全面分析RHCE（红帽认证工程师）考试题目之 ----SELinux篇

Posted 2020-10-20

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Linux 安全保护模式

DAC，自主访问控制

MAC，强制访问控制

SELinux

一套强化Linux安全的MAC扩展模块

美国国家安全局主导开发

SELinux的运作机制

集成Linux内核（2.6及以上）

操作系统提供可定制的策略，管理工具

[[email protected] ~]# cat /etc/redhat-release

Red Hat Enterprise Linux Server release 7.2 (Maipo)

[[email protected] ~]# uname -r

3.10.0-327.el7.x86_64

[[email protected] ~]# rpm -qa | grep -i selinux

selinux-policy-3.13.1-60.el7.noarch

libselinux-2.2.2-6.el7.x86_64

selinux-policy-targeted-3.13.1-60.el7.noarch

libselinux-utils-2.2.2-6.el7.x86_64

libselinux-python-2.2.2-6.el7.x86_64

查看当前SELinux的状态

[[email protected] ~]# sestatus

SELinux status: enabled

SELinuxfs mount: /sys/fs/selinux

SELinux root directory: /etc/selinux

Loaded policy name: targeted

Current mode: permissive

Mode from config file: enforcing

Policy MLS status: enabled

Policy deny_unknown status: allowed

Max kernel policy version: 28

[[email protected] ~]# ls /etc/selinux/

[[email protected] ~]# ls /sys/fs/selinux/

[[email protected] ~]# setenforce 0|1 #0:permissive 1:enforcing

[[email protected] ~]# getenforce #查看当前SELinux状态

[[email protected] ~]# vim /etc/selinux/config #配置文件

# This file controls the state of SELinux on the system.

# SELINUX= can take one of these three values:

# enforcing - SELinux security policy is enforced. #强制启动

# permissive - SELinux prints warnings instead of enforcing. #宽松/允许模式

# disabled - No SELinux policy is loaded. #禁用

SELINUX=enforcing

# SELINUXTYPE= can take one of three two values:

# targeted - Targeted processes are protected,

# minimum - Modification of targeted policy. Only selected processes are protected.

# mls - Multi Level Security protection. #提供多层次，全面的安全防护策略

SELINUXTYPE=targeted #推荐，仅保护最常见/关键的网络服务，其他不限制

SELinux策略设置

一，安全上下文

进程 ps aux -Z

文件 ls -lZ 文件名

[[email protected] ~]# ls -lZ /etc/passwd

-rw-r--r--. root root system_u:object_r:passwd_file_t:s0 /etc/passwd

[[email protected] ~]# ls -dZ /var/www/html/

drwxr-xr-x. root root system_u:object_r:httpd_sys_content_t:s0 /var/www/html/

[[email protected] ~]# ls -dZ /var/lib/mysql/

drwxr-x--x. mysql mysql system_u:object_r:mysqld_db_t:s0 /var/lib/mysql/

[[email protected] ~]# ps aux -Z | grep httpd

system_u:system_r:httpd_t:s0 root 5965 0.1 0.4 226128 5052 ? Ss 22:33 0:00 /usr/sbin/httpd -DFOREGROUND

system_u:system_r:httpd_t:s0 apache 5966 0.0 0.3 228212 3144 ? S 22:33 0:00 /usr/sbin/httpd -DFOREGROUND

安全上下文的组成

用户：角色：访问类型：选项

常见访问类型

bin_t #二进制执行文件

etc_t #系统配置文件

fsadm_exec_t #文件系统管理

admin_home_t #管理员账户的宿主目录

user_home_t #普通用户的宿主目录

httpd_sys_content_t #httpd网站内容

SELinux启用后一般的操作规律

新建文件或新建目录会继承父目录的安全上下文

[[email protected] ~]# touch /root/1.txt

[[email protected] ~]# ls -dZ /root/

dr-xr-x---. root root system_u:object_r:admin_home_t:s0 /root/

[[email protected] ~]# ls -lZ /root/1.txt

-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 /root/1.txt

拷贝时继承目标目录的安全上下文

[[email protected] ~]# cp /root/1.txt /var/www/html/

[[email protected] ~]# ls -lZ /var/www/html/1.txt

-rw-r--r--. root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/html/1.txt

移动时保留源文件的安全上下文

[[email protected] ~]# rm -rf /var/www/html/1.txt

[[email protected] ~]# mv /root/1.txt /var/www/html/

[[email protected] ~]# ls -lZ /var/www/html/1.txt

-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 /var/www/html/1.txt

修改安全上下文

chcon 修改安全上下文

选项： -t:指定访问类型

-u,-r:分别用来指定用户，角色

-R：递归修改

[[email protected] ~]# ls -lZ /var/www/html/1.txt

-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 /var/www/html/1.txt

[[email protected] ~]# chcon -t httpd_sys_content_t /var/www/html/1.txt

[[email protected] ~]# ls -lZ /var/www/html/1.txt

-rw-r--r--. root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/html/1.txt

restorecon 重置安全上下文

— 恢复为所在位置的默认上下文属性

-R：递归恢复

[[email protected] ~]# touch /root/2.txt

[[email protected] ~]# mv /root/2.txt /var/www/html/

[[email protected] ~]# ls -lZ /var/www/html/2.txt

-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 /var/www/html/2.txt

[[email protected] ~]# restorecon /var/www/html/2.txt

[[email protected] ~]# ls -lZ /var/www/html/2.txt

-rw-r--r--. root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/html/2.txt

二.SELinux布尔值：（功能开关）

getsebool 查看

-a 可列出所有布尔值

setsebool 设置

-P 永久更改，重启仍然有效

启用SELinux日志程序

[[email protected] ~]# rpm -qa | grep shoot

setroubleshoot-plugins-3.0.59-1.el7.noarch

setroubleshoot-3.2.24-1.1.el7.x86_64

setroubleshoot-server-3.2.24-1.1.el7.x86_64

练习：启用SELinux，允许本机的ftp服务，允许匿名用户上传和下在文件

[[email protected] ~]# yum -y install vsftpd

[[email protected] ~]# mkdir /var/ftp/sharedir

[[email protected] ~]# chmod o+w /var/ftp/sharedir/

[[email protected] ~]# cp /etc/hosts /var/ftp/sharedir/

[[email protected] ~]# vim /etc/vsftpd/vsftpd.conf

29 anon_upload_enable=YES

[[email protected] ~]# systemctl restart vsftpd

[[email protected] ~]# getsebool -a | grep ftp

[[email protected] ~]# setsebool -P ftpd_full_access=on

[[email protected] ~]# setsebool -P ftpd_anon_write=on

[[email protected] ~]# yum -y install ftp.x86_64

[[email protected] ~]# ftp 192.168.4.12

Connected to 192.168.4.12 (192.168.4.12).

220 (vsFTPd 3.0.2)

Name (192.168.4.12:root): ftp

Password:

ftp> cd sharedir

ftp> lcd /root #设定本地接受目录位置

ftp> put test.txt #上传本地文件

ftp> get hosts #下在文件

练习启用SELinux，修改本机网站服务监听的端口8090

[[email protected] ~]# sed -i '42s/80/8090/' /etc/httpd/conf/httpd.conf

[[email protected] ~]# grep -n 8090 /etc/httpd/conf/httpd.conf

42:Listen 8090

[[email protected] ~]# systemctl restart httpd

Job for httpd.service failed because the control process exited with error code. See "systemctl status httpd.service" and "journalctl -xe" for details.

[[email protected] ~]# grep -i "setroubleshoot" /var/log/messages | tail -1

Jan 3 01:43:44 test setroubleshoot: SELinux is preventing /usr/sbin/httpd from name_bind access on the tcp_socket port 8090. For complete SELinux messages. run sealert -l b044047d-64e3-425b-aa88-50ffb248f814

[[email protected] ~]# sealert -l b044047d-64e3-425b-aa88-50ffb248f814 #运行日志文件提供的解决方案在其中寻找解决办法

...

If you want to allow /usr/sbin/httpd to bind to network port 8090

Then you need to modify the port type.

# semanage port -a -t PORT_TYPE -p tcp 8090

其中 PORT_TYPE 是以下之一：http_cache_port_t, http_port_t, jboss_management_port_t, jboss_messaging_port_t, ntop_port_t, puppet_port_t。

...

[[email protected] ~]# semanage port -a -t http_port_t -p tcp 8090

[[email protected] ~]# systemctl restart httpd

[[email protected] ~]# netstat -pantu | grep httpd

tcp6 0 0 :::8090 :::* LISTEN 9668/httpd

在RHCE 的考试中有一道题目是：