{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "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  \tsize = 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-\u003efrag_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:  \tsize = min_t(u32, len, PAGE_SIZE); \ttruesize = size; \tpage = page_pool_dev_alloc(pool, \u0026page_off, \u0026truesize);  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-\u003ehead, and skb_shinfo(skb) == skb-\u003ehead + skb-\u003eend is misaligned with it.  skb_shinfo()-\u003edataref 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:    \u003cIRQ\u003e    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 \u0026 7:   0: 17035    5: 1    7: 1   frag_offset \u0026 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 -\u003e 0xffff8f4c53a9a9c4 (\u00267=4)   head 0xffff8f4d6a8a42c0 -\u003e 0xffff8f4c4f7b7a45 (\u00267=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(),  \t*size = max_size - *offset;  aligned, since max_size is a power of two -- which fixes the matching misalignment of skb-\u003eend.  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-\u003ehead         1120         0   dataref at line offset \u003e60     80         0  The last row counts the accesses that actually fault: skb_shinfo()-\u003edataref 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---",
  "id": "DEBIAN-CVE-2026-99127",
  "modified": "2026-10-29T05:47:27.046115042Z",
  "published": "2026-10-28T11:17:32.430Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-99127"
    }
  ],
  "upstream": [
    "CVE-2026-99127"
  ]
}