Impact of File-Open Hook Points on Backup Ratio in ROFBS on XFS

TL;DR

This study evaluates how different hook points in the Linux file-open process impact the effectiveness of ROFBS in mitigating ransomware damage, highlighting the importance of hook point selection for optimal defense.

Contribution

It systematically compares various hook points in the Linux file-open path, revealing their influence on backup ratio and damage reduction in ROFBS against multiple ransomware families.

Findings

xfs_file_open achieved highest backup ratio for some ransomware

Hook point choice significantly affects damage scale and recoverability

Using xfs_file_open reduces total encrypted files across ransomware types

Abstract

Ransomware continues encrypting files during the delay between attack onset and detection. ROFBS mitigates this problem by backing up pre-modification files in real time upon file-open events. However, because the Linux file-open path traverses multiple kernel functions, it remains unclear how the choice of hook point affects defense effectiveness. In this study, we kept the ROFBS mechanism fixed and changed only the hook points on the Linux file-open path. We compared may_open, inode_permission, do_dentry_open, security_file_open, and xfs_file_open on AlmaLinux with XFS using three ransomware families: AvosLocker, Conti, and IceFire. We used Backup Ratio as the main metric and also compared the number of encrypted files with backups and the total number of encrypted files. The results showed that hook-point selection substantially affected both recoverability and damage scale. For AvosLocker, security_file_open achieved the highest Backup Ratio (82.5%). For Conti and IceFire, xfs_file_open achieved the highest values (100.0% and 63.2%, respectively). Moreover, xfs_file_open minimized the total number of encrypted files for all three ransomware families. These results indicate that, in ROFBS, the layer at which file-open events are observed is a key design factor. In particular, on XFS, hooking the filesystem-specific callback xfs_file_open may be advantageous when the goal is to reduce overall damage.