Commit 2ebd69e8 authored Nov 17, 2017 by Oleg Nesterov Committed by Greg Kroah-Hartman Jan 10, 2018

kernel/signal.c: protect the traced SIGNAL_UNKILLABLE tasks from SIGKILL

commit 628c1bcba204052d19b686b5bac149a644cdb72e upstream.

The comment in sig_ignored() says "Tracers may want to know about even
ignored signals" but SIGKILL can not be reported to debugger and it is
just wrong to return 0 in this case: SIGKILL should only kill the
SIGNAL_UNKILLABLE task if it comes from the parent ns.

Change sig_ignored() to ignore ->ptrace if sig == SIGKILL and rely on
sig_task_ignored().

SISGTOP coming from within the namespace is not really right too but at
least debugger can intercept it, and we can't drop it here because this
will break "gdb -p 1": ptrace_attach() won't work.  Perhaps we will add
another ->ptrace check later, we will see.

Link: http://lkml.kernel.org/r/20171103184206.GB21036@redhat.com


Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Tested-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 22af48be

kernel/signal.c

+7 −5

Original line number	Diff line number	Diff line
		@@ -94,13 +94,15 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
		if (sigismember(&t->blocked, sig) \|\| sigismember(&t->real_blocked, sig))
		return 0;

		if (!sig_task_ignored(t, sig, force))
		return 0;

		/*
		* Tracers may want to know about even ignored signals.
		* Tracers may want to know about even ignored signal unless it
		* is SIGKILL which can't be reported anyway but can be ignored
		* by SIGNAL_UNKILLABLE task.
		*/
		return !t->ptrace;
		if (t->ptrace && sig != SIGKILL)
		return 0;

		return sig_task_ignored(t, sig, force);
		}

		/*