[PATCH 3/4][Trivial] lib/kobject.c : Check ktype in kobject_add_internal

[yan <clouds.yan@gmail.com>]

If someone calls kobject_init with null kobj_type, kobject_init can 
detect it. But it does not have a return value, it just dumps stack.
In this case, a kobject_add after that will result in:
   -->kobject_add_varg
    -->kobject_add_internal
     -->create_dir
      -->sysfs_create_dir
       -->sysfs_read_ns_type
        -->kobj_child_ns_ops
In the end, it will call ->ktype->child_ns_type directly and we have
an oops.

Check ktype before really add a kobject.

Signed-off-by: Yan Hong <clouds.yan@gmail.com>
---
 lib/kobject.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index 85d5e9b..3ba6216 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -164,6 +164,9 @@ static int kobject_add_internal(struct kobject *kobj)
 	if (!kobj)
 		return -ENOENT;
 
+	if (!kobj->ktype)
+		return -EINVAL;
+
 	if (!kobj->name || !kobj->name[0]) {
 		WARN(1, "kobject: (%p): attempted to be registered with empty "
 			 "name!\n", kobj);
-- 
1.7.5.1