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pidns: Deny strange cases when creating pid namespaces.

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task_active_pid_ns(current) != current->ns_proxy->pid_ns will
soon be allowed to support unshare and setns.

The definition of creating a child pid namespace when
task_active_pid_ns(current) != current->ns_proxy->pid_ns could be that
we create a child pid namespace of current->ns_proxy->pid_ns.  However
that leads to strange cases like trying to have a single process be
init in multiple pid namespaces, which is racy and hard to think
about.

The definition of creating a child pid namespace when
task_active_pid_ns(current) != current->ns_proxy->pid_ns could be that
we create a child pid namespace of task_active_pid_ns(current).  While
that seems less racy it does not provide any utility.

Therefore define the semantics of creating a child pid namespace when
task_active_pid_ns(current) != current->ns_proxy->pid_ns to be that the
pid namespace creation fails.  That is easy to implement and easy
to think about.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2012-08-02 08:35:35 -07:00
parent af4b8a83ad
commit 225778d68d
1 changed files with 2 additions and 0 deletions
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2
kernel/pid_namespace.c
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@ -146,6 +146,8 @@ struct pid_namespace *copy_pid_ns(unsigned long flags,
return get_pid_ns(old_ns);
if (flags & (CLONE_THREAD|CLONE_PARENT))
return ERR_PTR(-EINVAL);
if (task_active_pid_ns(current) != old_ns)
return ERR_PTR(-EINVAL);
return create_pid_namespace(user_ns, old_ns);
}