mm/pagewalk: fix race between concurrent split and refault

{
  "id": "cc0946bb1d1bc781028027453a30d939b25ed20bb9165bcbd99de616b6280cee",
  "url": "https://osv.dev/vulnerability/CVE-2026-31456",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mm/pagewalk: fix race between concurrent split and refault",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mm/pagewalk: fix race between concurrent split and refault The splitting of a PUD entry in walk_pud_range() can race with a concurrent thread refaulting the PUD leaf entry causing it to try walking a PMD range that has disappeared. An example and reproduction of this is to try reading numa_maps of a process while VFIO-PCI is setting up DMA (specifically the vfio_pin_pages_remote call) on a large BAR for that process. This will trigger a kernel BUG: vfio-pci 0000:03:00.0: enabling device (0000 -> 0002) BUG: unable to handle page fault for address: ffffa23980000000 PGD 0 P4D 0 Oops: Oops: 0000 [#1] SMP NOPTI ... RIP: 0010:walk_pgd_range+0x3b5/0x7a0 Code: 8d 43 ff 48 89 44 24 28 4d 89 ce 4d 8d a7 00 00 20 00 48 8b 4c 24 28 49 81 e4 00 00 e0 ff 49 8d 44 24 ff 48 39 c8 4c 0f 43 e3 <49> f7 06 9f ff ff ff 75 3b 48 8b 44 24 20 48 8b 40 28 48 85 c0 74 RSP: 0018:ffffac23e1ecf808 EFLAGS: 00010287 RAX: 00007f44c01fffff RBX: 00007f4500000000 RCX: 00007f44ffffffff RDX: 0000000000000000 RSI: 000ffffffffff000 RDI: ffffffff93378fe0 RBP: ffffac23e1ecf918 R08: 0000000000000004 R09: ffffa23980000000 R10: 0000000000000020 R11: 0000000000000004 R12: 00007f44c0200000 R13: 00007f44c0000000 R14: ffffa23980000000 R15: 00007f44c0000000 FS: 00007fe884739580(0000) GS:ffff9b7d7a9c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffa23980000000 CR3: 000000c0650e2005 CR4: 0000000000770ef0 PKRU: 555555",
    "evidence": "osv:CVE-2026-31456",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.84",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.21",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.11",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-31456",
      "aliases": [
        "CVE-2026-31456"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "f9e54c3a2f5b79ecc57c7bc7d0d3521e461a2101"
                },
                {
                  "fixed": "138ada1337b47cc5efb08e517674d46f86268274"
                },
                {
                  "fixed": "38ec58670a0c5fc1edabdeccd857e586b7b3f318"
                },
                {
                  "fixed": "9bbbebd94dd5be25ec8c899d46ef01b33d5d22c0"
                },
                {
                  "fixed": "3b89863c3fa482912911cd65a12a3aeef662c250"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31456.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.12.0"
                },
                {
                  "fixed": "6.12.84"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.21"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.11"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31456.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:39.633378749Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/138ada1337b47cc5efb08e517674d46f86268274",
        "https://git.kernel.org/stable/c/38ec58670a0c5fc1edabdeccd857e586b7b3f318",
        "https://git.kernel.org/stable/c/3b89863c3fa482912911cd65a12a3aeef662c250",
        "https://git.kernel.org/stable/c/9bbbebd94dd5be25ec8c899d46ef01b33d5d22c0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31456.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31456",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31456.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31456",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 506932,
  "published_at": "2026-04-22T13:53:49.568+00:00"
}