[RFC][PATCH 4/5] Protect cinit from fatal signals

Sukadev Bhattiprolu
2008-11-26T03:46:58Z

>From 4ea8f0b4ae48da5f18d44b68ce3634408c89f230 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Tue, 25 Nov 2008 10:29:10 -0800
Subject: [PATCH 4/5] Protect cinit from fatal signals

To protect container-init from fatal signals, set SIGNAL_UNKILLABLE but
clear it if it receives SIGKILL from parent namespace - so it is still
killable from ancestor namespace.

Note that container-init is still somewhat special compared to 'normal
processes' - unhandled fatal signals like SIGUSR1 to a container-init
are dropped even if they are from ancestor namespace. SIGKILL from an
ancestor namespace is the only reliable way to kill a container-init.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
kernel/fork.c | 2 ++
kernel/signal.c | 2 ++
2 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 28be39a..368f25c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -814,6 +814,8 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
atomic_set(&sig->live, 1);
init_waitqueue_head(&sig->wait_chldexit);
sig->flags = 0;
+ if (clone_flags & CLONE_NEWPID)
+ sig->flags |= SIGNAL_UNKILLABLE;
sig->group_exit_code = 0;
sig->group_exit_task = NULL;
sig->group_stop_count = 0;
diff --git a/kernel/signal.c b/kernel/signal.c
index 45aebf0..8c294c1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -828,6 +828,8 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
trace_sched_signal_send(sig, t);

from_ancestor_ns = siginfo_from_ancestor_ns(t, info);
+ if (from_ancestor_ns && sig == SIGKILL)
+ t->signal->flags &= ~SIGNAL_UNKILLABLE;

assert_spin_locked(&t->sighand->siglock);
if (!prepare_signal(sig, t))
--
1.5.2.5