Disallow placing entities outside safe boundaries

Entity positions are serialized as F1000. Disallow placing
entities outside safe borders with the minetest.add_entity
call.

Note that this patch only enforces those boundaries for
placing entities, moving entities that move outside boundaries
aren't affected.

Thanks to @nanepiwo for pointing this out.

src/environment.cpp

@@ -1493,6 +1493,15 @@ u16 ServerEnvironment::addActiveObjectRaw(ServerActiveObject *object,
 			delete object;
 		return 0;
 	}
+
+	if (objectpos_over_limit(object->getBasePosition())) {
+		errorstream << "ServerEnvironment::addActiveObjectRaw(): "
+			<< "object position outside maximum range" << std::endl;
+		if (object->environmentDeletes())
+			delete object;
+		return 0;
+	}
+
 	/*infostream<<"ServerEnvironment::addActiveObjectRaw(): "
 			<<"added (id="<<object->getId()<<")"<<std::endl;*/
 

src/mapblock.h

@@ -637,6 +637,18 @@ private:
 
 typedef std::vector<MapBlock*> MapBlockVect;
 
+inline bool objectpos_over_limit(v3f p)
+{
+	const static u16 map_gen_limit = MYMIN(MAX_MAP_GENERATION_LIMIT,
+		g_settings->getU16("map_generation_limit"));
+	return (p.X < -map_gen_limit
+		|| p.X >  map_gen_limit
+		|| p.Y < -map_gen_limit
+		|| p.Y >  map_gen_limit
+		|| p.Z < -map_gen_limit
+		|| p.Z >  map_gen_limit);
+}
+
 inline bool blockpos_over_limit(v3s16 p)
 {
 	const static u16 map_gen_limit = MYMIN(MAX_MAP_GENERATION_LIMIT,