signal: Always deliver the kernel's SIGKILL and SIGSTOP to a pid namespace init

[ Upstream commit 3597dfe01d12f570bc739da67f857fd222a3ea66 ]

Instead of playing whack-a-mole and changing SEND_SIG_PRIV to
SEND_SIG_FORCED throughout the kernel to ensure a pid namespace init
gets signals sent by the kernel, stop allowing a pid namespace init to
ignore SIGKILL or SIGSTOP sent by the kernel.  A pid namespace init is
only supposed to be able to ignore signals sent from itself and
children with SIG_DFL.

Fixes: 921cf9f63089 ("signals: protect cinit from unblocked SIG_DFL signals")
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index e4aad0e..092fb48 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1035,7 +1035,7 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
 
        result = TRACE_SIGNAL_IGNORED;
        if (!prepare_signal(sig, t,
-                       from_ancestor_ns || (info == SEND_SIG_FORCED)))
+                       from_ancestor_ns || (info == SEND_SIG_PRIV) || (info == SEND_SIG_FORCED)))
                goto ret;
 
        pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;