CVE-2026-23067 in Linux
Summary
by MITRE • 02/04/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/io-pgtable-arm: fix size_t signedness bug in unmap path
__arm_lpae_unmap() returns size_t but was returning -ENOENT (negative error code) when encountering an unmapped PTE. Since size_t is unsigned, -ENOENT (typically -2) becomes a huge positive value (0xFFFFFFFFFFFFFFFE on 64-bit systems).
This corrupted value propagates through the call chain: __arm_lpae_unmap() returns -ENOENT as size_t -> arm_lpae_unmap_pages() returns it -> __iommu_unmap() adds it to iova address -> iommu_pgsize() triggers BUG_ON due to corrupted iova
This can cause IOVA address overflow in __iommu_unmap() loop and trigger BUG_ON in iommu_pgsize() from invalid address alignment.
Fix by returning 0 instead of -ENOENT. The WARN_ON already signals the error condition, and returning 0 (meaning "nothing unmapped") is the correct semantic for size_t return type. This matches the behavior of other io-pgtable implementations (io-pgtable-arm-v7s, io-pgtable-dart) which return 0 on error conditions.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability described in CVE-2026-23067 represents a critical signedness mismatch issue within the Linux kernel's IOMMU subsystem, specifically affecting the arm64 architecture's page table management implementation. This flaw exists in the iommu/io-pgtable-arm component where the function __arm_lpae_unmap() is designed to return a size_t type value representing the number of pages unmapped. However, when encountering unmapped Page Table Entries (PTEs), the function incorrectly returns the negative error code -ENOENT, which is typically -2, instead of the appropriate zero value for successful operations. The fundamental problem arises from the semantic mismatch between the signed error code and the unsigned size_t return type, creating a scenario where negative values are interpreted as extremely large positive integers due to unsigned integer overflow behavior.
The operational impact of this vulnerability extends beyond simple arithmetic corruption to potentially cause system instability and security implications within virtualized environments. When the corrupted size_t value propagates through the call chain from __arm_lpae_unmap() through arm_lpae_unmap_pages() to __iommu_unmap(), it creates an IOVA address overflow condition that ultimately triggers a BUG_ON assertion in the iommu_pgsize() function. This occurs because the corrupted IOVA value, derived from the erroneous size_t return, leads to invalid address alignment that violates internal kernel assumptions about memory management boundaries. The vulnerability is particularly concerning in environments utilizing IOMMU for device isolation and memory protection, as it could potentially allow for memory corruption that might be exploited to bypass security boundaries or cause system crashes.
The fix implemented addresses the root cause by modifying the __arm_lpae_unmap() function to return zero instead of -ENOENT when encountering unmapped PTEs, aligning with established patterns used by other IOMMU implementations within the Linux kernel such as io-pgtable-arm-v7s and io-pgtable-dart. This approach maintains the existing error signaling through WARN_ON macros while ensuring semantic correctness for the size_t return type, as returning zero correctly indicates "no pages unmapped" rather than an error condition. The solution follows the principle of least surprise and maintains consistency with other kernel subsystems where successful operations that result in no actual work performed return zero values. This fix directly addresses CWE-194, which deals with unexpected signedness in arithmetic operations, and aligns with ATT&CK technique T1068 by potentially enabling privilege escalation through memory corruption vulnerabilities in kernel memory management subsystems. The remediation ensures that IOMMU operations maintain proper memory boundaries and prevent overflow conditions that could lead to system instability or security breaches in virtualized computing environments where IOMMU protection is critical for device isolation and memory security.