From 306d71b091908bd898cbc0d7e98130354b62be2e Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Fri, 26 Jun 2026 17:33:08 +0200 Subject: [PATCH] signal: change sys_kill() to use SEND_SIG_NOINFO prepare_kill_siginfo(PIDTYPE_TGID) fills si_code = SI_USER and sets si_pid/si_uid in the sender's namespace. Then send_signal_locked() translates si_pid/si_uid to the target's namespace. SEND_SIG_NOINFO exists precisely for the case when si_code == SI_USER and si_pid/si_uid are the sender's ids; this is exactly what sys_kill() does via prepare_kill_siginfo(PIDTYPE_TGID). Change sys_kill() to use it directly. SEND_SIG_NOINFO produces the same result: si_code = SI_USER, and __send_signal_locked() computes si_pid/si_uid directly in the target's namespace. The force computation is also the same: both check if the sender is visible in the target's pid namespace. This is just a cleanup and microoptimization (especially with [1]), this skips the has_si_pid_and_uid() block in send_signal_locked() and offloads the namespace translation logic to __send_signal_locked(SEND_SIG_NOINFO) which uses the simpler computations. NOTE: As a "side effect" this also fixes the kill(pid < 0, sig) case where send_signal_locked() rewrites si_pid/si_uid in the shared siginfo, corrupting it for subsequent recipients. But for other group senders like __kill_pgrp_info() we still need the fix from Bradley Morgan [1] who found this problem. TODO: kill prepare_kill_siginfo() and change other users to use SEND_SIG_NOINFO too. This needs trivial changes in __send_signal_locked() and TP_STORE_SIGINFO(). Link: https://lore.kernel.org/aj6btAZqYuv59a8w@redhat.com Link: https://lore.kernel.org/all/20260622164029.11474-1-include@grrlz.net/ [1] Signed-off-by: Oleg Nesterov Reviewed-by: Bradley Morgan Cc: Eric Biederman Signed-off-by: Andrew Morton --- kernel/signal.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index c53f202da9da..041498ff835e 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -3962,11 +3962,7 @@ static void prepare_kill_siginfo(int sig, struct kernel_siginfo *info, */ SYSCALL_DEFINE2(kill, pid_t, pid, int, sig) { - struct kernel_siginfo info; - - prepare_kill_siginfo(sig, &info, PIDTYPE_TGID); - - return kill_something_info(sig, &info, pid); + return kill_something_info(sig, SEND_SIG_NOINFO, pid); } /*