准确地说，我已经创建了这个简单的TCP程序，通过网络将简单的TCP数据包发送到目标计算机，但不知怎的，我真的不知道，我做错了什么，但它看起来不是将任何数据包发送到目标主机。我也无法在wirehark中找到它。
rawtcp.c：
//---cat rawtcp.c---
// Run as root or SUID 0, just datagram no data/payload
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
// Packet length
#define PCKT_LEN 8192
#pragma pack(push, 1)
// May create separate header file (.h) for all
// headers' structures
// IP header's structure
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;
unsigned char iph_ttl;
unsigned char iph_protocol;
unsigned short int iph_chksum;
unsigned int iph_sourceip;
unsigned int iph_destip;
};
/* Structure of a TCP header */
struct tcpheader {
unsigned short int tcph_srcport;
unsigned short int tcph_destport;
unsigned int tcph_seqnum;
unsigned int tcph_acknum;
unsigned char tcph_reserved:4, tcph_offset:4;
// unsigned char tcph_flags;
unsigned int
tcp_res1:4, /*little-endian*/
tcph_hlen:4, /*length of tcp header in 32-bit words*/
tcph_fin:1, /*Finish flag "fin"*/
tcph_syn:1, /*Synchronize sequence numbers to start a connection*/
tcph_rst:1, /*Reset flag */
tcph_psh:1, /*Push, sends data to the application*/
tcph_ack:1, /*acknowledge*/
tcph_urg:1, /*urgent pointer*/
tcph_res2:2;
unsigned short int tcph_win;
unsigned short int tcph_chksum;
unsigned short int tcph_urgptr;
};
#pragma pack(pop)
// Simple checksum function, may use others such as Cyclic Redundancy Check, CRC
unsigned short csum(unsigned short *buf, int len)
{
unsigned long sum;
for(sum=0; len>0; len--)
sum += *buf++;
sum = (sum >> 16) + (sum &0xffff);
sum += (sum >> 16);
return (unsigned short)(~sum);
}
int main(int argc, char *argv[])
{
int sd;
// No data, just datagram
char buffer[PCKT_LEN];
// The size of the headers
struct ipheader *ip = (struct ipheader *) buffer;
struct tcpheader *tcp = (struct tcpheader *) (buffer + sizeof(struct ipheader));
struct sockaddr_in sin, din;
int one = 1;
const int *val = &one;
memset(buffer, 0, PCKT_LEN);
if(argc != 5)
{
printf("- Invalid parameters!!!\n");
printf("- Usage: %s <source hostname/IP> <source port> <target hostname/IP> <target port>\n", argv[0]);
exit(-1);
}
sd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP);
if(sd < 0)
{
perror("socket() error");
exit(-1);
} else
printf("socket()-SOCK_RAW and tcp protocol is OK.\n");
// The source is redundant, may be used later if needed
// Address family
sin.sin_family = AF_INET;
din.sin_family = AF_INET;
// Source port, can be any, modify as needed
sin.sin_port = htons(atoi(argv[2]));
din.sin_port = htons(atoi(argv[4]));
// Source IP, can be any, modify as needed
sin.sin_addr.s_addr = inet_addr(argv[1]);
din.sin_addr.s_addr = inet_addr(argv[3]);
// IP structure
ip->iph_ihl = 5;
ip->iph_ver = 4;
ip->iph_tos = 16;
ip->iph_len = htons(sizeof(struct ipheader) + sizeof(struct tcpheader));
ip->iph_ident = htons(54321);
ip->iph_offset = 0;
ip->iph_ttl = 64;
ip->iph_protocol = 6; // TCP
ip->iph_chksum = 0; // Done by kernel
// Source IP, modify as needed, spoofed, we accept through command line argument
ip->iph_sourceip = inet_addr(argv[1]);
// Destination IP, modify as needed, but here we accept through command line argument
ip->iph_destip = inet_addr(argv[3]);
// The TCP structure. The source port, spoofed, we accept through the command line
tcp->tcph_srcport = htons(atoi(argv[2]));
// The destination port, we accept through command line
tcp->tcph_destport = htons(atoi(argv[4]));
tcp->tcph_seqnum = htonl(1);
tcp->tcph_acknum = 0;
tcp->tcph_offset = 5;
tcp->tcph_syn = 1;
tcp->tcph_ack = 0;
tcp->tcph_win = htons(32767);
tcp->tcph_chksum = 0; // Done by kernel
tcp->tcph_urgptr = 0;
// IP checksum calculation
ip->iph_chksum = htons(csum((unsigned short *) buffer, (sizeof(struct ipheader) + sizeof(struct tcpheader))));
// Inform the kernel do not fill up the headers' structure, we fabricated our own
if(setsockopt(sd, IPPROTO_IP, IP_HDRINCL, val, sizeof(one)) < 0)
{
perror("setsockopt() error");
exit(-1);
} else
printf("setsockopt() is OK\n");
printf("Using:::::Destination IP: %s port: %u, Source IP: %s port: %u.\n", argv[1], atoi(argv[2]), argv[3], atoi(argv[4]));
// sendto() loop, send every 2 second for 50 counts
unsigned int count;
for(count = 0; count < 20; count++)
{
if(sendto(sd, buffer, ip->iph_len, 0, (struct sockaddr *)&din, sizeof(din)) < 0)
// Verify
{
perror("sendto() error");
exit(-1);
} else
printf("Count #%u - sendto() is OK\n", count);
sleep(2);
}
close(sd);
return 0;
}
在编译时，它编译得很好。当我运行程序时，因为它假设为./rawtcp 192.168.1.152 1000 192.168.1.151 1000，它说：
socket()-SOCK_RAW and tcp protocol is OK.
setsockopt() is OK
Using:::::Destination IP: 192.168.1.151 port: 1000, Source IP: 192.168.1.152 port: 1000.
Count #0 - sendto() is OK
Count #1 - sendto() is OK
但是在将wireshark过滤为tcp.port == 1000时它永远不会显示（注意：源IP为192.168.1.152，目标IP为192.168.1.151）。但如果我做一个简单的hping3 -p 1000 192.168.1.151它就可以了，我也可以在wireshark中看到它。
如果你能在我的代码中告诉我我做错了什么，我真的很感激。）
答案 0 :(得分：2)
首先，您缺少<arpa/inet.h>标题，该标题提供您正在使用的inet_addr函数。由于隐式函数声明，你的程序仍然应该在C89下编译而没有这个，但依靠它可能会导致细微的错误。
一个问题是您滥用#pragma pack。
在声明结构之前，应该执行#pragma pack(push, 1)，它们将struct packing alignment设置为1，并将先前的打包对齐状态推送到堆栈。在完成声明结构之后，您可以执行#pragma pack(pop)以在以下任何声明中将结构包装重置为正常。对于您的程序，在您的声明之后省略#pragma pack(pop)仍然有效，但最好重新设置，以防您声明任何其他您不想紧密结构的结构 - 打包，或者之后包含任何其他头文件。
#pragma pack(push, 1)
struct a {
/* ... */
};
struct b {
/* ... */
};
#pragma pack(pop)
struct ipheader的另一个问题是，您同时拥有8位iph_flags和16位iph_offset，而IP标头中的标志字段应为3位偏移字段应为13位（这两者一起加起来为16位）。这意味着你的标题中还有8位不应该存在。由于您无论如何都要将这两个字段填充为零，因此可以通过从结构中完全删除iph_flags来修复此问题，并保留一个填充为0的16位iph_offset字段，实际跨越IP报头中3位和13位字段的空间。
通过这些修复程序，您的程序可以为我工作，并且可以在Wireshark中看到数据包。
答案 1 :(得分：-1)
我认为你的端口已被使用。
您应该将端口更改为30000或更高，1000端口通常由其他应用程序使用
您还应该使用 telnet [ip] [port]
进行调试