Linux 5.3 - Privilege Escalation via io_uring Offload of sendmsg() onto Kernel Thread with Kernel Creds

Since commit 0fa03c624d8f "iouring: add support for sendmsg", first in v5.3, iouring has support for asynchronously calling sendmsg. Unprivileged userspace tasks can submit IORINGOPSENDMSG submission queue entries, which cause sendmsg to be called either in syscall context in the original task, o...