cred: Refcount the user_ns pointed to by the cred.

struct user_struct will shortly loose it's user_ns reference
so make the cred user_ns reference a proper reference complete
with reference counting.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index 70febff..447fb76 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -858,7 +858,7 @@
 	new-> sgid	= old-> sgid;
 	new->fsgid	= old->fsgid;
 	new->user	= get_uid(old->user);
-	new->user_ns	= new->user_ns;
+	new->user_ns	= get_user_ns(new->user_ns);
 	new->group_info	= get_group_info(old->group_info);
 
 	new->securebits	= old->securebits;