CVE-2020-36775 in Linux
Summary
by MITRE • 02/26/2024
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to avoid potential deadlock
Using f2fs_trylock_op() in f2fs_write_compressed_pages() to avoid potential deadlock like we did in f2fs_write_single_data_page().
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Analysis
by VulDB Data Team • 11/23/2025
The vulnerability identified as CVE-2020-36775 resides within the Linux kernel's f2fs filesystem implementation, specifically addressing a critical deadlock condition that could compromise system stability and availability. This issue affects the Flash-Friendly File System which is designed for flash storage devices and is widely used in embedded systems, mobile devices, and storage solutions where reliable data persistence is essential. The vulnerability manifests when the f2fs_write_compressed_pages() function attempts to acquire locks without proper coordination, creating a scenario where multiple threads or processes can become indefinitely blocked waiting for resources that will never be released.
The technical flaw stems from inconsistent lock management practices within the f2fs subsystem where the function f2fs_write_compressed_pages() does not employ the same locking mechanism used elsewhere in the codebase. Specifically, the function fails to utilize f2fs_trylock_op() which serves as a protective mechanism against deadlock conditions that was previously implemented and validated in the f2fs_write_single_data_page() function. This inconsistency creates a race condition where the compressed page writing process can enter a deadlock state when multiple threads attempt to access shared resources simultaneously, particularly when dealing with compressed data blocks that require coordinated access to metadata structures.
The operational impact of this vulnerability extends beyond simple system performance degradation to potentially complete system lockups that could require manual intervention or system reboot. When a deadlock occurs during compressed page writing operations, it affects not only the specific filesystem operations but can also propagate to other kernel subsystems that depend on proper lock management. The vulnerability is particularly concerning in environments where high I/O throughput is expected, such as database servers, web applications, or storage appliances, where the likelihood of triggering this condition increases with concurrent write operations. Attackers could potentially exploit this vulnerability by creating specific workloads that force the system into the deadlock state, leading to denial of service conditions that could be difficult to diagnose and recover from.
The fix implemented addresses this vulnerability by standardizing lock acquisition patterns across similar functions within the f2fs subsystem. By incorporating f2fs_trylock_op() into f2fs_write_compressed_pages(), the kernel ensures that the same defensive mechanisms used in f2fs_write_single_data_page() are applied consistently throughout the codebase. This approach aligns with established best practices for concurrent programming and follows the principle of least privilege in resource management. The solution directly addresses the underlying cause of the deadlock condition rather than merely mitigating its symptoms, making it more robust against similar issues that might arise from future modifications to the filesystem code. This fix demonstrates adherence to security engineering principles and follows recommendations from industry standards such as CWE-362 which addresses race conditions and improper locking mechanisms that can lead to deadlock conditions.
From an attack surface perspective, this vulnerability aligns with ATT&CK technique T1499.001 which involves the exploitation of system resource consumption to cause denial of service. The fix ensures that the filesystem maintains proper lock ordering and prevents the specific deadlock scenario that could be triggered through normal filesystem operations. The implementation follows established patterns for lock management in kernel space and maintains compatibility with existing filesystem operations while providing the necessary protections against resource contention. This vulnerability represents a classic example of how seemingly minor inconsistencies in code implementation can lead to significant system stability issues, particularly in high-performance storage subsystems where proper locking is critical for maintaining data integrity and system availability. The resolution ensures that compressed data operations maintain the same level of reliability and concurrency control as other filesystem operations within the f2fs implementation.