CVE-2023-52810 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
fs/jfs: Add check for negative db_l2nbperpage
l2nbperpage is log2(number of blks per page), and the minimum legal value should be 0, not negative.
In the case of l2nbperpage being negative, an error will occur when subsequently used as shift exponent.
Syzbot reported this bug:
UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:799:12 shift exponent -16777216 is negative
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Analysis
by VulDB Data Team • 05/21/2024
The vulnerability CVE-2023-52810 represents a critical integer underflow condition within the Linux kernel's JFS (Journaled File System) implementation that can lead to undefined behavior and potential system instability. This flaw specifically resides in the fs/jfs directory where the kernel's file system handling code processes block allocation parameters. The issue manifests when the db_l2nbperpage parameter, which represents the base-2 logarithm of the number of blocks per page, receives a negative value during processing. This parameter should logically never be negative as it represents a count of blocks per page, which by definition must be a positive integer or zero. The vulnerability was identified through automated fuzzing analysis conducted by syzbot, which detected a userspace address sanitizer (UBSAN) error indicating a shift-out-of-bounds condition. The error message specifically indicates that a shift exponent of -16777216 was encountered, which clearly demonstrates the negative value being passed where only non-negative values are valid for bit shift operations.
The technical implementation flaw occurs in the fs/jfs/jfs_dmap.c file at line 799 where the kernel performs bit shift operations using the db_l2nbperpage parameter as the shift exponent. When this parameter becomes negative due to improper validation or calculation errors, the subsequent bit shifting operation fails catastrophically because bit shift operations in most computing architectures require non-negative integer values. This particular implementation violates the fundamental mathematical requirement that shift operations must operate on non-negative integers, as negative shift values would result in undefined behavior or hardware-level exceptions. The vulnerability directly relates to CWE-129, which addresses improper validation of array indices and other constructs that could lead to out-of-bounds memory access. The JFS implementation fails to properly validate that the calculated logarithmic block count parameter remains within acceptable bounds, creating a pathway for malicious input or calculation errors to propagate into system-level failures.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a potential vector for denial of service attacks and could theoretically be exploited to gain unauthorized access to system resources. When the kernel encounters a negative shift exponent, the system may experience immediate crashes or more subtle memory corruption that could allow for privilege escalation or data corruption. The JFS file system, while not as widely used as ext4 or XFS, remains present in certain embedded systems and specialized environments where reliable file system operations are critical. Attackers could potentially trigger this condition through malformed file system operations or by manipulating system parameters that influence block allocation calculations. The vulnerability's exploitation potential aligns with ATT&CK technique T1499.001, which involves network denial of service attacks, and T1068, which covers local privilege escalation through system-level vulnerabilities. The fact that this vulnerability was discovered through automated fuzzing tools like syzbot indicates that it represents a significant security gap that could be exploited by attackers with sufficient technical knowledge.
Mitigation strategies for CVE-2023-52810 should focus on implementing robust input validation and parameter checking within the JFS subsystem. The most effective approach involves adding explicit bounds checking for the db_l2nbperpage parameter before it is used in any bit shift operations, ensuring that negative values are rejected and appropriate error handling is implemented. Kernel developers should implement defensive programming practices that validate all parameters against their expected ranges, particularly those used in arithmetic operations that have strict mathematical requirements. The fix should include adding conditional checks that verify the calculated l2nbperpage value is greater than or equal to zero before proceeding with any bit manipulation operations. Additionally, system administrators should ensure that all kernel updates are applied promptly, as this vulnerability affects the core kernel file system handling code that is critical to system stability. Monitoring for unusual system behavior or kernel panic messages that might indicate this vulnerability being exploited should be implemented alongside traditional security measures. The fix should also consider implementing more comprehensive error logging to track when invalid parameters are encountered, which can help identify potential attack patterns or system misconfigurations that might lead to similar issues in other kernel subsystems.