Merge pull request ARMmbed#1684 from ARMmbed/IOTTHD-2476

FHSS: validate received synch info

Author: Jarkko Paso

source/Service_Libs/fhss/fhss.c

@@ -347,7 +347,7 @@ static int fhss_sync_with_beacon(fhss_structure_t *fhss_structure,
 
     if (fhss_structure) {
         // Do not allow synchronising devices above 253 hops.
-        if (payload->hop_count > 253) {
+        if (payload->hop_count > (FHSS_MAX_ALLOWED_HOPS-1)) {
             return 0;
         }
         // To make synchronization monitoring more effective, drop extra Beacons.
@@ -868,6 +868,35 @@ static void fhss_beacon_decode(fhss_synchronization_beacon_payload_s* dest, cons
     }
 }
 
+static int fhss_synch_info_validate(fhss_synchronization_beacon_payload_s *payload)
+{
+    if (!payload) {
+        return -1;
+    }
+    if (payload->data_start_delimeter != 0) {
+        return -1;
+    }
+    if (payload->current_superframe >= payload->number_of_superframes_per_channel) {
+        return -1;
+    }
+    if (payload->remaining_slots >= payload->superframe_length) {
+        return -1;
+    }
+    if (payload->hop_count > FHSS_MAX_ALLOWED_HOPS-1) {
+        return -1;
+    }
+    if (payload->number_of_broadcast_channels == 0) {
+        return -1;
+    }
+    if (payload->number_of_tx_slots == 0) {
+        return -1;
+    }
+    if (payload->number_of_superframes_per_channel == 0) {
+        return -1;
+    }
+    return 0;
+}
+
 static void fhss_beacon_received(fhss_structure_t *fhss_structure, const uint8_t *synch_info, const uint32_t elapsed_time)
 {
 
@@ -877,9 +906,11 @@ static void fhss_beacon_received(fhss_structure_t *fhss_structure, const uint8_t
             fhss_synchronization_beacon_payload_s temp_payload;
             temp_payload.processing_delay = fhss_structure->bs->fhss_configuration.fhss_tuning_parameters.rx_processing_delay;
             fhss_beacon_decode(&temp_payload, synch_info, elapsed_time, fhss_structure->number_of_channels);
-
-            // use the received information
-            fhss_sync_with_beacon(fhss_structure, &temp_payload);
+            if (!fhss_synch_info_validate(&temp_payload)) {
+                fhss_sync_with_beacon(fhss_structure, &temp_payload);
+            } else {
+                tr_err("Invalid synch info received");
+            }
         }
     }
 }

source/Service_Libs/fhss/fhss.h

@@ -23,6 +23,7 @@
 #define MAX_SYNCH_INFOS_PER_CHANNEL_LIST	2
 // FHSS randomly selects the starting superframe for broadcast channel. This defines how many superframes are used for randomization.
 #define NUMBER_OF_BC_START_SUPERFRAMES  3
+#define FHSS_MAX_ALLOWED_HOPS   254
 #define MAX_FHSS_TIMER_DIVIDER  100
 #define SYNCH_MONITOR_AVG_SAMPLES   5
 #define FHSS_DATA_START_DELIMETER   0x00