L2TP: Use the IANA assigned PW types for Decode As

Instead of registering subdissectors to arbitrary Wireshark
assigned numbers, register them to the actual pseudowire type
number assigned by IANA and present in the Pseudowire Type AVP.
Half of the previously registered types were never used, because
the dissector table could not be called with their Wireshark
internal number.

This makes it easier to add dissectors to support currently
unsupported but assigned types, and also makes it more intuitive
to use Decode As when the PW Type AVP is not present. Previously,
the dissector for the "default" type of CHDLC had to be changed to
a different subdissector.

1 files changed, 38 insertions, 52 deletions

diff --git a/epan/dissectors/packet-l2tp.c b/epan/dissectors/packet-l2tp.c
index c32834ffbd..88d62f4189 100644
--- a/epan/dissectors/packet-l2tp.c
+++ b/epan/dissectors/packet-l2tp.c
@@ -306,7 +306,6 @@ static const enum_val_t l2tpv3_cookies[] = {
 };
 
 #define L2TPv3_COOKIE_DEFAULT       0
-#define L2TPv3_PROTOCOL_DEFAULT     L2TPv3_PROTOCOL_CHDLC
 
 #define L2TPv3_L2_SPECIFIC_NONE         0
 #define L2TPv3_L2_SPECIFIC_DEFAULT      1
@@ -881,26 +880,26 @@ static const value_string l2tp_cablel_modulation_vals[] = {
 };
 
 static const value_string pw_types_vals[] = {
-    { 0x0001,  "Frame Relay DLCI" },
-    { 0x0002,  "ATM AAL5 SDU VCC transport" },
-    { 0x0003,  "ATM Cell transparent Port Mode" },
-    { 0x0004,  "Ethernet VLAN" },
-    { 0x0005,  "Ethernet" },
-    { 0x0006,  "HDLC" },
-    { 0x0007,  "PPP" },
-    { 0x0009,  "ATM Cell transport VCC Mode" },
-    { 0x000A,  "ATM Cell transport VPC Mode" },
-    { 0x000B,  "IP Transport" },
-    { 0x000C,  "MPEG-TS Payload Type (MPTPW)" },
-    { 0x000D,  "Packet Streaming Protocol (PSPPW)" },
+    { L2TPv3_PW_FR,          "Frame Relay DLCI" },
+    { L2TPv3_PW_AAL5,        "ATM AAL5 SDU VCC transport" },
+    { L2TPv3_PW_ATM_PORT,    "ATM Cell transparent Port Mode" },
+    { L2TPv3_PW_ETH_VLAN,    "Ethernet VLAN" },
+    { L2TPv3_PW_ETH,         "Ethernet" },
+    { L2TPv3_PW_CHDLC,       "HDLC" },
+    { L2TPv3_PW_PPP,         "PPP" }, /* Currently unassigned */
+    { L2TPv3_PW_ATM_VCC,     "ATM Cell transport VCC Mode" },
+    { L2TPv3_PW_ATM_VPC,     "ATM Cell transport VPC Mode" },
+    { L2TPv3_PW_IP,          "IP Transport" }, /* Currently unassigned */
+    { L2TPv3_PW_DOCSIS_DMPT, "MPEG-TS Payload Type (MPTPW)" },
+    { L2TPv3_PW_DOCSIS_PSP,  "Packet Streaming Protocol (PSPPW)" },
     /* 0x000E-0x0010 Unassigned */
-    { 0x0011,  "Structure-agnostic E1 circuit" },       /* [RFC5611] */
-    { 0x0012,  "Structure-agnostic T1 (DS1) circuit" }, /* [RFC5611]   */
-    { 0x0013,  "Structure-agnostic E3 circuit" },       /* [RFC5611]   */
-    { 0x0014,  "Structure-agnostic T3 (DS3) circuit" }, /* [RFC5611]   */
-    { 0x0015,  "CESoPSN basic mode" },                  /* [RFC5611]   */
-    { 0x0016,  "Unassigned" },
-    { 0x0017,  "CESoPSN TDM with CAS" },                /* [RFC5611]  */
+    { L2TPv3_PW_E1,          "Structure-agnostic E1 circuit" },       /* [RFC5611]  */
+    { L2TPv3_PW_T1,          "Structure-agnostic T1 (DS1) circuit" }, /* [RFC5611]  */
+    { L2TPv3_PW_E3,          "Structure-agnostic E3 circuit" },       /* [RFC5611]  */
+    { L2TPv3_PW_T3,          "Structure-agnostic T3 (DS3) circuit" }, /* [RFC5611]  */
+    { L2TPv3_PW_CESOPSN,     "CESoPSN basic mode" },                  /* [RFC5611]  */
+    { 0x0016,                "Unassigned" },
+    { L2TPv3_PW_CESOPSN_CAS, "CESoPSN TDM with CAS" },                /* [RFC5611]  */
 
     { 0,  NULL },
 };
@@ -1005,7 +1004,7 @@ typedef struct l2tpv3_session {
     lcce_settings_t lcce1;
     lcce_settings_t lcce2;
 
-    gint    pw_type;
+    guint    pw_type;
 } l2tpv3_session_t;
 
 static const gchar* shared_secret = "";
@@ -1243,7 +1242,7 @@ static void init_session(l2tpv3_session_t *session)
 {
     session->lcce1.cookie_len = session->lcce2.cookie_len = -1;
     session->lcce1.l2_specific = session->lcce2.l2_specific = -1;
-    session->pw_type = -1;
+    session->pw_type = L2TPv3_PW_DEFAULT;
 }
 
 static l2tpv3_session_t *alloc_session(void)
@@ -1350,8 +1349,6 @@ static l2tpv3_session_t *store_pw_type(l2tpv3_session_t *_session,
                                      int msg_type)
 {
     l2tpv3_session_t *session = _session;
-    gint result = -1;
-    guint16 pw_type;
 
     switch (msg_type) {
         case MESSAGE_TYPE_ICRQ:
@@ -1364,23 +1361,7 @@ static l2tpv3_session_t *store_pw_type(l2tpv3_session_t *_session,
     if (session == NULL)
         session = alloc_session();
 
-    pw_type = tvb_get_ntohs(tvb, offset);
-    switch (pw_type) {
-        case 0x0007:
-            result = L2TPv3_PROTOCOL_PPP; break;
-        case 0x0005:
-            result = L2TPv3_PROTOCOL_ETH; break;
-        case 0x0006:
-            result = L2TPv3_PROTOCOL_CHDLC; break;
-        case 0x0002:
-            result = L2TPv3_PROTOCOL_AAL5; break;
-        case 0x0001:
-            result = L2TPv3_PROTOCOL_FR; break;
-        default:
-            break;
-    }
-
-    session->pw_type = result;
+    session->pw_type = tvb_get_ntohs(tvb, offset);
 
     return session;
 }
@@ -1473,7 +1454,7 @@ static void update_session(l2tpv3_tunnel_t *tunnel, l2tpv3_session_t *session)
     if (session->lcce2.l2_specific != -1)
         existing->lcce2.l2_specific = session->lcce2.l2_specific;
 
-    if (session->pw_type != -1)
+    if (session->pw_type != L2TPv3_PW_DEFAULT)
         existing->pw_type = session->pw_type;
 
     if (tunnel->sessions == NULL) {
@@ -1486,7 +1467,7 @@ static void update_session(l2tpv3_tunnel_t *tunnel, l2tpv3_session_t *session)
 
 static void l2tp_prompt(packet_info *pinfo _U_, gchar* result)
 {
-    snprintf(result, MAX_DECODE_AS_PROMPT_LEN, "Decode L2TPv3 packet type 0x%04x as",
+    snprintf(result, MAX_DECODE_AS_PROMPT_LEN, "Decode L2TPv3 pseudowire type 0x%04x as",
         GPOINTER_TO_UINT(p_get_proto_data(pinfo->pool, pinfo, proto_l2tp, 0)));
 }
 
@@ -2536,7 +2517,7 @@ process_l2tpv3_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
     tvbuff_t   *next_tvb;
     gint        cookie_len  = l2tpv3_cookie;
     gint        l2_spec     = l2tpv3_l2_specific;
-    gint        pw_type     = -1;
+    guint       pw_type     = L2TPv3_PW_DEFAULT;
 
     lcce_settings_t  *lcce      = NULL;
     l2tpv3_session_t *session   = NULL;
@@ -2562,16 +2543,13 @@ process_l2tpv3_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
             l2_spec = lcce->l2_specific;
         if (cookie_len == -1)
             cookie_len = lcce->cookie_len;
-        if (pw_type == -1)
+        if (pw_type == L2TPv3_PW_DEFAULT)
             pw_type = session->pw_type;
     }
 
     if (l2_spec == -1)
         l2_spec = L2TPv3_L2_SPECIFIC_NONE;
 
-    if (pw_type == -1)
-        pw_type = L2TPv3_PROTOCOL_DEFAULT;
-
     if (cookie_len == -1)
         cookie_len = L2TPv3_COOKIE_DEFAULT;
 
@@ -2663,7 +2641,7 @@ process_l2tpv3_data(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
         break;
     }
 
-    p_add_proto_data(pinfo->pool, pinfo, proto_l2tp, 0, GUINT_TO_POINTER((guint)pw_type));
+    p_add_proto_data(pinfo->pool, pinfo, proto_l2tp, 0, GUINT_TO_POINTER(pw_type));
 
     if (!dissector_try_uint_new(pw_type_table, pw_type, next_tvb, pinfo, tree, FALSE, GUINT_TO_POINTER(oam_cell)))
     {
@@ -3754,7 +3732,7 @@ 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", proto_l2tp, FT_UINT32, BASE_DEC);
-    pw_type_table = register_dissector_table("l2tp.pw_type", "L2TPv3 payload type", proto_l2tp, FT_UINT32, BASE_DEC);
+    pw_type_table = register_dissector_table("l2tp.pw_type", "L2TPv3 pseudowire type", proto_l2tp, FT_UINT32, BASE_DEC);
 
     l2tp_module = prefs_register_protocol(proto_l2tp, NULL);
 
@@ -3774,7 +3752,10 @@ proto_register_l2tp(void)
                                    l2tpv3_l2_specifics,
                                    FALSE);
 
-    prefs_register_obsolete_preference(l2tp_module, "protocol");
+    prefs_register_static_text_preference(l2tp_module, "protocol",
+        "Dissection of pseudowire types is configured through \"Decode As\". "
+        "Type 0 is used for sessions with unknown pseudowire type.",
+        "Pseudowire Type \"Decode As\" instuctions");
 
     prefs_register_string_preference(l2tp_module,"shared_secret","Shared Secret",
                                    "Shared secret used for control message digest authentication",
@@ -3812,7 +3793,12 @@ proto_reg_handoff_l2tp(void)
     llc_handle            = find_dissector_add_dependency("llc", proto_l2tp);
 
     atm_oam_llc_handle = create_dissector_handle( dissect_atm_oam_llc, proto_l2tp );
-    dissector_add_uint("l2tp.pw_type", L2TPv3_PROTOCOL_AAL5, atm_oam_llc_handle);
+    dissector_add_uint("l2tp.pw_type", L2TPv3_PW_AAL5, atm_oam_llc_handle);
+
+    /*
+     * XXX: Should we register something (Ethernet?) to L2TPv3_PW_DEFAULT?
+     * The user could always change it with Decode As.
+     */
 }
 
 /*