namespace: remove the fsnotify marks of a mount namespace in process context

Summary

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.

Timeline

1. Oct 23, 2026, 12:20 PM UTCCVE published
2. Oct 23, 2026, 12:45 PM UTCFirst seen by cve.now

Affected versions

• Linux Linux

  From bf630c40164162ba1d3933c2f5e3397d083e0948 · fixed in 888363d74c3b5d32e2accf217add70f8b38e0e2b; From bf630c40164162ba1d3933c2f5e3397d083e0948 · fixed in 9e820a6becdd955a04adbedfd767253a47eedd9e; From bf630c40164162ba1d3933c2f5e3397d083e0948 · fixed in 1a116222acdcc1bc1a8350727ae6f28907d44594

• Linux Linux

  6.15

• KernelLinux

  From 6.15.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.11

References 3