wifidog 源码初分析（1）

因为最近公司内部有个关于路由器的项目使用了该开源项目做Demo，安装配置很简单，但是对运行机制不是太了解，所以抽了点时间初步对 wifidog 的源码进行了分析。

（对于 wifidog 是什么开源项目，以及如何安装配置，就不做解释了，直接 Google 吧）。

另外，wifidog 的核心还是依赖于 iptables 防火墙过滤规则来实现的，所以建议对 iptables 有了了解后再去阅读 wifidog 的源码。

在路由器上启动 wifidog 之后，wifidog 在启动时会初始化一堆的防火墙规则，如下：

/** Initialize the firewall rules
*/
int iptables_fw_init(void)
{
    … …
/*
     *
     * Everything in the NAT table
     *
     */
    /* Create new chains */
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_OUTGOING);
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_WIFI_TO_ROUTER);
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_WIFI_TO_INTERNET);
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_GLOBAL);
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_UNKNOWN);
    iptables_do_command("-t nat -N " TABLE_WIFIDOG_AUTHSERVERS);
    /* Assign links and rules to these new chains */
    iptables_do_command("-t nat -A PREROUTING -i %s -j " TABLE_WIFIDOG_OUTGOING, config->gw_interface);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_OUTGOING " -d %s -j " TABLE_WIFIDOG_WIFI_TO_ROUTER, config->gw_address);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_WIFI_TO_ROUTER " -j ACCEPT");
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_OUTGOING " -j " TABLE_WIFIDOG_WIFI_TO_INTERNET);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m mark --mark 0x%u -j ACCEPT", FW_MARK_KNOWN);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m mark --mark 0x%u -j ACCEPT", FW_MARK_PROBATION);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -j " TABLE_WIFIDOG_UNKNOWN);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_UNKNOWN " -j " TABLE_WIFIDOG_AUTHSERVERS);
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_UNKNOWN " -j " TABLE_WIFIDOG_GLOBAL);
    // 将 80 端口的访问重定向(REDIRECT)到 (本路由)网关web服务器的监听端口
    iptables_do_command("-t nat -A " TABLE_WIFIDOG_UNKNOWN " -p tcp --dport 80 -j REDIRECT --to-ports %d", gw_port);
    /*
     *
     * Everything in the FILTER table
     *
     */
    /* Create new chains */
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_WIFI_TO_INTERNET);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_AUTHSERVERS);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_LOCKED);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_GLOBAL);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_VALIDATE);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_KNOWN);
    iptables_do_command("-t filter -N " TABLE_WIFIDOG_UNKNOWN);
    /* Assign links and rules to these new chains */
    /* Insert at the beginning */
    iptables_do_command("-t filter -I FORWARD -i %s -j " TABLE_WIFIDOG_WIFI_TO_INTERNET, config->gw_interface);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m state --state INVALID -j DROP");
                                                                                                                            
    /* TCPMSS rule for PPPoE */
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -o %s -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu", ext_interface);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -j " TABLE_WIFIDOG_AUTHSERVERS);
    iptables_fw_set_authservers();
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m mark --mark 0x%u -j " TABLE_WIFIDOG_LOCKED, FW_MARK_LOCKED);
    iptables_load_ruleset("filter", "locked-users", TABLE_WIFIDOG_LOCKED);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -j " TABLE_WIFIDOG_GLOBAL);
    iptables_load_ruleset("filter", "global", TABLE_WIFIDOG_GLOBAL);
    iptables_load_ruleset("nat", "global", TABLE_WIFIDOG_GLOBAL);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m mark --mark 0x%u -j " TABLE_WIFIDOG_VALIDATE, FW_MARK_PROBATION);
    iptables_load_ruleset("filter", "validating-users", TABLE_WIFIDOG_VALIDATE);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -m mark --mark 0x%u -j " TABLE_WIFIDOG_KNOWN, FW_MARK_KNOWN);
    iptables_load_ruleset("filter", "known-users", TABLE_WIFIDOG_KNOWN);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_WIFI_TO_INTERNET " -j " TABLE_WIFIDOG_UNKNOWN);
    iptables_load_ruleset("filter", "unknown-users", TABLE_WIFIDOG_UNKNOWN);
    iptables_do_command("-t filter -A " TABLE_WIFIDOG_UNKNOWN " -j REJECT --reject-with icmp-port-unreachable");
    UNLOCK_CONFIG();
    return 1;
}

 

在该 防火墙规则的初始化过程中，会首先清除掉已有的防火墙规则，重新创建新的过滤链，另外，除了通过 iptables_do_command("-t nat -A "TABLE_WIFIDOG_UNKNOWN " -p tcp --dport 80 -j REDIRECT --to-ports %d",gw_port); 这个命令将 接入设备的 80 端口（HTTP）的访问重定向至网关自身的 HTTP 的端口之外，还通过 iptables_fw_set_authservers(); 函数设置了 鉴权服务器(auth-server) 的防火墙规则：

 

void iptables_fw_set_authservers(void)
{
    const s_config *config;
    t_auth_serv *auth_server;
    config = config_get_config();
    for (auth_server = config->auth_servers; auth_server != NULL; auth_server = auth_server->next) {
        if (auth_server->last_ip && strcmp(auth_server->last_ip, "0.0.0.0") != 0) {
            iptables_do_command("-t filter -A " TABLE_WIFIDOG_AUTHSERVERS " -d %s -j ACCEPT", auth_server->last_ip);
            iptables_do_command("-t nat -A " TABLE_WIFIDOG_AUTHSERVERS " -d %s -j ACCEPT", auth_server->last_ip);
        }
    }
}

 

首先从上面的代码可以看出 wifidog 支持多个 鉴权服务器，并且针对每一个鉴权服务器 设置了如下两条规则：

 

1)在filter表中追加一条[任何访问鉴权服务器都被接受]的WiFiDog_$ID$_AuthServers过滤链：

 

iptables -t filter -A  WiFiDog_$ID$_AuthServers -d auth-server地址 -j ACCEPT

 

2)在nat表中追加一条[任何访问鉴权服务器都被接受]的WiFiDog_$ID$_AuthServers过滤链：

 

iptables -t nat -A WiFiDog_$ID$_AuthServers  -d auth-server地址 -j ACCEPT

 

这样确保可以访问鉴权服务器，而不是拒绝所有的出口访问。