CVE-2024-44938 in Linux
Summary
by MITRE • 08/26/2024
In the Linux kernel, the following vulnerability has been resolved:
jfs: Fix shift-out-of-bounds in dbDiscardAG
When searching for the next smaller log2 block, BLKSTOL2() returned 0, causing shift exponent -1 to be negative.
This patch fixes the issue by exiting the loop directly when negative shift is found.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/29/2025
The vulnerability identified as CVE-2024-44938 resides within the Linux kernel's JFS (Journaled File System) implementation, specifically addressing a critical buffer overflow condition in the dbDiscardAG function. This flaw represents a classic case of improper bounds checking and arithmetic operation handling that could potentially lead to system instability or unauthorized access. The issue manifests when the BLKSTOL2() function attempts to calculate logarithmic block sizes during disk space management operations, creating a scenario where negative shift values are processed incorrectly.
The technical root cause stems from the BLKSTOL2() function returning a value of zero when searching for the next smaller log2 block size, which subsequently results in a shift exponent of negative one. This negative shift value creates undefined behavior in the underlying arithmetic operations, potentially allowing attackers to manipulate memory access patterns or cause kernel crashes. The vulnerability specifically affects the JFS filesystem's disk allocation management routines where block size calculations are performed during garbage collection and space reclamation processes. This type of arithmetic error falls under the CWE-191 category of Integer Underflow (Wrap or Wraparound) and demonstrates poor input validation in kernel-level memory management functions.
The operational impact of this vulnerability extends beyond simple system instability, as it could potentially be exploited to achieve privilege escalation or denial of service conditions within systems running affected Linux kernels. When the negative shift operation occurs, it may corrupt kernel memory structures or cause the system to execute unintended code paths, particularly during high I/O load scenarios where JFS filesystem operations are frequent. Attackers could potentially leverage this condition to cause system crashes or, in more sophisticated scenarios, to manipulate kernel memory contents. The vulnerability affects systems using JFS filesystems and is particularly concerning in enterprise environments where robust filesystem stability is critical for data integrity and system availability.
Mitigation strategies for CVE-2024-44938 should prioritize immediate kernel updates from trusted sources to ensure the patched version resolves the problematic shift operation handling in the dbDiscardAG function. System administrators should implement comprehensive monitoring for unusual I/O patterns or kernel panic messages that might indicate exploitation attempts. The fix implemented in the patch directly addresses the issue by exiting the loop immediately when negative shift values are detected, preventing the propagation of invalid arithmetic operations. Organizations should also consider implementing filesystem-specific monitoring tools to track JFS operations and establish baseline performance metrics to detect anomalous behavior that might indicate exploitation attempts. This vulnerability demonstrates the importance of rigorous input validation in kernel space operations and aligns with ATT&CK technique T1068 which involves exploiting privileges through kernel vulnerabilities, making proper patch management and kernel hardening essential defensive measures.