{"id":"CVE-2026-31429","state":"PUBLISHED","title":"net: skb: fix cross-cache free of KFENCE-allocated skb head","description":"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() -> 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.","publishedAt":"2026-04-20T09:43:03.194Z","updatedAt":"2026-05-11T22:08:32.321Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"128b03ccb2582a643983a48a37fda58df80edbde","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"60313768a8edc7094435975587c00c2d7b834083","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"2d64618ea846d8d033477311f805ca487d6a6696","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"474e00b935db250cac320d10c1d3cf4e44b46721","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/skbuff.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.3","versionType":"semver"},{"version":"6.6.136","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.82","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.23","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.13","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/skbuff.c"]}],"references":["https://git.kernel.org/stable/c/128b03ccb2582a643983a48a37fda58df80edbde","https://git.kernel.org/stable/c/60313768a8edc7094435975587c00c2d7b834083","https://git.kernel.org/stable/c/2d64618ea846d8d033477311f805ca487d6a6696","https://git.kernel.org/stable/c/474e00b935db250cac320d10c1d3cf4e44b46721","https://git.kernel.org/stable/c/0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31429.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31429","state":"PUBLISHED","datePublished":"2026-04-20T09:43:03.194Z","dateUpdated":"2026-05-11T22:08:32.321Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.089Z"},"containers":{"cna":{"title":"net: skb: fix cross-cache free of KFENCE-allocated skb head","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() -> 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"128b03ccb2582a643983a48a37fda58df80edbde","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"60313768a8edc7094435975587c00c2d7b834083","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"2d64618ea846d8d033477311f805ca487d6a6696","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"474e00b935db250cac320d10c1d3cf4e44b46721","versionType":"git"},{"version":"bf9f1baa279f0758dc2297080360c5a616843927","status":"affected","lessThan":"0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/skbuff.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.3","versionType":"semver"},{"version":"6.6.136","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.82","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.23","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"6.19.13","status":"unaffected","lessThanOrEqual":"6.19.*","versionType":"semver"},{"version":"7.0","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/core/skbuff.c"]}],"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"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T22:08:32.321Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3","versionEndExcluding":"6.6.136"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3","versionEndExcluding":"6.12.82"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3","versionEndExcluding":"6.18.23"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3","versionEndExcluding":"6.19.13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3","versionEndExcluding":"7.0"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}