Task OOM via overflowing multishot receive CQEs

Denial of service in Linux kernel 6.0 through 6.5.2 allows local users to exhaust a task's memory through io_uring multishot receives. The io_recv_finish function passes an overflow-permitting flag to io_aux_cqe when emitting an auxiliary completion queue entry, so continued multishot receives can accumulate overflow CQEs without the normal refusal. Triggering the condition requires a local process to create an io_uring multishot receive; the bounded reported consequence is degraded performance or out-of-memory termination of that task.