CVE-2023-52497 in Linux
Summary
by MITRE • 03/01/2024
In the Linux kernel, the following vulnerability has been resolved:
erofs: fix lz4 inplace decompression
Currently EROFS can map another compressed buffer for inplace decompression, that was used to handle the cases that some pages of compressed data are actually not in-place I/O.
However, like most simple LZ77 algorithms, LZ4 expects the compressed data is arranged at the end of the decompressed buffer and it explicitly uses memmove() to handle overlapping: __________________________________________________________ |_ direction of decompression --> ____ |_ compressed data _|
Although EROFS arranges compressed data like this, it typically maps two individual virtual buffers so the relative order is uncertain. Previously, it was hardly observed since LZ4 only uses memmove() for short overlapped literals and x86/arm64 memmove implementations seem to completely cover it up and they don't have this issue. Juhyung reported that EROFS data corruption can be found on a new Intel x86 processor. After some analysis, it seems that recent x86 processors with the new FSRM feature expose this issue with "rep movsb".
Let's strictly use the decompressed buffer for lz4 inplace decompression for now. Later, as an useful improvement, we could try to tie up these two buffers together in the correct order.
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Analysis
by VulDB Data Team • 01/09/2025
The vulnerability described in CVE-2023-52497 affects the Linux kernel's EROFS (Enhanced Read-Only File System) implementation, specifically concerning LZ4 compression handling during inplace decompression operations. This issue represents a critical flaw in how compressed data is managed during decompression processes, potentially leading to data corruption and system instability. The vulnerability manifests when EROFS attempts to perform inplace decompression using LZ4 compression algorithms, which require specific memory layout arrangements for proper operation.
The technical root cause of this vulnerability stems from how EROFS manages memory buffers during LZ4 decompression operations. The system maps two separate virtual buffers for compressed data handling, which creates uncertainty in the relative ordering of data within memory. While most simple LZ77 algorithms like LZ4 expect compressed data to be arranged at the end of the decompressed buffer, this expectation is violated when multiple virtual buffers are used. The LZ4 algorithm explicitly employs memmove() operations to handle overlapping data, but the inconsistent buffer ordering in EROFS creates conditions where these memory operations fail or produce incorrect results.
The operational impact of this vulnerability becomes particularly pronounced on newer x86 processors that feature the FSRM (Fast Short Repetition Move) instruction set. This hardware feature exposes the underlying memory management issue through "rep movsb" operations, which are more sensitive to buffer ordering than traditional memory operations. The vulnerability was first identified by Juhyung who observed data corruption patterns specifically on Intel x86 processors with newer architectures, demonstrating that the issue is not merely theoretical but has real-world implications for system reliability.
This vulnerability aligns with CWE-129, which addresses issues related to insufficient input validation, and CWE-787, concerning out-of-bounds writes. From an ATT&CK framework perspective, this represents a potential privilege escalation vector through file system corruption, falling under the T1068 technique for exploit development. The issue is particularly concerning because it operates at the kernel level, potentially allowing attackers to manipulate file system data integrity or cause system crashes. The fact that the problem manifests differently across processor architectures also suggests potential for targeted exploitation based on hardware capabilities.
The recommended mitigation strategy involves strictly using the decompressed buffer for LZ4 inplace decompression operations, eliminating the problematic dual-buffer approach that causes the ordering issues. This solution aligns with the principle of least privilege and secure coding practices by reducing complexity in memory management operations. Future improvements could involve more sophisticated buffer management techniques that properly tie together the compressed and decompressed buffers in the correct order, potentially implementing better memory layout strategies that comply with LZ4's specific requirements. Organizations should prioritize kernel updates that include this fix, particularly those running EROFS on systems with newer x86 processors that support the FSRM feature.