FKIE_CVE-2026-98215

Vulnerability from fkie_nvd - Published: 2026-10-06 09:18 - Updated: 2026-10-06 09:18
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
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "security/selinux/hooks.c",
            "security/selinux/include/objsec.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "caa1b913d90d5dc07073733326d2af0f0288f089",
              "status": "affected",
              "version": "bc6c380c1159de52a252ed11f19a42c47f60a735",
              "versionType": "git"
            },
            {
              "lessThan": "6aaeec59aadcd1eafc18b049f1b759fb6b9d9569",
              "status": "affected",
              "version": "8bacd09f12c27710228562e4d13163e58c5f4a45",
              "versionType": "git"
            },
            {
              "lessThan": "9d99b770e7b67b00bdef9005b928aad13e1d679b",
              "status": "affected",
              "version": "d844702198395d3f80222777030f69db6be6b709",
              "versionType": "git"
            },
            {
              "lessThan": "ff20d16b2e8230c034e21540043df47222dcc09b",
              "status": "affected",
              "version": "82544d36b1729153c8aeb179e84750f0c085d3b1",
              "versionType": "git"
            },
            {
              "lessThan": "8c0c602202b9a4909b00bc3354e3c0355bc69e65",
              "status": "affected",
              "version": "82544d36b1729153c8aeb179e84750f0c085d3b1",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "cd0e707a927a70cdfd8bc5a512a9719a87f5ed51",
              "versionType": "git"
            },
            {
              "lessThan": "6.6.158",
              "status": "affected",
              "version": "6.6.144",
              "versionType": "semver"
            },
            {
              "lessThan": "6.12.112",
              "status": "affected",
              "version": "6.12.95",
              "versionType": "semver"
            },
            {
              "lessThan": "6.18.54",
              "status": "affected",
              "version": "6.18.38",
              "versionType": "semver"
            },
            {
              "lessThan": "7.1",
              "status": "affected",
              "version": "7.0.4",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "security/selinux/hooks.c",
            "security/selinux/include/objsec.h"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "7.1"
            },
            {
              "lessThan": "7.1",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.54",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.8",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc4",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "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."
    }
  ],
  "id": "CVE-2026-98215",
  "lastModified": "2026-10-06T09:18:08.107",
  "metrics": {},
  "published": "2026-10-06T09:18:08.107",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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