statmount: read the parent of an unmounted mount under mount_lock

Summary

In the Linux kernel, the following vulnerability has been resolved: statmount: read the parent of an unmounted mount under mount_lock statmount_mnt_basic() reads the ids of the parent through m->mnt_parent with namespace_sem held for reading. That's fine for a mount that is in a namespace. Everything above it is pinned by that namespace. STATMOUNT_BY_FD also accepts a file descriptor on a mount that has been unmounted on purpose and that only the file descriptor keeps alive. If that mount stayed attached to its parent when it was unmounted the parent is unmounted as well and nothing pins it for the child. The final mntput() unmounts the children under mount_lock alone and frees the parent afterwards. Concurrently, statmount_mnt_basic() reads m->mnt_parent twice while that can happen and can easily dereference a mount that's already gone. Read the parent of an unmounted mount under mount_lock. The parent can't be put while it is held and both ids come from the same mount. A mounted mount's parent is pinned by the namespace and a mount can't leave its namespace while namespace_sem is held, so the common case takes no global lock.

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 0e5032237ee5530147fbdf33134297e1490d5ec3 · fixed in 98fc6c7b6ca676157d2c780bd0a537b2c10fe08f; From 0e5032237ee5530147fbdf33134297e1490d5ec3 · fixed in bb46094057520304073130920c223451c2a694a7

• Linux Linux

  7.0

• KernelLinux

  From 7.0.0 · fixed in 7.2.11

References 2