从本机发送出去的数据包.

发送的话需要自己组织tcp udp icmp等头部.可以setsockopt来自己包装ip头部

这种套接字用来写个ping程序比较适合

     

2. socket(PF_PACKET, SOCK_RAW, htons(x)); 

这个套接字比较强大,创建这种套接字可以监听网卡上的所有数据帧.从上面看就是20+20+8+100.最后一个以太网crc从来都不算进来的,因为内核已经判断过了,对程序来说没有任何意义了.

能: 接收发往本地mac的数据帧

能: 接收从本机发送出去的数据帧(第3个参数需要设置为ETH_P_ALL)

能: 接收非发往本地mac的数据帧(网卡需要设置为promisc混杂模式)

协议类型一共有四个

ETH_P_IP  0x800      只接收发往本机mac的ip类型的数据帧

ETH_P_ARP 0x806      只接受发往本机mac的arp类型的数据帧

ETH_P_ARP 0x8035     只接受发往本机mac的rarp类型的数据帧

ETH_P_ALL 0x3        接收发往本机mac的所有类型ip arp rarp的数据帧, 接收从本机发出的所有类型的数据帧.(混杂模式打开的情况下,会接收到非发往本地mac的数据帧)

 

发送的时候需要自己组织整个以太网数据帧.所有相关的地址使用struct sockaddr_ll 而不是struct sockaddr_in(因为协议簇是PF_PACKET不是AF_INET了),比如发送给某个机器,对方的地址需要使用struct sockaddr_ll.

 

这种socket大小通吃,强悍

下面是一段相关的代码:

 

     ...
    int sockfd = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
    struct sockaddr_ll sll;
    memset( &sll, 0, sizeof(sll) );
    sll.sll_family = AF_PACKET;
    struct ifreq ifstruct;
    strcpy(ifstruct.ifr_name, "eth0");
    ioctl(sockfd, SIOCGIFINDEX, &ifstruct);
    sll.sll_ifindex = ifstruct.ifr_ifindex;
    sll.sll_protocol = htons(ETH_P_ALL);
    if(bind(fd, (struct sockaddr *) &sll, sizeof(sll)) == -1 ) {
       perror("bind()");
    ...

 

int set_promisc(char *interface, int fd) {
        struct ifreq ifr;
        strcpy(ifr.ifr_name, interface);
        if(ioctl(fd, SIOCGIFFLAGS, &ifr) == -1) {
                perror("iotcl()");
                return -1;
        }
        ifr.ifr_flags |= IFF_PROMISC;
        if(ioctl(fd, SIOCSIFFLAGS, &ifr) == -1) {
                perror("iotcl()");
                return -1;
        }
        return 0;
}
 
int unset_promisc(char *interface, int fd) {
        struct ifreq ifr;
        strcpy(ifr.ifr_name, interface);
        if(ioctl(fd, SIOCGIFFLAGS, &ifr) == -1) {
                perror("iotcl()");
                return -1;
        }
        ifr.ifr_flags &= ~IFF_PROMISC;
        if(ioctl(fd, SIOCSIFFLAGS, &ifr) == -1) {
                perror("iotcl()");
                return -1;
        }
        return 0;
}

 

3. socket(AF_INET, SOCK_PACKET, htons(ETH_P_ALL))这个最好不要用,反正我不用...

 

总结使用方法: 1.只想收到发往本机某种协议的ip数据包的话用第一种就足够了

            2. 更多的详细的内容请使用第二种.包括ETH_P_ALL参数和混杂模式都可以使它的能力不断的加强.

ps:很多自己的想法.虚拟机测试环境.有错欢迎指出交流

qq:110024218

 

 

我写的ping

 

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
 
#include "unistd.h"
#include "sys/types.h"
#include "sys/socket.h"
#include "netinet/in.h"
#include "netinet/ip.h"
#include "netinet/ip_icmp.h"
#include "netdb.h"
#include "errno.h"
#include "arpa/inet.h"
#include "signal.h"
#include "sys/time.h"
 
extern int errno;
 
int sockfd;
struct sockaddr_in addr; //peer addr
char straddr[128]; //peer addr ip(char*)
char sendbuf[2048];
char recvbuf[2048];
int sendnum;
int recvnum;
int datalen = 30;
 
 
unsigned short my_cksum(unsigned short *data, int len) {
        int result = 0;
        for(int i=0; i<len/2; i++) {
                result += *data;
                data++;
        }
        while(result >> 16)result = (result&0xffff) + (result>>16);
        return ~result;
}
void tv_sub(struct timeval* recvtime, const struct timeval* sendtime) {
        int sec = recvtime->tv_sec - sendtime->tv_sec;
        int usec = recvtime->tv_usec - sendtime->tv_usec;
        if(usec >= 0) {
                recvtime->tv_sec = sec;
                recvtime->tv_usec = usec;
        } else {
                recvtime->tv_sec = sec-1;
                recvtime->tv_usec = -usec;
        }
}
 
void send_icmp() {
        struct icmp* icmp = (struct icmp*)sendbuf;
        icmp->icmp_type = ICMP_ECHO;
        icmp->icmp_code = 0;
        icmp->icmp_cksum = 0;
        icmp->icmp_id = getpid(); //needn't use htons() call, because peer networking kernel didn't handle this data and won't make different meanings(bigdian litteldian)
        icmp->icmp_seq = ++sendnum; //needn't use hotns() call too.
        gettimeofday((struct timeval*)icmp->icmp_data, NULL);
        int len = 8+datalen;
        icmp->icmp_cksum = my_cksum((unsigned short*)icmp, len);
        int retval = sendto(sockfd, sendbuf, len, 0, (struct sockaddr*)&addr, sizeof(addr));
        if(retval == -1){
                perror("sendto()");
                exit(-1);
        } else {
// printf("send icmp request to %s(%d) bytes\n", straddr, len);
        }
}
void recv_icmp() {
        struct timeval *sendtime;
        struct timeval recvtime;
 
        for(;;) {
                int n = recvfrom(sockfd, recvbuf, sizeof(recvbuf), 0, 0, 0);
                if(n == -1) {
                        if(errno == EINTR)continue;
                        else {
                                perror("recvfrom()");
                                exit(-1);
                        }
                } else {
                        gettimeofday(&recvtime, NULL);
                        struct ip *ip = (struct ip*)recvbuf;
                        if(ip->ip_src.s_addr != addr.sin_addr.s_addr) {
// printf("ip_src is not : %s\n", straddr);
                                continue;
                        }
                        struct icmp *icmp = (struct icmp*)(recvbuf + ((ip->ip_hl)<<2));
                        if(icmp->icmp_id != getpid()) {
// printf("icmp_id is not :%d\n", getpid());
                                continue;
                        }
                        recvnum++;
                        sendtime = (struct timeval*)icmp->icmp_data;
                        tv_sub(&recvtime, sendtime);
                        printf("imcp echo from %s(%dbytes)\tttl=%d\tseq=%d\ttime=%d.%06d s\n", straddr, n, ip->ip_ttl, icmp->icmp_seq, recvtime.tv_sec, recvtime.tv_usec);
                }
        }
}
void catch_sigalrm(int signum) {
        send_icmp();
        alarm(1);
}
void catch_sigint(int signum) {
        printf("\nPing statics:send %d packets, recv %d packets, %d%% lost...\n", sendnum, recvnum, (int)((float)(sendnum-recvnum)/sendnum)*100);
        exit(0);
}
 
int main(int argc, char **argv) {
        if(argc != 2) {
                printf("please use format: ping hostname\n");
                exit(-1);
        }
 
        sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
        if(sockfd == -1) {
                perror("socket()");
                return -1;
        }
 
/*
        int sendbufsize = 180;
        socklen_t sendbufsizelen = sizeof(sendbufsize);
        if(setsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &sendbufsize, sendbufsizelen) == -1)perror("setsockopt()");
        int recvbufsize;
        socklen_t recvbufsizelen;
        if(getsockopt(sockfd, SOL_SOCKET, SO_RCVBUF, &recvbufsize, &recvbufsizelen) == -1)perror("getsockopt()");
*/
 
        memset(&addr, 0, sizeof(addr));
        addr.sin_family = AF_INET;
        int retval = inet_pton(AF_INET, argv[1], &addr.sin_addr);
        if(retval == -1 || retval == 0) {
                struct hostent* host = gethostbyname(argv[1]);
                if(host == NULL) {
                        fprintf(stderr, "gethostbyname(%s):%s\n", argv[1], strerror(errno));
                        exit(-1);
                }
/*
                if(host->h_name != NULL)printf("hostent.h_name:%s\n", host->h_name);
                if(host->h_aliases != NULL && *(host->h_aliases) != NULL)printf("hostent.h_aliases:%s\n", *(host->h_aliases));
                printf("hostent.h_addrtype:%d\n", host->h_addrtype);
                printf("hostent.h_length:%d\n", host->h_length);
*/
                if(host->h_addr_list != NULL && *(host->h_addr_list) != NULL) {
                        strncpy((char*)&addr.sin_addr, *(host->h_addr_list), 4);
                        inet_ntop(AF_INET, *(host->h_addr_list), straddr, sizeof(straddr));
                }
                printf("Ping address:%s(%s)\n\n", host->h_name, straddr);
        } else {
                strcpy(straddr, argv[1]);
                printf("Ping address:%s(%s)\n\n", straddr, straddr);
        }
 
        struct sigaction sa1;
        memset(&sa1, 0, sizeof(sa1));
        sa1.sa_handler = catch_sigalrm;
        sigemptyset(&sa1.sa_mask);
        sa1.sa_flags = 0;
        if(sigaction(SIGALRM, &sa1, NULL) == -1)perror("sigaction()");
        struct sigaction sa2;
        memset(&sa2, 0, sizeof(sa2));
        sa2.sa_handler = catch_sigint;
        sigemptyset(&sa2.sa_mask);
        sa2.sa_flags = 0;
        if(sigaction(SIGINT, &sa2, NULL) == -1)perror("sigaction()");
 
        alarm(1);
        recv_icmp();
 
        return 0;
}