CVE-2026-98986 namespace: remove the fsnotify marks of a mount namespace in process context
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-98986?
CVE-2026-98986 is a vulnerability in Linux, published on 23 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
namespace: remove the fsnotify marks of a mount namespace in process context
mnt_ns_release() drops the last passive reference of a mount namespace and removes its fanotify marks via fsnotify_mntns_delete(). That takes the mutex of every group with a mark on the namespace and the spinlock of the connector. Fine from process context. But mnt_ns_tree_remove() hands the reference the namespace was allocated with to call_rcu() and so the marks are removed from the RCU softirq:
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:623 in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/3 __mutex_lock+0x113/0x24b0 fsnotify_destroy_marks+0x11b/0x3d0 mnt_ns_release_rcu+0x57/0xa0 rcu_core+0x6b6/0x1e40
and lockdep complains about the connector lock being taken from softirq context. A fanotify group with a FAN_MARK_MNTNS mark on the mount namespace of another task is all that's needed. Root in a user namespace can do that for a mount namespace it owns. The task exits and the namespace is freed with the mark still on it.
Remove the marks in free_mnt_ns() before the namespace is handed to RCU. That runs in process context once the last active reference is gone. A mark is added through a file descriptor to the namespace which holds an active reference so no mark can show up after that.
Which versions are affected by CVE-2026-98986?
How do I fix CVE-2026-98986?
Upgrade to a fixed version.
Is CVE-2026-98986 being exploited?
There is no known exploitation of CVE-2026-98986 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-98986, DEBIAN-CVE-2026-98986, GHSA-6338-gv67-39m8, UBUNTU-CVE-2026-98986.