linux-kernel - [PATCH 09/26] signal: Don't allow sending SIGKILL or SIGSTOP to init

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Date:   Tue,  6 Jun 2017 14:03:21 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-api@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...omium.org>,
        Roland McGrath <roland@...k.frob.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 09/26] signal: Don't allow sending SIGKILL or SIGSTOP to init

Even to init SIGKILL and SIGSTOP are alwasys delivered if they are
sent, so don't allow tracing an init task allow them.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/signal.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 5eff2f9f8c42..627b482fa3f8 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -98,8 +98,12 @@ static int sig_ignored(struct task_struct *t, int sig, bool force)
 
 	/*
 	 * Tracers may want to know about even ignored signals.
+	 * We can never safely allow SIGKILL or SIGSTOP to
+	 * be sent to init from it's children.
 	 */
-	return !t->ptrace;
+	return !t->ptrace ||
+		((t->signal->flags & SIGNAL_UNKILLABLE) &&
+		 sig_kernel_only(sig) && !force);
 }
 
 /*
-- 
2.10.1