CVE-2026-72034

In the Linux kernel, the following vulnerability has been resolved:

fhandle: reject detached mounts in capable_wrt_mount()

The recent fhandle RCU fix moved the mount namespace capability check

into capable_wrt_mount(), so a non-NULL mnt_namespace survives the

ns_capable() dereference. The helper still assumes the later

READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh()

checked is_mounted() first.

That assumption is not stable. A detached mount from

open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while

open_by_handle_at() is between those checks, and umount_tree() can

clear mount->mnt_ns. If the helper observes NULL, it dereferences

mnt_ns->user_ns and panics.

Return false when the RCU read observes a detached mount. This keeps

the relaxed permission path conservative: a mount no longer attached

to a namespace cannot authorize open_by_handle_at() access.