make the sbus dissector nwe-style and make it check that the packet does

indeed look like sbus before taking it.

this fixes bug 1871

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@23057 f5534014-38df-0310-8fa8-9805f1628bb7

diff --git a/plugins/sbus/packet-sbus.c b/plugins/sbus/packet-sbus.c
index a761143c584053531e78a58dd59b295e8d27a5ef..3279f7931999fa1cdeb7c30045eab8d2ad0a82f3 100644 (file)
--- a/plugins/sbus/packet-sbus.c
+++ b/plugins/sbus/packet-sbus.c
@@ -515,8 +515,40 @@ static void sbus_init_protocol(void){
               G_ALLOC_AND_FREE);
 }
 
+/* check whether the packet looks like SBUS or not */
+static gboolean
+is_sbus_pdu(tvbuff_t *tvb)
+{
+       guint32 length;
+
+       /* we need at least 8 bytes to determine whether this is sbus or
+          not
+       */
+       if(tvb_length(tvb)<8){
+               return FALSE;
+       }
+
+       /* the length must be >= 8 bytes to accomodate the header,
+          it also must be <65536 to fit inside a udp packet
+        */
+       length=tvb_get_ntohl(tvb, 0);
+       if ( (length<8) || (length>65535) ) {
+               return FALSE;
+       }
+       if (tvb_reported_length(tvb) != length) {
+               return FALSE;
+       }
+
+       /* XXX */
+       /* We should also test version and protocol    but that requires
+          someone to look at the specification for SBUS
+       */
+       
+       return TRUE;
+}
+
 /*Dissect the telegram*/
-static void
+static int
 dissect_sbus(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 {
 
@@ -551,7 +583,12 @@ dissect_sbus(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
        conversation_t *conversation = NULL;
        sbus_request_key request_key, *new_request_key;
        sbus_request_val *request_val = NULL;
-       
+
+       /* does this look like an sbus pdu? */       
+       if(!is_sbus_pdu(tvb)){
+           return 0;
+       }
+
        conversation = find_conversation(pinfo->fd->num, &pinfo->src, &pinfo->dst,
               pinfo->ptype, pinfo->srcport, pinfo->destport, 0);
        
@@ -1278,6 +1315,7 @@ dissect_sbus(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
               }
               offset += 2; /*now at the end of the telegram*/
        }
+       return tvb_length(tvb);
 /*End of dissect_sbus*/
 }
 
@@ -1620,7 +1658,7 @@ proto_reg_handoff_sbus(void)
 {
        dissector_handle_t sbus_handle;
 
-       sbus_handle = create_dissector_handle(dissect_sbus, proto_sbus);
+       sbus_handle = new_create_dissector_handle(dissect_sbus, proto_sbus);
        dissector_add("udp.port", 5050, sbus_handle);
 }