doc: modbus keyword

diff --git a/doc/sphinx/modbus-keyword.rst b/doc/sphinx/modbus-keyword.rst
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+Modbus Keyword
+==============
+
+The modbus keyword can be used for matching on various properties of
+Modbus requests.
+
+There are two ways of using this keyword:
+
+* matching on functions properties with the setting "function";
+* matching on directly on data access with the setting "access".
+
+With the setting **function**, you can match on:
+
+* an action based on a function code field and a sub-function code when applicable;
+* one of three categories of Modbus functions;
+* public functions that are publicly defined (setting "public")
+* user-defined functions (setting "user")
+* reserved functions that are dedicated to proprietary extensions of Modbus (keyword "reserved")
+* one of the two sub-groups of public functions:
+
+  * assigned functions whose definition is already given in the Modbus specification (keyword "assigned");
+  * unassigned functions, which are reserved for future use (keyword "unassigned").
+
+Syntax::
+
+  modbus: function <value>
+  modbus: function <value>, subfunction <value>
+  modbus: function [!] <assigned | unassigned | public | user | reserved | all>
+
+Sign '!' is negation
+
+Examples::
+
+  modbus: function 21                # Write File record function
+  modbus: function 4, subfunction 4  # Force Listen Only Mode (Diagnostics) function
+  modbus: function assigned          # defined by Modbus Application Protocol Specification V1.1b3
+  modbus: function public            # validated by the Modbus.org community
+  modbus: function user              # internal use and not supported by the specification
+  modbus: function reserved          # used by some companies for legacy products and not available for public use
+  modbus: function !reserved         # every function but reserved function
+
+With the **access** setting, you can match on:
+
+* a type of data access (read or write);
+* one of primary tables access (Discretes Input, Coils, Input Registers and Holding Registers);
+* a range of addresses access;
+* a written value.
+
+Syntax::
+
+  modbus: access <read | write>
+  modbus: access <read | write> <discretes | coils | input | holding>
+  modbus: access <read | write> <discretes | coils | input | holding>, address <value>
+  modbus: access <read | write> <discretes | coils | input | holding>, address <value>, value <value>
+
+With _<value>_ setting matches on the address or value as it is being
+accessed or written as follows::
+
+  address 100      # exactly address 100
+  address 100<>200 # greater than address 100 and smaller than address 200
+  address >100     # greater than address 100
+  address <100     # smaller than address 100
+
+Examples::
+
+  modbus: access read                                    # Read access
+  modbus: access write                                   # Write access
+  modbus: access read input                              # Read access to Discretes Input table
+  modbus: access write coils                             # Write access to Coils table
+  modbus: access read discretes, address <100            # Read access at address smaller than 100 of Discretes Input table
+  modbus: access write holding, address 500, value >200  # Write value greather than 200 at address 500 of Holding Registers table
+
+(cf. http://www.modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf)
+
+**Note:** Address of read and write are starting at 1. So if your system
+is using a start at 0, you need to add 1 the address values.
+
+**Note:** According to MODBUS Messaging on TCP/IP Implementation Guide
+V1.0b, it is recommended to keep the TCP connection opened with a
+remote device and not to open and close it for each MODBUS/TCP
+transaction. In that case, it is important to set the depth of the
+stream reassembling as unlimited (stream.reassembly.depth: 0)
+
+(cf. http://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf)
+
+Paper and presentation (in french) on Modbus support are available :
+http://www.ssi.gouv.fr/fr/anssi/publications/publications-scientifiques/articles-de-conferences/detection-d-intrusion-dans-les-systemes-industriels-suricata-et-le-cas-modbus.html

diff --git a/doc/sphinx/rules.rst b/doc/sphinx/rules.rst
index 4d5fd074a4040d552094e40d240e6f8a48653b3c..2bff9ed05f563ed2df3d2ee759288a189545897b 100644 (file)
--- a/doc/sphinx/rules.rst
+++ b/doc/sphinx/rules.rst
@@ -19,3 +19,4 @@ Rules
    tls-keywords
    normalized-buffers
    rule-profiling
+   modbus-keyword