#40 RTU sequence number verification

reactor-plc/plc.lua

@@ -457,11 +457,9 @@ function comms_init(id, modem, local_port, server_port, reactor, iss)
                                 send_status(plc_state.degraded)
                                 log._debug("re-sent initial status data")
                             elseif link_ack == RPLC_LINKING.DENY then
-                                -- @todo: make sure this doesn't become a MITM security risk
                                 println_ts("received unsolicited link denial, unlinking")
                                 log._debug("unsolicited RPLC link request denied")
                             elseif link_ack == RPLC_LINKING.COLLISION then
-                                -- @todo: make sure this doesn't become a MITM security risk
                                 println_ts("received unsolicited link collision, unlinking")
                                 log._warning("unsolicited RPLC link request collision")
                             else
@@ -562,7 +560,11 @@ function comms_init(id, modem, local_port, server_port, reactor, iss)
 
     local is_scrammed = function () return self.scrammed end
     local is_linked = function () return self.linked end
-    local unlink = function () self.linked = false end
+
+    local unlink = function ()
+        self.linked = false
+        self.r_seq_num = nil
+    end
 
     return {
         reconnect_modem = reconnect_modem,

reactor-plc/startup.lua

@@ -12,7 +12,7 @@ os.loadAPI("config.lua")
 os.loadAPI("plc.lua")
 os.loadAPI("threads.lua")
 
-local R_PLC_VERSION = "alpha-v0.4.9"
+local R_PLC_VERSION = "alpha-v0.4.10"
 
 local print = util.print
 local println = util.println

rtu/rtu.lua

@@ -120,6 +120,7 @@ end
 function rtu_comms(modem, local_port, server_port)
     local self = {
         seq_num = 0,
+        r_seq_num = nil,
         txn_id = 0,
         modem = modem,
         s_port = server_port,
@@ -193,8 +194,23 @@ function rtu_comms(modem, local_port, server_port)
     end
 
     -- handle a MODBUS/SCADA packet
-    local handle_packet = function(packet, units, rtu_state)
+    local handle_packet = function(packet, units, rtu_state, conn_watchdog)
         if packet ~= nil then
+            local seq_ok = true
+
+            -- check sequence number
+            if self.r_seq_num == nil then
+                self.r_seq_num = packet.scada_frame.seq_num()
+            elseif rtu_state.linked and self.r_seq_num >= packet.scada_frame.seq_num() then
+                log._warning("sequence out-of-order: last = " .. self.r_seq_num .. ", new = " .. packet.scada_frame.seq_num())
+                return
+            else
+                self.r_seq_num = packet.scada_frame.seq_num()
+            end
+
+            -- feed watchdog on valid sequence number
+            conn_watchdog.feed()
+
             local protocol = packet.scada_frame.protocol()
 
             if protocol == PROTOCOLS.MODBUS_TCP then
@@ -220,6 +236,7 @@ function rtu_comms(modem, local_port, server_port)
                 if packet.type == SCADA_MGMT_TYPES.REMOTE_LINKED then
                     -- acknowledgement
                     rtu_state.linked = true
+                    self.r_seq_num = nil
                 elseif packet.type == SCADA_MGMT_TYPES.RTU_ADVERT then
                     -- request for capabilities again
                     send_advertisement(units)
@@ -279,11 +296,17 @@ function rtu_comms(modem, local_port, server_port)
         _send(SCADA_MGMT_TYPES.RTU_HEARTBEAT, {})
     end
 
+    local unlink = function (rtu_state)
+        rtu_state.linked = false
+        self.r_seq_num = nil
+    end
+
     return {
         reconnect_modem = reconnect_modem,
         parse_packet = parse_packet,
         handle_packet = handle_packet,
         send_advertisement = send_advertisement,
-        send_heartbeat = send_heartbeat
+        send_heartbeat = send_heartbeat,
+        unlink = unlink
     }
 end

rtu/startup.lua

@@ -19,7 +19,7 @@ os.loadAPI("dev/boiler_rtu.lua")
 os.loadAPI("dev/imatrix_rtu.lua")
 os.loadAPI("dev/turbine_rtu.lua")
 
-local RTU_VERSION = "alpha-v0.4.6"
+local RTU_VERSION = "alpha-v0.4.7"
 
 local print = util.print
 local println = util.println
@@ -53,6 +53,7 @@ local __shared_memory = {
     -- system objects
     rtu_sys = {
         rtu_comms = nil,
+        conn_watchdog = nil,
         units = {}
     },
 
@@ -203,6 +204,10 @@ end
 local main_thread  = threads.thread__main(__shared_memory)
 local comms_thread = threads.thread__comms(__shared_memory)
 
+-- start connection watchdog
+smem_sys.conn_watchdog = util.new_watchdog(5)
+log._debug("init> conn watchdog started")
+
 -- run threads
 parallel.waitForAll(main_thread.exec, comms_thread.exec)
 

rtu/threads.lua

@@ -26,13 +26,35 @@ function thread__main(smem)
         local rtu_state     = smem.rtu_state
         local rtu_dev       = smem.rtu_dev
         local rtu_comms     = smem.rtu_sys.rtu_comms
+        local conn_watchdog = smem.rtu_sys.conn_watchdog
         local units         = smem.rtu_sys.units
 
         -- event loop
         while true do
             local event, param1, param2, param3, param4, param5 = os.pullEventRaw()
 
-            if event == "peripheral_detach" then
+            if event == "timer" and param1 == loop_clock then
+                -- start next clock timer
+                loop_clock = os.startTimer(MAIN_CLOCK)
+
+                -- period tick, if we are linked send heartbeat, if not send advertisement
+                if rtu_state.linked then
+                    rtu_comms.send_heartbeat()
+                else
+                    -- advertise units
+                    rtu_comms.send_advertisement(units)
+                end
+            elseif event == "modem_message" then
+                -- got a packet
+                local packet = rtu_comms.parse_packet(param1, param2, param3, param4, param5)
+                if packet ~= nil then
+                    -- pass the packet onto the comms message queue
+                    smem.q.mq_comms.push_packet(packet)
+                end
+            elseif event == "timer" and param1 == conn_watchdog.get_timer() then
+                -- haven't heard from server recently? unlink
+                rtu_comms.unlink(rtu_state)
+            elseif event == "peripheral_detach" then
                 -- handle loss of a device
                 local device = ppm.handle_unmount(param1)
 
@@ -94,23 +116,6 @@ function thread__main(smem)
                         end
                     end
                 end
-            elseif event == "timer" and param1 == loop_clock then
-                -- start next clock timer
-                loop_clock = os.startTimer(MAIN_CLOCK)
-
-                -- period tick, if we are linked send heartbeat, if not send advertisement
-                if rtu_state.linked then
-                    rtu_comms.send_heartbeat()
-                else
-                    -- advertise units
-                    rtu_comms.send_advertisement(units)
-                end
-            elseif event == "modem_message" then
-                -- got a packet
-                local packet = rtu_comms.parse_packet(param1, param2, param3, param4, param5)
-                if packet ~= nil then
-                    smem.q.mq_comms.push_packet(packet)
-                end
             end
 
             -- check for termination request
@@ -134,6 +139,7 @@ function thread__comms(smem)
         -- load in from shared memory
         local rtu_state     = smem.rtu_state
         local rtu_comms     = smem.rtu_sys.rtu_comms
+        local conn_watchdog = smem.rtu_sys.conn_watchdog
         local units         = smem.rtu_sys.units
 
         local comms_queue   = smem.q.mq_comms
@@ -153,7 +159,8 @@ function thread__comms(smem)
                 elseif msg.qtype == mqueue.TYPE.PACKET then
                     -- received a packet
                     -- handle the packet (rtu_state passed to allow setting link flag)
-                    rtu_comms.handle_packet(msg.message, units, rtu_state) 
+                    --                   (conn_watchdog passed to allow feeding watchdog)
+                    rtu_comms.handle_packet(msg.message, units, rtu_state, conn_watchdog)
                 end
 
                 -- quick yield