dnp3: bound the maximum number of objects per tx

Default to 2048, but provide a user configuration value.

Ticket: #8181

doc/userguide/upgrade.rst

@@ -57,10 +57,11 @@ Other Changes
   - tcp.window
 
 - ``dnp3`` has reduced the maximum number of open transactions from
-  500 down to 32, and the maximum number of points per message from
-  unbounded to 16384. Configuration options, ``max-tx`` and
-  ``max-points`` have been added for users who may need to change
-  these defaults.
+  500 down to 32, the maximum number of points per message from
+  unbounded to 16384, and the maximum number of objects per message
+  from unbounded to 2048. Configuration options, ``max-tx``,
+  ``max-points``, and ``max-objects`` have been added for users who
+  may need to change these defaults.
 
 Upgrading to 8.0.1
 ------------------

rules/dnp3-events.rules

@@ -30,3 +30,9 @@ alert dnp3 any any -> any any (msg:"SURICATA DNP3 Too many points in message"; \
       app-layer-event:dnp3.too_many_points; \
       threshold:type backoff, track by_flow, count 1, multiplier 10; \
       classtype:protocol-command-decode; sid:2270005; rev:1;)
+
+# Too many objects.
+alert dnp3 any any -> any any (msg:"SURICATA DNP3 Too many objects"; \
+      app-layer-event:dnp3.too_many_objects; \
+      threshold:type backoff, track by_flow, count 1, multiplier 10; \
+      classtype:protocol-command-decode; sid:2270006; rev:1;)

src/app-layer-dnp3.c

@@ -94,6 +94,9 @@ static uint64_t dnp3_max_tx = 32;
 /* The maximum number of points allowed per message (configurable). */
 static uint64_t max_points = 16384;
 
+/* The maximum number of objects allowed per message (configurable). */
+static uint64_t dnp3_max_objects = 2048;
+
 /* Decoder event map. */
 SCEnumCharMap dnp3_decoder_event_table[] = {
     { "FLOODED", DNP3_DECODER_EVENT_FLOODED },
@@ -103,6 +106,7 @@ SCEnumCharMap dnp3_decoder_event_table[] = {
     { "MALFORMED", DNP3_DECODER_EVENT_MALFORMED },
     { "UNKNOWN_OBJECT", DNP3_DECODER_EVENT_UNKNOWN_OBJECT },
     { "TOO_MANY_POINTS", DNP3_DECODER_EVENT_TOO_MANY_POINTS },
+    { "TOO_MANY_OBJECTS", DNP3_DECODER_EVENT_TOO_MANY_OBJECTS },
     { NULL, -1 },
 };
 
@@ -703,6 +707,7 @@ static int DNP3DecodeApplicationObjects(DNP3Transaction *tx, const uint8_t *buf,
 {
     int retval = 0;
     uint64_t point_count = 0;
+    uint64_t object_count = 0;
 
     if (buf == NULL || len == 0) {
         return 1;
@@ -717,6 +722,12 @@ static int DNP3DecodeApplicationObjects(DNP3Transaction *tx, const uint8_t *buf,
         DNP3ObjHeader *header = (DNP3ObjHeader *)buf;
         offset += sizeof(DNP3ObjHeader);
 
+        /* Check if we've exceeded the maximum number of objects. */
+        if (++object_count > dnp3_max_objects) {
+            DNP3SetEventTx(tx, DNP3_DECODER_EVENT_TOO_MANY_OBJECTS);
+            goto done;
+        }
+
         DNP3Object *object = DNP3ObjectAlloc();
         if (unlikely(object == NULL)) {
             goto done;
@@ -1615,6 +1626,13 @@ void RegisterDNP3Parsers(void)
                 max_points = (uint64_t)value;
             }
         }
+
+        /* Parse max-objects configuration. */
+        if (SCConfGetInt("app-layer.protocols.dnp3.max-objects", &value)) {
+            if (value > 0) {
+                dnp3_max_objects = (uint64_t)value;
+            }
+        }
     } else {
         SCLogConfig("Parser disabled for protocol %s. "
             "Protocol detection still on.", proto_name);

src/app-layer-dnp3.h

@@ -110,6 +110,7 @@ enum {
     DNP3_DECODER_EVENT_MALFORMED,
     DNP3_DECODER_EVENT_UNKNOWN_OBJECT,
     DNP3_DECODER_EVENT_TOO_MANY_POINTS,
+    DNP3_DECODER_EVENT_TOO_MANY_OBJECTS,
 };
 
 /**

suricata.yaml.in

@@ -1231,6 +1231,7 @@ app-layer:
         dp: 20000
       #max-tx: 32
       #max-points: 16384
+      #max-objects: 2048
 
     # SCADA EtherNet/IP and CIP protocol support
     enip: