MXS-2457 Add treat_string_as_field to firewall

Necessary if the firewall should be able to block columns when
'ANSI_QUOTES' as enabled and " instead of backticks are used.

Without this, the following

    > set @@sql_mode='ANSI_QUOTES';
    > select "ssn" from person;

will not be blocked if the database firewall has been configured
to block the column ssn.

Documentation/Filters/Database-Firewall-Filter.md

@@ -146,16 +146,32 @@ query itself is logged. The log messages are logged at the notice level.
 Log all queries that do not match a rule. The matched user and the query is
 logged. The log messages are logged at the notice level.
 
+#### `treat_string_as_field`
+This optional parameter specifies how the database firewall should treat
+strings. If true, they will be handled as fields, which will cause column
+blocking rules to match even if `ANSI_QUOTES` has been enabled and `"` is
+used instead of backtick.
+```
+treat_string_as_field=false
+```
+The default value is `true`.
+
+Note that this may cause a false positive, if a "true" string contains the
+name of a column to be blocked.
+
 #### `treat_string_arg_as_field`
 This optional parameter specifies how the database firewall should treat
 strings used as arguments to functions. If true, they will be handled
-as fields, which will cause fields to be masked even if `ANSI_QUOTES` has
-been enabled and `"` is used instead of backtick.
+as fields, which will cause function column blocking rules to match even
+even if `ANSI_QUOTES` has been enabled and `"` is used instead of backtick.
 ```
 treat_string_arg_as_field=false
 ```
 The default value is `true`.
 
+Note that this may cause a false positive, if a "true" string contains the
+name of a column to be blocked.
+
 ## Rule syntax
 
 The rules are defined by using the following syntax:

server/modules/filter/dbfwfilter/dbfwfilter.cc

@@ -632,6 +632,11 @@ MXS_MODULE* MXS_CREATE_MODULE()
                 MXS_MODULE_PARAM_BOOL,
                 "true"
             },
+            {
+                "treat_string_as_field",
+                MXS_MODULE_PARAM_BOOL,
+                "true"
+            },
             {MXS_END_MODULE_PARAMS}
         }
     };
@@ -1247,6 +1252,7 @@ int global_version = 1;
 Dbfw::Dbfw(MXS_CONFIG_PARAMETER* params)
     : m_action((enum fw_actions)config_get_enum(params, "action", action_values))
     , m_log_match(0)
+    , m_treat_string_as_field(config_get_bool(params, "treat_string_as_field"))
     , m_treat_string_arg_as_field(config_get_bool(params, "treat_string_arg_as_field"))
     , m_filename(config_get_string(params, "rules"))
     , m_version(atomic_add(&global_version, 1))
@@ -1276,6 +1282,32 @@ Dbfw* Dbfw::create(const char* zName, MXS_CONFIG_PARAMETER* pParams)
     if (process_rule_file(file, &rules, &users))
     {
         rval = new(std::nothrow) Dbfw(pParams);
+
+        if (rval)
+        {
+            if (rval->treat_string_as_field() || rval->treat_string_arg_as_field())
+            {
+                MXS_NOTICE("The parameter 'treat_string_arg_as_field' and/or "
+                           "'treat_string_as_field' is enabled for %s. "
+                           "As a consequence, the query classifier cache must be disabled.",
+                           zName);
+
+                QC_CACHE_PROPERTIES cache_properties;
+                qc_get_cache_properties(&cache_properties);
+
+                if (cache_properties.max_size != 0)
+                {
+                    cache_properties.max_size = 0;
+                    qc_set_cache_properties(&cache_properties);
+
+                    MXS_NOTICE("Query classifier cache disabled.");
+                }
+                else
+                {
+                    MXS_NOTICE("The query classifier cache was disabled already.");
+                }
+            }
+        }
     }
 
     return rval;
@@ -1517,7 +1549,18 @@ int DbfwSession::routeQuery(GWBUF* buffer)
     }
     else
     {
-        uint32_t option = m_instance->treat_string_arg_as_field() ? QC_OPTION_STRING_ARG_AS_FIELD : 0;
+        uint32_t option = 0;
+
+        if (m_instance->treat_string_as_field())
+        {
+            option |= QC_OPTION_STRING_AS_FIELD;
+        }
+
+        if (m_instance->treat_string_arg_as_field())
+        {
+            option |= QC_OPTION_STRING_ARG_AS_FIELD;
+        }
+
         EnableOption enable(option);
         GWBUF* analyzed_queue = buffer;
 

server/modules/filter/dbfwfilter/dbfwfilter.hh

@@ -224,6 +224,16 @@ public:
      */
     fw_actions get_action() const;
 
+    /**
+     * Should strings be treated as fields?
+     *
+     * @return True, if they should, false otherwise.
+     */
+    bool treat_string_as_field() const
+    {
+        return m_treat_string_as_field;
+    }
+
     /**
      * Should string args be treated as fields?
      *
@@ -277,6 +287,7 @@ public:
 private:
     fw_actions         m_action;    /*< Default operation mode, defaults to deny */
     int                m_log_match; /*< Log matching and/or non-matching queries */
+    bool               m_treat_string_as_field;
     bool               m_treat_string_arg_as_field;
     mutable std::mutex m_lock;      /*< Instance spinlock */
     std::string        m_filename;  /*< Path to the rule file */