Problem Description:
The FIOSSHMLPGCNF ioctl(2) operation configures the page size
for a largepage shared memory object. This is intended to be used
immediately after creating the object, before any memory is allocated
for the object. The handler checked whether a page size had already
been configured without holding the rangelock. Two concurrent
callers could both observe an unconfigured object and set conflicting
page sizes, leaving the object in an inconsistent state.
Impact:
An unprivileged local user can exploit this race to escalate
privileges.