CVE-2025-21984 (GCVE-0-2025-21984)
Vulnerability from cvelistv5
Published
2025-04-01 15:47
Modified
2026-08-05 11:55
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "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",
              "status": "affected",
              "version": "adef440691bab824e39c1b17382322d195e1fab0",
              "versionType": "git"
            },
            {
              "lessThan": "b1e11bd86c0943bb7624efebdc384340a50ad683",
              "status": "affected",
              "version": "adef440691bab824e39c1b17382322d195e1fab0",
              "versionType": "git"
            },
            {
              "lessThan": "c50f8e6053b0503375c2975bf47f182445aebb4c",
              "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---"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerability is reached only through local syscalls \u2014 `userfaultfd(2)`/`/dev/userfaultfd` plus the `UFFDIO_MOVE` ioctl and `madvise`/page-fault activity on the attacker\u0027s own address space. There is no network- or adjacent-reachable path.\nAC:L - The attacker creates and drives both sides of the race himself: `madvise(MADV_PAGEOUT)` deterministically pushes a chosen folio into the swapcache with swap PTEs, while a second thread loops `UFFDIO_MOVE` over the same address, retrying until the window is hit. A trivial reproducer accompanied the fix, and swap (zram on Android/embedded, swapfiles on servers) is a standard configuration.\nPR:L - Only an unprivileged local user is needed \u2014 `userfaultfd_syscall_allowed()` always permits `UFFD_USER_MODE_ONLY` contexts regardless of the `vm.unprivileged_userfaultfd` sysctl, and `UFFDIO_MOVE` acts on the caller\u0027s own mm with no capability check. Android app sandboxes routinely have userfaultfd access for ART GC compaction.\nUI:N - The attacking process performs every step itself \u2014 register uffd, page out, move the PTE, then touch the destination. No victim action or interaction is required.\nS:U - The corruption stays within the kernel\u0027s own memory-management state and the attacking process\u0027s mm; there is no hypervisor, IOMMU, or other security-authority boundary crossed. This is standard local kernel compromise, so scope is unchanged.\nC:H - The folio ends up mapped in `dst_vma` while `folio-\u003emapping` still references the source anon_vma and `folio-\u003eindex` is stale, breaking the invariant that a mapped folio\u0027s anon_vma cannot be freed; a subsequently freed/reused anon_vma dereferenced by rmap walks yields a use-after-free read primitive over attacker-groomed slab contents, and mis-addressed rmap walks can expose unrelated mapping state.\nI:H - The same dangling anon_vma plus stale index corrupts reverse-mapping metadata for a live, writable anonymous folio, which is the classic shape for heap-spray-driven write primitives and control-flow hijack; with KSM enabled the bug additionally causes a silent unexpected CoW that breaks UFFDIO_MOVE atomicity and corrupts the userspace GC heap that depends on it.\nA:H - The reported outcome is `kernel BUG at mm/rmap.c` in `__page_check_anon_rmap()` reached from `do_swap_page()` \u2014 an oops taken with page-table locks held and IRQs disabled (`exited with preempt_count 2`), which panics the box on `panic_on_oops` and wedges the mm otherwise. Even without `CONFIG_DEBUG_VM`, the resulting rmap corruption and dangling anon_vma produce later crashes."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:55:50.769Z",
        "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": "2026-08-05T11:55:50.769Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"cvssV3_1\": {\"scope\": \"UNCHANGED\", \"version\": \"3.1\", \"baseScore\": 4.7, \"attackVector\": \"LOCAL\", \"baseSeverity\": \"MEDIUM\", \"vectorString\": \"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H\", \"integrityImpact\": \"NONE\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"availabilityImpact\": \"HIGH\", \"privilegesRequired\": \"LOW\", \"confidentialityImpact\": \"NONE\"}}, {\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2025-21984\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2025-10-01T17:14:21.959942Z\"}}}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-362\", \"description\": \"CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization (\u0027Race Condition\u0027)\"}]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2025-10-01T14:38:56.065Z\"}}], \"cna\": {\"title\": \"mm: fix kernel BUG when userfaultfd_move encounters swapcache\", \"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.8, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"AV:L - The vulnerability is reached only through local syscalls \\u2014 `userfaultfd(2)`/`/dev/userfaultfd` plus the `UFFDIO_MOVE` ioctl and `madvise`/page-fault activity on the attacker\u0027s own address space. There is no network- or adjacent-reachable path.\\nAC:L - The attacker creates and drives both sides of the race himself: `madvise(MADV_PAGEOUT)` deterministically pushes a chosen folio into the swapcache with swap PTEs, while a second thread loops `UFFDIO_MOVE` over the same address, retrying until the window is hit. A trivial reproducer accompanied the fix, and swap (zram on Android/embedded, swapfiles on servers) is a standard configuration.\\nPR:L - Only an unprivileged local user is needed \\u2014 `userfaultfd_syscall_allowed()` always permits `UFFD_USER_MODE_ONLY` contexts regardless of the `vm.unprivileged_userfaultfd` sysctl, and `UFFDIO_MOVE` acts on the caller\u0027s own mm with no capability check. Android app sandboxes routinely have userfaultfd access for ART GC compaction.\\nUI:N - The attacking process performs every step itself \\u2014 register uffd, page out, move the PTE, then touch the destination. No victim action or interaction is required.\\nS:U - The corruption stays within the kernel\u0027s own memory-management state and the attacking process\u0027s mm; there is no hypervisor, IOMMU, or other security-authority boundary crossed. This is standard local kernel compromise, so scope is unchanged.\\nC:H - The folio ends up mapped in `dst_vma` while `folio-\u003emapping` still references the source anon_vma and `folio-\u003eindex` is stale, breaking the invariant that a mapped folio\u0027s anon_vma cannot be freed; a subsequently freed/reused anon_vma dereferenced by rmap walks yields a use-after-free read primitive over attacker-groomed slab contents, and mis-addressed rmap walks can expose unrelated mapping state.\\nI:H - The same dangling anon_vma plus stale index corrupts reverse-mapping metadata for a live, writable anonymous folio, which is the classic shape for heap-spray-driven write primitives and control-flow hijack; with KSM enabled the bug additionally causes a silent unexpected CoW that breaks UFFDIO_MOVE atomicity and corrupts the userspace GC heap that depends on it.\\nA:H - The reported outcome is `kernel BUG at mm/rmap.c` in `__page_check_anon_rmap()` reached from `do_swap_page()` \\u2014 an oops taken with page-table locks held and IRQs disabled (`exited with preempt_count 2`), which panics the box on `panic_on_oops` and wedges the mm otherwise. Even without `CONFIG_DEBUG_VM`, the resulting rmap corruption and dangling anon_vma produce later crashes.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"adef440691bab824e39c1b17382322d195e1fab0\", \"lessThan\": \"4e9507246298fd6f1ca7bb42ef01a6e34fb93684\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"adef440691bab824e39c1b17382322d195e1fab0\", \"lessThan\": \"b1e11bd86c0943bb7624efebdc384340a50ad683\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"adef440691bab824e39c1b17382322d195e1fab0\", \"lessThan\": \"c50f8e6053b0503375c2975bf47f182445aebb4c\", \"versionType\": \"git\"}], \"programFiles\": [\"mm/userfaultfd.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"6.8\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"6.8\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"6.12.20\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.13.8\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.13.*\"}, {\"status\": \"unaffected\", \"version\": \"6.14\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"mm/userfaultfd.c\"], \"defaultStatus\": \"affected\"}], \"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\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"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---\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.20\", \"versionStartIncluding\": \"6.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.13.8\", \"versionStartIncluding\": \"6.8\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.14\", \"versionStartIncluding\": \"6.8\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T11:55:50.769Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-21984\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T11:55:50.769Z\", \"dateReserved\": \"2024-12-29T08:45:45.799Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2025-04-01T15:47:11.523Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.