In the Linux kernel, the following vulnerability has been resolved:
namespace: don't inherit MNT_UMOUNT in clone_mnt()
MNT_UMOUNT gets raised on a mount that umount_tree() or umount_one() has
taken out of its namespace. It's never cleared. __detach_mounts()
unhooks a mount that carries it instead of unmounting it.
disconnect_mount() lets an unmounted child stay attached only if its
parent carries it. propagate_umount() takes it as the sign that a mount
is going to be unmounted when it decides what else can be unmounted,
where a chain of locked mounts ends and where a for reparenting an
overmount.
clone_mnt() copies the flags of the source and only masks
MNT_INTERNAL_FLAGS which doesn't include MNT_UMOUNT. A mount that was
lazily unmounted but is kept alive by a file descriptor can still be
copied when its root is an nsfs or pidfs file because may_copy_tree()
accepts those before checking whether the source is mounted at all:
mount --bind /proc/self/ns/net /tmp/x
exec 3< /tmp/x
umount -l /tmp/x
mount --bind /proc/self/fd/3 /tmp/y
The mount on /tmp/y is attached to the caller's namespace with
MNT_UMOUNT already set and every copy of it inherits the flag again.
That causes a number of bugs:
- Unlink its mountpoint from a mount namespace where it isn't one.
__detach_mounts() takes it for a mount that was unmounted earlier,
unhooks it from its parent and drops the reference the namespace
holds on it. It stays in the namespace with one reference too few
and as its own parent, so it can't be unmounted through the file
descriptor anymore and the namespace never finds it again. When the
namespace goes away it's leaked and points to a freed struct
mnt_namespace that may_change_propagation() and anon_ns_root() read
on the next propagation change or mount_setattr() through the file
descriptor.
- Make it shared and unmount a peer. trace_transfers() follows the
flag from the peer into it and strips it from its peer group.
- Let a propagated umount reach it. gather_candidates() marks it with
T_UMOUNT_CANDIDATE but never puts it on the candidate list, so the
mark is never cleared and every later propagated umount skips it. If
it's the parent of a locked mount handle_locked() takes it as the
cutoff and commits the locked child that should have stayed and
disconnect_mount() leaves that child attached to it, unmounted under
a mounted parent, which is what disconnect_mount() exists to
prevent. When the namespace goes away umount_tree() visits the child
a second time. And once __detach_mounts() has made it its own parent
reparent() never finds the end of the chain of unmounted parents.
A clone is a new mount that has never been unmounted. Add MNT_UMOUNT
to MNT_INTERNAL_FLAGS so clone_mnt() never copies it. And warn when
umount_tree() reaches a mount that already has it set.
namespace: don't inherit MNT_UMOUNT in clone_mnt()
MNT_UMOUNT gets raised on a mount that umount_tree() or umount_one() has
taken out of its namespace. It's never cleared. __detach_mounts()
unhooks a mount that carries it instead of unmounting it.
disconnect_mount() lets an unmounted child stay attached only if its
parent carries it. propagate_umount() takes it as the sign that a mount
is going to be unmounted when it decides what else can be unmounted,
where a chain of locked mounts ends and where a for reparenting an
overmount.
clone_mnt() copies the flags of the source and only masks
MNT_INTERNAL_FLAGS which doesn't include MNT_UMOUNT. A mount that was
lazily unmounted but is kept alive by a file descriptor can still be
copied when its root is an nsfs or pidfs file because may_copy_tree()
accepts those before checking whether the source is mounted at all:
mount --bind /proc/self/ns/net /tmp/x
exec 3< /tmp/x
umount -l /tmp/x
mount --bind /proc/self/fd/3 /tmp/y
The mount on /tmp/y is attached to the caller's namespace with
MNT_UMOUNT already set and every copy of it inherits the flag again.
That causes a number of bugs:
- Unlink its mountpoint from a mount namespace where it isn't one.
__detach_mounts() takes it for a mount that was unmounted earlier,
unhooks it from its parent and drops the reference the namespace
holds on it. It stays in the namespace with one reference too few
and as its own parent, so it can't be unmounted through the file
descriptor anymore and the namespace never finds it again. When the
namespace goes away it's leaked and points to a freed struct
mnt_namespace that may_change_propagation() and anon_ns_root() read
on the next propagation change or mount_setattr() through the file
descriptor.
- Make it shared and unmount a peer. trace_transfers() follows the
flag from the peer into it and strips it from its peer group.
- Let a propagated umount reach it. gather_candidates() marks it with
T_UMOUNT_CANDIDATE but never puts it on the candidate list, so the
mark is never cleared and every later propagated umount skips it. If
it's the parent of a locked mount handle_locked() takes it as the
cutoff and commits the locked child that should have stayed and
disconnect_mount() leaves that child attached to it, unmounted under
a mounted parent, which is what disconnect_mount() exists to
prevent. When the namespace goes away umount_tree() visits the child
a second time. And once __detach_mounts() has made it its own parent
reparent() never finds the end of the chain of unmounted parents.
A clone is a new mount that has never been unmounted. Add MNT_UMOUNT
to MNT_INTERNAL_FLAGS so clone_mnt() never copies it. And warn when
umount_tree() reaches a mount that already has it set.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||||||||
| Linux | Linux | affected |
|
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Fixes
Solution
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Workaround
No workaround given by the vendor.
References
History
Fri, 23 Oct 2026 15:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-459 |
Fri, 23 Oct 2026 12:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: namespace: don't inherit MNT_UMOUNT in clone_mnt() MNT_UMOUNT gets raised on a mount that umount_tree() or umount_one() has taken out of its namespace. It's never cleared. __detach_mounts() unhooks a mount that carries it instead of unmounting it. disconnect_mount() lets an unmounted child stay attached only if its parent carries it. propagate_umount() takes it as the sign that a mount is going to be unmounted when it decides what else can be unmounted, where a chain of locked mounts ends and where a for reparenting an overmount. clone_mnt() copies the flags of the source and only masks MNT_INTERNAL_FLAGS which doesn't include MNT_UMOUNT. A mount that was lazily unmounted but is kept alive by a file descriptor can still be copied when its root is an nsfs or pidfs file because may_copy_tree() accepts those before checking whether the source is mounted at all: mount --bind /proc/self/ns/net /tmp/x exec 3< /tmp/x umount -l /tmp/x mount --bind /proc/self/fd/3 /tmp/y The mount on /tmp/y is attached to the caller's namespace with MNT_UMOUNT already set and every copy of it inherits the flag again. That causes a number of bugs: - Unlink its mountpoint from a mount namespace where it isn't one. __detach_mounts() takes it for a mount that was unmounted earlier, unhooks it from its parent and drops the reference the namespace holds on it. It stays in the namespace with one reference too few and as its own parent, so it can't be unmounted through the file descriptor anymore and the namespace never finds it again. When the namespace goes away it's leaked and points to a freed struct mnt_namespace that may_change_propagation() and anon_ns_root() read on the next propagation change or mount_setattr() through the file descriptor. - Make it shared and unmount a peer. trace_transfers() follows the flag from the peer into it and strips it from its peer group. - Let a propagated umount reach it. gather_candidates() marks it with T_UMOUNT_CANDIDATE but never puts it on the candidate list, so the mark is never cleared and every later propagated umount skips it. If it's the parent of a locked mount handle_locked() takes it as the cutoff and commits the locked child that should have stayed and disconnect_mount() leaves that child attached to it, unmounted under a mounted parent, which is what disconnect_mount() exists to prevent. When the namespace goes away umount_tree() visits the child a second time. And once __detach_mounts() has made it its own parent reparent() never finds the end of the chain of unmounted parents. A clone is a new mount that has never been unmounted. Add MNT_UMOUNT to MNT_INTERNAL_FLAGS so clone_mnt() never copies it. And warn when umount_tree() reaches a mount that already has it set. | |
| Title | namespace: don't inherit MNT_UMOUNT in clone_mnt() | |
| 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: 2026-10-23T12:20:12.266Z
Reserved: 2026-09-25T10:25:14.384Z
Link: CVE-2026-98993
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-23T13:17:21.410
Modified: 2026-10-23T13:17:21.410
Link: CVE-2026-98993
Redhat
No data.
OpenCVE Enrichment
Updated: 2026-10-23T15:00:13Z
Weaknesses