ipoib: validate struct ipoib_cb size

To catch future errors sooner.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/infiniband/ulp/ipoib/ipoib.h

@@ -131,6 +131,12 @@ struct ipoib_cb {
 	u8			hwaddr[INFINIBAND_ALEN];
 };
 
+static inline struct ipoib_cb *ipoib_skb_cb(const struct sk_buff *skb)
+{
+	BUILD_BUG_ON(sizeof(skb->cb) < sizeof(struct ipoib_cb));
+	return (struct ipoib_cb *)skb->cb;
+}
+
 /* Used for all multicast joins (broadcast, IPv4 mcast and IPv6 mcast) */
 struct ipoib_mcast {
 	struct ib_sa_mcmember_rec mcmember;

drivers/infiniband/ulp/ipoib/ipoib_main.c

@@ -716,7 +716,7 @@ static int ipoib_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ipoib_dev_priv *priv = netdev_priv(dev);
 	struct ipoib_neigh *neigh;
-	struct ipoib_cb *cb = (struct ipoib_cb *) skb->cb;
+	struct ipoib_cb *cb = ipoib_skb_cb(skb);
 	struct ipoib_header *header;
 	unsigned long flags;
 
@@ -813,7 +813,7 @@ static int ipoib_hard_header(struct sk_buff *skb,
 			     const void *daddr, const void *saddr, unsigned len)
 {
 	struct ipoib_header *header;
-	struct ipoib_cb *cb = (struct ipoib_cb *) skb->cb;
+	struct ipoib_cb *cb = ipoib_skb_cb(skb);
 
 	header = (struct ipoib_header *) skb_push(skb, sizeof *header);