Description
In the Linux kernel, the following vulnerability has been resolved:
namespace: refuse an automount below a mount that is in no namespace
It's possible to add autmounts even when the parent mount isn't in the
mount namespace of the caller. The only requirement we have is that the
parent mount namespace must not be NULL, i.e., unmounted.
Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes
that trivially true. So that passes the test and attach_recursive_mnt()
accepts that as a mount point and funny enough, count_mounts()
dereferences MNT_NS_INTERNAL. The problem is it is an error pointer...
So we can reach this in userspace via fanotify. A filesystem mark on the
lower filesystem of an overlay reports paths on the layer clone and
reading the event hands out a descriptor on it. For example with debugfs
as the lower layer it goes kaboom:
openat(evfd, "tracing", O_DIRECTORY)
Oops: general protection fault
KASAN: null-ptr-deref in range [0x1d0-0x1d7]
RIP: 0010:count_mounts+0x35/0x200
attach_recursive_mnt
finish_automount
And since that sleeping beauty happens under namespace_sem held for
writing every mount operation on the system blocks from then on.
Congrats.
Use is_mounted() instead which rejects unmounted and internal mounts
alike. The open fails with EINVAL just as it did before
clone_private_mount() used MNT_NS_INTERNAL.
namespace: refuse an automount below a mount that is in no namespace
It's possible to add autmounts even when the parent mount isn't in the
mount namespace of the caller. The only requirement we have is that the
parent mount namespace must not be NULL, i.e., unmounted.
Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes
that trivially true. So that passes the test and attach_recursive_mnt()
accepts that as a mount point and funny enough, count_mounts()
dereferences MNT_NS_INTERNAL. The problem is it is an error pointer...
So we can reach this in userspace via fanotify. A filesystem mark on the
lower filesystem of an overlay reports paths on the layer clone and
reading the event hands out a descriptor on it. For example with debugfs
as the lower layer it goes kaboom:
openat(evfd, "tracing", O_DIRECTORY)
Oops: general protection fault
KASAN: null-ptr-deref in range [0x1d0-0x1d7]
RIP: 0010:count_mounts+0x35/0x200
attach_recursive_mnt
finish_automount
And since that sleeping beauty happens under namespace_sem held for
writing every mount operation on the system blocks from then on.
Congrats.
Use is_mounted() instead which rejects unmounted and internal mounts
alike. The open fails with EINVAL just as it did before
clone_private_mount() used MNT_NS_INTERNAL.
Published:
2026-10-23
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
Analysis and contextual insights are available on OpenCVE Cloud.
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 |
|
No data.
No data.
No data available yet.
Remediation
No vendor fix or workaround currently provided.
Additional remediation guidance may be available on OpenCVE Cloud.
Tracking
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Advisories
No advisories yet.
References
History
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: refuse an automount below a mount that is in no namespace It's possible to add autmounts even when the parent mount isn't in the mount namespace of the caller. The only requirement we have is that the parent mount namespace must not be NULL, i.e., unmounted. Problem is that clone_private_mount() has MNT_NS_INTERNAL which makes that trivially true. So that passes the test and attach_recursive_mnt() accepts that as a mount point and funny enough, count_mounts() dereferences MNT_NS_INTERNAL. The problem is it is an error pointer... So we can reach this in userspace via fanotify. A filesystem mark on the lower filesystem of an overlay reports paths on the layer clone and reading the event hands out a descriptor on it. For example with debugfs as the lower layer it goes kaboom: openat(evfd, "tracing", O_DIRECTORY) Oops: general protection fault KASAN: null-ptr-deref in range [0x1d0-0x1d7] RIP: 0010:count_mounts+0x35/0x200 attach_recursive_mnt finish_automount And since that sleeping beauty happens under namespace_sem held for writing every mount operation on the system blocks from then on. Congrats. Use is_mounted() instead which rejects unmounted and internal mounts alike. The open fails with EINVAL just as it did before clone_private_mount() used MNT_NS_INTERNAL. | |
| Title | namespace: refuse an automount below a mount that is in no namespace | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-23T12:19:52.523Z
Reserved: 2026-09-25T10:25:14.383Z
Link: CVE-2026-98979
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-23T13:17:19.627
Modified: 2026-10-23T13:17:19.627
Link: CVE-2026-98979
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.