linux-kernel - [PATCH 1/1] CLONE_PARENT shouldn't allow to set ->exit

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Date:	Wed, 14 Mar 2012 19:55:38 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Djalal Harouni <tixxdz@...ndz.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Al Viro <viro@...iv.linux.org.uk>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Kees Cook <keescook@...omium.org>,
	Solar Designer <solar@...nwall.com>,
	WANG Cong <xiyou.wangcong@...il.com>,
	James Morris <james.l.morris@...cle.com>,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Greg KH <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...e.hu>, Stephen Wilson <wilsons@...rt.ca>,
	"Jason A. Donenfeld" <Jason@...c4.com>,
	Roland McGrath <roland@...k.frob.com>
Subject: [PATCH 1/1] CLONE_PARENT shouldn't allow to set ->exit_signal

The child must not control its ->exit_signal, it is the parent who
decides which signal the child should use for notification.

This means that CLONE_PARENT should not use "clone_flags & CSIGNAL",
the forking task is the sibling of the new process and their parent
doesn't control exit_signal in this case.

This patch uses ->exit_signal of the forking process, but perhaps
we should simply use SIGCHLD.

We read group_leader->exit_signal lockless, this can race with the
ORIGINAL_SIGNAL -> SIGCHLD transition, but this is fine.

Potentially this change allows to kill self_exec_id/parent_exec_id.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/fork.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index b77fd55..34d7ed1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1310,7 +1310,13 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	clear_all_latency_tracing(p);
 
 	/* ok, now we should be set up.. */
-	p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
+	if (clone_flags & CLONE_THREAD)
+		p->exit_signal = -1;
+	else if (clone_flags & CLONE_PARENT)
+		p->exit_signal = current->group_leader->exit_signal;
+	else
+		p->exit_signal = (clone_flags & CSIGNAL);
+
 	p->pdeath_signal = 0;
 	p->exit_state = 0;
 
-- 
1.5.5.1


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