[PATCH AUTOSEL 4.18 122/126] signal: Always deliver the kernel's SIGKILL and SIGSTOP to a pid namespace init

From: Sasha Levin
Date: Wed Oct 31 2018 - 19:29:55 EST

From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

[ 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@xxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
kernel/signal.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 41a5dd2df27d..1628b67992d6 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1009,7 +1009,7 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,

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 = group ? &t->signal->shared_pending : &t->pending;