CVE-2026-43121 io_uring/zcrx: fix user_ref race between scrub and refill paths

In the Linux kernel, the following vulnerability has been resolved: iouring/zcrx: fix userref race between scrub and refill paths The iozcrxputniovuref function uses a non-atomic check-then-decrement pattern atomicread followed by separate atomicdec to manipulate userrefs. This is serialized...