lnwire: ensure zlib short chan id's are sorted

lnwire/query_short_chan_ids.go

@@ -181,7 +181,10 @@ func decodeShortChanIDs(r io.Reader) (ShortChanIDEncoding, []ShortChannelID, err
 			return 0, nil, fmt.Errorf("unable to create zlib reader: %v", err)
 		}
 
-		var shortChanIDs []ShortChannelID
+		var (
+			shortChanIDs []ShortChannelID
+			lastChanID   ShortChannelID
+		)
 		for {
 			// We'll now attempt to read the next short channel ID
 			// encoded in the payload.
@@ -208,6 +211,18 @@ func decodeShortChanIDs(r io.Reader) (ShortChanIDEncoding, []ShortChannelID, err
 			// We successfully read the next ID, so well collect
 			// that in the set of final ID's to return.
 			shortChanIDs = append(shortChanIDs, cid)
+
+			// Finally, we'll ensure that this short chan ID is
+			// greater than the last one. This is a requirement
+			// within the encoding, and if violated can aide us in
+			// detecting malicious payloads.
+			if cid.ToUint64() <= lastChanID.ToUint64() {
+				return 0, nil, fmt.Errorf("current sid of %v "+
+					"isn't greater than last sid of %v", cid,
+					lastChanID)
+			}
+
+			lastChanID = cid
 		}
 
 	default: