In the Linux kernel, the following vulnerability has been resolved:
selinux: recheck intermediate backing files on mprotect()
mprotect() can be used to bypass the SELinux checks that mmap() performs
against the intermediate layers of a stacked filesystem.
mmap() checks every backing layer as the request descends through the
stack. mprotect() only has the lowest backing file in vma->vm_file, so it
rechecks the top-level user and the lowest mounter, but skips the mounters
of every layer in between. With two nested overlayfs mounts and a policy
denying mounter_t -> middle_file_t:file { execute }, a direct
mmap(PROT_EXEC) is denied:
avc: denied { execute } for pid=71 comm="nested_exec"
path="/payload" dev="overlay" ino=9
scontext=user_u:base_r:mounter_t
tcontext=user_u:object_r:middle_file_t tclass=file permissive=0
while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds.
Preserve each intermediate path, mounter SID and file-description SID in
the backing-file security blob, copying the saved entries when another
backing layer is opened. Allocate the array only for nested backing files,
and release it and the path references in the backing_file_free hook.
During mprotect(), recheck fd { use } and the requested inode permissions
for every saved mounter, and include the intermediate layers in the execmod
checks. Policy for nested stacking may then need to grant intermediate
mounters what a direct mmap() already requires, and execmod on intermediate
labels for binaries using text relocations.
Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built
SELinux policy, on a mainline tree containing
commit f2381b546e7e ("fs: fix user path of nested backing files").
[PM: subject tweak]
selinux: recheck intermediate backing files on mprotect()
mprotect() can be used to bypass the SELinux checks that mmap() performs
against the intermediate layers of a stacked filesystem.
mmap() checks every backing layer as the request descends through the
stack. mprotect() only has the lowest backing file in vma->vm_file, so it
rechecks the top-level user and the lowest mounter, but skips the mounters
of every layer in between. With two nested overlayfs mounts and a policy
denying mounter_t -> middle_file_t:file { execute }, a direct
mmap(PROT_EXEC) is denied:
avc: denied { execute } for pid=71 comm="nested_exec"
path="/payload" dev="overlay" ino=9
scontext=user_u:base_r:mounter_t
tcontext=user_u:object_r:middle_file_t tclass=file permissive=0
while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds.
Preserve each intermediate path, mounter SID and file-description SID in
the backing-file security blob, copying the saved entries when another
backing layer is opened. Allocate the array only for nested backing files,
and release it and the path references in the backing_file_free hook.
During mprotect(), recheck fd { use } and the requested inode permissions
for every saved mounter, and include the intermediate layers in the execmod
checks. Policy for nested stacking may then need to grant intermediate
mounters what a direct mmap() already requires, and execmod on intermediate
labels for binaries using text relocations.
Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built
SELinux policy, on a mainline tree containing
commit f2381b546e7e ("fs: fix user path of nested backing files").
[PM: subject tweak]
Metrics
Affected Vendors & Products
Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Tue, 06 Oct 2026 09:00:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: selinux: recheck intermediate backing files on mprotect() mprotect() can be used to bypass the SELinux checks that mmap() performs against the intermediate layers of a stacked filesystem. mmap() checks every backing layer as the request descends through the stack. mprotect() only has the lowest backing file in vma->vm_file, so it rechecks the top-level user and the lowest mounter, but skips the mounters of every layer in between. With two nested overlayfs mounts and a policy denying mounter_t -> middle_file_t:file { execute }, a direct mmap(PROT_EXEC) is denied: avc: denied { execute } for pid=71 comm="nested_exec" path="/payload" dev="overlay" ino=9 scontext=user_u:base_r:mounter_t tcontext=user_u:object_r:middle_file_t tclass=file permissive=0 while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds. Preserve each intermediate path, mounter SID and file-description SID in the backing-file security blob, copying the saved entries when another backing layer is opened. Allocate the array only for nested backing files, and release it and the path references in the backing_file_free hook. During mprotect(), recheck fd { use } and the requested inode permissions for every saved mounter, and include the intermediate layers in the execmod checks. Policy for nested stacking may then need to grant intermediate mounters what a direct mmap() already requires, and execmod on intermediate labels for binaries using text relocations. Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built SELinux policy, on a mainline tree containing commit f2381b546e7e ("fs: fix user path of nested backing files"). [PM: subject tweak] | |
| Title | selinux: recheck intermediate backing files on mprotect() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-06T08:44:50.209Z
Reserved: 2026-09-25T10:25:14.325Z
Link: CVE-2026-98214
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-06T09:18:07.943
Modified: 2026-10-06T09:18:07.943
Link: CVE-2026-98214
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.