Support in 6lowpan for RFC4944 address generation

For the conversion of a 16-bit short address in 6lowpan to an IID, there
are several RFCs that produce different results. RFC 4944 section 6
specifies that the conversion uses the given PAN ID and the 16-bit short
address. RFC 6282, on the other hand, specifies thta the conversion only
uses the 16-bit short address and no longer uses the PAN ID.

The current version of the 6lowpan dissector supports only the newer RFC
6282, but there are protocols out there that assume that the address
conversion still abides to RFC 4944.

In order to support these protocols and following the discussion from

https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=8970

this patch introduces a boolean preference in the 6lowpan dissector that
indicates whether or not the older RFC 4944 should be used for address
conversion. By default, it is set to FALSE, thus leaving the behavior of
the dissector unchanged.

Besides the boolean preference, another helper function
lowpan_addr16_with_panid_to_ifcid has been written that implements the
expected behavior from RFC 4944 using the same hint mechanism already in
place in the dissector for the support of RFC 6282.

Change-Id: I8d202c69a225d7b1212080a174e0111e5203553c
Reviewed-on: https://code.wireshark.org/review/10902
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>

1 files changed, 81 insertions, 5 deletions

diff --git a/epan/dissectors/packet-6lowpan.c b/epan/dissectors/packet-6lowpan.c
index fa91101e3a..ea0816e90b 100644
--- a/epan/dissectors/packet-6lowpan.c
+++ b/epan/dissectors/packet-6lowpan.c
@@ -455,6 +455,9 @@ static lowpan_context_data  lowpan_context_local;
 static lowpan_context_data  lowpan_context_default;
 static const gchar *        lowpan_context_prefs[LOWPAN_CONTEXT_MAX];
 
+/* Preferences */
+static gboolean rfc4944_short_address_format = FALSE;
+
 /* Helper macro to convert a bit offset/length into a byte count. */
 #define BITS_TO_BYTE_LEN(bitoff, bitlen)    ((bitlen)?(((bitlen) + ((bitoff)&0x07) + 7) >> 3):(0))
 
@@ -497,6 +500,7 @@ static void         dissect_6lowpan_unknown     (tvbuff_t *tvb, packet_info *pin
 static gboolean     lowpan_dlsrc_to_ifcid   (packet_info *pinfo, guint8 *ifcid);
 static gboolean     lowpan_dldst_to_ifcid   (packet_info *pinfo, guint8 *ifcid);
 static void         lowpan_addr16_to_ifcid  (guint16 addr, guint8 *ifcid);
+static void         lowpan_addr16_with_panid_to_ifcid(guint16 panid, guint16 addr, guint8 *ifcid);
 static tvbuff_t *   lowpan_reassemble_ipv6  (tvbuff_t *tvb, struct ip6_hdr * ipv6, struct lowpan_nhdr * nhdr_list);
 static guint8       lowpan_parse_nhc_proto  (tvbuff_t *tvb, gint offset);
 
@@ -678,7 +682,7 @@ lowpan_context_free(gpointer data)
  *      lowpan_addr16_to_ifcid
  *  DESCRIPTION
  *      Converts a short address to in interface identifier as
- *      per rfc 4944 section 6.
+ *      per rfc 6282 section 3.2.2.
  *  PARAMETERS
  *      addr            ; 16-bit short address.
  *      ifcid           ; interface identifier (output).
@@ -702,6 +706,34 @@ lowpan_addr16_to_ifcid(guint16 addr, guint8 *ifcid)
 
 /*FUNCTION:------------------------------------------------------
  *  NAME
+ *      lowpan_addr16_with_panid_to_ifcid
+ *  DESCRIPTION
+ *      Converts a short address to in interface identifier as
+ *      per rfc 4944 section 6.
+ *  PARAMETERS
+ *      panid           ; 16-bit PAN ID.
+ *      addr            ; 16-bit short address.
+ *      ifcid           ; interface identifier (output).
+ *  RETURNS
+ *      void            ;
+ *---------------------------------------------------------------
+ */
+static void
+lowpan_addr16_with_panid_to_ifcid(guint16 panid, guint16 addr, guint8 *ifcid)
+{
+    /* Note: The PANID is used in building the IID following RFC 2464 section 4. */
+    ifcid[0] = (panid >> 8) & 0xfd; /* the U/L bit must be cleared. */
+    ifcid[1] = (panid >> 0) & 0xff;
+    ifcid[2] = 0x00;
+    ifcid[3] = 0xff;
+    ifcid[4] = 0xfe;
+    ifcid[5] = 0x00;
+    ifcid[6] = (addr >> 8) & 0xff;
+    ifcid[7] = (addr >> 0) & 0xff;
+} /* lowpan_addr16_with_panid_to_ifcid  */
+
+/*FUNCTION:------------------------------------------------------
+ *  NAME
  *      lowpan_dlsrc_to_ifcid
  *  DESCRIPTION
  *      Finds an interface identifier from the data-link source
@@ -731,7 +763,14 @@ lowpan_dlsrc_to_ifcid(packet_info *pinfo, guint8 *ifcid)
     hints = (ieee802154_hints_t *)p_get_proto_data(wmem_file_scope(), pinfo,
                 proto_get_id_by_filter_name(IEEE802154_PROTOABBREV_WPAN), 0);
     if (hints) {
-        lowpan_addr16_to_ifcid(hints->src16, ifcid);
+
+        /* Convert the 16-bit short address to an IID using the PAN ID (RFC 4944) or not depending on the preference */
+        if (rfc4944_short_address_format) {
+            lowpan_addr16_with_panid_to_ifcid(hints->src_pan, hints->src16, ifcid);
+        } else {
+            lowpan_addr16_to_ifcid(hints->src16, ifcid);
+        }
+
         return TRUE;
     } else {
         /* Failed to find a link-layer source address. */
@@ -770,7 +809,14 @@ lowpan_dldst_to_ifcid(packet_info *pinfo, guint8 *ifcid)
     hints = (ieee802154_hints_t *)p_get_proto_data(wmem_file_scope(), pinfo,
                 proto_get_id_by_filter_name(IEEE802154_PROTOABBREV_WPAN), 0);
     if (hints) {
-        lowpan_addr16_to_ifcid(hints->dst16, ifcid);
+
+        /* Convert the 16-bit short address to an IID using the PAN ID (RFC 4944) or not depending on the preference */
+        if (rfc4944_short_address_format) {
+            lowpan_addr16_with_panid_to_ifcid(hints->src_pan, hints->dst16, ifcid);
+        } else {
+            lowpan_addr16_to_ifcid(hints->dst16, ifcid);
+        }
+
         return TRUE;
     } else {
         /* Failed to find a link-layer destination address. */
@@ -2227,6 +2273,8 @@ dissect_6lowpan_mesh(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint8
     const guint8 *      src_ifcid;
     const guint8 *      dst_ifcid;
 
+    ieee802154_hints_t  *hints;
+
     /* Create a tree for the mesh header. */
     mesh_tree = proto_tree_add_subtree(tree, tvb, offset, 0, ett_6lowpan_mesh, &ti, "Mesh Header");
 
@@ -2270,7 +2318,18 @@ dissect_6lowpan_mesh(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint8
             proto_tree_add_uint(mesh_tree, hf_6lowpan_mesh_orig16, tvb, offset, 2, addr16);
         }
         ifcid = (guint8 *)wmem_alloc(pinfo->pool, 8);
-        lowpan_addr16_to_ifcid(addr16, ifcid);
+
+        /* Lookup the IEEE 802.15.4 addressing hints wanting RFC 2464 compatibility. */
+        hints = (ieee802154_hints_t *)p_get_proto_data(wmem_file_scope(), pinfo,
+                                proto_get_id_by_filter_name(IEEE802154_PROTOABBREV_WPAN), 0);
+
+        /* Convert the 16-bit short address to an IID using the PAN ID (RFC 4944) or not depending on the preference and the presence of hints from lower layers */
+        if (hints && rfc4944_short_address_format) {
+            lowpan_addr16_with_panid_to_ifcid(hints->src_pan, addr16, ifcid);
+        } else {
+            lowpan_addr16_to_ifcid(addr16, ifcid);
+        }
+
         src_ifcid = ifcid;
         /* Update source IID */
         memcpy(siid, src_ifcid, LOWPAN_IFC_ID_LEN);
@@ -2299,7 +2358,18 @@ dissect_6lowpan_mesh(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, guint8
             proto_tree_add_uint(mesh_tree, hf_6lowpan_mesh_dest16, tvb, offset, 2, addr16);
         }
         ifcid = (guint8 *)wmem_alloc(pinfo->pool, 8);
-        lowpan_addr16_to_ifcid(addr16, ifcid);
+
+        /* Lookup the IEEE 802.15.4 addressing hints wanting RFC 2464 compatibility. */
+        hints = (ieee802154_hints_t *)p_get_proto_data(wmem_file_scope(), pinfo,
+                                proto_get_id_by_filter_name(IEEE802154_PROTOABBREV_WPAN), 0);
+
+        /* Convert the 16-bit short address to an IID using the PAN ID (RFC 4944) or not depending on the preference and the presence of hints from lower layers */
+        if (hints && rfc4944_short_address_format) {
+            lowpan_addr16_with_panid_to_ifcid(hints->src_pan, addr16, ifcid);
+        } else {
+            lowpan_addr16_to_ifcid(addr16, ifcid);
+        }
+
         dst_ifcid = ifcid;
         /* Update destination IID */
         memcpy(diid, dst_ifcid, LOWPAN_IFC_ID_LEN);
@@ -2855,6 +2925,12 @@ proto_register_6lowpan(void)
 
     /* Register preferences. */
     prefs_module = prefs_register_protocol(proto_6lowpan, prefs_6lowpan_apply);
+
+    prefs_register_bool_preference(prefs_module, "rfc4944_short_address_format",
+                                   "Derive IID according to RFC 4944",
+                                   "Derive IID from a short 16-bit address according to RFC 4944 (using the PAN ID).",
+                                   &rfc4944_short_address_format);
+
     for (i = 0; i < LOWPAN_CONTEXT_MAX; i++) {
         char *pref_name, *pref_title;