Server-side checking of digging; disable_anticheat setting

minetest.conf.example

@@ -158,6 +158,8 @@
 #static_spawnpoint = 0, 10, 0
 # If true, new players cannot join with an empty password
 #disallow_empty_password = false
+# If true, disable cheat prevention in multiplayer
+#disable_anticheat = false
 
 # Profiler data print interval. #0 = disable.
 #profiler_print_interval = 0

src/content_sao.cpp

@@ -764,6 +764,8 @@ PlayerSAO::PlayerSAO(ServerEnvironment *env_, Player *player_, u16 peer_id_,
 	m_last_good_position(0,0,0),
 	m_last_good_position_age(0),
 	m_time_from_last_punch(0),
+	m_nocheat_dig_pos(32767, 32767, 32767),
+	m_nocheat_dig_time(0),
 	m_wield_index(0),
 	m_position_not_sent(false),
 	m_armor_groups_sent(false),
@@ -874,8 +876,9 @@ void PlayerSAO::step(float dtime, bool send_recommended)
 	}
 
 	m_time_from_last_punch += dtime;
+	m_nocheat_dig_time += dtime;
 	
-	if(m_is_singleplayer)
+	if(m_is_singleplayer || g_settings->getBool("disable_anticheat"))
 	{
 		m_last_good_position = m_player->getPosition();
 		m_last_good_position_age = 0;
@@ -888,7 +891,8 @@ void PlayerSAO::step(float dtime, bool send_recommended)
 			NOTE: Actually the server should handle player physics like the
 			client does and compare player's position to what is calculated
 			on our side. This is required when eg. players fly due to an
-			explosion.
+			explosion. Altough a node-based alternative might be possible
+			too, and much more lightweight.
 		*/
 
 		float player_max_speed = 0;

src/content_sao.h

@@ -173,6 +173,9 @@ public:
 	{
 		return m_peer_id;
 	}
+
+	// Cheat prevention
+
 	v3f getLastGoodPosition() const
 	{
 		return m_last_good_position;
@@ -183,6 +186,26 @@ public:
 		m_time_from_last_punch = 0.0;
 		return r;
 	}
+	void noCheatDigStart(v3s16 p)
+	{
+		m_nocheat_dig_pos = p;
+		m_nocheat_dig_time = 0;
+	}
+	v3s16 getNoCheatDigPos()
+	{
+		return m_nocheat_dig_pos;
+	}
+	float getNoCheatDigTime()
+	{
+		return m_nocheat_dig_time;
+	}
+	void noCheatDigEnd()
+	{
+		m_nocheat_dig_pos = v3s16(32767, 32767, 32767);
+	}
+
+	// Other
+
 	void updatePrivileges(const std::set<std::string> &privs,
 			bool is_singleplayer)
 	{
@@ -196,9 +219,14 @@ private:
 	Player *m_player;
 	u16 m_peer_id;
 	Inventory *m_inventory;
+
+	// Cheat prevention
 	v3f m_last_good_position;
 	float m_last_good_position_age;
 	float m_time_from_last_punch;
+	v3s16 m_nocheat_dig_pos;
+	float m_nocheat_dig_time;
+
 	int m_wield_index;
 	bool m_position_not_sent;
 	ItemGroupList m_armor_groups;

src/defaultsettings.cpp

@@ -121,6 +121,7 @@ void set_default_settings(Settings *settings)
 	settings->setDefault("unlimited_player_transfer_distance", "true");
 	settings->setDefault("enable_pvp", "true");
 	settings->setDefault("disallow_empty_password", "false");
+	settings->setDefault("disable_anticheat", "false");
 
 	settings->setDefault("profiler_print_interval", "0");
 	settings->setDefault("enable_mapgen_debug_info", "false");

src/game.cpp

@@ -2112,7 +2112,9 @@ void the_game(
 					ldown_for_dig = true;
 				}
 				MapNode n = client.getEnv().getClientMap().getNode(nodepos);
-
+				
+				// NOTE: Similar piece of code exists on the server side for
+				// cheat detection.
 				// Get digging parameters
 				DigParams params = getDigParams(nodedef->get(n).groups,
 						&playeritem_toolcap);
@@ -2160,7 +2162,7 @@ void the_game(
 				{
 					dig_index = crack_animation_length;
 				}
-				
+
 				// Don't show cracks if not diggable
 				if(dig_time_complete >= 100000.0)
 				{

src/server.cpp

@@ -3014,6 +3014,8 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 				}
 				if(n.getContent() != CONTENT_IGNORE)
 					scriptapi_node_on_punch(m_lua, p_under, n, playersao);
+				// Cheat prevention
+				playersao->noCheatDigStart(p_under);
 			}
 			else if(pointed.type == POINTEDTHING_OBJECT)
 			{
@@ -3051,7 +3053,7 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 		*/
 		else if(action == 2)
 		{
-			// Only complete digging of nodes
+			// Only digging of nodes
 			if(pointed.type == POINTEDTHING_NODE)
 			{
 				MapNode n(CONTENT_IGNORE);
@@ -3067,10 +3069,65 @@ void Server::ProcessData(u8 *data, u32 datasize, u16 peer_id)
 					m_emerge_queue.addBlock(peer_id,
 							getNodeBlockPos(p_above), BLOCK_EMERGE_FLAG_FROMDISK);
 				}
-				if(n.getContent() != CONTENT_IGNORE)
+
+				/* Cheat prevention */
+				bool is_valid_dig = true;
+				if(!isSingleplayer() && !g_settings->getBool("disable_anticheat"))
+				{
+					v3s16 nocheat_p = playersao->getNoCheatDigPos();
+					float nocheat_t = playersao->getNoCheatDigTime();
+					playersao->noCheatDigEnd();
+					// If player didn't start digging this, ignore dig
+					if(nocheat_p != p_under){
+						infostream<<"Server: NoCheat: "<<player->getName()
+								<<" started digging "
+								<<PP(nocheat_p)<<" and completed digging "
+								<<PP(p_under)<<"; not digging."<<std::endl;
+						is_valid_dig = false;
+					}
+					// Get player's wielded item
+					ItemStack playeritem;
+					InventoryList *mlist = playersao->getInventory()->getList("main");
+					if(mlist != NULL)
+						playeritem = mlist->getItem(playersao->getWieldIndex());
+					ToolCapabilities playeritem_toolcap =
+							playeritem.getToolCapabilities(m_itemdef);
+					// Get diggability and expected digging time
+					DigParams params = getDigParams(m_nodedef->get(n).groups,
+							&playeritem_toolcap);
+					// If can't dig, try hand
+					if(!params.diggable){
+						const ItemDefinition &hand = m_itemdef->get("");
+						const ToolCapabilities *tp = hand.tool_capabilities;
+						if(tp)
+							params = getDigParams(m_nodedef->get(n).groups, tp);
+					}
+					// If can't dig, ignore dig
+					if(!params.diggable){
+						infostream<<"Server: NoCheat: "<<player->getName()
+								<<" completed digging "<<PP(p_under)
+								<<", which is not diggable with tool. not digging."
+								<<std::endl;
+						is_valid_dig = false;
+					}
+					// If time is considerably too short, ignore dig
+					// Check time only for medium and slow timed digs
+					if(params.diggable && params.time > 0.3 && nocheat_t < 0.5 * params.time){
+						infostream<<"Server: NoCheat: "<<player->getName()
+								<<" completed digging "
+								<<PP(p_under)<<" in "<<nocheat_t<<"s; expected "
+								<<params.time<<"s; not digging."<<std::endl;
+						is_valid_dig = false;
+					}
+				}
+
+				/* Actually dig node */
+
+				if(is_valid_dig && n.getContent() != CONTENT_IGNORE)
 					scriptapi_node_on_dig(m_lua, p_under, n, playersao);
 
-				if (m_env->getMap().getNodeNoEx(p_under).getContent() != CONTENT_AIR)
+				// Send unusual result (that is, node not being removed)
+				if(m_env->getMap().getNodeNoEx(p_under).getContent() != CONTENT_AIR)
 				{
 					// Re-send block to revert change on client-side
 					RemoteClient *client = getClient(peer_id);