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Specification of Security Policy for Containers

Policy Specification

Here is the specification of a security policy.

apiVersion: security.kubearmor.com/v1
kind:KubeArmorPolicy
metadata:
  name: [policy name]
  namespace: [namespace name]

spec:
  severity: [1-10]                         # --> optional (1 by default)
  tags: ["tag", ...]                       # --> optional
  message: [message]                       # --> optional

  selector:
    matchLabels:
      [key1]: [value1]
      [keyN]: [valueN]

  process:
    matchPaths:
    - path: [absolute executable path]
      ownerOnly: [true|false]              # --> optional
      fromSource:                          # --> optional
      - path: [absolute exectuable path]
    matchDirectories:
    - dir: [absolute directory path]
      recursive: [true|false]              # --> optional
      ownerOnly: [true|false]              # --> optional
      fromSource:                          # --> optional
      - path: [absolute exectuable path]
    matchPatterns:
    - pattern: [regex pattern]
      ownerOnly: [true|false]              # --> optional

  file:
    matchPaths:
    - path: [absolute file path]
      readOnly: [true|false]               # --> optional
      ownerOnly: [true|false]              # --> optional
      fromSource:                          # --> optional
      - path: [absolute exectuable path]
    matchDirectories:
    - dir: [absolute directory path]
      recursive: [true|false]              # --> optional
      readOnly: [true|false]               # --> optional
      ownerOnly: [true|false]              # --> optional
      fromSource:                          # --> optional
      - path: [absolute exectuable path]
    matchPatterns:
    - pattern: [regex pattern]
      readOnly: [true|false]               # --> optional
      ownerOnly: [true|false]              # --> optional

  network:
    matchProtocols:
    - protocol: [TCP|tcp|UDP|udp|ICMP|icmp]
      fromSource:                          # --> optional
      - path: [absolute exectuable path]

  capabilities:
    matchCapabilities:
    - capability: [capability name]
      fromSource:                          # --> optional
      - path: [absolute exectuable path]

  action: [Allow|Audit|Block] (Block by default)

For better understanding, you can check the KubeArmorPolicy spec diagram.

Policy Spec Description

Now, we will briefly explain how to define a security policy.

  • Common

A security policy starts with the base information such as apiVersion, kind, and metadata. The apiVersion and kind would be the same in any security policies. In the case of metadata, you need to specify the names of a policy and a namespace where you want to apply the policy.

  apiVersion: security.kubearmor.com/v1
  kind:KubeArmorPolicy
  metadata:
    name: [policy name]
    namespace: [namespace name]
  • Severity

The severity part is somewhat important. You can specify the severity of a given policy from 1 to 10. This severity will appear in alerts when policy violations happen.

severity: [1-10]
  • Tags

The tags part is optional. You can define multiple tags (e.g., WARNNING, SENSITIVE, MITRE, STIG, etc.) to categorize security policies.

tags: ["tag1", ..., "tagN"]
  • Message

The message part is optional. You can add an alert message, and then the message will be presented in alert logs.

message: [message]
  • Selector

The selector part is relatively straightforward. Similar to other Kubernetes configurations, you can specify \(a group of\) pods based on labels.

  selector:
    matchLabels:
      [key1]: [value1]
      [keyN]: [valueN]
  • Process

In the process section, there are three types of matches: matchPaths, matchDirectories, and matchPatterns. You can define specific executables using matchPaths or all executables in specific directories using matchDirectories. In the case of matchPatterns, advanced operators may be able to determine particular patterns for executables by using regular expressions. However, the coverage of regular expressions is highly dependent on AppArmor \([Policy Core Reference](https://gitlab.com/apparmor/apparmor/-/wikis/AppArmor_Core_Policy_Reference)\). Thus, we generally do not recommend using this match.

  process:
    matchPaths:
    - path: [absolute executable path]
      ownerOnly: [true|false]            # --> optional
      fromSource:                        # --> optional
      - path: [absolute executable path]
    matchDirectories:
    - dir: [absolute directory path]
      recursive: [true|false]            # --> optional
      ownerOnly: [true|false]            # --> optional
      fromSource:                        # --> optional
      - path: [absolute exectuable path]
    matchPatterns:
    - pattern: [regex pattern]
      ownerOnly: [true|false]            # --> optional

In each match, there are three options.

  • ownerOnly \(static action: allow owner only; otherwise block all\)

    If this is enabled, the owners of the executable\(s\) defined with matchPaths and matchDirectories will be only allowed to execute.

  • recursive

    If this is enabled, the coverage will extend to the subdirectories of the directory defined with matchDirectories.

  • fromSource

    If a path is specified in fromSource, the executable at the path will be allowed/blocked to execute the executables defined with matchPaths or matchDirectories. For better understanding, let us say that an operator defines a policy as follows. Then, /bin/bash will be only allowed (blocked) to execute /bin/sleep. Otherwise, the execution of /bin/sleep will be blocked (allowed).

      process:
        matchPaths:
        - path: /bin/sleep
          fromSource:
          - path: /bin/bash
    
  • File

The file section is quite similar to the process section.

  file:
    matchPaths:
    - path: [absolute file path]
      readOnly: [true|false]             # --> optional
      ownerOnly: [true|false]            # --> optional
      fromSource:                        # --> optional
      - path: [absolute file path]
    matchDirectories:
    - dir: [absolute directory path]
      recursive: [true|false]            # --> optional
      readOnly: [true|false]             # --> optional
      ownerOnly: [true|false]            # --> optional
      fromSource:                        # --> optional
      - path: [absolute file path]
    matchPatterns:
    - pattern: [regex pattern]
      readOnly: [true|false]             # --> optional
      ownerOnly: [true|false]            # --> optional

The only difference between 'process' and 'file' is the readOnly option.

  • readOnly \(static action: allow to read only; otherwise block all\)

    If this is enabled, the read operation will be only allowed, and any other operations \(e.g., write\) will be blocked.

  • Network

In the case of network, there is currently one match type: matchProtocols. You can define specific protocols among TCP, UDP, and ICMP.

  network:
    matchProtocols:
    - protocol: [protocol]               # --> [ TCP | tcp | UDP | udp | ICMP | icmp ]
      fromSource:                        # --> optional
      - path: [absolute file path]
  • Capabilities

In the case of capabilities, there is currently one match type: matchCapabilities. You can define specific capability names to allow or block using matchCapabilities. You can check available capabilities in Capability List.

  capabilities:
    matchCapabilities:
    - capability: [capability name]
      fromSource:                        # --> optional
      - path: [absolute file path]
  • Action

The action could be Allow, Audit, or Block. Security policies would be handled in a blacklist manner or a whitelist manner according to the action. Thus, you need to define the action carefully. You can refer to Consideration in Policy Action for more details. In the case of the Audit action, we can use this action for policy verification before applying a security policy with the Block action.

  action: [Allow|Audit|Block]
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