mm/ksm: fix flag-dropping behavior in ksm_madvise

{
  "id": "7a3d32ad1f38d215fb9187872bf9812c329f5d0459c4fd51ed44bb4734d9f5a9",
  "url": "https://osv.dev/vulnerability/CVE-2025-40040",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mm/ksm: fix flag-dropping behavior in ksm_madvise",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: mm/ksm: fix flag-dropping behavior in ksm_madvise syzkaller discovered the following crash: (kernel BUG) [ 44.607039] ------------[ cut here ]------------ [ 44.607422] kernel BUG at mm/userfaultfd.c:2067! [ 44.608148] Oops: invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN NOPTI [ 44.608814] CPU: 1 UID: 0 PID: 2475 Comm: reproducer Not tainted 6.16.0-rc6 #1 PREEMPT(none) [ 44.609635] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 [ 44.610695] RIP: 0010:userfaultfd_release_all+0x3a8/0x460 [ 44.617726] Call Trace: [ 44.617926] [ 44.619284] userfaultfd_release+0xef/0x1b0 [ 44.620976] __fput+0x3f9/0xb60 [ 44.621240] fput_close_sync+0x110/0x210 [ 44.622222] __x64_sys_close+0x8f/0x120 [ 44.622530] do_syscall_64+0x5b/0x2f0 [ 44.622840] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 44.623244] RIP: 0033:0x7f365bb3f227 Kernel panics because it detects UFFD inconsistency during userfaultfd_release_all(). Specifically, a VMA which has a valid pointer to vma->vm_userfaultfd_ctx, but no UFFD flags in vma->vm_flags. The inconsistency is caused in ksm_madvise(): when user calls madvise() with MADV_UNMEARGEABLE on a VMA that is registered for UFFD in MINOR mode, it accidentally clears all flags stored in the upper 32 bits of vma->vm_flags. Assuming x86_64 kernel build, unsigned long is 64-bit and unsigned int and int are 32-bit wide. This setup causes the fol",
    "evidence": "osv:CVE-2025-40040",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.4.302",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.10.247",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.197",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.158",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.114",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.55",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.17.3",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-40040",
      "aliases": [
        "CVE-2025-40040"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "63c17fb8e5a46a16e10e82005748837fd11a2024"
                },
                {
                  "fixed": "850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71"
                },
                {
                  "fixed": "788e5385d0ff69cdba1cabccb9dab8d9647b9239"
                },
                {
                  "fixed": "b69f19244c2b6475c8a6eb72f0fb0d53509e48cd"
                },
                {
                  "fixed": "41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693"
                },
                {
                  "fixed": "92b82e232b8d8b116ac6e57aeae7a6033db92c60"
                },
                {
                  "fixed": "ac50c6e0a8f91a02b681af81abb2362fbb67cc18"
                },
                {
                  "fixed": "76385629f45740b7888f8fcd83bde955b10f61fe"
                },
                {
                  "fixed": "f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-40040.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "4.6.0"
                },
                {
                  "fixed": "5.4.302"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.5.0"
                },
                {
                  "fixed": "5.10.247"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
                },
                {
                  "fixed": "5.15.197"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.158"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.114"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.55"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.17.3"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-40040.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.291326138Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/41cb9fd904fe0c39d52e82dd84dc3c96b7aa9693",
        "https://git.kernel.org/stable/c/76385629f45740b7888f8fcd83bde955b10f61fe",
        "https://git.kernel.org/stable/c/788e5385d0ff69cdba1cabccb9dab8d9647b9239",
        "https://git.kernel.org/stable/c/850f1ea245bdc0ce6a3fd36bfb80d8cf9647cb71",
        "https://git.kernel.org/stable/c/92b82e232b8d8b116ac6e57aeae7a6033db92c60",
        "https://git.kernel.org/stable/c/ac50c6e0a8f91a02b681af81abb2362fbb67cc18",
        "https://git.kernel.org/stable/c/b69f19244c2b6475c8a6eb72f0fb0d53509e48cd",
        "https://git.kernel.org/stable/c/f04aad36a07cc17b7a5d5b9a2d386ce6fae63e93",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/40xxx/CVE-2025-40040.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-40040",
        "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/2025/40xxx/CVE-2025-40040.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-40040",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 520007,
  "published_at": "2025-10-28T11:48:20.395+00:00"
}