SSHとfirewallの設定(CentoOS7)


# Userの追加
useradd dev-user
passwd dev-user
パスワード入力

※この時点でdev-userでSSHログインできるはず


# 秘密鍵と公開鍵の作成

### 鍵を作る
```
$ ssh-keygen -t rsa -b 4096
Generating public/private rsa key pair.
Enter file in which to save the key (/home/www-data/.ssh/id_rsa): (→空Enter)
Created directory '/home/dev-user/.ssh'.
Enter passphrase (empty for no passphrase):  (→パスワード入力)
Enter same passphrase again:   (→パスワード入力)
Your identification has been saved in /home/dev-user/.ssh/id_rsa.
Your public key has been saved in /home/dev-user/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:kxg8DaNRswVpv3k0clPQHM3bnFr5FtxBH1zQ4KWPkPk dev-user@localhost.localdomain
The key's randomart image is:
+---[RSA 4096]----+
|    ..*o. .+.+=*+|
|     +oB    ++o=+|
|    ..=..  .+ ++*|
|       +o.=  o.O+|
|      . S* o  E +|
|        o..  .  o|
|         .     . |
|                 |
|                 |
+----[SHA256]-----+

```
↓秘密鍵
/home/dev-user/.ssh/id_rsa
↓公開鍵
/home/dev-user/.ssh/id_rsa.pub


###  公開鍵のファイル名とパーミッションの変更
```
$ mv /home/dev-user/.ssh/id_rsa.pub /home/dev-user/.ssh/authorized_keys
$ chmod 700 /home/dev-user/.ssh
$ chmod 600 /home/dev-user/.ssh/authorized_keys
```

# sshd_configの設定変更


```diff_conf
$ vi /etc/ssh/sshd_config

#       $OpenBSD: sshd_config,v 1.100 2016/08/15 12:32:04 naddy Exp $

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.

# This sshd was compiled with PATH=/usr/local/bin:/usr/bin

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options override the
# default value.

# If you want to change the port on a SELinux system, you have to tell
# SELinux about this change.
# semanage port -a -t ssh_port_t -p tcp #PORTNUMBER
#
- #Port 22
+ Port 12345
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

# Ciphers and keying
#RekeyLimit default none

# Logging
#SyslogFacility AUTH
SyslogFacility AUTHPRIV
#LogLevel INFO

# Authentication:

#LoginGraceTime 2m
- #PermitRootLogin yes
+ PermitRootLogin no

#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#PubkeyAuthentication yes

# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
# but this is overridden so installations will only check .ssh/authorized_keys
AuthorizedKeysFile      .ssh/authorized_keys

#AuthorizedPrincipalsFile none

#AuthorizedKeysCommand none
#AuthorizedKeysCommandUser nobody

# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes
#PermitEmptyPasswords no
- PasswordAuthentication yes
+ PasswordAuthentication no

# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes
ChallengeResponseAuthentication no

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no
#KerberosUseKuserok yes

# GSSAPI options
GSSAPIAuthentication yes
GSSAPICleanupCredentials no
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no
#GSSAPIEnablek5users no

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
# WARNING: 'UsePAM no' is not supported in Red Hat Enterprise Linux and may cause several
# problems.
UsePAM yes

#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
X11Forwarding yes
#X11DisplayOffset 10
#X11UseLocalhost yes
#PermitTTY yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#UseLogin no
#UsePrivilegeSeparation sandbox
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#ShowPatchLevel no
#UseDNS yes
#PidFile /var/run/sshd.pid
#MaxStartups 10:30:100
#PermitTunnel no
#ChrootDirectory none
#VersionAddendum none

# no default banner path
#Banner none

# Accept locale-related environment variables
AcceptEnv LANG LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE LC_MONETARY LC_MESSAGES
AcceptEnv LC_PAPER LC_NAME LC_ADDRESS LC_TELEPHONE LC_MEASUREMENT
AcceptEnv LC_IDENTIFICATION LC_ALL LANGUAGE
AcceptEnv XMODIFIERS

# override default of no subsystems
Subsystem       sftp    /usr/libexec/openssh/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#       X11Forwarding no
#       AllowTcpForwarding no
#       PermitTTY no
#       ForceCommand cvs server

+ AllowUsers dev-user
```

* `Port` → SSH接続ポートを変更
* `PermitRootLogin` → rootでログインできないように
* `PasswordAuthentication` →　パスワードでログインできないように
* `AllowUsers` →　SSHログインできるユーザーを設定
* 
※デフォルトの22ポートだと不正アクセスがうっとおしいので変更をお勧めします。


# ファイアウォールの設定の変更
ポート変更しない場合は設定しなくてOK

### 現在の設定を確認
```
$ sudo systemctl start firewalld
$ firewall-cmd --list-all
public (default, active)
  interfaces: eth0
  sources:
  services: dhcpv6-client ssh
  ports:
  masquerade: no
  forward-ports:
  icmp-blocks:
  rich rules:
```

### 設定を変更
```diff_conf
# 既存のSSHの設定を削除
$ sudo firewall-cmd --permanent --remove-service=ssh

#設定をコピー
$ sudo cp /usr/lib/firewalld/services/ssh.xml /etc/firewalld/services/ssh-123456.xml
```

### コピーしたファイルを変更
```diff_conf
$ sudo vi /etc/firewalld/services/ssh-123456.xml
-  <port protocol="tcp" port="22"/>
+  <port protocol="tcp" port="123456"/>
```

### 反映
```
$ sudo firewall-cmd --permanent --add-service=ssh-123456

# ついでにHTTP、HTTPSも解放
$ sudo firewall-cmd --permanent --add-service=http
$ sudo firewall-cmd --permanent --add-service=https

# 設定を反映
$ sudo firewall-cmd --reload
```

### 確認

```
$ firewall-cmd --list-all
public
  target: default
  icmp-block-inversion: no
  interfaces: 
  sources: 
  services: dhcpv6-client http https ssh-123456
  ports: 
  protocols: 
  masquerade: no
  forward-ports: 
  source-ports: 
  icmp-blocks: 
  rich rules: 
```
servicesの箇所に下記が含まれていたらOK
* `ssh-123456 `
* `http ` 
* `https`




# さあログインできるかな？
```
$ sudo systemctl start firewalld
$ sudo systemctl start sshd
```

# ログインできない場合、ログをみてエラーで検索しよう！
```
tail -f /var/log/secure
```


# パスワードなしで、sudo su出来るユーザーに設定する
```
$ sudo visudo

#下記をファイルに追加
dev-user ALL=NOPASSWD: ALL
```



以上、セキュリティ対策はこれぐらいかなー
またあれば追記