CVE-2025-21984 (GCVE-0-2025-21984)
Vulnerability from cvelistv5
Published
2025-04-01 15:47
Modified
2026-05-11 21:10
Severity ?
4.7 (Medium) - CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: fix kernel BUG when userfaultfd_move encounters swapcache userfaultfd_move() checks whether the PTE entry is present or a swap entry. - If the PTE entry is present, move_present_pte() handles folio migration by setting: src_folio->index = linear_page_index(dst_vma, dst_addr); - If the PTE entry is a swap entry, move_swap_pte() simply copies the PTE to the new dst_addr. This approach is incorrect because, even if the PTE is a swap entry, it can still reference a folio that remains in the swap cache. This creates a race window between steps 2 and 4. 1. add_to_swap: The folio is added to the swapcache. 2. try_to_unmap: PTEs are converted to swap entries. 3. pageout: The folio is written back. 4. Swapcache is cleared. If userfaultfd_move() occurs in the window between steps 2 and 4, after the swap PTE has been moved to the destination, accessing the destination triggers do_swap_page(), which may locate the folio in the swapcache. However, since the folio's index has not been updated to match the destination VMA, do_swap_page() will detect a mismatch. This can result in two critical issues depending on the system configuration. If KSM is disabled, both small and large folios can trigger a BUG during the add_rmap operation due to: page_pgoff(folio, page) != linear_page_index(vma, address) [ 13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c [ 13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0 [ 13.337716] memcg:ffff00000405f000 [ 13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff) [ 13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361 [ 13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000 [ 13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001 [ 13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000 [ 13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address)) [ 13.340190] ------------[ cut here ]------------ [ 13.340316] kernel BUG at mm/rmap.c:1380! [ 13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [ 13.340969] Modules linked in: [ 13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299 [ 13.341470] Hardware name: linux,dummy-virt (DT) [ 13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 13.341815] pc : __page_check_anon_rmap+0xa0/0xb0 [ 13.341920] lr : __page_check_anon_rmap+0xa0/0xb0 [ 13.342018] sp : ffff80008752bb20 [ 13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001 [ 13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001 [ 13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00 [ 13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff [ 13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f [ 13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0 [ 13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40 [ 13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8 [ 13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000 [ 13.343645] x2 : 0000000000000000 x1 : ffff0000062db980 x0 : 000000000000005f [ 13.343876] Call trace: [ 13.344045] __page_check_anon_rmap+0xa0/0xb0 (P) [ 13.344234] folio_add_anon_rmap_ptes+0x22c/0x320 [ 13.344333] do_swap_page+0x1060/0x1400 [ 13.344417] __handl ---truncated---
References
Impacted products
Vendor Product Version
Linux Linux Version: adef440691bab824e39c1b17382322d195e1fab0
Version: adef440691bab824e39c1b17382322d195e1fab0
Version: adef440691bab824e39c1b17382322d195e1fab0
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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "HIGH",
              "attackVector": "LOCAL",
              "availabilityImpact": "HIGH",
              "baseScore": 4.7,
              "baseSeverity": "MEDIUM",
              "confidentialityImpact": "NONE",
              "integrityImpact": "NONE",
              "privilegesRequired": "LOW",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2025-21984",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2025-10-01T17:14:21.959942Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "problemTypes": [
          {
            "descriptions": [
              {
                "cweId": "CWE-362",
                "description": "CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization (\u0027Race Condition\u0027)",
                "lang": "en",
                "type": "CWE"
              }
            ]
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2025-10-01T17:14:24.524Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/userfaultfd.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "4e9507246298fd6f1ca7bb42ef01a6e34fb93684",
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              "versionType": "git"
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              "lessThan": "b1e11bd86c0943bb7624efebdc384340a50ad683",
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              "status": "affected",
              "version": "adef440691bab824e39c1b17382322d195e1fab0",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "mm/userfaultfd.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.8"
            },
            {
              "lessThan": "6.8",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.20",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.13.*",
              "status": "unaffected",
              "version": "6.13.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.14",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.20",
                  "versionStartIncluding": "6.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.13.8",
                  "versionStartIncluding": "6.8",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.14",
                  "versionStartIncluding": "6.8",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: fix kernel BUG when userfaultfd_move encounters swapcache\n\nuserfaultfd_move() checks whether the PTE entry is present or a\nswap entry.\n\n- If the PTE entry is present, move_present_pte() handles folio\n  migration by setting:\n\n  src_folio-\u003eindex = linear_page_index(dst_vma, dst_addr);\n\n- If the PTE entry is a swap entry, move_swap_pte() simply copies\n  the PTE to the new dst_addr.\n\nThis approach is incorrect because, even if the PTE is a swap entry,\nit can still reference a folio that remains in the swap cache.\n\nThis creates a race window between steps 2 and 4.\n 1. add_to_swap: The folio is added to the swapcache.\n 2. try_to_unmap: PTEs are converted to swap entries.\n 3. pageout: The folio is written back.\n 4. Swapcache is cleared.\nIf userfaultfd_move() occurs in the window between steps 2 and 4,\nafter the swap PTE has been moved to the destination, accessing the\ndestination triggers do_swap_page(), which may locate the folio in\nthe swapcache. However, since the folio\u0027s index has not been updated\nto match the destination VMA, do_swap_page() will detect a mismatch.\n\nThis can result in two critical issues depending on the system\nconfiguration.\n\nIf KSM is disabled, both small and large folios can trigger a BUG\nduring the add_rmap operation due to:\n\n page_pgoff(folio, page) != linear_page_index(vma, address)\n\n[   13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c\n[   13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0\n[   13.337716] memcg:ffff00000405f000\n[   13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff)\n[   13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361\n[   13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000\n[   13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361\n[   13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000\n[   13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001\n[   13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000\n[   13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address))\n[   13.340190] ------------[ cut here ]------------\n[   13.340316] kernel BUG at mm/rmap.c:1380!\n[   13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP\n[   13.340969] Modules linked in:\n[   13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299\n[   13.341470] Hardware name: linux,dummy-virt (DT)\n[   13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)\n[   13.341815] pc : __page_check_anon_rmap+0xa0/0xb0\n[   13.341920] lr : __page_check_anon_rmap+0xa0/0xb0\n[   13.342018] sp : ffff80008752bb20\n[   13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001\n[   13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001\n[   13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00\n[   13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff\n[   13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f\n[   13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0\n[   13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40\n[   13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8\n[   13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000\n[   13.343645] x2 : 0000000000000000 x1 : ffff0000062db980 x0 : 000000000000005f\n[   13.343876] Call trace:\n[   13.344045]  __page_check_anon_rmap+0xa0/0xb0 (P)\n[   13.344234]  folio_add_anon_rmap_ptes+0x22c/0x320\n[   13.344333]  do_swap_page+0x1060/0x1400\n[   13.344417]  __handl\n---truncated---"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-11T21:10:23.419Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4e9507246298fd6f1ca7bb42ef01a6e34fb93684"
        },
        {
          "url": "https://git.kernel.org/stable/c/b1e11bd86c0943bb7624efebdc384340a50ad683"
        },
        {
          "url": "https://git.kernel.org/stable/c/c50f8e6053b0503375c2975bf47f182445aebb4c"
        }
      ],
      "title": "mm: fix kernel BUG when userfaultfd_move encounters swapcache",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21984",
    "datePublished": "2025-04-01T15:47:11.523Z",
    "dateReserved": "2024-12-29T08:45:45.799Z",
    "dateUpdated": "2026-05-11T21:10:23.419Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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