main(cherry): restrict calls to dns_servers from agent-uid

[h0x0er]

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[step-security-bot]

Please find StepSecurity AI-CodeWise code comments below.

Code Comments

.gitignore

• [Low]Ensure consistent newline at end of file
  The patch adds lines but lacks a newline at the end of the file. According to POSIX standards and common best practices (e.g., GNU Coding Standards), text files should end with a newline character to prevent issues with some tools and to support proper file concatenation. Add a newline character at the end of the file after the last line (local) to ensure compliance with POSIX and common best practices.
• [Low]Use explicit patterns in .gitignore to avoid unintended exclusions
  The patch adds directories 'dist' and 'local' to the ignore list without specifying if these are directories explicitly. Defining them with trailing slashes (e.g., 'dist/') clarifies intent as directory ignores. This is recommended in the official Git documentation to avoid confusion and unintended ignore behavior. Modify the entries to include trailing slashes for directories as follows: 'dist/' and 'local/'.

firewall.go

• [High]Handle privilege separation and ensure appropriate permissions when using os.Getuid() in firewall rule additions
  The use of os.Getuid() in applying UID filtering in firewall rules assumes the process runs with sufficient privileges and the UID corresponds to the agent needing access. According to 'Principle of Least Privilege' (NIST SP 800-53), the process should ensure minimal privilege. Failure to verify permissions and context can cause incorrect firewall behavior or security gaps. Add a check to confirm the process has the required permissions to manipulate iptables rules and consider making the UID filter configurable instead of hardcoding os.Getuid(). Also, handle the security implications if the UID changes or the process is run by a different user.
• [High]Validate input parameters like dnsServers and ensure no malicious data can result in malformed firewall rules
  The dnsServers slice is iterated to append firewall rules. Unvalidated input used in system command arguments can lead to injection or malformed iptables rules. OWASP Secure Coding Guidelines highlight the importance of input validation when executing system-level commands or configurations. Add validation logic to verify dnsServers values conform to expected IP address format before they are used in rule addition. Reject or sanitize invalid entries.
• [Medium]Consistently handle errors with context to ease debugging and operational troubleshooting
  In the new block of code handling UID-filtered rules for DNS servers, errors are wrapped with context, which is good. However, the original dnsServer rules had the same error handling removed, which could reduce overall consistency and robustness in error reporting. Consistent error wrapping and logging are recommended per Go’s error handling best practices (Go Blog). Ensure all ipt.Append calls have error wrapping with meaningful messages. Avoid removing existing error handling when refactoring.
• [Medium]Avoid redundant firewall rules by checking existence before appending rules
  Appending iptables rules without first checking if they already exist can cause duplicate entries and degrade firewall performance. The iptables best practices suggest checking existing rules before appending to prevent duplication. Use ipt.Exists method or equivalent to check if a rule already exists before appending it to the chain.
• [Medium]Refactor long functions by extracting the new UID-based DNS rules logic into a separate helper function
  The new code adding UID-based firewall rules is embedded inside a large function. Clean code principles recommend modularization to improve readability, maintainability, and testability (Robert C. Martin). Extract the addition of UID filtered DNS server rules to a dedicated function with clear parameters.
• [Low]Use constants or configuration for protocol and port strings instead of hardcoded literals
  Hardcoded protocol ('tcp') and port ('443') strings reduce flexibility and increase risk of typos. The Go standard library recommends using constants or configuration for repeated string values to enhance maintainability. Define protocol tcp and port 443 as constants or configurable variables at the package level.
• [Low]Add comments clarifying the UID filtering applies only to the OUTPUT chain and the rationale behind the choice
  Clear comments help maintainers understand design decisions and avoid misapplication of rules. This aligns with best practice guidance from Clean Code (Robert C. Martin). Expand the existing comment to explain why UID filtering is limited to OUTPUT chain and the security implications.
• [Low]Ensure imported packages are used and clean up any redundant imports
  The addition of 'os' package is necessary for os.Getuid(). Ensure no unused imports remain to keep code clean, per Go import guidelines. Verify that all imports are used and remove any redundant ones.

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