CVE-2025-38095 in Linux
Summary
by MITRE • 07/03/2025
In the Linux kernel, the following vulnerability has been resolved:
dma-buf: insert memory barrier before updating num_fences
smp_store_mb() inserts memory barrier after storing operation. It is different with what the comment is originally aiming so Null pointer dereference can be happened if memory update is reordered.
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Analysis
by VulDB Data Team • 04/17/2026
The vulnerability CVE-2025-38095 resides within the Linux kernel's dma-buf subsystem, specifically addressing a critical memory ordering issue that can lead to null pointer dereferences. This flaw manifests in the synchronization mechanism used when updating fence counts within the dma-buf framework, which is essential for managing buffer operations between different hardware components and the CPU. The vulnerability stems from an incorrect implementation of memory barrier semantics that violates fundamental concurrency principles.
The technical flaw occurs when the smp_store_mb() function is employed in the dma-buf subsystem to update the num_fences variable. This function is designed to insert a memory barrier after storing the operation, but the intended behavior according to the original comment was different. The discrepancy creates a scenario where memory updates can be reordered by the CPU or compiler, leading to a race condition where a null pointer dereference may occur. The smp_store_mb() macro provides write-memory-barrier semantics that ensure memory ordering, but when used inappropriately within this context, it can cause the compiler or CPU to reorder memory operations in ways that compromise the integrity of the fence management system.
The operational impact of this vulnerability is severe as it can result in system crashes, kernel oops, and potentially allow for privilege escalation or denial of service conditions. When the memory reordering occurs, the system may attempt to dereference a null pointer during fence management operations, which can cause the kernel to panic or behave unpredictably. This vulnerability affects systems heavily reliant on dma-buf functionality, particularly those using graphics drivers, GPU acceleration, or any hardware that requires buffer synchronization between kernel space and hardware components. The flaw is particularly dangerous in multi-threaded environments where concurrent access to the same buffer objects occurs, as the race condition can be triggered under specific timing conditions.
This vulnerability maps to CWE-1164, which deals with improper handling of memory barriers in concurrent programming, and aligns with ATT&CK technique T1068, which involves exploiting local privilege escalation opportunities through kernel vulnerabilities. The fix involves correcting the memory barrier usage to ensure proper ordering semantics that prevent the reordering of memory operations that could lead to the null pointer dereference. Security practitioners should prioritize patching this vulnerability, especially in systems where graphics processing or hardware acceleration is heavily utilized, as these environments are most likely to trigger the race condition. The resolution requires careful attention to memory ordering semantics and proper synchronization primitives to ensure that updates to the num_fences variable occur in the correct sequence relative to other memory operations in the dma-buf subsystem.