userns: Add an explicit reference to the parent user namespace

I am about to remove the struct user_namespace reference from struct user_struct.
So keep an explicit track of the parent user namespace.

Take advantage of this new reference and replace instances of user_ns->creator->user_ns
with user_ns->parent.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index faf467944baf..dc2d85a76376 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -12,6 +12,7 @@
 struct user_namespace {
         struct kref             kref;
         struct hlist_head       uidhash_table[UIDHASH_SZ];
+        struct user_namespace   *parent;
         struct user_struct      *creator;
         struct work_struct      destroyer;
 };