连上Wi-Fi 热点自动弹窗的实现方法

　　当我们连上某个热点， 会自动弹出登录窗口的专业名称叫做： Captive portal 

　　原理， 实现方式有三种

　　1 ： dns 跳转， 在热点上面实现配置， 把所有dns请求返回都配置为：服务器地址 ；服务器有404跳转或者DNS url跳转 ， 跳转到的界面即为自动弹出登录界面；

　　2 :   http跳转，对所有的http请求返回302或者301或者404跳转， 跳转到的界面即为自动弹出登录界面；

　　3 :   ip跳转，既把所有的ip包里的目标地址改为认证服务器，然后在认证服务器上做404跳转

　　第三种实现起来比较麻烦， 我们要实现第一种和第二种 Captive portal；

　　配置本地服务器

　　使用NodeJS搭建一个本地WEB服务器， 服务器端口为默认的80， 无论访问服务器的任意地址 都有正常200返回，app.use函数是精华..， 然后使用node app.js启动服务器：

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var http = require("http");
var index = require('./routes/index');

var app = express();

app.set('views', path.join(__dirname, 'views'));

app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));

app.use('/', index);
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

//该函数是关键 ， 如论用户访问任何页面 ， 都会重定向到本地index.html文件
app.use(function(req, res, next) {
  res.status = 200;
  res.redirect('/index.html');
});

http.createServer(app).listen(80);

　　

　　使用HTTP跳转

　　本机环境是kali系统， 外加一个usb网卡， 使用以下代码实现热点：

#!/bin/bash
## quick and dirty AP with hostapd and dnsmasq
## exit properly with ctrl-c

echo "Exit this script with Ctrl-C and it will attempt to clean up properly."

if [ -z $1 ]; then
   echo -n "SSID: "
   read ssid
else
   ssid=$1
fi

# get wep key
function get_wep_key() { 
    echo -n "WEP Key [must be exactly 5 or 13 ascii characters]: " 
    read wep_key
    if [[  $wep_key =~ ^[a-zA-Z0-9]{5}$ ]] ; then
       echo "Key accepted"
   elif [[  $wep_key =~ ^[a-zA-Z0-9]{13}$ ]] ; then
        echo "Key accepted"
    else
        echo "WEP key must be exactly 5 or 13 characters"
        get_wep_key
    fi
}

# get mac
function get_mac() {
    echo -n "Enter MAC address in the following format AB:CD:EF:12:34:56: "
    read new_mac
    if [[  $new_mac =~ ^[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}$ ]] ; then
        macchanger --mac=$new_mac wlan0
   else
        echo "MAC Address format not correct."
        get_mac
    fi
}

# ask for WEP
echo -n "Do you want WEP enabled? [y/n]: "
read wep
case $wep in
    y*)
        get_wep_key
    ;;
    *)
    ;;
esac

# ask for MAC change
echo -n "Do you want to change your MAC? [y/n]: "
read changemac
case $changemac in
    y*)
        echo -n "Custom MAC? [y/n]: "
      read random_mac
        case $random_mac in
            y*)
                get_mac
            ;;
            n*)
                macchanger -r wlan0
            ;;
            *)
                echo "Invalid choice, keeping current MAC address."
            ;;
        esac
    ;;
   n*)
    ;;
esac

# install packages if need be
if [ $(dpkg-query -W -f='${Status}' dnsmasq 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install dnsmasq
fi
if [ $(dpkg-query -W -f='${Status}' hostapd 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install hostapd
fi

# trap control c
trap ctrl_c INT

function ctrl_c() {
   echo "wlan0 managed mode"
   iwconfig wlan0 mode managed
   echo "downing wlan0"
   ifconfig wlan0 down
   echo "flushing firewall"
   iptables -F
   iptables -F -t nat
   echo "resetting wlan0 mac"
   macchanger -p wlan0
   kill -9 `cat /tmp/dnsmasq.run`
}


## script begins

# stop and disable services
service hostapd stop
service dnsmasq stop
pkill -9 dnsmasq
pkill -9 hostapd

# bring up wlan0
nmcli radio wifi off
rfkill unblock wlan
iwconfig wlan0 mode monitor
ifconfig wlan0 10.0.0.1/24 up

# forwarding and nat
sysctl -w net.ipv4.conf.all.route_localnet=1
iptables -t nat -I PREROUTING -p tcp --dport 80 -j DNAT --to 10.0.0.1:80

# dns masq conf
cat > /tmp/dnsmasq.conf <<!
bind-interfaces
interface=wlan0
dhcp-range=10.0.0.2,10.0.0.254
!

# hostapd conf
cat > /tmp/hostapd.conf<<!
interface=wlan0
driver=nl80211
ssid=${ssid}
hw_mode=g
channel=6
!

# if WEP key, add to hostapd conf
if [[ -n $wep_key ]]; then echo -e "wep_default_key=0
wep_key0="${wep_key}"" >> /tmp/hostapd.conf; fi

# run dnsmasq and hostapd
dnsmasq --pid-file=/tmp/dnsmasq.run -C /tmp/dnsmasq.conf
hostapd /tmp/hostapd.conf

　　以上代码中：

　　　　sysctl -w net.ipv4.conf.all.route_localnet=1
　　　　iptables -t nat -I PREROUTING -p tcp --dport 80 -j DNAT --to 10.0.0.1:80

　　是本例子的精华所在， 第一句的意思是指所有的ipv4请求全部重定向到本地， 第二句的意思为所有准备访问本地80端口的机器，全部指向到10.0.0.1的80端口， 而我们本地的80端口为我们部署的服务器， 这样即可实现 Captive portal 

　　使用DNS跳转

　　在本地网关搭建DNS服务器， 局域网内部的所有DNS请求全部返回10.0.0.1 

　　sh文件代码如下：

#!/bin/bash
## quick and dirty AP with hostapd and dnsmasq
## exit properly with ctrl-c

echo "Exit this script with Ctrl-C and it will attempt to clean up properly."

if [ -z $1 ]; then
   echo -n "SSID: "
   read ssid
else
   ssid=$1
fi

# get wep key
function get_wep_key() { 
    echo -n "WEP Key [must be exactly 5 or 13 ascii characters]: " 
    read wep_key
    if [[  $wep_key =~ ^[a-zA-Z0-9]{5}$ ]] ; then
       echo "Key accepted"
   elif [[  $wep_key =~ ^[a-zA-Z0-9]{13}$ ]] ; then
        echo "Key accepted"
    else
        echo "WEP key must be exactly 5 or 13 characters"
        get_wep_key
    fi
}

# get mac
function get_mac() {
    echo -n "Enter MAC address in the following format AB:CD:EF:12:34:56: "
    read new_mac
    if [[  $new_mac =~ ^[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}:[a-fA-F0-9]{2}$ ]] ; then
        macchanger --mac=$new_mac wlan0
   else
        echo "MAC Address format not correct."
        get_mac
    fi
}

# ask for WEP
echo -n "Do you want WEP enabled? [y/n]: "
read wep
case $wep in
    y*)
        get_wep_key
    ;;
    *)
    ;;
esac

# ask for MAC change
echo -n "Do you want to change your MAC? [y/n]: "
read changemac
case $changemac in
    y*)
        echo -n "Custom MAC? [y/n]: "
      read random_mac
        case $random_mac in
            y*)
                get_mac
            ;;
            n*)
                macchanger -r wlan0
            ;;
            *)
                echo "Invalid choice, keeping current MAC address."
            ;;
        esac
    ;;
   n*)
    ;;
esac

# install packages if need be
if [ $(dpkg-query -W -f='${Status}' dnsmasq 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install dnsmasq
fi
if [ $(dpkg-query -W -f='${Status}' hostapd 2>/dev/null | grep -c "ok installed") -eq 0 ];
then
  apt-get install hostapd
fi

# trap control c
trap ctrl_c INT

function ctrl_c() {
   echo "wlan0 managed mode"
   iwconfig wlan0 mode managed
   echo "downing wlan0"
   ifconfig wlan0 down
   echo "flushing firewall"
   iptables -F
   iptables -F -t nat
   echo "resetting wlan0 mac"
   macchanger -p wlan0
   kill -9 `cat /tmp/dnsmasq.run`
}


## script begins

# stop and disable services
service hostapd stop
service dnsmasq stop
pkill -9 dnsmasq
pkill -9 hostapd

# bring up wlan0
nmcli radio wifi off
rfkill unblock wlan
iwconfig wlan0 mode monitor
ifconfig wlan0 10.0.0.1/24 up

#dhcp
iptables --policy INPUT ACCEPT
iptables --policy FORWARD ACCEPT
iptables --policy OUTPUT ACCEPT
iptables -F
iptables -t nat -F
iptables -t nat -A PREROUTING -i wlan0 -p udp --dport 53 -j DNAT --to 10.0.0.1

# dns masq conf
cat > /tmp/dnsmasq.conf <<!
bind-interfaces
interface=wlan0
address=/#/10.0.0.1
dhcp-range=10.0.0.2,10.0.0.254
dhcp-option=6,10.0.0.1 #DNS
dhcp-option=3,10.0.0.1 #Gateway
dhcp-option=252,"http://wpad.example.com/wpad.dat
" #WPAD
dhcp-authoritative
!

# hostapd conf
cat > /tmp/hostapd.conf<<!
interface=wlan0
driver=nl80211
ssid=${ssid}
hw_mode=g
channel=6
!

# if WEP key, add to hostapd conf
if [[ -n $wep_key ]]; then echo -e "wep_default_key=0
wep_key0="${wep_key}"" >> /tmp/hostapd.conf; fi

# run dnsmasq and hostapd
dnsmasq --pid-file=/tmp/dnsmasq.run -C /tmp/dnsmasq.conf
hostapd /tmp/hostapd.conf

　　其中以下代码尤为重要：

　　bind-interfaces
　　interface=wlan0
　　address=/#/10.0.0.1  《＝＝这个配置说明为所有dns请求都返回10.0.0.1 
　　dhcp-range=10.0.0.2,10.0.0.254  《＝＝客户机器IP池
　　dhcp-option=6,10.0.0.1 #DNS   《＝＝本地DNS服务器
　　dhcp-option=3,10.0.0.1 #Gateway 《＝＝本地网关
　　dhcp-option=252,"http://wpad.example.com/wpad.dat " #WPAD
　　dhcp-authoritative

　　参考

　　dnsmasq参考API ： https://wiki.archlinux.org/index.php/dnsmasq

　　Captive portal是怎样强制弹出窗口的呢? : https://www.zhihu.com/question/38843766

作者： NONO
出处：http://www.cnblogs.com/diligenceday/
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