{"id":"CVE-2026-98215","published":"2026-10-06T09:18:08.107","lastModified":"2026-10-06T09:18:08.107","description":"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->vm_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->sid 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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569","tags":[]},{"url":"https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65","tags":[]},{"url":"https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b","tags":[]},{"url":"https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089","tags":[]},{"url":"https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}