[NETLINK]: Limit NLMSG_GOODSIZE to 8K.

Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netlink.h

@@ -171,9 +171,16 @@ int netlink_sendskb(struct sock *sk, struct sk_buff *skb, int protocol);
 
 /*
  *	skb should fit one page. This choice is good for headerless malloc.
+ *	But we should limit to 8K so that userspace does not have to
+ *	use enormous buffer sizes on recvmsg() calls just to avoid
+ *	MSG_TRUNC when PAGE_SIZE is very large.
  */
-#define NLMSG_GOODORDER 0
-#define NLMSG_GOODSIZE (SKB_MAX_ORDER(0, NLMSG_GOODORDER))
+#if PAGE_SIZE < 8192UL
+#define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(PAGE_SIZE)
+#else
+#define NLMSG_GOODSIZE	SKB_WITH_OVERHEAD(8192UL)
+#endif
+
 #define NLMSG_DEFAULT_SIZE (NLMSG_GOODSIZE - NLMSG_HDRLEN)
 
 

include/linux/skbuff.h

@@ -39,9 +39,11 @@
 
 #define SKB_DATA_ALIGN(X)	(((X) + (SMP_CACHE_BYTES - 1)) & \
 				 ~(SMP_CACHE_BYTES - 1))
-#define SKB_MAX_ORDER(X, ORDER)	(((PAGE_SIZE << (ORDER)) - (X) - \
-				  sizeof(struct skb_shared_info)) & \
-				  ~(SMP_CACHE_BYTES - 1))
+#define SKB_WITH_OVERHEAD(X)	\
+	(((X) - sizeof(struct skb_shared_info)) & \
+	 ~(SMP_CACHE_BYTES - 1))
+#define SKB_MAX_ORDER(X, ORDER) \
+	SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X))
 #define SKB_MAX_HEAD(X)		(SKB_MAX_ORDER((X), 0))
 #define SKB_MAX_ALLOC		(SKB_MAX_ORDER(0, 2))