linux-kernel - Re: [RFC][PATCH] Disable CLONE

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Message-ID: <20090701214805.GA25734@us.ibm.com>
Date:	Wed, 1 Jul 2009 14:48:05 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oren Laadan <orenl@...columbia.edu>, serue@...ibm.com,
	Alexey Dobriyan <adobriyan@...il.com>,
	Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Disable CLONE_PARENT for init

| This won't fix the problem. The child won't autoreap itself if ->exit_signal
| != SIGCHLD.
| 
| > If you want to make this change because of container-init issues, I think
| > you should just say so independent of this global-init case.
| 
| Yes, agreed, the comment looks confusing.
| 
| Oleg

Here is an updated patch with comments fixed.

Roland pls ack again if this is better.

---

Disable CLONE_PARENT for init.

When global or container-init processes use CLONE_PARENT, they create a
multi-rooted process tree. Besides if the siblings of init exit, the
SIGCHLD is not sent to init process resulting in the zombies sticking
around indefinitely.

Changelog[v3]:
	- [Roland, Oleg] Simplify comment describing the change
Changelog[v2]:
	- Simplify patch description based on comments from Eric Biederman
	  and Oleg Nesterov.
	- [Oleg Nesterov] Use SIGNAL_UNKILLABLE instead of is_global_init()

Signed-off-by: Sukadev Bhattiprolu <sukadev@...ibm.com>
---
 kernel/fork.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-mmotm/kernel/fork.c
===================================================================
--- linux-mmotm.orig/kernel/fork.c	2009-06-30 23:01:06.000000000 -0700
+++ linux-mmotm/kernel/fork.c	2009-07-01 14:43:10.000000000 -0700
@@ -974,6 +974,14 @@ static struct task_struct *copy_process(
 	if ((clone_flags & CLONE_SIGHAND) && !(clone_flags & CLONE_VM))
 		return ERR_PTR(-EINVAL);
 
+	/*
+	 * To avoid multi-rooted process-trees prevent global and container
+	 * inits from creating siblings.
+	 */
+	if ((clone_flags & CLONE_PARENT) &&
+				current->signal->flags & SIGNAL_UNKILLABLE)
+		return ERR_PTR(-EINVAL);
+
 	retval = security_task_create(clone_flags);
 	if (retval)
 		goto fork_out;
--
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