我正在尝试使用 C 中的原始套接字(在 Debian 系统上)创建 TCP 连接，但我很难让它工作。它会发送一个数据包，但我没有收到服务器的任何响应。我已经测试并将该数据包与从 nmap 发送的数据包进行比较，我看不出有任何重大差异。

这是服务器端收到的TCP数据包，服务器端从不发送SYN ACK数据包(我在服务器端使用Wireshark进行监控)

No.     Time           Source                Destination           Protocol Length Info
     75 1.893700000    192.168.1.129         192.168.1.114         TCP      74         56540→445 [SYN] Seq=0 Win=1024 Len=0 MSS=1460 SACK_PERM=1 WS=128 TSval=863195 TSecr=0

Frame 75: 74 bytes on wire (592 bits), 74 bytes captured (592 bits) on interface 0
Ethernet II, Src: Vmware_77:f0:a0 (00:0c:29:77:f0:a0), Dst: IntelCor_07:f9:e5     (e8:b1:fc:07:f9:e5)
Internet Protocol Version 4, Src: 192.168.1.129 (192.168.1.129), Dst: 192.168.1.114 (192.168.1.114)
Version: 4
Header Length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
Total Length: 60
Identification: 0xb88d (47245)
Flags: 0x00
Fragment offset: 0
Time to live: 255
Protocol: TCP (6)
Header checksum: 0x7eea [validation disabled]
Source: 192.168.1.129 (192.168.1.129)
Destination: 192.168.1.114 (192.168.1.114)
[Source GeoIP: Unknown]
[Destination GeoIP: Unknown]
Transmission Control Protocol, Src Port: 56540 (56540), Dst Port: 445 (445), Seq: 0, Len: 0
Source Port: 56540 (56540)
Destination Port: 445 (445)
[Stream index: 3]
[TCP Segment Len: 0]
Sequence number: 0    (relative sequence number)
Acknowledgment number: 0
Header Length: 40 bytes
.... 0000 0000 0010 = Flags: 0x002 (SYN)
Window size value: 1024
[Calculated window size: 1024]
Checksum: 0x7ff8 [validation disabled]
Urgent pointer: 0
Options: (20 bytes), Maximum segment size, SACK permitted, Window scale, No-Operation (NOP), Timestamps
    Maximum segment size: 1460 bytes
        Kind: Maximum Segment Size (2)
        Length: 4
        MSS Value: 1460
    TCP SACK Permitted Option: True
        Kind: SACK Permitted (4)
        Length: 2
    Window scale: 7 (multiply by 128)
        Kind: Window Scale (3)
        Length: 3
        Shift count: 7
        [Multiplier: 128]
    No-Operation (NOP)
        Type: 1
    Timestamps: TSval 863195, TSecr 0
        Kind: Time Stamp Option (8)
        Length: 10
        Timestamp value: 863195
        Timestamp echo reply: 0

0000  e8 b1 fc 07 f9 e5 00 0c 29 77 f0 a0 08 00 45 00   ........)w....E.
0010  00 3c b8 8d 00 00 ff 06 7e ea c0 a8 01 81 c0 a8   .<......~.......
0020  01 72 dc dc 01 bd db 0f 13 02 00 00 00 00 a0 02   .r..............
0030  04 00 7f f8 00 00 02 04 05 b4 04 02 03 03 07 01   ................
0040  08 0a 00 0d 2b db 00 00 00 00                     ....+.....

这是我的代码，我知道它很乱，我只是想学习如何使用原始套接字

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>
#include <time.h>

struct ipheader {
 unsigned char          iph_ihl:4, /* Little-endian */
                        iph_ver:4;
 unsigned char          iph_tos;
 unsigned short int     iph_len;
 unsigned short int     iph_ident;
 unsigned short int     iph_offset:13,  /* Little-endian*/
                        iph_flags:3;
 unsigned char          iph_ttl;
 unsigned char          iph_protocol;
 unsigned short int     iph_chksum;
 unsigned int           iph_sourceip;
 unsigned int           iph_destip;
};

struct tcpheader {
 u_int16_t      tcph_srcport;
 u_int16_t      tcph_destport;
 u_int32_t      tcph_seqnum;
 u_int32_t      tcph_acknum;
 u_int16_t
                tcph_ns:1,
                tcph_reserved:3,
                tcph_offset:4,
                tcph_fin:1,
                tcph_syn:1,
                tcph_rst:1,
                tcph_psh:1,
                tcph_ack:1,
                tcph_urg:1,
                tcph_ece:1,
                tcph_cwr:1;
 u_int16_t      tcph_win;
 u_int16_t      tcph_chksum;
 u_int16_t      tcph_urgptr;
};

struct tcpheaderOptions
{

    u_int16_t 
        tcph_mssOpt:8,
        tcph_mssLen:8;
    u_int16_t
        tcph_mss;
    u_int16_t
        tcph_sack:8,
        tcph_sackLen:8;
    u_int16_t
        tcph_winOpt:8,
        tcph_winLen:8;
    u_int32_t
        tcph_win:8,
        tcph_winNOP:8,
        tcph_timeOpt:8,
        tcph_timeLen:8;
    u_int32_t tcph_time;
    u_int32_t tcph_timeEcho;
};

unsigned short          /* this function generates header checksums */
csum (unsigned short *buf, int nwords)
{
  unsigned long sum;
  for (sum = 0; nwords > 0; nwords--)
    sum += *buf++;
  sum = (sum >> 16) + (sum & 0xffff);
  sum += (sum >> 16);
  return ~sum;
}



int main(void)
{
  char datagram[4096];
  char data[] = "Hello my name is Keith, this is my first packet";
  memset(datagram,0,4096);
  struct ipheader *IPInfo = (struct ipheader *) datagram;
  struct tcpheader *TCPHeader = (struct tcpheader *) (datagram + sizeof(struct ipheader));
  struct tcpheaderOptions *TCPOptions = (struct tcpheaderOptions *) (datagram + sizeof(struct tcpheader) + sizeof(struct ipheader));
  struct sockaddr_in sin;               //Te destination
  sin.sin_family = AF_INET;
  sin.sin_port = htons(4);
  sin.sin_addr.s_addr = inet_addr("192.168.1.114");

  IPInfo->iph_ver       = 4;            //What IP version are we using? v4
  IPInfo->iph_ihl       = 5;            //The IP header size in bytes
  IPInfo->iph_tos       = 0;            //The IP header type of service 0x00 is normal
  IPInfo->iph_len       = sizeof(struct ipheader) + sizeof(struct tcpheader) + sizeof(struct tcpheaderOptions);            //The IP length of the IP datagram
  IPInfo->iph_ident     = htonl(54321);         //The IP header ID (used when fragmented)
  IPInfo->iph_offset    = 0;            //IP fragment offset
  IPInfo->iph_ttl       = 255;          //The IP TTL
  IPInfo->iph_protocol          = 6;            //The transport layer protocol (6 for TCP, 1 for ICMP, 17 for UDP)
  IPInfo->iph_chksum    = 0;            //Checksum
  IPInfo->iph_sourceip  = inet_addr("192.168.1.129"); //source
//  IPInfo->iph_destip = sin.sin_addr.s_addr;
  IPInfo->iph_destip    = inet_addr("192.168.1.114");
char source[20];
char dest[20];
inet_ntop(AF_INET, &(IPInfo->iph_sourceip), source, 20);
inet_ntop(AF_INET, &(IPInfo->iph_destip), dest, 20);
printf("Source: %s\n", source);
printf("Dest: %s\n", dest);
  //IPInfo->ip_dst.s_addr       = inet_addr("192.168.1.114");
  TCPHeader->tcph_srcport       = htons(56540);           //The source port
  TCPHeader->tcph_destport      = htons(445);          //The destination port
  srand(time(NULL));
  TCPHeader->tcph_seqnum        = rand();          //the sequence number
  TCPHeader->tcph_acknum        = 0;                 //ACK packet
  TCPHeader->tcph_reserved      = 0;                    //Not used
  TCPHeader->tcph_offset        = 10;                 //
  TCPHeader->tcph_cwr           = 0;
  TCPHeader->tcph_ns            = 0;
  TCPHeader->tcph_syn           = 1;
  TCPHeader->tcph_rst           = 0;
  TCPHeader->tcph_psh           = 0;
  TCPHeader->tcph_ack           = 0;
  TCPHeader->tcph_urg           = 0;
  TCPHeader->tcph_ece           = 0;
  TCPHeader->tcph_cwr           = 0;
  TCPHeader->tcph_ns            = 0;
  TCPHeader->tcph_win           = htons(1024);
  TCPHeader->tcph_chksum        = 0;
  TCPHeader->tcph_urgptr        = 0;
  TCPOptions->tcph_mssOpt       = 2;
  TCPOptions->tcph_mssLen       = 4;
  TCPOptions->tcph_winOpt       = 3;
  TCPOptions->tcph_winLen       = 3;
  TCPOptions->tcph_sack         = 4;
  TCPOptions->tcph_sackLen      = 2;
  TCPOptions->tcph_win          = 7;
  TCPOptions->tcph_winNOP       = 1;
  TCPOptions->tcph_mss          = htons(1460);
  TCPOptions->tcph_timeOpt      = 8;
  TCPOptions->tcph_timeLen      = 10;
  TCPOptions->tcph_time         = 0xdb2b0d00;
  //Adding the data
  //strcpy(datagram + sizeof(struct ipheader) + sizeof(struct tcpheader),data);
  TCPHeader->tcph_chksum = csum((unsigned short *) datagram,TCPHeader->tcph_offset >> 1);
  IPInfo->iph_chksum = csum((unsigned short *) datagram, IPInfo->iph_len >> 1);


  int sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);
  if(sockfd == -1) {
    perror("sockfd");
    exit(1);
  }

  //Setting IP_HDRINCL so that the system doesnt add headers to my packets
  {
    int one = 1;
    const int *val = &one;
    if(setsockopt(sockfd,IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0) {
      perror("setsockopt");
      return -1;
    }
    else
      printf("Using your own header\n");
  }
  //Creating a raw socket to send info on
    if(sendto(sockfd, datagram, IPInfo->iph_len, 0, (struct sockaddr *) &sin, sizeof (sin)) < 0)
      perror("send");
    else
      printf("sending\n");

  printf("Sent sequence number: %d\n",TCPHeader->tcph_seqnum);

        //Now we will wait to receive a message back
        memset(datagram,0,4096);
        int results = recv(sockfd,datagram,sizeof(datagram),0);
        printf("Results: %d\n",results);
        IPInfo = (struct ipheader *) datagram;
        TCPHeader = (struct tcpheader * ) (datagram + (IPInfo->iph_ihl * 4));
        printf("Packet: IPInfo->iph_ihl %d\n",IPInfo->iph_ihl);
        printf("ACK num = %d\n",TCPHeader->tcph_ack);

char source1[20];
char dest1[20];
inet_ntop(AF_INET, &(IPInfo->iph_sourceip), source, 20);
inet_ntop(AF_INET, &(IPInfo->iph_destip), dest, 20);    

    printf("Source: %s\n",source1);
    printf("Dest: %s\n",dest1);

    printf("Size of ipheader %d\n",sizeof(struct ipheader));
    printf("size of tcpheader %d\n",sizeof(struct tcpheader));

  return 0;
}

最佳答案

在 wireshark 中启用校验和验证，这样您至少可以确定您没有计算错误的校验和(在 IP 或 TCP header 中)– nos

谢谢，我的 TCP 校验和无效 – Keith

关于c - Linux C 原始套接字 TCP 握手，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27630216/