Add proper "Decode As" mechanism for L2TPv3 subdissectors instead of preference.

Change-Id: I87f6f9f40e1c33148de43b53a8881d51416f5d2c
Reviewed-on: https://code.wireshark.org/review/7898
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

1 files changed, 46 insertions, 97 deletions

diff --git a/epan/dissectors/packet-l2tp.c b/epan/dissectors/packet-l2tp.c
index e506809315..3ec831de67 100644
--- a/epan/dissectors/packet-l2tp.c
+++ b/epan/dissectors/packet-l2tp.c
@@ -60,6 +60,7 @@
 #include <epan/prefs.h>
 #include <epan/conversation.h>
 #include <epan/expert.h>
+#include <epan/decode_as.h>
 #include <wsutil/md5.h>
 #include <wsutil/sha1.h>
 
@@ -207,6 +208,7 @@ static int hf_l2tp_zero_length_bit_message = -1;
 static int hf_l2tp_offset_padding = -1;
 
 static dissector_table_t l2tp_vendor_avp_dissector_table;
+static dissector_table_t pw_type_table;
 
 #define UDP_PORT_L2TP   1701
 
@@ -251,36 +253,8 @@ static const enum_val_t l2tpv3_cookies[] = {
 };
 
 #define L2TPv3_COOKIE_DEFAULT       0
-
-#define L2TPv3_PROTOCOL_ETH         0
-#define L2TPv3_PROTOCOL_CHDLC       1
-#define L2TPv3_PROTOCOL_FR          2
-#define L2TPv3_PROTOCOL_PPP         3
-#define L2TPv3_PROTOCOL_IP          4
-#define L2TPv3_PROTOCOL_MPLS        5
-#define L2TPv3_PROTOCOL_AAL5        6
-#define L2TPv3_PROTOCOL_LAPD        7
-#define L2TPv3_PROTOCOL_DOCSIS_DMPT 8
-#define L2TPv3_PROTOCOL_ERICSSON    9
-#define L2TPv3_PROTOCOL_MAX         (L2TPv3_PROTOCOL_ERICSSON + 1)
-
 #define L2TPv3_PROTOCOL_DEFAULT     L2TPv3_PROTOCOL_CHDLC
 
-static const enum_val_t l2tpv3_protocols[] = {
-    {"detect",      "Detect",        -1},
-    {"eth",         "Ethernet",      L2TPv3_PROTOCOL_ETH},
-    {"chdlc",       "Cisco HDLC",    L2TPv3_PROTOCOL_CHDLC},
-    {"fr",          "Frame Relay",   L2TPv3_PROTOCOL_FR},
-    {"ppp",         "PPP",           L2TPv3_PROTOCOL_PPP},
-    {"ip",          "IP",            L2TPv3_PROTOCOL_IP},
-    {"mpls",        "MPLS",          L2TPv3_PROTOCOL_MPLS},
-    {"aal5",        "AAL5",          L2TPv3_PROTOCOL_AAL5},
-    {"lapd",        "LAPD",          L2TPv3_PROTOCOL_LAPD},
-    {"docsis-dmpt", "DOCSIS-DMPT",   L2TPv3_PROTOCOL_DOCSIS_DMPT},
-    {"ehdlc",       "Ericsson HDLC", L2TPv3_PROTOCOL_ERICSSON},
-    {NULL, NULL, 0}
-};
-
 #define L2TPv3_L2_SPECIFIC_NONE         0
 #define L2TPv3_L2_SPECIFIC_DEFAULT      1
 #define L2TPv3_L2_SPECIFIC_ATM          2
@@ -299,7 +273,6 @@ static const enum_val_t l2tpv3_l2_specifics[] = {
 };
 
 static gint l2tpv3_cookie = -1;
-static gint l2tpv3_protocol = -1;
 static gint l2tpv3_l2_specific = -1;
 
 #define MESSAGE_TYPE_SCCRQ         1
@@ -770,16 +743,8 @@ static const true_false_string tfs_new_existing = { "New", "Existing" };
 static dissector_handle_t ppp_hdlc_handle;
 static dissector_handle_t ppp_lcp_options_handle;
 
-static dissector_handle_t eth_withoutfcs_handle;
-static dissector_handle_t chdlc_handle;
-static dissector_handle_t fr_handle;
-static dissector_handle_t ip_handle;
-static dissector_handle_t mpls_handle;
 static dissector_handle_t atm_oam_handle;
 static dissector_handle_t llc_handle;
-static dissector_handle_t lapd_handle;
-static dissector_handle_t mp2t_handle;
-static dissector_handle_t ehdlc_handle;
 static dissector_handle_t data_handle;
 
 static dissector_handle_t l2tp_udp_handle;
@@ -1159,7 +1124,7 @@ static l2tpv3_session_t *store_pw_type(l2tpv3_session_t *_session,
                                      int msg_type)
 {
     l2tpv3_session_t *session = _session;
-    gint result = l2tpv3_protocol;
+    gint result = -1;
     guint16 pw_type;
 
     switch (msg_type) {
@@ -1292,6 +1257,16 @@ static void update_session(l2tpv3_tunnel_t *tunnel, l2tpv3_session_t *session)
     }
 }
 
+static void l2tp_prompt(packet_info *pinfo _U_, gchar* result)
+{
+    g_snprintf(result, MAX_DECODE_AS_PROMPT_LEN, "Decode L2TPv3 packet type 0x%04x as",
+        GPOINTER_TO_UINT(p_get_proto_data(pinfo->pool, pinfo, proto_l2tp, 0)));
+}
+
+static gpointer l2tp_value(packet_info *pinfo _U_)
+{
+    return p_get_proto_data(pinfo->pool, pinfo, proto_l2tp, 0);
+}
 
 /*
  * Dissect CISCO AVP:s
@@ -2030,13 +2005,13 @@ process_l2tpv3_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
 {
     int         idx         = *pIdx;
     int         sid;
-    guint8      oam_cell    = 0;
+    guint32      oam_cell   = 0;
     proto_tree *l2_specific = NULL;
     proto_item *ti          = NULL;
     tvbuff_t   *next_tvb;
     gint        cookie_len  = l2tpv3_cookie;
     gint        l2_spec     = l2tpv3_l2_specific;
-    gint        pw_type     = l2tpv3_protocol;
+    gint        pw_type     = -1;
 
     lcce_settings_t  *lcce      = NULL;
     l2tpv3_session_t *session   = NULL;
@@ -2162,49 +2137,11 @@ process_l2tpv3_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
         break;
     }
 
-    switch(pw_type){
-    case L2TPv3_PROTOCOL_ETH:
-        call_dissector(eth_withoutfcs_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_CHDLC:
-        call_dissector(chdlc_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_FR:
-        call_dissector(fr_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_PPP:
-        /*
-         * PPP is transported without Address and Control
-         * fields, ppp_hdlc_handle can handle that as if if
-         * was ACFC (NULL Address and Control)
-         */
-        call_dissector(ppp_hdlc_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_IP:
-        call_dissector(ip_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_MPLS:
-        call_dissector(mpls_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_DOCSIS_DMPT:
-        call_dissector(mp2t_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_AAL5:
-        if (oam_cell) {
-            call_dissector(atm_oam_handle, next_tvb, pinfo, tree);
-        } else {
-            call_dissector(llc_handle, next_tvb, pinfo, tree);
-        }
-        break;
-    case L2TPv3_PROTOCOL_LAPD:
-        call_dissector(lapd_handle, next_tvb, pinfo, tree);
-        break;
-    case L2TPv3_PROTOCOL_ERICSSON:
-        call_dissector(ehdlc_handle, next_tvb, pinfo, tree);
-        break;
-    default:
+    p_add_proto_data(pinfo->pool, pinfo, proto_l2tp, 0, GUINT_TO_POINTER((guint)pw_type));
+
+    if (!dissector_try_uint_new(pw_type_table, pw_type, next_tvb, pinfo, tree, FALSE, GUINT_TO_POINTER(oam_cell)))
+    {
         call_dissector(data_handle, next_tvb, pinfo, tree);
-        break;
     }
 }
 
@@ -2709,6 +2646,19 @@ dissect_l2tp_ip(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
     return;
 }
 
+static int dissect_atm_oam_llc(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data)
+{
+    guint32      oam_cell   = GPOINTER_TO_UINT(data);
+
+    if (oam_cell) {
+        call_dissector(atm_oam_handle, tvb, pinfo, tree);
+    } else {
+        call_dissector(llc_handle, tvb, pinfo, tree);
+    }
+
+    return tvb_captured_length(tvb);
+}
+
 static void init_l2tp_dissection(void)
 {
     GSList *iterator = list_heads;
@@ -3039,6 +2989,12 @@ proto_register_l2tp(void)
     module_t *l2tp_module;
     expert_module_t* expert_l2tp;
 
+    /* Decode As handling */
+    static build_valid_func l2tp_da_build_value[1] = {l2tp_value};
+    static decode_as_value_t l2tp_da_values = {l2tp_prompt, 1, l2tp_da_build_value};
+    static decode_as_t l2tp_da = {"l2tp", "L2TPv3 payload", "l2tp.pw_type", 1, 0, &l2tp_da_values, NULL, NULL,
+                                    decode_as_default_populate_list, decode_as_default_reset, decode_as_default_change, NULL};
+
     proto_l2tp = proto_register_protocol(
         "Layer 2 Tunneling Protocol", "L2TP", "l2tp");
     proto_register_field_array(proto_l2tp, hf, array_length(hf));
@@ -3047,6 +3003,7 @@ proto_register_l2tp(void)
     expert_register_field_array(expert_l2tp, ei, array_length(ei));
 
     l2tp_vendor_avp_dissector_table = register_dissector_table("l2tp.vendor_avp", "L2TP vendor AVP dissector table", FT_UINT32, BASE_DEC);
+    pw_type_table = register_dissector_table("l2tp.pw_type", "L2TPv3 payload type", FT_UINT32, BASE_DEC);
 
     l2tp_module = prefs_register_protocol(proto_l2tp, NULL);
 
@@ -3066,24 +3023,21 @@ proto_register_l2tp(void)
                                    l2tpv3_l2_specifics,
                                    FALSE);
 
-    prefs_register_enum_preference(l2tp_module,
-                                   "protocol",
-                                   "Decode L2TPv3 packet contents as this protocol",
-                                   "Decode L2TPv3 packet contents as this protocol",
-                                   &l2tpv3_protocol,
-                                   l2tpv3_protocols,
-                                   FALSE);
+    prefs_register_obsolete_preference(l2tp_module, "protocol");
 
     prefs_register_string_preference(l2tp_module,"shared_secret","Shared Secret",
                                    "Shared secret used for control message digest authentication",
                                    &shared_secret);
 
     register_init_routine(init_l2tp_dissection);
+    register_decode_as(&l2tp_da);
 }
 
 void
 proto_reg_handoff_l2tp(void)
 {
+    dissector_handle_t atm_oam_llc_handle;
+
     l2tp_udp_handle = new_create_dissector_handle(dissect_l2tp_udp, proto_l2tp);
     dissector_add_uint("udp.port", UDP_PORT_L2TP, l2tp_udp_handle);
 
@@ -3103,17 +3057,12 @@ proto_reg_handoff_l2tp(void)
     /*
      * Get a handle for the dissectors used in v3.
      */
-    eth_withoutfcs_handle = find_dissector("eth_withoutfcs");
-    chdlc_handle          = find_dissector("chdlc");
-    fr_handle             = find_dissector("fr");
-    ip_handle             = find_dissector("ip");
-    mpls_handle           = find_dissector("mpls");
     atm_oam_handle        = find_dissector("atm_oam_cell");
     llc_handle            = find_dissector("llc");
-    lapd_handle           = find_dissector("lapd");
-    mp2t_handle           = find_dissector("mp2t");
-    ehdlc_handle          = find_dissector("ehdlc");
     data_handle           = find_dissector("data");
+
+    atm_oam_llc_handle = new_create_dissector_handle( dissect_atm_oam_llc, proto_l2tp );
+    dissector_add_uint("l2tp.pw_type", L2TPv3_PROTOCOL_AAL5, atm_oam_llc_handle);
 }
 
 /*