CVE-2024-39482 in Linux
Summary
by MITRE • 07/05/2024
In the Linux kernel, the following vulnerability has been resolved:
bcache: fix variable length array abuse in btree_iter
btree_iter is used in two ways: either allocated on the stack with a fixed size MAX_BSETS, or from a mempool with a dynamic size based on the specific cache set. Previously, the struct had a fixed-length array of size MAX_BSETS which was indexed out-of-bounds for the dynamically-sized iterators, which causes UBSAN to complain.
This patch uses the same approach as in bcachefs's sort_iter and splits the iterator into a btree_iter with a flexible array member and a btree_iter_stack which embeds a btree_iter as well as a fixed-length data array.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/30/2024
The vulnerability identified as CVE-2024-39482 resides within the Linux kernel's bcache subsystem, specifically affecting the btree_iter data structure implementation. This issue represents a classic case of improper memory management and buffer over-read conditions that can lead to undefined behavior and potential system instability. The bcache subsystem serves as a caching layer in the Linux kernel that provides caching functionality for block devices, making it a critical component in storage stack operations. The flaw manifests when the btree_iter structure is used in two distinct allocation contexts, creating a mismatch between the expected fixed-size array and the actual dynamically allocated memory.
The technical root cause of this vulnerability stems from the improper handling of variable-length arrays within the btree_iter structure. Previously, the implementation maintained a fixed-length array of size MAX_BSETS regardless of the actual allocation context. When the iterator was allocated from a mempool with dynamic sizing based on specific cache set requirements, the fixed array size created an out-of-bounds memory access scenario. This condition triggers undefined behavior as the code attempts to access memory locations beyond the allocated array boundaries, leading to potential memory corruption and system crashes. The vulnerability specifically affects the UBSAN (Undefined Behavior Sanitizer) runtime checks, which are designed to detect such memory safety issues during development and testing phases.
The operational impact of CVE-2024-39482 extends beyond simple memory corruption, potentially enabling privilege escalation and system stability issues within kernel space operations. Attackers could exploit this vulnerability to cause denial of service conditions by triggering the out-of-bounds memory access, or in more sophisticated scenarios, potentially leverage the memory corruption for privilege escalation attacks. The bcache subsystem's role in caching block device operations means that exploitation could affect storage performance and data integrity across affected systems. This vulnerability particularly impacts systems utilizing bcache functionality, which includes various enterprise storage configurations and virtualization environments where caching layers are prevalent. The issue demonstrates a fundamental flaw in kernel memory management practices where static array sizing conflicts with dynamic allocation patterns.
The fix implemented for CVE-2024-39482 follows established kernel development patterns by introducing a flexible array member approach similar to that used in bcachefs's sort_iter implementation. This solution separates the btree_iter structure into two distinct components: a btree_iter with a flexible array member and a btree_iter_stack that embeds both the btree_iter and a fixed-length data array. This architectural change aligns with common kernel security practices and follows the principles outlined in the Common Weakness Enumeration (CWE) category CWE-129, which addresses improper validation of array indices. The mitigation strategy also reflects techniques recommended in the ATT&CK framework for kernel-level exploitation prevention, specifically addressing the T1068 technique related to privilege escalation through kernel vulnerabilities. The patch ensures that memory allocation contexts properly match the data structure requirements, eliminating the out-of-bounds access conditions that previously triggered UBSAN warnings and potential system instability.