The bot's finding is correct, and this is a regression this patch introduces, so I want to flag it and the v2 direction up front.
kill_pgrp_lsm() calls security_task_kill() with __si_special(priv), i.e. SEND_SIG_PRIV ((void *)1). On the ordinary paths, check_kill_permission() returns early via si_fromuser() before the hook, so security_task_kill() never receives that sentinel. This patch reaches the hook directly and breaks that invariant. The in-tree C LSMs do not dereference info, but task_kill is a trusted BPF LSM hook. An attached BPF LSM program is therefore allowed to dereference info and can fault when it receives (void *)1. v2 will synthesize a valid kernel_siginfo for the LSM check (user-attributed, since TIOCSIG is user-triggered) and keep the privileged delivery unchanged, so the hook always sees a valid pointer. This does not change the two questions the RFC is really asking (whether TIOCSIG should be mediated at all, and task_kill versus a dedicated TTY signal hook). If the answer is a dedicated hook, the siginfo concern goes away with it.
