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

futex: Also allocate private hash on vfork()

As Jann demonstrated, it is entirely feasible to access the mm through vfork().
Therefore we need to allocate a private hash on vfork() as well as any other
CLONE_VM user.

Specifically, it must be avoided to have (private) futex waiters before
allocating the private hash.