Use after free in io_uring in the Linux Kernel

Due to a vulnerability in the io_uring subsystem, it is possible to leak kernel memory information to the user process. timens_install calls current_is_single_threaded to determine if the current process is single-threaded, but this call does not consider io_uring's io_worker threads, thus it is possible to insert a time namespace's vvar page to process's memory space via a page fault. When this time namespace is destroyed, the vvar page is also freed, but not removed from the process' memory, and a next page allocated by the kernel will be still available from the user-space process and can leak memory contents via this (read-only) use-after-free vulnerability. We recommend upgrading past version 5.10.161 or commit  788d0824269bef539fe31a785b1517882eafed93 https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/io_uring