Linux iptables与sudo / 憋错料

1、详述iptables五链

Iptables的主要功能是实现网络数据包进出设备及转发的控制，当数据包需要进入设备、从设备中流出或者经该设备转发、路由时，都可以使用iptables进行控制。
Netfilter/iptables IP 信息包过滤系统是一种功能强大的工具，可用于添加、编辑和除去规则，这些规则是在做信息包过滤决定时，防火墙所遵循和组成的规则。这些规则存储在专用的信息包过滤表中，而这些表集成在Linux内核中。在信息包过滤表中，规则被分组放在我们所谓的链（chain）中。
Netfilter/iptables IP 信息包过滤系统都被称为单个实体，但它实际上由两个组件netfilter和iptables组成。
Netfilter组件也称为内核空间（kernelspace）,是内核的一部分，由一些信息表过滤表组成，这些表包含内核用来控制信息包过滤处理的规则集。

Iptables组件是一种工具，也称为用户空间（userspace）,它使插入、修改和除去信息包过滤表中的规则变得容易。Iptables包含4个表，5个链。

Iptables 五链

如上图所示，iptables五种链接分别是prerouting、input、output、forward、postrouting
prerouting: 流入的数据包进入路由表之前
input: 通过路由表判断后目的地址是本机，然后进入本机内部资源
output: 由本机产生的数据向外转发
forward: 通过路由表判断目的地址是本机，然后通过路由转发到其他地方

postrouting: 传出的数据包到达网卡出口前

流入本机： prerouting --> input ==> 用户空间进程；
流出本机： 用户空间进程==> output --> postrouting;
转发： prerouting --> forward --> postrouting;

四表：

filter:过滤表，能被INPUT、FORWARD、OUTPU这三个规则链使用。
nat: 网络地址转换表，能被PREROUTING、OUTPUT、POSTROUTING使用。
mangle: 报文修改表，能被PREROUTING,INPUT,FORWARD,OUTPUT,POSTROUTING使用。
raw: 一般是为了不再让iptables对数据包进行跟踪，提高性能，能被PREROUTING、OUTPUT使用。
其执行顺序是raw>mangle>nat>filter

2、举例实现iptables多端口匹配、连接追踪、字符串匹配、时间匹配、并发连接限制、速率匹配、报文状态匹配等应用

iptables 多端口匹配

[root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 237 packets, 17727 bytes)
pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 151 packets, 17334 bytes)
pkts bytes target     prot opt in     out     source               destination
[root@xiaochen ~]# iptables -I INPUT 1 -d 192.168.10.10 -p tcp -m multiport --dports 21,22,80,8080,443 -j ACCEPT
[root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 3 packets, 176 bytes)
 pkts bytes target     prot opt in     out     source               destination
    8   576 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 8 packets, 1388 bytes)
 pkts bytes target     prot opt in     out     source               destination

连接追踪：

[root@xiaochen ~]# iptables -A INPUT -d 192.168.10.10 -p tcp -m multiport --dports 21,22,80 -m state --state INVALID -j REJECT
  [root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
  343 22920 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 30 packets, 3048 bytes)
 pkts bytes target     prot opt in     out     source               destination

字符串匹配：

[root@xiaochen ~]# iptables -A OUTPUT -s 192.168.10.10 -d 192.168.10.0/24 -p tcp --sport 80 -m string --algo bm --string "sex" -j REJECT
  [root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 2 packets, 100 bytes)
 pkts bytes target     prot opt in     out     source               destination
  755 53000 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 44 packets, 4388 bytes)
 pkts bytes target     prot opt in     out     source               destination
0     0 REJECT     tcp  --  *      *       192.168.10.10        192.168.10.0/24      tcp spt:80 STRING match  "sex" ALGO name bm TO 65535 reject-with icmp-port-unreachable

时间匹配：

[root@xiaochen ~]# iptables -A INPUT -s 192.168.10.0/24 -d 192.168.10.10 -p tcp --dport 80 -m time --timestart 00:30 --timestop 12:30 --weekdays Mon,Sun -j DROP
   [root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 4 packets, 200 bytes)
 pkts bytes target     prot opt in     out     source               destination
 1133 78104 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable
    0     0 DROP       tcp  --  *      *       192.168.10.0/24      192.168.10.10        tcp dpt:80 TIME from 00:30:00 to 12:30:00 on Mon,Sun UTC

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 41 packets, 3852 bytes)
 pkts bytes target     prot opt in     out     source               destination
0     0 REJECT     tcp  --  *      *       192.168.10.10        192.168.10.0/24      tcp spt:80 STRING match  "sex" ALGO name bm TO 65535 reject-with icmp-port-unreachable

并发连接限制：

[root@xiaochen ~]# iptables -A INPUT -d 192.168.10.10 -p tcp --dport 21 -m connlimit --connlimit-above 2 -j REJECT
 [root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
 1403 96028 ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable
    0     0 DROP       tcp  --  *      *       192.168.10.0/24      192.168.10.10        tcp dpt:80 TIME from 00:30:00 to 12:30:00 on Mon,Sun UTC
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        tcp dpt:21 #conn src/32 > 2 reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 16 packets, 1584 bytes)
 pkts bytes target     prot opt in     out     source               destination
0     0 REJECT     tcp  --  *      *       192.168.10.10        192.168.10.0/24      tcp spt:80 STRING match  "sex" ALGO name bm TO 65535 reject-with icmp-port-unreachable

速率匹配：

[root@xiaochen ~]# iptables -I INPUT -d 192.168.10.10 -p icmp --icmp-type 8 -m limit --limit 5/minute --limit-burst 3 -j ACCEPT
  [root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            192.168.10.10        icmptype 8 limit: avg 5/min burst 3
 1665  113K ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable
    0     0 DROP       tcp  --  *      *       192.168.10.0/24      192.168.10.10        tcp dpt:80 TIME from 00:30:00 to 12:30:00 on Mon,Sun UTC
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        tcp dpt:21 #conn src/32 > 2 reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 20 packets, 1944 bytes)
 pkts bytes target     prot opt in     out     source               destination
0     0 REJECT     tcp  --  *      *       192.168.10.10        192.168.10.0/24      tcp spt:80 STRING match  "sex" ALGO name bm TO 65535 reject-with icmp-port-unreachable

报文状态匹配：

[root@xiaochen ~]# iptables -I INPUT -p tcp -m tcp --dport 22 --tcp-flags SYN,ACK,FIN,RST,URG,PSH SYN -j REJECT
[root@xiaochen ~]# iptables -L -nv
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22 flags:0x3F/0x02 reject-with icmp-port-unreachable
    0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            192.168.10.10        icmptype 8 limit: avg 5/min burst 3
 1910  130K ACCEPT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80,8080,443
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        multiport dports 21,22,80 state INVALID reject-with icmp-port-unreachable
    0     0 DROP       tcp  --  *      *       192.168.10.0/24      192.168.10.10        tcp dpt:80 TIME from 00:30:00 to 12:30:00 on Mon,Sun UTC
    0     0 REJECT     tcp  --  *      *       0.0.0.0/0            192.168.10.10        tcp dpt:21 #conn src/32 > 2 reject-with icmp-port-unreachable

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 17 packets, 1724 bytes)
 pkts bytes target     prot opt in     out     source               destination
0     0 REJECT     tcp  --  *      *       192.168.10.10        192.168.10.0/24      tcp spt:80 STRING match  "sex" ALGO name bm TO 65535 reject-with icmp-port-unreachable

3、举例实现iptables之SNAT源地址修改及DNAT目标地址修改和PNAT端口修改等应用

一台网关主机用上nat的主要目的是要隐藏网关内网中的主机。如果一个网关设备不开启nat功能，仅仅只能将报文实现网络转发，而不会修改报文的任何源ip和目标ip。此时内网中的客户端和互联网外的主机通信时，一个怀有恶意的外网主机会得到内网客户端的地址，然后用扫描工具扫描客户端主机的各种端口服务，找到有薄弱项的服务发起远程***，此时很容易攻克这台主机，并用这台主机当作跳板，继续从内网去***内部其他的重要的主机。当网关主机上开启了nat功能后，网关在转发报文到互联网或者从互联网转发报文到内网服务器的时候，把报文中的内网主机地址统统改成网关的外网地址，外部的主机只能看到网关的地址，这样就做到安全保护内网中主机的操作。
网关开启nat后，请求报文和相应报文是通过内存中的连接追踪表来进行地址转换的。内网中的客户端通过网关的地址转换访问外网的服务器主机叫做SNAT（source network address translation），外网主机访问经过网关地址转换的内网中提供各种服务的主机叫做DNAT(destination network address translation)，httpd只开放8080端口，把8080端口映射到80，能正常以80访问叫做PNAT

环境搭建

[root@localhost ~]# sysctl -w net.ipv4.ip_forward=1
net.ipv4.ip_forward = 1
[root@localhost ~]# route add default gw 192.168.10.11
[root@localhost ~]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.10.11   0.0.0.0         UG    0      0        0 eno16777736
default         192.168.10.2    0.0.0.0         UG    100    0        0 eno16777736
default         192.168.50.1    0.0.0.0         UG    101    0        0 eno33554960
192.168.10.0    0.0.0.0         255.255.255.0   U     100    0        0 eno16777736
192.168.50.0    0.0.0.0         255.255.255.0   U     100    0        0 eno33554960
[root@localhost ~]# route add -net 192.168.0.0/24 gw 192.168.50.10
[root@localhost ~]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.10.11   0.0.0.0         UG    0      0        0 eno16777736
default         192.168.10.2    0.0.0.0         UG    100    0        0 eno16777736
default         192.168.50.1    0.0.0.0         UG    101    0        0 eno33554960
192.168.0.0     192.168.50.10   255.255.255.0   UG    0      0        0 eno33554960
192.168.10.0    0.0.0.0         255.255.255.0   U     100    0        0 eno16777736
192.168.50.0    0.0.0.0         255.255.255.0   U     100    0        0 eno33554960

实现SNAT

[root@localhost ~]# iptables -t nat -A POSTROUTING -s 192.168.0.0/24 -j SNAT --to-source 192.168.50.10
[root@localhost ~]# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
[root@localhost ~]# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
SNAT       all  --  192.168.0.0/24       anywhere             to:192.168.50.10

DNAT:

[root@localhost ~]# iptables -t nat -A PREROUTING -d 192.168.0.0/24 -j DNAT --to-destination 192.168.10.10
[root@localhost ~]# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination
DNAT       all  --  anywhere             192.168.0.0/24       to:192.168.10.10

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
SNAT       all  --  192.168.0.0/24       anywhere             to:192.168.50.10

PNAT:

[root@localhost ~]# iptables -t nat -A PREROUTING -d 192.168.0.0/24 -p tcp --dport 80 -j REDIRECT --to-ports 8080
[root@localhost ~]#
[root@localhost ~]#
[root@localhost ~]# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination
DNAT       all  --  anywhere             192.168.0.0/24       to:192.168.10.10
REDIRECT   tcp  --  anywhere             192.168.0.0/24       tcp dpt:http redir ports 8080

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
SNAT       all  --  192.168.0.0/24       anywhere             to:192.168.50.10

4、简述sudo安全切换工具，及详细讲解visudoer

sudo : 当我们去执行某个命令时，是切换用户以另外一个用户的身份运行。这个是在sudo文件中设定的另外一个发起人，这个发起人一般是管理员，并在文件中定义好发起人能够运行的命令列表，之后就能够临时切换发起人来执行这些命令，这种授权机制就是sudo,其中sudo的配置文件位置在/etc/sudoers,可以使用专用命令visudo来编辑这个文件完成授权。
sudo：

su：switch user
用户切换

(1) su  -l  user
(2) su  -l  user  -c   ‘COMMAND‘

sudo：
能够让获得授权的用户以另外一个用户的身份运行指定的命令；

授权机制：授权文件 /etc/sudoers
    root    ALL=(ALL)   ALL
    %wheel  ALL=(ALL)   ALL 

编译此文件的专用命令：visudo

    授权项：
        who     where=(whom)    commands

        users   hosts=(runas)       commands

            users：
                username
                #uid
                %groupname
                %#gid
                user_alias

                支持将多个用户定义为一组用户，称之为用户别名，即user_alias；

            hosts:
                ip
                hostname
                NetAddr
                host_alias

            runas:
                ...
                runas_alias

            commands:
                command

                directory
                sudoedit：特殊权限，可用于向其它用户授予sudo权限；
                cmnd_alias

        定义别名的方法：
            ALIAS_TYPE  NAME=item1, item2, item3, ...
                NAME：别名名称，必须使用全大写字符；
            ALIAS_TYPE:
                User_Alias
                Host_Alias
                Runas_Alias
                Cmnd_Alias

示例：

[root@localhost ~]# useradd fedora
[root@localhost ~]# echo fedora | passwd --stdin fedora
Changing password for user fedora.
passwd: all authentication tokens updated successfully.
[root@localhost ~]# su – fedora
[fedora@localhost ~]$ useradd user1
-bash: /usr/sbin/useradd: Permission denied
[fedora@localhost ~]$ exit
logout
[root@localhost ~]# visudo
fedora  ALL=(ALL)       /usr/sbin/useradd,/usr/sbin/userdel   ##添加一行内容
[root@localhost ~]# su – fedora
fedora@localhost ~]$ sudo useradd user1

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.
    #2) Think before you type.
    #3) With great power comes great responsibility.

[sudo] password for fedora:
[fedora@localhost ~]$ tail -1 /etc/passwd
user1:x:1001:1001::/home/user1:/bin/bash
[fedora@localhost ~]$ sudo userdel user1
[fedora@localhost ~]$ id user1
id: user1: no such user

以定义组的方式实现用户sudo

[root@localhost ~]# usermod -a -G wheel fedora
[root@localhost ~]# newgrp wheel
[root@localhost ~]# id fedora
uid=1000(fedora) gid=1000(fedora) groups=1000(fedora),10(wheel)
[root@localhost ~]# visudo
%wheel  ALL=(ALL)       /usr/sbin/useradd,/usr/sbin/userdel
[root@localhost ~]# su - fedora
Last login: Wed Feb 13 23:19:34 CST 2019 on pts/0
[fedora@localhost ~]$ sudo -k
[fedora@localhost ~]$ sudo useradd user3
[sudo] password for fedora:
[fedora@localhost ~]$ id user3
uid=1001(user3) gid=1001(user3) groups=1001(user3)
[fedora@localhost ~]$ sudo userdel user3
[fedora@localhost ~]$ id user3
id: user3: no such user

原文地址：http://blog.51cto.com/13929964/2349801

时间： 2024-10-12 01:27:41

Linux iptables与sudo

Iptables 五链

四表：

2、举例实现iptables多端口匹配、连接追踪、字符串匹配、时间匹配、并发连接限制、速率匹配、报文状态匹配等应用

3、举例实现iptables之SNAT源地址修改及DNAT目标地址修改和PNAT端口修改等应用

4、简述sudo安全切换工具，及详细讲解visudoer

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