hotplug: netns aware uevent_helper

It only makes sense for uevent_helper to get events
in the intial namespaces.  It's invocation is not
per namespace and it is not clear how we could make
it's invocation namespace aware.
Signed-off-by: NEric W. Biederman <ebiederm@xmission.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

lib/kobject_uevent.c

@@ -19,7 +19,7 @@
 #include <linux/kobject.h>
 #include <linux/module.h>
 #include <linux/slab.h>
-
+#include <linux/user_namespace.h>
 #include <linux/socket.h>
 #include <linux/skbuff.h>
 #include <linux/netlink.h>
@@ -99,6 +99,21 @@ static int kobj_bcast_filter(struct sock *dsk, struct sk_buff *skb, void *data)
 	return 0;
 }
 
+static int kobj_usermode_filter(struct kobject *kobj)
+{
+	const struct kobj_ns_type_operations *ops;
+
+	ops = kobj_ns_ops(kobj);
+	if (ops) {
+		const void *init_ns, *ns;
+		ns = kobj->ktype->namespace(kobj);
+		init_ns = ops->initial_ns();
+		return ns != init_ns;
+	}
+
+	return 0;
+}
+
 /**
  * kobject_uevent_env - send an uevent with environmental data
  *
@@ -274,7 +289,7 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 #endif
 
 	/* call uevent_helper, usually only enabled during early boot */
-	if (uevent_helper[0]) {
+	if (uevent_helper[0] && !kobj_usermode_filter(kobj)) {
 		char *argv [3];
 
 		argv [0] = uevent_helper;