An issue was discovered in the Linux kernel before 5.9.3. io_uring takes a non-refcounted reference to the files_struct of the process that submitted a request, causing execve() to incorrectly optimize unshare_fd(), aka CID-0f2122045b94.
https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.9.3
https://bugs.chromium.org/p/project-zero/issues/detail?id=2089