selinux: preserve user SID across nested backing files
Summary
| CVE | CVE-2026-98215 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-06 09:18:08 UTC |
| Updated | 2026-10-06 09:18:08 UTC |
| Description | 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. |
Risk And Classification
EPSS: 0.002090000 probability, percentile 0.100660000 (date 2026-10-06)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected bc6c380c1159de52a252ed11f19a42c47f60a735 caa1b913d90d5dc07073733326d2af0f0288f089 git | Not specified |
| CNA | Linux | Linux | affected 8bacd09f12c27710228562e4d13163e58c5f4a45 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569 git | Not specified |
| CNA | Linux | Linux | affected d844702198395d3f80222777030f69db6be6b709 9d99b770e7b67b00bdef9005b928aad13e1d679b git | Not specified |
| CNA | Linux | Linux | affected 82544d36b1729153c8aeb179e84750f0c085d3b1 ff20d16b2e8230c034e21540043df47222dcc09b git | Not specified |
| CNA | Linux | Linux | affected 82544d36b1729153c8aeb179e84750f0c085d3b1 8c0c602202b9a4909b00bc3354e3c0355bc69e65 git | Not specified |
| CNA | Linux | Linux | affected cd0e707a927a70cdfd8bc5a512a9719a87f5ed51 git | Not specified |
| CNA | Linux | Linux | affected 6.6.144 6.6.158 semver | Not specified |
| CNA | Linux | Linux | affected 6.12.95 6.12.112 semver | Not specified |
| CNA | Linux | Linux | affected 6.18.38 6.18.54 semver | Not specified |
| CNA | Linux | Linux | affected 7.0.4 7.1 semver | Not specified |
| CNA | Linux | Linux | affected 7.1 | Not specified |
| CNA | Linux | Linux | unaffected 7.1 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.6.158 6.6.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.112 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.54 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.2.8 7.2.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.3-rc4 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.