CVE-2023-52804 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
fs/jfs: Add validity check for db_maxag and db_agpref
Both db_maxag and db_agpref are used as the index of the db_agfree array, but there is currently no validity check for db_maxag and db_agpref, which can lead to errors.
The following is related bug reported by Syzbot:
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:639:20 index 7936 is out of range for type 'atomic_t[128]'
Add checking that the values of db_maxag and db_agpref are valid indexes for the db_agfree array.
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability identified as CVE-2023-52804 affects the Linux kernel's JFS (Journaled File System) implementation and represents a critical array index out-of-bounds access flaw that could potentially lead to system instability or privilege escalation. This vulnerability specifically impacts the fs/jfs subsystem where the db_maxag and db_agpref parameters are utilized as array indices for accessing the db_agfree array. The absence of proper validation checks for these parameters creates a scenario where maliciously crafted input could cause the kernel to access memory outside the bounds of the allocated array, resulting in undefined behavior and potential system crashes.
The technical flaw manifests when the kernel processes filesystem operations that involve these parameters without first validating their range against the actual size of the db_agfree array. According to the UBSAN (Undefined Behavior Sanitizer) report, the specific error occurs at line 639 in fs/jfs/jfs_dmap.c where an index value of 7936 exceeds the valid range for a type 'atomic_t[128]' array, indicating that the maximum allowed index should be 127 but the code attempts to access index 7936. This represents a classic buffer overflow condition that violates the fundamental principle of array bounds checking and falls under the CWE-129 vulnerability category, which addresses insufficient bounds checking for array data structures.
The operational impact of this vulnerability extends beyond simple system crashes as it represents a potential attack vector for privilege escalation within the kernel space. When an attacker can manipulate the db_maxag and db_agpref parameters to exceed array bounds, they may be able to trigger memory corruption that could be exploited to execute arbitrary code with kernel privileges. The vulnerability is particularly concerning because it occurs in the file system layer where kernel memory management is critical, and such flaws can provide attackers with pathways to compromise the entire system. The ATT&CK framework would categorize this under privilege escalation techniques, specifically targeting kernel vulnerabilities through memory corruption methods that could enable persistent access to compromised systems.
Mitigation strategies for CVE-2023-52804 should focus on implementing proper parameter validation before array access operations. The fix requires adding explicit checks to ensure that db_maxag and db_agpref values fall within the valid range of 0 to 127 for the db_agfree array. This approach aligns with the principle of defensive programming and input validation that is fundamental to secure coding practices. System administrators should prioritize applying the kernel patches that address this vulnerability, as the fix involves straightforward bounds checking that does not introduce significant performance overhead while providing robust protection against the array index out-of-bounds condition. The vulnerability also highlights the importance of automated testing tools like Syzbot in identifying kernel-level memory corruption issues that could otherwise remain undetected until exploited in real-world scenarios.