detect: add mqtt.connect.protocolstring

Ticket:  OISF#6396

doc/userguide/rules/mqtt-keywords.rst

@@ -163,6 +163,19 @@ Examples::
 ``mqtt.connect.password`` is a 'sticky buffer' and can be used as ``fast_pattern``.
 
 
+mqtt.connect.protocol_string
+----------------------------
+
+Match on the protocol string in the MQTT CONNECT message. In contrast to ``mqtt.protocol_version`` this is a property that is only really relevant in the initial CONNECT communication and never used again; hence it is organized under ``mqtt.connect``.
+
+Examples::
+
+  mqtt.connect.protocol_string; content:"MQTT";
+  mqtt.connect.protocol_string; content:"MQIsdp";
+
+``mqtt.connect.protocol_string`` is a 'sticky buffer' and can be used as ``fast_pattern``.
+
+
 mqtt.connect.username
 ---------------------
 

rust/src/mqtt/detect.rs

@@ -231,6 +231,26 @@ pub unsafe extern "C" fn rs_mqtt_tx_get_connect_willmessage(
     return 0;
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn rs_mqtt_tx_get_connect_protocol_string(
+    tx: &MQTTTransaction, buffer: *mut *const u8, buffer_len: *mut u32,
+) -> u8 {
+    for msg in tx.msg.iter() {
+        if let MQTTOperation::CONNECT(ref cv) = msg.op {
+            let p = &cv.protocol_string;
+            if !p.is_empty() {
+                *buffer = p.as_ptr();
+                *buffer_len = p.len() as u32;
+                return 1;
+            }
+        }
+    }
+
+    *buffer = ptr::null();
+    *buffer_len = 0;
+    return 0;
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn rs_mqtt_tx_get_connack_sessionpresent(
     tx: &MQTTTransaction, session_present: *mut bool,

src/Makefile.am

@@ -250,6 +250,7 @@ noinst_HEADERS = \
 	detect-mqtt-connect-clientid.h \
 	detect-mqtt-connect-flags.h \
 	detect-mqtt-connect-password.h \
+	detect-mqtt-connect-protocol-string.h \
 	detect-mqtt-connect-username.h \
 	detect-mqtt-connect-willmessage.h \
 	detect-mqtt-connect-willtopic.h \
@@ -862,6 +863,7 @@ libsuricata_c_a_SOURCES = \
 	detect-mqtt-connect-clientid.c \
 	detect-mqtt-connect-flags.c \
 	detect-mqtt-connect-password.c \
+	detect-mqtt-connect-protocol-string.c \
 	detect-mqtt-connect-username.c \
 	detect-mqtt-connect-willmessage.c \
 	detect-mqtt-connect-willtopic.c \

src/detect-engine-register.c

@@ -219,6 +219,7 @@
 #include "detect-mqtt-connect-clientid.h"
 #include "detect-mqtt-connect-username.h"
 #include "detect-mqtt-connect-password.h"
+#include "detect-mqtt-connect-protocol-string.h"
 #include "detect-mqtt-connect-willtopic.h"
 #include "detect-mqtt-connect-willmessage.h"
 #include "detect-mqtt-connack-sessionpresent.h"
@@ -677,6 +678,7 @@ void SigTableSetup(void)
     DetectMQTTConnectClientIDRegister();
     DetectMQTTConnectUsernameRegister();
     DetectMQTTConnectPasswordRegister();
+    DetectMQTTConnectProtocolStringRegister();
     DetectMQTTConnectWillTopicRegister();
     DetectMQTTConnectWillMessageRegister();
     DetectMQTTConnackSessionPresentRegister();

src/detect-engine-register.h

@@ -299,6 +299,7 @@ enum DetectKeywordId {
     DETECT_AL_MQTT_CONNECT_CLIENTID,
     DETECT_AL_MQTT_CONNECT_USERNAME,
     DETECT_AL_MQTT_CONNECT_PASSWORD,
+    DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING,
     DETECT_AL_MQTT_CONNECT_WILLTOPIC,
     DETECT_AL_MQTT_CONNECT_WILLMESSAGE,
     DETECT_AL_MQTT_CONNACK_SESSION_PRESENT,

src/detect-mqtt-connect-protocol-string.c

@@ -0,0 +1,94 @@
+/* Copyright (C) 2023 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ *
+ * \author Sascha Steinbiss <sascha@steinbiss.name>
+ *
+ * Implements the mqtt.connect.protocolstring sticky buffer
+ */
+
+#include "suricata-common.h"
+#include "detect.h"
+#include "detect-parse.h"
+#include "detect-engine.h"
+#include "detect-engine-mpm.h"
+#include "detect-engine-prefilter.h"
+#include "detect-mqtt-connect-protocol-string.h"
+#include "rust.h"
+
+#define KEYWORD_NAME "mqtt.connect.protocol_string"
+#define KEYWORD_DOC  "mqtt-keywords.html#mqtt-connect-protocol_string"
+#define BUFFER_NAME  "mqtt.connect.protocol_string"
+#define BUFFER_DESC  "MQTT CONNECT protocol string"
+static int g_buffer_id = 0;
+
+static int DetectMQTTConnectProtocolStringSetup(
+        DetectEngineCtx *de_ctx, Signature *s, const char *arg)
+{
+    if (DetectBufferSetActiveList(de_ctx, s, g_buffer_id) < 0)
+        return -1;
+
+    if (DetectSignatureSetAppProto(s, ALPROTO_MQTT) < 0)
+        return -1;
+
+    return 0;
+}
+
+static InspectionBuffer *GetData(DetectEngineThreadCtx *det_ctx,
+        const DetectEngineTransforms *transforms, Flow *_f, const uint8_t _flow_flags, void *txv,
+        const int list_id)
+{
+    InspectionBuffer *buffer = InspectionBufferGet(det_ctx, list_id);
+    if (buffer->inspect == NULL) {
+        const uint8_t *b = NULL;
+        uint32_t b_len = 0;
+
+        if (rs_mqtt_tx_get_connect_protocol_string(txv, &b, &b_len) != 1)
+            return NULL;
+        if (b == NULL || b_len == 0)
+            return NULL;
+
+        InspectionBufferSetup(det_ctx, list_id, buffer, b, b_len);
+        InspectionBufferApplyTransforms(buffer, transforms);
+    }
+    return buffer;
+}
+
+void DetectMQTTConnectProtocolStringRegister(void)
+{
+    /* mqtt.connect.protocol_string sticky buffer */
+    sigmatch_table[DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING].name = KEYWORD_NAME;
+    sigmatch_table[DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING].desc =
+            "sticky buffer to match on the MQTT CONNECT protocol string";
+    sigmatch_table[DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING].url = "/rules/" KEYWORD_DOC;
+    sigmatch_table[DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING].Setup =
+            DetectMQTTConnectProtocolStringSetup;
+    sigmatch_table[DETECT_AL_MQTT_CONNECT_PROTOCOL_STRING].flags |= SIGMATCH_NOOPT;
+
+    DetectAppLayerInspectEngineRegister2(BUFFER_NAME, ALPROTO_MQTT, SIG_FLAG_TOSERVER, 0,
+            DetectEngineInspectBufferGeneric, GetData);
+
+    DetectAppLayerMpmRegister2(BUFFER_NAME, SIG_FLAG_TOSERVER, 2, PrefilterGenericMpmRegister,
+            GetData, ALPROTO_MQTT, 1);
+
+    DetectBufferTypeSetDescriptionByName(BUFFER_NAME, BUFFER_DESC);
+
+    g_buffer_id = DetectBufferTypeGetByName(BUFFER_NAME);
+
+    SCLogDebug("registering " BUFFER_NAME " rule option");
+}

src/detect-mqtt-connect-protocol-string.h

@@ -0,0 +1,29 @@
+/* Copyright (C) 2023 Open Information Security Foundation
+ *
+ * You can copy, redistribute or modify this Program under the terms of
+ * the GNU General Public License version 2 as published by the Free
+ * Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * version 2 along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+/**
+ * \file
+ *
+ * \author Sascha Steinbiss <sascha@steinbiss.name>
+ */
+
+#ifndef __DETECT_MQTT_CONNECT_PROTOCOLSTRING_H__
+#define __DETECT_MQTT_CONNECT_PROTOCOLSTRING_H__
+
+void DetectMQTTConnectProtocolStringRegister(void);
+
+#endif /* __DETECT_MQTT_CONNECT_PROTOCOLSTRING_H__ */