core/rawdb: add sanity-limit to header accessor

Author: andrepatta

core/rawdb/accessors_chain.go

@@ -333,9 +333,8 @@ func ReadHeaderRange(db prldb.Reader, number uint64, count uint64) []rlp.RawValu
 	if count == 0 {
 		return rlpHeaders
 	}
-	// read remaining from ancients
-	max := count * 700
-	data, err := db.AncientRange(freezerHeaderTable, i+1-count, count, max)
+	// read remaining from ancients, cap at 2M
+	data, err := db.AncientRange(freezerHeaderTable, i+1-count, count, 2*1024*1024)
 	if err == nil && uint64(len(data)) == count {
 		// the data is on the order [h, h+1, .., n] -- reordering needed
 		for i := range data {