CVE-2026-31429 (GCVE-0-2026-31429)

Vulnerability from cvelistv5 – Published: 2026-04-20 09:43 – Updated: 2026-05-11 22:08
VLAI?
Title
net: skb: fix cross-cache free of KFENCE-allocated skb head
Summary
In 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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 128b03ccb2582a643983a48a37fda58df80edbde (git)
Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 60313768a8edc7094435975587c00c2d7b834083 (git)
Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 2d64618ea846d8d033477311f805ca487d6a6696 (git)
Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 474e00b935db250cac320d10c1d3cf4e44b46721 (git)
Affected: bf9f1baa279f0758dc2297080360c5a616843927 , < 0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516 (git)
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    Linux Linux Affected: 6.3
Unaffected: 0 , < 6.3 (semver)
Unaffected: 6.6.136 , ≤ 6.6.* (semver)
Unaffected: 6.12.82 , ≤ 6.12.* (semver)
Unaffected: 6.18.23 , ≤ 6.18.* (semver)
Unaffected: 6.19.13 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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{
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              "version": "7.0",
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      ],
      "cpeApplicability": [
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          "nodes": [
            {
              "cpeMatch": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skb: fix cross-cache free of KFENCE-allocated skb head\n\nSKB_SMALL_HEAD_CACHE_SIZE is intentionally set to a non-power-of-2\nvalue (e.g. 704 on x86_64) to avoid collisions with generic kmalloc\nbucket sizes. This ensures that skb_kfree_head() can reliably use\nskb_end_offset to distinguish skb heads allocated from\nskb_small_head_cache vs. generic kmalloc caches.\n\nHowever, when KFENCE is enabled, kfence_ksize() returns the exact\nrequested allocation size instead of the slab bucket size. If a caller\n(e.g. bpf_test_init) allocates skb head data via kzalloc() and the\nrequested size happens to equal SKB_SMALL_HEAD_CACHE_SIZE, then\nslab_build_skb() -\u003e ksize() returns that exact value. After subtracting\nskb_shared_info overhead, skb_end_offset ends up matching\nSKB_SMALL_HEAD_HEADROOM, causing skb_kfree_head() to incorrectly free\nthe object to skb_small_head_cache instead of back to the original\nkmalloc cache, resulting in a slab cross-cache free:\n\n  kmem_cache_free(skbuff_small_head): Wrong slab cache. Expected\n  skbuff_small_head but got kmalloc-1k\n\nFix this by always calling kfree(head) in skb_kfree_head(). This keeps\nthe free path generic and avoids allocator-specific misclassification\nfor KFENCE objects."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-11T22:08:32.321Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/128b03ccb2582a643983a48a37fda58df80edbde"
        },
        {
          "url": "https://git.kernel.org/stable/c/60313768a8edc7094435975587c00c2d7b834083"
        },
        {
          "url": "https://git.kernel.org/stable/c/2d64618ea846d8d033477311f805ca487d6a6696"
        },
        {
          "url": "https://git.kernel.org/stable/c/474e00b935db250cac320d10c1d3cf4e44b46721"
        },
        {
          "url": "https://git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516"
        }
      ],
      "title": "net: skb: fix cross-cache free of KFENCE-allocated skb head",
      "x_generator": {
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      }
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31429",
    "datePublished": "2026-04-20T09:43:03.194Z",
    "dateReserved": "2026-03-09T15:48:24.089Z",
    "dateUpdated": "2026-05-11T22:08:32.321Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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