CVE-2026-64294 (GCVE-0-2026-64294)
Vulnerability from cvelistv5
Published
2026-07-25 08:49
Modified
2026-08-23 12:45
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: do file ownership checks with the proper mount idmap Ever since idmapped mounts were introduced, inode ownership checks (for side-channel protection) in mincore() and madvise(MADV_PAGEOUT) were done against the nop_mnt_idmap, which completely ignores the file's mount's idmap. This results in odd edgecases like: 1) mount/bind-mount with an idmap userA:userB:1 2) userB runs an owner_or_capable() check on file that is owned by userA on-disk/in-memory, but owned by userB after idmap translation 3) owner_or_capable() mysteriously fails as the correct idmap wasn't supplied In the case of mincore/madvise MADV_PAGEOUT, this is usually benign, because file_permission(file, MAY_WRITE) will probably succeed, as it uses the proper idmap internally, but it does not need to be the case on e.g a 0444 file where even the owner itself doesn't have permissions to write to it. Since this is clearly not trivial to get right, introduce a file_owner_or_capable() that can carry the correct semantics, and switch the various users in mm to it. The issue was found by manual code inspection & an off-list discussion with Jan Kara.
References
Impacted products
Vendor Product Version
Linux Linux Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
Version: 9caccd41541a6f7d6279928d9f971f6642c361af
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{
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          "programFiles": [
            "include/linux/fs.h",
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: do file ownership checks with the proper mount idmap\n\nEver since idmapped mounts were introduced, inode ownership checks (for\nside-channel protection) in mincore() and madvise(MADV_PAGEOUT) were done\nagainst the nop_mnt_idmap, which completely ignores the file\u0027s mount\u0027s\nidmap.  This results in odd edgecases like:\n\n1) mount/bind-mount with an idmap userA:userB:1\n2) userB runs an owner_or_capable() check on file that is owned by userA\non-disk/in-memory, but owned by userB after idmap translation\n3) owner_or_capable() mysteriously fails as the correct idmap wasn\u0027t supplied\n\nIn the case of mincore/madvise MADV_PAGEOUT, this is usually benign,\nbecause file_permission(file, MAY_WRITE) will probably succeed, as it uses\nthe proper idmap internally, but it does not need to be the case on e.g a\n0444 file where even the owner itself doesn\u0027t have permissions to write to\nit.\n\nSince this is clearly not trivial to get right, introduce a\nfile_owner_or_capable() that can carry the correct semantics, and switch\nthe various users in mm to it.\n\nThe issue was found by manual code inspection \u0026 an off-list discussion\nwith Jan Kara."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-23T12:45:40.258Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/7368bec565bac3e536cd43579dbde1e715e6ba61"
        },
        {
          "url": "https://git.kernel.org/stable/c/b2f3d94ea310bea9d36d53e9d9b3f45e86c1d893"
        },
        {
          "url": "https://git.kernel.org/stable/c/744b23aa430d52f5c8e4dbff7d71496d6643bed2"
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        {
          "url": "https://git.kernel.org/stable/c/8344bdf0629457e532797b42d9d2bbf2a2900bbf"
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          "url": "https://git.kernel.org/stable/c/5c942ad7df75925ee166e7f0fb36892d8dde376b"
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          "url": "https://git.kernel.org/stable/c/04ba248d02d9eaa3d9077b00a6134caa75fa3e90"
        },
        {
          "url": "https://git.kernel.org/stable/c/e187bc02f8fa4226d62814592cf064ee4557c470"
        }
      ],
      "title": "mm: do file ownership checks with the proper mount idmap",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64294",
    "datePublished": "2026-07-25T08:49:32.570Z",
    "dateReserved": "2026-07-19T15:36:31.778Z",
    "dateUpdated": "2026-08-23T12:45:40.258Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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