linux-kernel - [PATCH review 1/3] pidns: Outlaw thread creation after unshare(CLONE

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Message-ID: <877goaela9.fsf@xmission.com>
Date:	Fri, 21 Dec 2012 20:57:34 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linux Containers <containers@...ts.linux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: [PATCH review 1/3] pidns: Outlaw thread creation after unshare(CLONE_NEWPID)


The sequence:
unshare(CLONE_NEWPID)
clone(CLONE_THREAD|CLONE_SIGHAND|CLONE_VM)

Creates a new process in the new pid namespace without setting
pid_ns->child_reaper.  After forking this results in a NULL
pointer dereference.

Avoid this and other nonsense scenarios that can show up after
creating a new pid namespace with unshare by adding a new
check in copy_prodcess.

Pointed-out-by:  Oleg Nesterov <oleg@...hat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 kernel/fork.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index a31b823..65ca6d2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1166,6 +1166,14 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 				current->signal->flags & SIGNAL_UNKILLABLE)
 		return ERR_PTR(-EINVAL);
 
+	/*
+	 * If the new process will be in a different pid namespace
+	 * don't allow the creation of threads.
+	 */
+	if ((clone_flags & (CLONE_VM|CLONE_NEWPID)) &&
+	    (task_active_pid_ns(current) != current->nsproxy->pid_ns))
+		return ERR_PTR(-EINVAL);
+
 	retval = security_task_create(clone_flags);
 	if (retval)
 		goto fork_out;
-- 
1.7.5.4

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