CVE-2025-39992 (GCVE-0-2025-39992)

Vulnerability from cvelistv5 – Published: 2025-10-15 07:58 – Updated: 2025-12-01 06:16
VLAI?
Title
mm: swap: check for stable address space before operating on the VMA
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: swap: check for stable address space before operating on the VMA It is possible to hit a zero entry while traversing the vmas in unuse_mm() called from swapoff path and accessing it causes the OOPS: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000446--> Loading the memory from offset 0x40 on the XA_ZERO_ENTRY as address. Mem abort info: ESR = 0x0000000096000005 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x05: level 1 translation fault The issue is manifested from the below race between the fork() on a process and swapoff: fork(dup_mmap()) swapoff(unuse_mm) --------------- ----------------- 1) Identical mtree is built using __mt_dup(). 2) copy_pte_range()--> copy_nonpresent_pte(): The dst mm is added into the mmlist to be visible to the swapoff operation. 3) Fatal signal is sent to the parent process(which is the current during the fork) thus skip the duplication of the vmas and mark the vma range with XA_ZERO_ENTRY as a marker for this process that helps during exit_mmap(). 4) swapoff is tried on the 'mm' added to the 'mmlist' as part of the 2. 5) unuse_mm(), that iterates through the vma's of this 'mm' will hit the non-NULL zero entry and operating on this zero entry as a vma is resulting into the oops. The proper fix would be around not exposing this partially-valid tree to others when droping the mmap lock, which is being solved with [1]. A simpler solution would be checking for MMF_UNSTABLE, as it is set if mm_struct is not fully initialized in dup_mmap(). Thanks to Liam/Lorenzo/David for all the suggestions in fixing this issue.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: d2406291483775ecddaee929231a39c70c08fda2 , < 4e5f060d7347466f77aaff1c0d5a6c4f1fb217ac (git)
Affected: d2406291483775ecddaee929231a39c70c08fda2 , < 9cddad3b26dac830407d2d3c0de5205ff6d6dda0 (git)
Affected: d2406291483775ecddaee929231a39c70c08fda2 , < e4e99d69b8b8295c501b2eef89e13306b738b667 (git)
Affected: d2406291483775ecddaee929231a39c70c08fda2 , < 1367da7eb875d01102d2ed18654b24d261ff5393 (git)
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    Linux Linux Affected: 6.8
Unaffected: 0 , < 6.8 (semver)
Unaffected: 6.12.51 , ≤ 6.12.* (semver)
Unaffected: 6.16.11 , ≤ 6.16.* (semver)
Unaffected: 6.17.1 , ≤ 6.17.* (semver)
Unaffected: 6.18 , ≤ * (original_commit_for_fix)
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          "programFiles": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: swap: check for stable address space before operating on the VMA\n\nIt is possible to hit a zero entry while traversing the vmas in unuse_mm()\ncalled from swapoff path and accessing it causes the OOPS:\n\nUnable to handle kernel NULL pointer dereference at virtual address\n0000000000000446--\u003e Loading the memory from offset 0x40 on the\nXA_ZERO_ENTRY as address.\nMem abort info:\n  ESR = 0x0000000096000005\n  EC = 0x25: DABT (current EL), IL = 32 bits\n  SET = 0, FnV = 0\n  EA = 0, S1PTW = 0\n  FSC = 0x05: level 1 translation fault\n\nThe issue is manifested from the below race between the fork() on a\nprocess and swapoff:\nfork(dup_mmap())\t\t\tswapoff(unuse_mm)\n---------------                         -----------------\n1) Identical mtree is built using\n   __mt_dup().\n\n2) copy_pte_range()--\u003e\n\tcopy_nonpresent_pte():\n       The dst mm is added into the\n    mmlist to be visible to the\n    swapoff operation.\n\n3) Fatal signal is sent to the parent\nprocess(which is the current during the\nfork) thus skip the duplication of the\nvmas and mark the vma range with\nXA_ZERO_ENTRY as a marker for this process\nthat helps during exit_mmap().\n\n\t\t\t\t     4) swapoff is tried on the\n\t\t\t\t\t\u0027mm\u0027 added to the \u0027mmlist\u0027 as\n\t\t\t\t\tpart of the 2.\n\n\t\t\t\t     5) unuse_mm(), that iterates\n\t\t\t\t\tthrough the vma\u0027s of this \u0027mm\u0027\n\t\t\t\t\twill hit the non-NULL zero entry\n\t\t\t\t\tand operating on this zero entry\n\t\t\t\t\tas a vma is resulting into the\n\t\t\t\t\toops.\n\nThe proper fix would be around not exposing this partially-valid tree to\nothers when droping the mmap lock, which is being solved with [1].  A\nsimpler solution would be checking for MMF_UNSTABLE, as it is set if\nmm_struct is not fully initialized in dup_mmap().\n\nThanks to Liam/Lorenzo/David for all the suggestions in fixing this\nissue."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-12-01T06:16:02.393Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4e5f060d7347466f77aaff1c0d5a6c4f1fb217ac"
        },
        {
          "url": "https://git.kernel.org/stable/c/9cddad3b26dac830407d2d3c0de5205ff6d6dda0"
        },
        {
          "url": "https://git.kernel.org/stable/c/e4e99d69b8b8295c501b2eef89e13306b738b667"
        },
        {
          "url": "https://git.kernel.org/stable/c/1367da7eb875d01102d2ed18654b24d261ff5393"
        }
      ],
      "title": "mm: swap: check for stable address space before operating on the VMA",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2025-39992",
    "datePublished": "2025-10-15T07:58:17.927Z",
    "dateReserved": "2025-04-16T07:20:57.150Z",
    "dateUpdated": "2025-12-01T06:16:02.393Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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