linux 修改数据包

sudo setcap cap_net_raw,cap_net_admin=eip /path/to/your/application

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/ip.h>

int main() {
    int sockfd;
    struct sockaddr_in dest_addr;
    char packet[1024];

    // 创建原始套接字
    if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_TCP)) < 0) {
        perror("socket");
        exit(EXIT_FAILURE);
    }

    // 设置目标地址
    memset(&dest_addr, 0, sizeof(dest_addr));
    dest_addr.sin_family = AF_INET;
    dest_addr.sin_port = htons(80);
    inet_pton(AF_INET, "192.168.1.1", &dest_addr.sin_addr);

    // 构造数据包
    memset(packet, 0, sizeof(packet));
    struct ip *ip_header = (struct ip *)packet;
    ip_header->ip_v = IPVERSION;
    ip_header->ip_hl = 5;
    ip_header->ip_tos = 0;
    ip_header->ip_len = htons(sizeof(struct ip) + sizeof(struct tcphdr));
    ip_header->ip_id = htons(54321);
    ip_header->ip_off = 0;
    ip_header->ip_ttl = 64;
    ip_header->ip_p = IPPROTO_TCP;
    ip_header->ip_src.s_addr = inet_addr("192.168.1.2");
    ip_header->ip_dst.s_addr = dest_addr.sin_addr.s_addr;

    struct tcphdr *tcp_header = (struct tcphdr *)(packet + sizeof(struct ip));
    tcp_header->th_sport = htons(1234);
    tcp_header->th_dport = htons(80);
    tcp_header->th_seq = htonl(1);
    tcp_header->th_ack = 0;
    tcp_header->th_off = 5;
    tcp_header->th_flags = TH_SYN;
    tcp_header->th_win = htons(32767);
    tcp_header->th_sum = 0;
    tcp_header->th_urp = 0;

    // 计算IP头校验和
    ip_header->ip_sum = checksum((unsigned short *)ip_header, sizeof(struct ip));

    // 发送数据包
    if (sendto(sockfd, packet, sizeof(struct ip) + sizeof(struct tcphdr), 0, (struct sockaddr *)&dest_addr, sizeof(dest_addr)) < 0) {
        perror("sendto");
        exit(EXIT_FAILURE);
    }

    close(sockfd);
    return 0;
}

unsigned short checksum(unsigned short *buf, int len) {
    unsigned long sum = 0;
    while (len > 1) {
        sum += *buf++;
        len -= 2;
    }
    if (len == 1) {
        sum += *(unsigned char *)buf;
    }
    sum = (sum >> 16) + (sum & 0xffff);
    sum += (sum >> 16);
    return (unsigned short)(~sum);
}