pidns: Deny strange cases when creating pid namespaces.

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" <[email protected]>
ambv · Nov 19, 2012 · 225778d · 225778d
1 parent af4b8a8
commit 225778d
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
@@ -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);
 }