Use after free in io_uring in the Linux Kernel

There is a logic error in io_uring's implementation which can be used to trigger a use-after-free vulnerability leading to privilege escalation.

In the io_prep_async_work function the assumption that the last io_grab_identity call cannot return false is not true, and in this case the function will use the init_cred or the previous linked requests identity to do operations instead of using the current identity. This can lead to reference counting issues causing use-after-free. We recommend upgrading past version 5.10.161.