CVE-2026-98215 (GCVE-0-2026-98215)
Vulnerability from cvelistv5
Published
2026-10-06 08:44
Modified
2026-10-19 09:15
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: selinux: preserve user SID across nested backing files SELinux saves the user file SID in a backing-file security blob so it remains available after mmap() replaces vma->vm_file with a backing file. For nested backing files (overlayfs over overlayfs, or FUSE passthrough backed by overlayfs), user_file may itself be a backing file. Its fsec->sid is the SID of the mounter that opened it, rather than the user that opened the top-level file. mprotect() then checks fd { use } against the mounter SID. This can incorrectly deny access without a domain transition, or check the wrong target SID after one. Copy the saved user SID when user_file is a backing file. Keep using the regular file SID for the first backing layer. With two nested overlayfs mounts and SELinux enforcing, mprotect(PROT_READ) returns EACCES with an fd { use } denial against the mounter SID. With this change, mprotect() succeeds. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy. The original test was also repeated with Fedora Cloud Base 44 userspace and gave the same result.
References
Impacted products
Vendor Product Version
Linux Linux Version: bc6c380c1159de52a252ed11f19a42c47f60a735
Version: 8bacd09f12c27710228562e4d13163e58c5f4a45
Version: d844702198395d3f80222777030f69db6be6b709
Version: 82544d36b1729153c8aeb179e84750f0c085d3b1
Version: 82544d36b1729153c8aeb179e84750f0c085d3b1
Version: cd0e707a927a70cdfd8bc5a512a9719a87f5ed51
Version: 6.6.144   ≤
Version: 6.12.95   ≤
Version: 6.18.38   ≤
Version: 7.0.4   ≤
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{
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nselinux: preserve user SID across nested backing files\n\nSELinux saves the user file SID in a backing-file security blob so it\nremains available after mmap() replaces vma-\u003evm_file with a backing file.\n\nFor nested backing files (overlayfs over overlayfs, or FUSE passthrough\nbacked by overlayfs), user_file may itself be a backing file.  Its\nfsec-\u003esid is the SID of the mounter that opened it, rather than the user\nthat opened the top-level file.  mprotect() then checks fd { use } against\nthe mounter SID.  This can incorrectly deny access without a domain\ntransition, or check the wrong target SID after one.\n\nCopy the saved user SID when user_file is a backing file.  Keep using the\nregular file SID for the first backing layer.\n\nWith two nested overlayfs mounts and SELinux enforcing,\nmprotect(PROT_READ) returns EACCES with an fd { use } denial against the\nmounter SID.  With this change, mprotect() succeeds.\n\nTested on arm64 QEMU with a small BusyBox initramfs and a purpose-built\nSELinux policy.  The original test was also repeated with Fedora Cloud\nBase 44 userspace and gave the same result."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:15:46.038Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089"
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        {
          "url": "https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569"
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          "url": "https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b"
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        {
          "url": "https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b"
        },
        {
          "url": "https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65"
        }
      ],
      "title": "selinux: preserve user SID across nested backing files",
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98215",
    "datePublished": "2026-10-06T08:44:51.412Z",
    "dateReserved": "2026-09-25T10:25:14.326Z",
    "dateUpdated": "2026-10-19T09:15:46.038Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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