CVE-2026-72095 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
dma-fence: Make dma_fence_dedup_array() robust against 0-count input
dma_fence_dedup_array() returns 1 when called with num_fences == 0: the for-loop body never executes, j stays at 0, and the final `return ++j` yields 1. This contradicts both the kernel-doc ("Return: Number of unique fences remaining in the array") and the natural expectation that 0 input gives 0 output.
The caller __dma_fence_unwrap_merge() bails out via the `if (count == 0 || count == 1)` fast path and so is save.
But amdgpu_userq_wait_*() could reach the dedup call with a zero local count and dereference an uninitialized fence slot in the array.
Make the contract match the documentation by returning 0 early. This also skips an unnecessary sort() call on an empty array.
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Analysis
by VulDB Data Team • 08/15/2026
This vulnerability exists within the linux kernel's dma-fence subsystem where the dma_fence_dedup_array() function fails to properly handle edge cases involving zero-length input arrays. The flaw manifests when the function receives num_fences == 0 as input, causing it to return 1 instead of the expected 0, creating a contract violation between implementation and documentation. According to kernel documentation, this function should return the number of unique fences remaining in the array, making a return value of 1 for zero input fundamentally inconsistent with its stated purpose. The technical execution path involves a for-loop that never executes when num_fences equals zero, leaving the variable j at value 0, and subsequently returning ++j which yields 1 rather than 0 as would be logically expected.
The operational impact of this vulnerability extends beyond simple documentation mismatch to potential runtime errors in downstream consumers of this function. While the primary caller _dma_fence_unwrap_merge() correctly handles zero input through an early exit condition with if (count == 0 || count == 1), other subsystems like amdgpu_userq_wait* functions can reach the problematic code path with zero local counts, leading to dereference of uninitialized fence slots in arrays. This creates potential memory access violations and undefined behavior that could compromise system stability or provide attack vectors for privilege escalation. The vulnerability specifically affects graphics processing units utilizing amd gpu drivers where user queue wait operations might pass empty fence arrays to the deduplication routine.
The fix implemented addresses this issue by adding an early return of 0 when num_fences equals zero, ensuring the function contract aligns with its documented behavior and expectations. This change not only corrects the logical inconsistency but also provides performance optimization by avoiding unnecessary sort() operations on empty arrays. From a cybersecurity perspective, this represents a classic case of input validation failure that could lead to information disclosure through memory corruption or system instability. The vulnerability demonstrates poor adherence to defensive programming principles where edge cases are not properly considered in function implementations. This aligns with common weakness patterns identified in CWE-252, which covers unchecked return values and incorrect assumptions about function behavior under boundary conditions. The fix follows established security practices by implementing proper input validation and ensuring consistent behavior across all code paths. From an attack surface perspective, this vulnerability could be leveraged by malicious actors to cause denial of service or potentially gain elevated privileges through memory corruption in graphics driver contexts where the affected code path is executed. The resolution effectively mitigates these risks by establishing clear preconditions for the function's operation and ensuring predictable behavior regardless of input parameters.
The fix specifically addresses the root cause by implementing early validation that prevents execution of the problematic loop structure when zero-length arrays are presented, thereby eliminating both the incorrect return value and the unnecessary computational overhead. This approach aligns with established security engineering principles that emphasize robust input validation and clear error handling mechanisms within kernel subsystems where reliability and predictability are paramount for system integrity.