fix: secure temp file handling in diff.bash to prevent symlink attacks

[anandppatil]

Title: fix: use secure temporary directory in diff.bash to prevent symlink attacks

Description:

This PR addresses a CWE-59 / CWE-377 vulnerability in private/tools/diff.bash. The script was writing to a predictable, world-writable path (/tmp/cfg.json), which allows a local attacker to perform an arbitrary file overwrite via a symlink.

Changes:

Replaced hardcoded /tmp paths with a secure, randomized temporary directory using mktemp -d.

Added a trap mechanism to ensure all temporary artifacts (config, certificates, storage) are automatically cleaned up on exit.

Restricted permissions on the temporary directory to 0700 to prevent unauthorized local access.

Impact: Prevents a local privilege escalation (LPE) primitive where an attacker could hijack the script to overwrite sensitive system files or another user's configuration.

This issue was previously reported to the Google OSS VRP (Issue 471071574), where the Bug Hunter Team suggested public disclosure and a public fix.

[google-cla]

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[gemini-code-assist]

Summary of Changes

Hello @anandppatil, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the security of the diff.bash script by overhauling its temporary file handling. The changes eliminate a critical vulnerability that could have allowed local attackers to exploit predictable temporary file paths, thereby preventing potential local privilege escalation through symlink attacks and arbitrary file overwrites.

Highlights

• Secure Temporary Directory: Implemented a secure, randomized temporary directory using mktemp -d with restricted permissions (0700) to prevent unauthorized access and predictable paths.
• Automated Cleanup: Added a trap mechanism to ensure all temporary artifacts, including configuration files, certificates, and storage directories, are automatically cleaned up upon script exit.
• Vulnerability Mitigation: Addressed a CWE-59 / CWE-377 vulnerability by replacing hardcoded /tmp paths with the newly created secure temporary directory, preventing symlink attacks and arbitrary file overwrites.

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[gemini-code-assist]

Code Review

This pull request effectively addresses a security vulnerability (CWE-59) by replacing insecure temporary file handling with the use of a secure, temporary directory created via mktemp -d. The changes are well-implemented, including the addition of a trap for cleanup and restricting directory permissions. Furthermore, the pull request includes several valuable improvements to the script's robustness, such as better variable quoting, safer conditional checks, and improved readability. The fix is comprehensive and significantly improves the security posture of the script. I have one minor suggestion to further enhance the robustness of the cleanup mechanism.

[anandppatil]

The cla/google check is now passing, and I have addressed the automated feedback by adding a robustness guard to the cleanup mechanism in commit 47ffb18.

This PR is now ready for a final human review and for the CI workflows to be triggered. Thank you for your patience!