CVE-2026-98215
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.
How to fix
- Linux Linuxcaa1b913d90d5dc07073733326d2af0f0288f089, 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569, 9d99b770e7b67b00bdef9005b928aad13e1d679b, ff20d16b2e8230c034e21540043df47222dcc09b, 8c0c602202b9a4909b00bc3354e3c0355bc69e65, 6.6.158, 6.12.112, 6.18.54, 7.1 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Linux Linux | bc6c380c1159de52a252ed11f19a42c47f60a735 ≤ v < caa1b913d90d5dc07073733326d2af0f0288f089, 8bacd09f12c27710228562e4d13163e58c5f4a45 ≤ v < 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569, d844702198395d3f80222777030f69db6be6b709 ≤ v < 9d99b770e7b67b00bdef9005b928aad13e1d679b, 82544d36b1729153c8aeb179e84750f0c085d3b1 ≤ v < ff20d16b2e8230c034e21540043df47222dcc09b, 82544d36b1729153c8aeb179e84750f0c085d3b1 ≤ v < 8c0c602202b9a4909b00bc3354e3c0355bc69e65, cd0e707a927a70cdfd8bc5a512a9719a87f5ed51, 6.6.144 ≤ v < 6.6.158, 6.12.95 ≤ v < 6.12.112, 6.18.38 ≤ v < 6.18.54, 7.0.4 ≤ v < 7.1, 7.1 | caa1b913d90d5dc07073733326d2af0f0288f089, 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569, 9d99b770e7b67b00bdef9005b928aad13e1d679b, ff20d16b2e8230c034e21540043df47222dcc09b, 8c0c602202b9a4909b00bc3354e3c0355bc69e65, 6.6.158, 6.12.112, 6.18.54, 7.1 |
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