# CVE-2026-99127: page_pool: keep frag_offset aligned for odd-sized requests - **Severity:** Not scored - **Exploited in the wild:** Not known - **Fix available:** Yes - **Published:** 28 Oct 2026 - **Updated:** 28 Oct 2026 - **Also known as:** AZL-111236, BELL-CVE-2026-99127, DEBIAN-CVE-2026-99127, GHSA-4j2x-r727-jfq6, UBUNTU-CVE-2026-99127 ## What is CVE-2026-99127? CVE-2026-99127 is a vulnerability in Linux, published on 28 Oct 2026. ### Official 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--- ## Which versions are affected by CVE-2026-99127? ## How do I fix CVE-2026-99127? Upgrade to a fixed version. ## Is CVE-2026-99127 being exploited? There is no known exploitation of CVE-2026-99127 in the wild and no public exploit code. ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-99127 and fix it if it is affected. What it is: CVE-2026-99127 is a vulnerability in Linux, published on 28 Oct 2026. Exploitation: There is no known exploitation of CVE-2026-99127 in the wild and no public exploit code. Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page. Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-99127/ (Markdown: https://insights.sbomify.com/CVE-2026-99127/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99127 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99127 - OSV: https://osv.dev/vulnerability/CVE-2026-99127 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-99127/ Summaries are generated and may contain mistakes; the official description above is the record.