{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-99127", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.394Z", "datePublished": "2026-10-28T10:34:41.448Z", "dateUpdated": "2026-10-28T10:34:41.448Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-28T10:34:41.448Z" }, "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 \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": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/core/page_pool.c" ], "versions": [ { "version": "53e0961da1c7bbdabd1abebb20de403ec237ec09", "lessThan": "813a72beaa5d3f4bb135e0def9b3f07a3511ca0e", "status": "affected", "versionType": "git" }, { "version": "53e0961da1c7bbdabd1abebb20de403ec237ec09", "lessThan": "dca1b51693c81eaf77e50980be373e01ae857394", "status": "affected", "versionType": "git" }, { "version": "53e0961da1c7bbdabd1abebb20de403ec237ec09", "lessThan": "dc0df5a0c62ccea1d0e08d39a4dc9064de81d411", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/core/page_pool.c" ], "versions": [ { "version": "5.15", "status": "affected" }, { "version": "0", "lessThan": "5.15", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.59", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.13", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "6.18.59" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "7.2.13" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/813a72beaa5d3f4bb135e0def9b3f07a3511ca0e" }, { "url": "https://git.kernel.org/stable/c/dca1b51693c81eaf77e50980be373e01ae857394" }, { "url": "https://git.kernel.org/stable/c/dc0df5a0c62ccea1d0e08d39a4dc9064de81d411" } ], "title": "page_pool: keep frag_offset aligned for odd-sized requests", "x_generator": { "engine": "bippy-1.2.0" } } } }