iptables源码深度解析，如何构建高效的防火墙规则集？

iptables是一个用于配置Linux内核防火墙的工具，它允许用户定义一系列的规则来控制网络数据包的流动，以下是一个简单的iptables源码示例，展示了如何使用C语言编写一个基本的iptables规则：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
static void add_rule(const char *protocol, const char *src_ip, const char *dst_ip, const char *src_port, const char *dst_port) {
    struct sockaddr_in src, dest;
    int protocol_num = 0;
    if (strcmp(protocol, "tcp") == 0) {
        protocol_num = IPPROTO_TCP;
    } else if (strcmp(protocol, "udp") == 0) {
        protocol_num = IPPROTO_UDP;
    } else {
        printf("Invalid protocol: %s
", protocol);
        return;
    }
    inet_aton(src_ip, &src.sin_addr);
    inet_aton(dst_ip, &dest.sin_addr);
    src.sin_family = AF_INET;
    dest.sin_family = AF_INET;
    src.sin_port = htons(atoi(src_port));
    dest.sin_port = htons(atoi(dst_port));
    struct ipt_entry entry;
    memset(&entry, 0, sizeof(entry));
    entry.ip.src.s_addr = src.sin_addr.s_addr;
    entry.ip.dst.s_addr = dest.sin_addr.s_addr;
    entry.ip.proto = protocol_num;
    entry.ip.invflags = IPT_INV_SRCIP | IPT_INV_DSTIP;
    entry.ip.frag_policy = IP_NODEFRAG;
    entry.ip.flags = IPT_F_FRAG;
    entry.ip.daddr = dest.sin_addr.s_addr;
    entry.ip.saddr = src.sin_addr.s_addr;
    entry.ip.tos = 0;
    entry.ip.dport = dest.sin_port;
    entry.ip.sport = src.sin_port;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip.checksum = 0;
    entry.ip.flags = 0;
    entry.ip.invflags = 0;
    entry.ip.frag_policy = 0;
    entry.ip.src = src;
    entry.ip.dst = dest;
    entry.ip.proto = protocol_num;
    entry.ip.target_off = 0;
    entry.ip.next_offset = 0;
    entry.ip.ttl = 0;
    entry.ip

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