From f008faff0e2777c8b3fe853891b774ca465938d8 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Thu, 2 Apr 2009 16:58:02 -0700 Subject: [PATCH] signals: protect init from unwanted signals more (This is a modified version of the patch submitted by Oleg Nesterov http://lkml.org/lkml/2008/11/18/249 and tries to address comments that came up in that discussion) init ignores the SIG_DFL signals but we queue them anyway, including SIGKILL. This is mostly OK, the signal will be dropped silently when dequeued, but the pending SIGKILL has 2 bad implications: - it implies fatal_signal_pending(), so we confuse things like wait_for_completion_killable/lock_page_killable. - for the sub-namespace inits, the pending SIGKILL can mask (legacy_queue) the subsequent SIGKILL from the parent namespace which must kill cinit reliably. (preparation, cinits don't have SIGNAL_UNKILLABLE yet) The patch can't help when init is ptraced, but ptracing of init is not "safe" anyway. Signed-off-by: Sukadev Bhattiprolu Acked-by: Roland McGrath Signed-off-by: Oleg Nesterov Cc: "Eric W. Biederman" Cc: Daniel Lezcano Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/signal.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/kernel/signal.c b/kernel/signal.c index 92a1ab00449..8bf7a40e5c7 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -55,10 +55,21 @@ static int sig_handler_ignored(void __user *handler, int sig) (handler == SIG_DFL && sig_kernel_ignore(sig)); } -static int sig_ignored(struct task_struct *t, int sig) +static int sig_task_ignored(struct task_struct *t, int sig) { void __user *handler; + handler = sig_handler(t, sig); + + if (unlikely(t->signal->flags & SIGNAL_UNKILLABLE) && + handler == SIG_DFL) + return 1; + + return sig_handler_ignored(handler, sig); +} + +static int sig_ignored(struct task_struct *t, int sig) +{ /* * Blocked signals are never ignored, since the * signal handler may change by the time it is @@ -67,8 +78,7 @@ static int sig_ignored(struct task_struct *t, int sig) if (sigismember(&t->blocked, sig) || sigismember(&t->real_blocked, sig)) return 0; - handler = sig_handler(t, sig); - if (!sig_handler_ignored(handler, sig)) + if (!sig_task_ignored(t, sig)) return 0; /*