Description (CNA)
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.
Affected (CNA)
| Vendor / product | Versions |
|---|---|
| Linux / Linux | affected bc6c380c1159de52a252ed11f19a42c47f60a735 before caa1b913d90d5dc07073733326d2af0f0288f089; affected 8bacd09f12c27710228562e4d13163e58c5f4a45 before 6aaeec59aadcd1eafc18b049f1b759fb6b9d9569; affected d844702198395d3f80222777030f69db6be6b709 before 9d99b770e7b67b00bdef9005b928aad13e1d679b; affected 82544d36b1729153c8aeb179e84750f0c085d3b1 before ff20d16b2e8230c034e21540043df47222dcc09b; affected 82544d36b1729153c8aeb179e84750f0c085d3b1 before 8c0c602202b9a4909b00bc3354e3c0355bc69e65; affected cd0e707a927a70cdfd8bc5a512a9719a87f5ed51; affected 6.6.144 before 6.6.158; affected 6.12.95 before 6.12.112; affected 6.18.38 before 6.18.54; affected 7.0.4 before 7.1 |
| Linux / Linux | affected 7.1; unaffected 0 before 7.1; unaffected 6.6.158 through 6.6.*; unaffected 6.12.112 through 6.12.*; unaffected 6.18.54 through 6.18.*; unaffected 7.2.8 through 7.2.*; unaffected 7.3 through * |
CWE
No CWE identifiers supplied.
References
- https://git.kernel.org/stable/c/caa1b913d90d5dc07073733326d2af0f0288f089
- https://git.kernel.org/stable/c/6aaeec59aadcd1eafc18b049f1b759fb6b9d9569
- https://git.kernel.org/stable/c/9d99b770e7b67b00bdef9005b928aad13e1d679b
- https://git.kernel.org/stable/c/ff20d16b2e8230c034e21540043df47222dcc09b
- https://git.kernel.org/stable/c/8c0c602202b9a4909b00bc3354e3c0355bc69e65