CVE-2025-39698: Use After Free

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

io_uring/futex: ensure io_futex_wait() cleans up properly on failure

The io_futex_data is allocated upfront and assigned to the io_kiocb async_data field, but the request isn't marked with REQ_F_ASYNC_DATA at that point. Those two should always go together, as the flag tells io_uring whether the field is valid or not.

Additionally, on failure cleanup, the futex handler frees the data but does not clear ->async_data. Clear the data and the flag in the error path as well.

Thanks to Trend Micro Zero Day Initiative and particularly ReDress for reporting this.