Kernel API Modernization: Refactor Deprecated File Operations.

[CyberForgeEx]

Summary

This PR updates the file handling code to use modern kernel APIs by replacing the deprecated filp_close() function with fput() and improving error handling.

Changes Made

• Replaced filp_close(file, 0) with fput(file) - The filp_close() function has been deprecated/removed in newer kernel versions.
• Improved error handling - Changed from NULL check to IS_ERR() for proper error detection with filp_open()
• Maintained backward compatibility - Changes work across multiple kernel versions.

Why This Change is

1. Kernel Compatibility: filp_close() was removed in Linux 4.9+ kernels, causing compilation failures.
2. Memory Safety: fput() properly handles reference counting, preventing use-after-free vulnerabilities.
3. Stability: Using deprecated APIs can cause kernel panics and instability.
4. Future-proofing: Ensures compatibility with current and future kernel versions.

Security Impact

• Improves stability of core file hiding functionality.
• Prevents potential kernel crashes from deprecated API usage.
• Maintains stealth capabilities while using proper kernel APIs.

Files Changed

• rootkit.c - Updated get_fop() function with modern file handling.