Bug 2436817 (CVE-2026-23067)

Summary: CVE-2026-23067 kernel: iommu/io-pgtable-arm: fix size_t signedness bug in unmap path
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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OS: Linux   
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An integer signedness bug was found in the Linux kernel's ARM IOMMU page table implementation. The __arm_lpae_unmap() function returns size_t (unsigned) but was returning -ENOENT (negative error code) on error. The negative value becomes a huge positive number (0xFFFFFFFFFFFFFFFE on 64-bit) which propagates through the call chain, causing IOVA address overflow in __iommu_unmap() and triggering a BUG_ON in iommu_pgsize() due to invalid address alignment.
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Description OSIDB Bzimport 2026-02-04 17:04:49 UTC 
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.
Comment 1 TEJ RATHI 2026-02-05 07:03:22 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026020417-CVE-2026-23067-b41f@gregkh/T