配置和检查 CIS 合规性

本文档介绍了 CIS 基准是什么、基准与 Container-Optimized OS (COS) 有何关系、如何审核实例中的合规性状态,以及如何在发生故障时进行问题排查。

概览

互联网安全中心 (CIS) 发布了针对各平台的最佳做法安全建议的基准。Container-Optimized OS CIS Benchmark 是一系列关于配置使用 Container-Optimized OS 来支持强大安全状况的实例的建议。

访问基准

CIS 网站上提供了 Container-Optimized OS CIS 基准:

安全建议等级

CIS 针对 Container-Optimized OS 定义了以下建议级别。

第 1 级

此级别的建议适用于大多数环境。此级别提供如下建议:

  • 地址随机分配功能处于启用状态
  • /tmp 不能用于运行可执行二进制文件
  • 数据包重定向发送功能已停用

2 级

此级别的建议会扩展第 1 级建议,从而实现更严格的安全环境。2 级建议并不一定适用于所有情况,因为可能需要对应用做出更改。采纳之前,您应先评估环境级别 2 中的建议。此级别提供如下建议:

  • 所有开放端口都有防火墙规则
  • 不接受 ICMP 重定向和路由器通告
  • 默认用户 shell 超时不得超过 900 秒

Container-Optimized OS 如何符合 CIS 基准

Milestone 97 开始,Container-Optimized OS 映像默认符合 CIS 1 级,并提供了符合 CIS 2 级的选项。我们还提供了一个扫描器,可用于根据 CIS 建议级别审核您的实例。

定义建议的 CIS 配置位于 /usr/share/google/security/cis-compliance/cis_config.textproto 中。CIS 扫描工具使用该配置来检查实例的合规性状态。每次 CIS 级合规性扫描程序运行的结果都会写入 /var/lib/google/cis_scanner_scan_result.textproto。每次运行 CIS 扫描程序时,此文件都会被覆盖。如果任何 CIS 第 1 级或第 2 级扫描失败,cis_scanner_scan_result.textproto 文件会包含所有失败的检查的列表。

检查实例合规性状态

Container-Optimized OS 映像提供以下 systemd 服务,用于检查和配置合规性:

  • cis-level1.service:默认处于启用状态,启动时启动。服务启动时,会检查实例是否符合 CIS 1 级。
  • cis-level2.service:默认处于停用状态。此服务可让您将实例配置为符合 CIS 2 级标准,并对照 1 级和 2 级标准检查实例的状态。

以下部分介绍了如何检查实例的合规状态,以及如何自动执行审核流程。

检查 CIS 1 级合规性状态

如需查看您的实例是否符合 CIS 1 级标准,请检查 cis-level1.service 的状态:

systemctl status cis-level1

输出内容类似如下:

Reading scan config from /usr/share/google/security/cis-compliance/cis_config.textproto
Running scan of 62 benchmarks
Scan status: SUCCEEDED
Found 0 non-compliant benchmarks
Writing scan results to /var/lib/google/cis_scanner_scan_result.textproto

如果发现任何不符合规定的检查,请参阅 CIS 合规性 1 级/2 级检查失败

cis-level1.service 仅在实例启动时检查一次 CIS 1 级合规性。要配置定期合规性检查,请参阅定期检查 CIS 合规性状态

配置 CIS 2 级合规性并检查状态

您可以使用 cis-level2 服务对实例进行配置,以符合 CIS 第 2 级,并对照 1 级和 2 级系统检查合规状态。systemd 服务支持所有 CIS 2 级建议,但以下建议除外

  • 4.1.1.2 确保 Stackdriver 服务正在运行

    此建议仅适用于默认使用 Stackdriver 日志记录代理的实例。由于用户可能更喜欢不同类型的日志记录代理,因此我们会让用户自行启动。因此,cis-level2 服务不会配置实例,也不会检查此建议的合规性。

对于以下建议,cis-level2 服务会配置实例,但不会验证这些建议的合规状态。

  • 3.3.1.1 确保 IPv6 默认拒绝防火墙政策
  • 3.3.1.2 确保已配置 IPv6 环回流量
  • 3.3.1.3 确保已配置 IPv6 出站和已建立的连接
  • 3.3.1.4 确保所有开放端口都存在 IPv6 防火墙规则
  • 3.3.2.1 确保默认拒绝防火墙政策
  • 3.3.2.2 确保环回流量已配置
  • 3.3.2.3 确保已配置出站和已建立的连接

cis-level2 服务默认处于停用状态。如需启动该服务,请运行以下命令:

systemctl start cis-level2.service

如需查看您的实例是否已成功配置并符合 CIS 2 级建议,请检查 cis-level2.service 的状态:

systemctl status cis-level2

输出内容类似如下:

Reading scan config from /usr/share/google/security/cis-compliance/cis_config.textproto
Running scan of 112 benchmarks
Scan status: SUCCEEDED
Found 0 non-compliant benchmarks
Writing scan results to /var/lib/google/cis_scanner_scan_result.textproto

如果实例配置失败或发现任何不符合规定的检查,请参阅问题排查

cis-level2 服务仅配置一次实例并检查 CIS 2 级合规性是否符合要求。要配置定期合规性检查,请参阅定期检查 CIS 合规性状态

CIS 合规性状态的定期检查

Container-Optimized OS 映像包含以下服务,以定期检查 CIS 合规性:

  • cis-compliance-tracker.service:根据 /etc/cis-scanner/env_vars 中定义的环境变量检查合规性状态。默认情况下,此服务会检查是否符合 CIS 1 级合规性,并处于停用状态。
  • cis-compliance-tracker.timer:定期运行 cis-compliance-scanner.service。默认周期为一天一次。

配置扫描器服务

cis-compliance-scanner.service 负责根据 /etc/cis-scanner/env_vars 中定义的环境变量检查 CIS 合规性的状态。默认情况下,此服务会检查 CIS 1 级合规性。

如需检查 CIS 2 级合规性,请将 /etc/cis-scanner/env_vars 中的 LEVEL 环境变量设置为 2/etc/cis-scanner/env_vars 文件类似于以下内容:

# cis-compliance-scanner.service environment variables
# The config file defines which checks to perform by cis_scanner
CONFIG="/usr/share/google/security/cis-compliance/cis_config.textproto"
# Where to store the result of the scan
RESULT="/var/lib/google/cis_scanner_scan_result.textproto"
# Upto which level to scan. It can be 1 or 2
LEVEL="2"
# Extra options that can be passed to cis_scanner
# For valid options, see output of `cis_scanner -h`
EXTRA_OPTIONS=""

配置计时器

如需设置定期合规性扫描,请启动 cis-compliance-scanner.timer 单元:

systemctl start cis-compliance-scanner.timer

默认情况下,cis-compliance-scanner.timer 每天启动 cis-compliance-scanner.service 次。如需更改扫描周期,请替换 cis-compliance-scanner.timer 单位的 OnUnitActiveSec 字段:

sudo mkdir /etc/systemd/system/cis-compliance-scanner.timer.d
sudo tee /etc/systemd/system/cis-compliance-scanner.timer.d/override.conf <<EOF
[Unit]
Description=Run CIS Scanner once an hour
[Timer]
OnUnitActiveSec=1h
EOF

此示例将扫描仪时间段设置为每小时一次。

如需应用更改,请重新加载 systemd 单元:

systemctl daemon-reload

停用特定的 CIS 合规性检查

CIS 1 级和 2 级建议适用于大多数环境。不过,有些建议可能不适用于特定的环境。如需停用特定建议,请使用 /etc/cis-scanner/env_vars 中的 EXTRA_OPTIONS 环境变量。

以下 env_vars 文件示例选择停用 etc-passwd-permissions 建议:

# cis-compliance-scanner.service environment variables
# The config file defines which checks to perform by cis_scanner
CONFIG="/usr/share/google/security/cis-compliance/cis_config.textproto"
# Where to store the result of the scan
RESULT="/var/lib/google/cis_scanner_scan_result.textproto"
# Upto which level to scan. It can be 1 or 2
LEVEL="1"
# Extra options that can be passed to cis_scanner
# For valid options:`cis_scanner -h`
EXTRA_OPTIONS="--benchmark-opt-out-ids=etc-passwd-permissions"

自动启用和检查 CIS 合规状态

您可以使用 cloud-init 或 OS Policy 自动执行实例的合规性检查过程。以下示例展示了每个工具的一些用例:

  • 示例 1:每天检查一次 CIS 1 级合规性。
  • 示例 2:每小时检查一次 CIS 1 级合规性。
  • 示例 3:每天检查一次 CIS 2 级合规性。
  • 示例 4:停用特定的 CIS 合规性检查。

使用 cloud-init

在尝试以下示例之前,请确保您已按照将 Cloud-init 与 Cloud 配置格式搭配使用中的说明熟悉使用 cloud-init 配置 COS 实例。

示例 1

以下示例配置开始默认 CIS 1 级定期扫描(每天一次),

#cloud-config

runcmd:
# Check the compliance status of the instance once a day.
- systemctl start cis-compliance-scanner.timer

示例 2

以下示例每小时配置一次 CIS 1 级定期扫描。

#cloud-config

# Override cis-compliance-scanner.timer with 1 hour frequency.
write_files:

- path: /etc/systemd/system/cis-compliance-scanner.timer.d/override.conf
  permissions: 0600
  owner: root
  content: |
    [Unit]
    Description=Run CIS Scanner once an hour

    [Timer]
    OnUnitActiveSec=1h

runcmd:
# Reload systemd units.
- systemctl daemon-reload
# Check the compliance status of the instance once an hour.
- systemctl start cis-compliance-scanner.timer

示例 3

以下示例将 CIS 第 2 级定期扫描配置为默认周期为每天一次。

#cloud-config

runcmd:
# Configure the instance for CIS level 2.
- systemctl start cis-level2.service
# Change the scan level to CIS Level 2.
- sed -i 's/^LEVEL=.*$/LEVEL="2"/' /etc/cis-scanner/env_vars
# Check the compliance status of the instance once a day.
- systemctl start cis-compliance-scanner.timer

示例 4

以下示例将扫描器配置为每天运行一次,并选择停用特定的 CIS 建议。

#cloud-config

runcmd:
# Opt-out of the etc-passwd-permissions check.
- sed -i 's/^EXTRA.*$/EXTRA_OPTIONS="--benchmark-opt-out-ids=etc-passwd-permissions"/' /etc/cis-scanner/env_vars
# Check the compliance of the instance once a day.
- systemctl start cis-compliance-scanner.timer

使用操作系统政策

您可以使用操作系统政策来配置 CIS 基准扫描。在开始之前,请确保您已熟悉操作系统政策,包括:

此外,如需进行部署,用户还需要在以下示例配置中添加 instanceFilterrollout

示例 1

以下示例配置开始默认 CIS 1 级定期扫描(每天一次),

# An OS policy to check CIS level 1 compliance once a day.
osPolicies:
- id: ensure-cis-level1-compliance-once-a-day-policy
  mode: ENFORCEMENT
  resourceGroups:
  - resources:
      id: ensure-cis-level1-compliance-once-a-day
      exec:
        validate:
          interpreter: SHELL
          # If cis-compliance-scanner.service is active, return an exit code
          # 100 to indicate that the instance is in compliant state.
          # Otherwise, return an exit code of 101 to run `enforce` step.
          script: |-
            is_active=$(systemctl is-active cis-compliance-scanner.timer)
            result=$(systemctl show -p Result --value cis-compliance-scanner.service)

            if [ "$is_active" == "active" ] && [ "$result" == "success" ]; then
              exit 100;
            else
              exit 101;
            fi
        enforce:
          interpreter: SHELL
          # COS 97 images are by-default CIS Level 1 compliant and there is no
          # additional configuration needed. However, if certain changes
          # cause non-compliance because of the workload on the instance, this
          # section can be used to automate to make fixes. For example, the
          # workload might generate a file that does not comply with the
          # recommended file permissions.
          # Return an exit code of 100 to indicate that the desired changes
          # successfully applied.
          script: |-
            # optional <your code>
            # Check the compliance of the instance once a day.
            systemctl start cis-compliance-scanner.timer && exit 100

示例 2

以下示例每小时配置一次 CIS 1 级定期扫描。

# An OS policy to check CIS level 1 compliance once an hour.
osPolicies:
- id: ensure-cis-level1-compliance-once-an-hour-policy
  mode: ENFORCEMENT
  resourceGroups:
  - resources:
      id: ensure-cis-level1-compliance-once-an-hour
      exec:
        validate:
          interpreter: SHELL
          # If cis-compliance-scanner.service is active, return an exit code
          # 100 to indicate that the instance is in compliant state.
          # Otherwise, return an exit code of 101 to run `enforce` step.
          script: |-
            is_active=$(systemctl is-active cis-compliance-scanner.timer)
            result=$(systemctl show -p Result --value cis-compliance-scanner.service)

            if [ "$is_active" == "active" ] && [ "$result" == "success" ]; then
              exit 100;
            else
              exit 101;
            fi
        enforce:
          interpreter: SHELL
          # Return an exit code of 100 to indicate that the desired changes
          # were successfully applied.
          script: |-
            # Overwrite "OnUnitActiveSec" field of the
            # cis-compliance-scanner.timer to trigger
            # cis-compliance-scanner.service once an hour
            # instead of once a day.
            mkdir /etc/systemd/system/cis-compliance-scanner.timer.d
            tee /etc/systemd/system/cis-compliance-scanner.timer.d/override.conf <<EOF
            [Unit]
            Description=Run CIS Scanner once an hour

            [Timer]
            OnUnitActiveSec=1h
            EOF
            # Reload systemd units.
            systemctl daemon-reload
            # Check the compliance of the instance once an hour.
            systemctl start cis-compliance-scanner.timer && exit 100

示例 3

以下示例将 CIS 第 2 级定期扫描配置为默认周期为每天一次。

# An OS policy to check CIS level 2 compliance once a day.
osPolicies:
- id: ensure-cis-level2-compliance-once-a-day-policy
  mode: ENFORCEMENT
  resourceGroups:
  - resources:
      id: ensure-cis-level2-compliance-once-a-day
      exec:
        validate:
          interpreter: SHELL
          # If cis-compliance-scanner.service is active, return an exit code
          # 100 to indicate that the instance is in compliant state.
          # Otherwise, return an exit code of 101 to run `enforce` step.
          script: |-
            is_active=$(systemctl is-active cis-compliance-scanner.timer)
            result=$(systemctl show -p Result --value cis-compliance-scanner.service)

            if [ "$is_active" == "active" ] && [ "$result" == "success" ]; then
              exit 100;
            else
              exit 101;
            fi
        enforce:
          interpreter: SHELL
          # Return an exit code of 100 to indicate that the desired changes
          # were successfully applied.
          script: |-
            # Configure the instance for CIS level 2.
            systemctl start cis-level2.service
            # Change the scan level to 2.
            sed -i 's/^LEVEL=.*$/LEVEL="2"/' /etc/cis-scanner/env_vars
            # Check the compliance of the instance once a day.
            systemctl start cis-compliance-scanner.timer && exit 100

示例 4

以下示例将扫描器配置为每天运行一次,并选择停用特定的 CIS 建议。

# An OS policy to opt-out of CIS check and check compliance status once a day.
osPolicies:
- id: exclude-cis-check-and-check-compliance-once-a-day-policy
  mode: ENFORCEMENT
  resourceGroups:
  - resources:
      id: exclude-cis-check-and-check-compliance-once-a-day
      exec:
        validate:
          interpreter: SHELL
          # If cis-compliance-scanner.service is active, return an exit code
          # 100 to indicate that the instance is in compliant state.
          # Otherwise, return an exit code of 101 to run `enforce` step.
          script: |-
            is_active=$(systemctl is-active cis-compliance-scanner.timer)
            result=$(systemctl show -p Result --value cis-compliance-scanner.service)

            if [ "$is_active" == "active" ] && [ "$result" == "success" ]; then
              exit 100;
            else
              exit 101;
            fi
        enforce:
          interpreter: SHELL
          # Return an exit code of 100 to indicate that the desired changes
          # were successfully applied.
          script: |-
            # Opt-out of the etc-passwd-permissions check.
            sed -i 's/^EXTRA.*$/EXTRA_OPTIONS="--benchmark-opt-out-ids=etc-passwd-permissions"/' /etc/cis-scanner/env_vars
            # Check the compliance of the instance once a day.
            systemctl start cis-compliance-scanner.timer && exit 100

问题排查

配置实例以符合 CIS 2 级建议失败

cis-level2 服务会先配置实例以符合 CIS 2 级建议,然后检查其是否符合 CIS 1 级和 2 级。如果实例配置失败,cis-level2 服务会退出,并显示以下错误消息:

Job for cis-level2.service failed because the control process exited with error code.
See "systemctl status cis-level2.service" and "journalctl -xeu cis-level2.service" for details.

日志日志将提及未能应用于实例并导致 cis-level2 systemd 服务失败的建议。

CIS 合规级别 1 / 级别 2 检查失败

每次运行 CIS 级别的合规性的扫描结果会写入 /var/lib/google/cis_scanner_scan_result.textproto。如果任何 CIS 第 1 级或第 2 级扫描失败,textproto 文件将包含所有失败检查的列表,如以下示例所示:

cat /var/lib/google/cis_scanner_scan_result.textproto

# Output
start_time: {
  seconds: 1648241700
  nanos: 763152171
}
end_time: {
  seconds: 1648241700
  nanos: 812992527
}
scanner_version: "1.1.4.3"
benchmark_version: "1.0.0"
status: {
  status: SUCCEEDED
}
non_compliant_benchmarks: {
  id: "etc-passwd-permissions"
  compliance_occurrence: {
    non_compliant_files: {
      path: "/etc/passwd"
      reason: "File permission is 0664, expected the following bits to be set: 0444 and the following bits to be clear: 0133"
    }
  }
}
compliant_benchmarks:  {
  id:  "etc-passwd-permissions"
  compliance_occurrence:  {}
}

如需缓解失败的检查,请使用 CIS 基准,并按照 Remediation 部分中的步骤检查未通过的检查,使实例合规。如需查找与 CIS 基准中的未通过检查相对应的建议,请在位于 /usr/share/google/security/cis-compliance/cis_config.textproto 的 CIS 扫描程序配置文件中查找 non_compliant_benchmark's ID。