{"api_version":"1","generated_at":"2026-11-11T04:48:55+00:00","cve":"CVE-2026-99127","urls":{"html":"https://cve.report/CVE-2026-99127","api":"https://cve.report/api/cve/CVE-2026-99127.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-99127","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-99127"},"summary":{"title":"page_pool: keep frag_offset aligned for odd-sized requests","description":"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---","state":"PUBLISHED","assigner":"Linux","published_at":"2026-10-28 11:17:32","updated_at":"2026-10-30 13:21:46"},"problem_types":[],"metrics":[],"references":[{"url":"https://git.kernel.org/stable/c/813a72beaa5d3f4bb135e0def9b3f07a3511ca0e","name":"https://git.kernel.org/stable/c/813a72beaa5d3f4bb135e0def9b3f07a3511ca0e","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/dc0df5a0c62ccea1d0e08d39a4dc9064de81d411","name":"https://git.kernel.org/stable/c/dc0df5a0c62ccea1d0e08d39a4dc9064de81d411","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/dca1b51693c81eaf77e50980be373e01ae857394","name":"https://git.kernel.org/stable/c/dca1b51693c81eaf77e50980be373e01ae857394","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2","name":"https://git.kernel.org/stable/c/22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8ab058f49e801803c4a755b09fe4a920d194da7f","name":"https://git.kernel.org/stable/c/8ab058f49e801803c4a755b09fe4a920d194da7f","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/31e1a71995f23446c9d9e6ba170a6b16b110d243","name":"https://git.kernel.org/stable/c/31e1a71995f23446c9d9e6ba170a6b16b110d243","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb","name":"https://git.kernel.org/stable/c/ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-99127","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99127","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 8ab058f49e801803c4a755b09fe4a920d194da7f git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 31e1a71995f23446c9d9e6ba170a6b16b110d243 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 813a72beaa5d3f4bb135e0def9b3f07a3511ca0e git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 dca1b51693c81eaf77e50980be373e01ae857394 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 53e0961da1c7bbdabd1abebb20de403ec237ec09 dc0df5a0c62ccea1d0e08d39a4dc9064de81d411 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 5.15","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.224 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.191 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.161 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.115 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.59 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2.13 7.2.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.3 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"99127","cve":"CVE-2026-99127","epss":"0.001730000","percentile":"0.067370000","score_date":"2026-11-01","updated_at":"2026-11-02 00:05:55"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["net/core/page_pool.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"8ab058f49e801803c4a755b09fe4a920d194da7f","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"31e1a71995f23446c9d9e6ba170a6b16b110d243","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"813a72beaa5d3f4bb135e0def9b3f07a3511ca0e","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"dca1b51693c81eaf77e50980be373e01ae857394","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"},{"lessThan":"dc0df5a0c62ccea1d0e08d39a4dc9064de81d411","status":"affected","version":"53e0961da1c7bbdabd1abebb20de403ec237ec09","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["net/core/page_pool.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"5.15"},{"lessThan":"5.15","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.224","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.191","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.161","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.115","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.59","versionType":"semver"},{"lessThanOrEqual":"7.2.*","status":"unaffected","version":"7.2.13","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.3","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.224","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.191","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.161","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.115","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.59","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2.13","versionStartIncluding":"5.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.3","versionStartIncluding":"5.15","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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---"}],"providerMetadata":{"dateUpdated":"2026-10-30T12:42:01.046Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/8ab058f49e801803c4a755b09fe4a920d194da7f"},{"url":"https://git.kernel.org/stable/c/31e1a71995f23446c9d9e6ba170a6b16b110d243"},{"url":"https://git.kernel.org/stable/c/ccc28e498ef1c6eaaa16e61c6edb52c32a4f14bb"},{"url":"https://git.kernel.org/stable/c/22b67b0f59f5a7f4fa1e6043a1987e167c5d06d2"},{"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"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-99127","datePublished":"2026-10-28T10:34:41.448Z","dateReserved":"2026-09-25T10:25:14.394Z","dateUpdated":"2026-10-30T12:42:01.046Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-28 11:17:32","lastModifiedDate":"2026-10-30 13:21:46","problem_types":[],"metrics":[],"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"99127","Ordinal":"1","Title":"page_pool: keep frag_offset aligned for odd-sized requests","CVE":"CVE-2026-99127","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"99127","Ordinal":"1","NoteData":"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---","Type":"Description","Title":"page_pool: keep frag_offset aligned for odd-sized requests"}]}}}