Commit f008faff authored Apr 02, 2009 by Oleg Nesterov Committed by Linus Torvalds Apr 02, 2009

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 <sukadev@linux.vnet.ibm.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 43918f2b

kernel/signal.c

+13 −3

Original line number	Diff line number	Diff line
		@@ -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;

		/*

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