Kernel service interruption via sleeping BPF signal call

Improper input validation in Linux and Siemens embedded Linux products allows local users to interrupt service through a BPF program. The bpf_send_signal() kfunc can sleep, but its guard checks only whether interrupts are disabled and can therefore invoke sleeping work from another non-preemptible context. Reachability requires local privileges sufficient to load and run a BPF program that calls the helper from a non-preemptible context.