Описание
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]
A flaw was found in the Linux kernel. A local user can bypass Security-Enhanced Linux (SELinux) access controls to execute restricted files on stacked filesystems. When modifying memory protections using the mprotect() system call, the kernel fails to recheck security permissions on intermediate layers of layered filesystems. This flaw allows an attacker to map a restricted file without execution permissions and subsequently mark it executable, bypassing established security policies to execute unauthorized code.
Отчет
This flaw is rated with Moderate severity because exploitation requires existing local system access and depends on non-default environments utilizing nested stacked filesystem configurations alongside specialized SELinux policy rules. Standard Red Hat Enterprise Linux deployments do not typically utilize multi-tiered overlay mounts with granular execution denials assigned to intermediate backing layers. Consequently, the risk of an authenticated local attacker successfully circumventing security policy constraints to run unauthorized code is confined to these specialized configurations.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Affected | ||
| Red Hat Enterprise Linux 6 | kernel | Out of support scope | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Affected | ||
| Red Hat Enterprise Linux 9 | kernel | Affected | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Affected |
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Дополнительная информация
Статус:
EPSS
7 High
CVSS3
Связанные уязвимости
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,...
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-fi
selinux: recheck intermediate backing files on mprotect()
In the Linux kernel, the following vulnerability has been resolved: s ...
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...
EPSS
7 High
CVSS3