From: Jiayuan Chen Date: Fri, 3 Apr 2026 01:45:12 +0000 (+0800) Subject: net: skb: fix cross-cache free of KFENCE-allocated skb head X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0f42e3f4fe2a58394e37241d02d9ca6ab7b7d516;p=thirdparty%2Fkernel%2Flinux.git 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. Fixes: bf9f1baa279f ("net: add dedicated kmem_cache for typical/small skb->head") Reported-by: Antonius Closes: https://lore.kernel.org/netdev/CAK8a0jxC5L5N7hq-DT2_NhUyjBxrPocoiDazzsBk4TGgT1r4-A@mail.gmail.com/ Signed-off-by: Jiayuan Chen Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20260403014517.142550-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski --- diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 0e217041958a..43ee86dcf2ea 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1083,10 +1083,7 @@ static int skb_pp_frag_ref(struct sk_buff *skb) static void skb_kfree_head(void *head, unsigned int end_offset) { - if (end_offset == SKB_SMALL_HEAD_HEADROOM) - kmem_cache_free(net_hotdata.skb_small_head_cache, head); - else - kfree(head); + kfree(head); } static void skb_free_head(struct sk_buff *skb)