CVE-2024-40936 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
cxl/region: Fix memregion leaks in devm_cxl_add_region()
Move the mode verification to __create_region() before allocating the memregion to avoid the memregion leaks.
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Analysis
by VulDB Data Team • 07/12/2024
The vulnerability identified as CVE-2024-40936 resides within the Linux kernel's CXL (Compute Express Link) subsystem, specifically affecting the memory region management functionality. This issue manifests in the cxl/region component where improper handling of memory region allocation leads to resource leaks that can accumulate over time and potentially impact system stability. The vulnerability occurs within the devm_cxl_add_region() function which is responsible for managing CXL memory regions in a device-managed context, where automatic cleanup should occur upon device removal or driver unloading.
The technical flaw stems from the sequence of operations within the CXL memory region creation process. During the execution of devm_cxl_add_region(), the function performs mode verification after memory region allocation has already occurred. This ordering creates a scenario where if mode validation fails, the allocated memory region remains in an unmanaged state, leading to memory leaks. The memory region allocation happens before the mode validation check, meaning that resources are consumed even when the operation ultimately fails due to invalid mode parameters. This represents a classic resource management issue where the allocation phase occurs before proper validation, violating fundamental principles of defensive programming and resource safety.
The operational impact of this vulnerability extends beyond simple memory consumption, as persistent memory leaks can degrade system performance over time and potentially lead to resource exhaustion under sustained load conditions. In environments where CXL devices are actively utilized for high-performance computing or data center applications, these leaks could compound and affect overall system reliability. The vulnerability affects systems running Linux kernels that incorporate the affected CXL subsystem code, particularly those utilizing CXL memory expansion capabilities in server or high-performance computing environments. The leak occurs in a device management context, meaning that each failed region creation attempt contributes to cumulative resource waste that may not be immediately apparent but can accumulate over extended system uptime.
The fix implemented addresses this issue by reordering the operations within the __create_region() function to perform mode verification before memory region allocation occurs. This approach follows established security principles and aligns with CWE-459, which addresses incomplete cleanup issues in software systems. By ensuring that validation occurs prior to resource allocation, the implementation prevents memory leaks from occurring in the event of validation failures. The solution also relates to ATT&CK technique T1490, which involves resource exhaustion through memory leaks, as it prevents the accumulation of unmanaged memory resources that could otherwise be exploited to degrade system performance or availability.
Mitigation strategies for this vulnerability should focus on applying the kernel updates that contain the fix, which typically involves upgrading to a kernel version that includes the corrected code path. System administrators should prioritize patching environments where CXL devices are actively used, particularly in production data center or HPC environments where resource management is critical. Monitoring for memory usage patterns and resource consumption should be implemented to detect potential impacts from this vulnerability in environments where patching may not be immediately possible. Additionally, the fix demonstrates proper defensive programming practices that should be considered when implementing similar resource management functions in other kernel subsystems or device drivers to prevent similar issues from occurring in related components.