GHSA-4RHV-8VQV-P9W9
Vulnerability from github – Published: 2026-10-06 09:31 – Updated: 2026-10-06 09:31In 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.
{
"affected": [],
"aliases": [
"CVE-2026-98215"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-10-06T09:18:08Z",
"severity": null
},
"details": "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": "GHSA-4rhv-8vqv-p9w9",
"modified": "2026-10-06T09:31:30Z",
"published": "2026-10-06T09:31:30Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98215"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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