CVE-2026-98994

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.