CVE-2026-99127
Full vulnerability record from the local CVENow database.
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: <IRQ> 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---
View original CVE JSON
{
"id": "CVE-2026-99127",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-10-28T11:17:32.430",
"lastModified": "2026-10-28T11:17:32.430",
"vulnStatus": "Received",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\npage_pool: keep frag_offset aligned for odd-sized requests\n\npage_pool_alloc_frag_netmem() rounds the requested fragment size with\n\n\tsize = ALIGN(size, dma_get_cache_alignment());\n\ndma_get_cache_alignment() returns 1 unless the architecture defines\nARCH_DMA_MINALIGN, which DMA-coherent architectures such as x86 do not.\nThere the ALIGN() is a no-op and pool->frag_offset advances by the raw,\nunrounded size.\n\nA single caller asking for an odd size then leaves frag_offset misaligned\nfor every fragment carved out of that page afterwards. The pool is shared,\nso the damage is not confined to the caller that caused it.\n\nThe per-cpu system_page_pool used by generic XDP hits this.\nskb_pp_cow_data() allocates its fragments with the raw packet length:\n\n\tsize = min_t(u32, len, PAGE_SIZE);\n\ttruesize = size;\n\tpage = page_pool_dev_alloc(pool, &page_off, &truesize);\n\nleaving frag_offset odd for whatever is carved out of that page next. Its\nown head allocation is already aligned -- SKB_HEAD_ALIGN(size) plus the\nXDP_PACKET_HEADROOM its callers pass -- so it is a later user of the shared\npool that pays: page_pool_dev_alloc_va() returns a misaligned buffer,\nnapi_build_skb() installs it as skb->head, and skb_shinfo(skb) ==\nskb->head + skb->end is misaligned with it.\n\nskb_shinfo()->dataref is a 4-byte atomic_t at offset 0x20, so the\natomic_inc() in __skb_clone() straddles a cache line. On x86 with split\nlock detection -- fatal for kernel split locks by default -- this panics\nthe machine:\n\n Oops: Split lock detected\n RIP: 0010:skb_clone+0x154/0x1e0\n Call Trace:\n <IRQ>\n raw_local_deliver+0x1ed/0x2c0\n ip_protocol_deliver_rcu+0x54/0x1c0\n ip_local_deliver_finish+0x85/0x100\n ip_local_deliver+0x67/0x100\n __netif_receive_skb_one_core+0x85/0xa0\n process_backlog+0x87/0x130\n\nReproduced by attaching any generic-mode XDP program to loopback and\nopening a RAW IPPROTO_UDP socket, which makes raw_local_deliver() clone\nevery locally delivered UDP packet; ordinary DNS traffic then triggers it,\nroughly once per 2500 clones. Observed on 6.12.101 and 7.1.8.\n\nTracing page_pool_alloc_frag_netmem() over one such run shows the\namplification -- two odd-sized requests, nine misaligned offsets:\n\n requested size & 7: 0: 17035 5: 1 7: 1\n frag_offset & 7: 0: 17028 3: 1 4: 1 5: 1 6: 1 7: 5\n\nand skb_pp_cow_data() returning heads that were aligned on entry:\n\n head 0xffff8f4c86aeac00 -> 0xffff8f4c53a9a9c4 (&7=4)\n head 0xffff8f4d6a8a42c0 -> 0xffff8f4c4f7b7a45 (&7=5)\n\nRound the fragment size up to at least the alignment struct skb_shared_info\nrequires, so fragments are always suitably aligned for the objects callers\nbuild on them. Architectures needing a larger DMA alignment keep it.\n\nThis also makes the remainder computed in page_pool_alloc_netmem(),\n\n\t*size = max_size - *offset;\n\naligned, since max_size is a power of two -- which fixes the matching\nmisalignment of skb->end.\n\nVerified with a controlled A/B under QEMU/KVM: same tree, same config,\nsame compiler, same rootfs and identical traffic, differing only by this\npatch. A SEC(\"xdp.frags\") XDP_PASS program on lo plus UDP datagrams\nlarger than max_head_size drives skb_pp_cow_data()'s fragment loop, which\npasses raw packet lengths to the pool. Measured at the return of\nskb_pp_cow_data():\n\n unpatched patched\n skb_pp_cow_data calls 40800 40800\n misaligned skb->head 1120 0\n dataref at line offset >60 80 0\n\nThe last row counts the accesses that actually fault:\nskb_shinfo()->dataref sits at head+end+0x20 and is a 4-byte atomic, so\n`lock incl` splits a 64-byte cache line only when that address lands at\noffset 61..63. All 80 occurrences were at offset 61; the panic reported\nabove was at offset 62. Eliminating the misalignment removes every one\nof them.\n\nSame class of bug as commit 3bed3cc4156e (\"net: Do not allocate page\nfragments t\n---truncated---"
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"net/core/page_pool.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "53e0961da1c7bbdabd1abebb20de403ec237ec09",
"lessThan": "813a72beaa5d3f4bb135e0def9b3f07a3511ca0e",
"versionType": "git",
"status": "affected"
},
{
"version": "53e0961da1c7bbdabd1abebb20de403ec237ec09",
"lessThan": "dca1b51693c81eaf77e50980be373e01ae857394",
"versionType": "git",
"status": "affected"
},
{
"version": "53e0961da1c7bbdabd1abebb20de403ec237ec09",
"lessThan": "dc0df5a0c62ccea1d0e08d39a4dc9064de81d411",
"versionType": "git",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"net/core/page_pool.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "5.15",
"status": "affected"
},
{
"version": "0",
"lessThan": "5.15",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.18.59",
"lessThanOrEqual": "6.18.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.2.13",
"lessThanOrEqual": "7.2.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.3",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {},
"references": [
{
"url": "https://git.kernel.org/stable/c/813a72beaa5d3f4bb135e0def9b3f07a3511ca0e",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/dc0df5a0c62ccea1d0e08d39a4dc9064de81d411",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/dca1b51693c81eaf77e50980be373e01ae857394",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
]
}