userns: Convert ipc to use kuid and kgid where appropriate

- Store the ipc owner and creator with a kuid
- Store the ipc group and the crators group with a kgid.
- Add error handling to ipc_update_perms, allowing it to
  fail if the uids and gids can not be converted to kuids
  or kgids.
- Modify the proc files to display the ipc creator and
  owner in the user namespace of the opener of the proc file.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

include/linux/ipc.h

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 30e8161..ca833fd 100644
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -79,6 +79,7 @@
 
 #ifdef __KERNEL__
 #include <linux/spinlock.h>
+#include <linux/uidgid.h>
 
 #define IPCMNI 32768  /* <= MAX_INT limit for ipc arrays (including sysctl changes) */
 
@@ -89,10 +90,10 @@
 	int		deleted;
 	int		id;
 	key_t		key;
-	uid_t		uid;
-	gid_t		gid;
-	uid_t		cuid;
-	gid_t		cgid;
+	kuid_t		uid;
+	kgid_t		gid;
+	kuid_t		cuid;
+	kgid_t		cgid;
 	umode_t		mode; 
 	unsigned long	seq;
 	void		*security;