ipc, msg: forbid negative values for "msg{max,mnb,mni}"

Negative message lengths make no sense -- so don't do negative queue
lenghts or identifier counts. Prevent them from getting negative.

Also change the underlying data types to be unsigned to avoid hairy
surprises with sign extensions in cases where those variables get
evaluated in unsigned expressions with bigger data types, e.g size_t.

In case a user still wants to have "unlimited" sizes she could just use
INT_MAX instead.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index 19c19a5..f6c82de 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -34,9 +34,9 @@
 	int		sem_ctls[4];
 	int		used_sems;
 
-	int		msg_ctlmax;
-	int		msg_ctlmnb;
-	int		msg_ctlmni;
+	unsigned int	msg_ctlmax;
+	unsigned int	msg_ctlmnb;
+	unsigned int	msg_ctlmni;
 	atomic_t	msg_bytes;
 	atomic_t	msg_hdrs;
 	int		auto_msgmni;