net: skb: fix cross-cache free of KFENCE-allocated skb head

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Summary

CVECVE-2026-31429
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-20 10:16:16 UTC
Updated2026-05-20 19:23:01 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: skb: fix cross-cache free of KFENCE-allocated skb head SKB_SMALL_HEAD_CACHE_SIZE is intentionally set to a non-power-of-2 value (e.g. 704 on x86_64) to avoid collisions with generic kmalloc bucket sizes. This ensures that skb_kfree_head() can reliably use skb_end_offset to distinguish skb heads allocated from skb_small_head_cache vs. generic kmalloc caches. However, when KFENCE is enabled, kfence_ksize() returns the exact requested allocation size instead of the slab bucket size. If a caller (e.g. bpf_test_init) allocates skb head data via kzalloc() and the requested size happens to equal SKB_SMALL_HEAD_CACHE_SIZE, then slab_build_skb() -> ksize() returns that exact value. After subtracting skb_shared_info overhead, skb_end_offset ends up matching SKB_SMALL_HEAD_HEADROOM, causing skb_kfree_head() to incorrectly free the object to skb_small_head_cache instead of back to the original kmalloc cache, resulting in a slab cross-cache free: kmem_cache_free(skbuff_small_head): Wrong slab cache. Expected skbuff_small_head but got kmalloc-1k Fix this by always calling kfree(head) in skb_kfree_head(). This keeps the free path generic and avoids allocator-specific misclassification for KFENCE objects.

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.000230000 probability, percentile 0.064070000 (date 2026-04-27)

Problem Types: CWE-401

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected bf9f1baa279f0758dc2297080360c5a616843927 128b03ccb2582a643983a48a37fda58df80edbde git Not specified
CNA Linux Linux affected bf9f1baa279f0758dc2297080360c5a616843927 60313768a8edc7094435975587c00c2d7b834083 git Not specified
CNA Linux Linux affected bf9f1baa279f0758dc2297080360c5a616843927 2d64618ea846d8d033477311f805ca487d6a6696 git Not specified
CNA Linux Linux affected bf9f1baa279f0758dc2297080360c5a616843927 474e00b935db250cac320d10c1d3cf4e44b46721 git Not specified
CNA Linux Linux affected bf9f1baa279f0758dc2297080360c5a616843927 0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 git Not specified
CNA Linux Linux affected 6.3 Not specified
CNA Linux Linux unaffected 6.3 semver Not specified
CNA Linux Linux unaffected 6.6.136 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.82 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.23 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.13 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/474e00b935db250cac320d10c1d3cf4e44b46721 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/60313768a8edc7094435975587c00c2d7b834083 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/128b03ccb2582a643983a48a37fda58df80edbde 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/2d64618ea846d8d033477311f805ca487d6a6696 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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