Add CRC verification to Modbus RTU dissector. CRC algorithm is the same as the "crc16-plain" with a different initial CRC (0xFFFF instead of 0). Created crc16_plain_tvb_offset_seed to "replace" crc16_plain_tvb_offset, but didn't remove crc16_plain_tvb_offset for backwards compatibility worries. Updated only dissector that used crc16_plain_tvb_offset (profinet/packet-pn-rt.c) to use crc16_plain_tvb_offset_seed(..., 0)

svn path=/trunk/; revision=45854

4 files changed, 46 insertions, 4 deletions

diff --git a/epan/crc16-tvb.c b/epan/crc16-tvb.c
index ea86e4b12a..ee77803a31 100644
--- a/epan/crc16-tvb.c
+++ b/epan/crc16-tvb.c
@@ -102,3 +102,14 @@ guint16 crc16_plain_tvb_offset(tvbuff_t *tvb, guint offset, guint len)
     return crc16_plain_finalize(crc);
 }
 
+guint16 crc16_plain_tvb_offset_seed(tvbuff_t *tvb, guint offset, guint len, guint16 crc)
+{
+    const guint8 *buf;
+
+    tvb_ensure_bytes_exist(tvb, offset, len);  /* len == -1 not allowed */
+    buf = tvb_get_ptr(tvb, offset, len);
+
+    crc = crc16_plain_update(crc, buf, len);
+    
+    return crc16_plain_finalize(crc);
+}
diff --git a/epan/crc16-tvb.h b/epan/crc16-tvb.h
index 0a49bda326..bad28217e3 100644
--- a/epan/crc16-tvb.h
+++ b/epan/crc16-tvb.h
@@ -86,6 +86,22 @@ extern guint16 crc16_ccitt_tvb_offset_seed(tvbuff_t *tvb, guint offset,
  @return The CRC16 checksum. */
 extern guint16 crc16_plain_tvb_offset(tvbuff_t *tvb, guint offset, guint len);
 
+/** Compute the "plain" CRC16 checksum of a tv buffer using the following
+ * parameters:
+ *    Width        = 16
+ *    Poly         = 0x8005
+ *    XorIn        = 0x0000
+ *    ReflectIn    = True
+ *    XorOut       = 0x0000
+ *    ReflectOut   = True
+ *    Algorithm    = table-driven
+ *    Direct       = True
+ @param tvb The tv buffer containing the data.
+ @param offset The offset into the tv buffer.
+ @param len The number of bytes to include in the computation.
+ @param crc Starting CRC value
+ @return The CRC16 checksum. */
+extern guint16 crc16_plain_tvb_offset_seed(tvbuff_t *tvb, guint offset, guint len, guint16 crc);
 
 #ifdef __cplusplus
 }
diff --git a/epan/dissectors/packet-mbtcp.c b/epan/dissectors/packet-mbtcp.c
index d0c13224d0..4605f58196 100644
--- a/epan/dissectors/packet-mbtcp.c
+++ b/epan/dissectors/packet-mbtcp.c
@@ -77,6 +77,7 @@
 #include "packet-mbtcp.h"
 #include <epan/prefs.h>
 #include <epan/expert.h>
+#include <epan/crc16-tvb.h> /* For CRC verification */\
 
 /* Initialize the protocol and registered fields */
 static int proto_mbtcp = -1;
@@ -172,6 +173,7 @@ static gboolean mbrtu_desegment = TRUE;
 static guint global_mbus_rtu_port = PORT_MBRTU; /* 0, by default        */
 static gint global_mbus_rtu_register_format = MBTCP_PREF_REGISTER_FORMAT_UINT16;
 static gint global_mbus_rtu_register_addr_type = MBTCP_PREF_REGISTER_ADDR_RAW;
+static gboolean mbrtu_crc = FALSE;
 
 static int
 classify_mbtcp_packet(packet_info *pinfo)
@@ -474,14 +476,14 @@ static void
 dissect_mbrtu_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 {
 /* Set up structures needed to add the protocol subtree and manage it */
-    proto_item    *mi;
+    proto_item    *mi, *crc_item;
     proto_tree    *mbrtu_tree;
     gint           offset, packet_type;
     tvbuff_t      *next_tvb;
     const char    *func_string = "";
     const char    *pkt_type_str = "";
     const char    *err_str = "";
-    guint16       len, crc16;
+    guint16       len, crc16, calc_crc16;
     guint8        unit_id, function_code, exception_code, subfunction_code;
     void          *p_save_proto_data;
     modbus_request_info_t *request_info;
@@ -578,9 +580,15 @@ dissect_mbrtu_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
 
     /* Add items to protocol tree specific to Modbus RTU */
     proto_tree_add_uint(mbrtu_tree, hf_mbrtu_unitid, tvb, offset, 1, unit_id);
-    proto_tree_add_uint(mbrtu_tree, hf_mbrtu_crc16, tvb, len-2, 2, crc16);
+    crc_item = proto_tree_add_uint(mbrtu_tree, hf_mbrtu_crc16, tvb, len-2, 2, crc16);
 
-    /* XXX - TODO CRC validation */
+    /* CRC validation */
+    if (mbrtu_crc)
+    {
+        calc_crc16 = crc16_plain_tvb_offset_seed(tvb, offset, len-2, 0xFFFF);
+        if (g_htons(calc_crc16) != crc16)
+            expert_add_info_format(pinfo, crc_item, PI_PROTOCOL, PI_WARN, "Incorrect CRC - should be 0x%04x", g_htons(calc_crc16));
+    }
 
     /* make sure to ignore the CRC-16 footer bytes */
     len = len - 2;
@@ -1736,6 +1744,12 @@ proto_register_modbus(void)
                                   "Whether the Modbus RTU dissector should desegment all messages spanning multiple TCP segments",
                                   &mbrtu_desegment);
 
+    /* Modbus RTU Preference - CRC verification, defaults to FALSE (not do verification)*/
+    prefs_register_bool_preference(mbrtu_module, "crc_verification",
+                                  "Validate CRC",
+                                  "Whether to validate the CRC",
+                                  &mbrtu_crc);
+
     /* Modbus RTU Preference - Default TCP Port, defaults to zero, allows custom user port. */
     prefs_register_uint_preference(mbrtu_module, "tcp.port", "Modbus RTU Port",
                        "Set the TCP port for encapsulated Modbus RTU packets",
diff --git a/epan/libwireshark.def b/epan/libwireshark.def
index 28eaadad69..ffffe1b042 100644
--- a/epan/libwireshark.def
+++ b/epan/libwireshark.def
@@ -116,6 +116,7 @@ copy_file_binary_mode
 copy_persconffile_profile
 crc16_ccitt_tvb
 crc16_plain_tvb_offset
+crc16_plain_tvb_offset_seed
 crc16_ccitt_tvb_offset
 crc16_ccitt_tvb_offset_seed
 crc16_ccitt_tvb_seed