From 8382fcac1b813ad0a4e68a838fc7ae93fa39eda0 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xmission.com>
Date: Thu, 20 Dec 2012 19:26:06 -0800
Subject: [PATCH] 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@redhat.com>
Acked-by:  Oleg Nesterov <oleg@redhat.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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