net: 802: Use memset_startat() to clear struct fields

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Use memset_startat() so memset() doesn't get confused about writing
beyond the destination member that is intended to be the starting point
of zeroing through the end of the struct.
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/802/hippi.c

@@ -65,7 +65,7 @@ static int hippi_header(struct sk_buff *skb, struct net_device *dev,
 	hip->le.src_addr_type	= 2;	/* 12 bit SC address */
 
 	memcpy(hip->le.src_switch_addr, dev->dev_addr + 3, 3);
-	memset(&hip->le.reserved, 0, 16);
+	memset_startat(&hip->le, 0, reserved);
 
 	hip->snap.dsap		= HIPPI_EXTENDED_SAP;
 	hip->snap.ssap		= HIPPI_EXTENDED_SAP;