Mod security: Allow read-only access to all mod paths

src/script/cpp_api/s_security.cpp

@@ -336,8 +336,12 @@ bool ScriptApiSecurity::safeLoadFile(lua_State *L, const char *path)
 }
 
 
-bool ScriptApiSecurity::checkPath(lua_State *L, const char *path)
+bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
+		bool write_required, bool *write_allowed)
 {
+	if (write_allowed)
+		*write_allowed = false;
+
 	std::string str;  // Transient
 
 	std::string norel_path = fs::RemoveRelativePathComponents(path);
@@ -380,32 +384,53 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path)
 
 		// Builtin can access anything
 		if (mod_name == BUILTIN_MOD_NAME) {
+			if (write_allowed) *write_allowed = true;
 			return true;
 		}
 
 		// Allow paths in mod path
-		const ModSpec *mod = server->getModSpec(mod_name);
-		if (mod) {
-			str = fs::AbsolutePath(mod->path);
-			if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
-				return true;
+		// Don't bother if write access isn't important, since it will be handled later
+		if (write_required || write_allowed != NULL) {
+			const ModSpec *mod = server->getModSpec(mod_name);
+			if (mod) {
+				str = fs::AbsolutePath(mod->path);
+				if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
+					if (write_allowed) *write_allowed = true;
+					return true;
+				}
 			}
 		}
 	}
 	lua_pop(L, 1);  // Pop mod name
 
-	str = fs::AbsolutePath(server->getWorldPath());
-	if (str.empty()) return false;
-	// Don't allow access to world mods.  We add to the absolute path
-	// of the world instead of getting the absolute paths directly
-	// because that won't work if they don't exist.
-	if (fs::PathStartsWith(abs_path, str + DIR_DELIM + "worldmods") ||
-			fs::PathStartsWith(abs_path, str + DIR_DELIM + "game")) {
-		return false;
+	// Allow read-only access to all mod directories
+	if (!write_required) {
+		const std::vector<ModSpec> mods = server->getMods();
+		for (size_t i = 0; i < mods.size(); ++i) {
+			str = fs::AbsolutePath(mods[i].path);
+			if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
+				return true;
+			}
+		}
 	}
-	// Allow all other paths in world path
-	if (fs::PathStartsWith(abs_path, str)) {
-		return true;
+
+	str = fs::AbsolutePath(server->getWorldPath());
+	if (!str.empty()) {
+		// Don't allow access to other paths in the world mod/game path.
+		// These have to be blocked so you can't override a trusted mod
+		// by creating a mod with the same name in a world mod directory.
+		// We add to the absolute path of the world instead of getting
+		// the absolute paths directly because that won't work if they
+		// don't exist.
+		if (fs::PathStartsWith(abs_path, str + DIR_DELIM + "worldmods") ||
+				fs::PathStartsWith(abs_path, str + DIR_DELIM + "game")) {
+			return false;
+		}
+		// Allow all other paths in world path
+		if (fs::PathStartsWith(abs_path, str)) {
+			if (write_allowed) *write_allowed = true;
+			return true;
+		}
 	}
 
 	// Default to disallowing
@@ -476,7 +501,7 @@ int ScriptApiSecurity::sl_g_loadfile(lua_State *L)
 
 	if (lua_isstring(L, 1)) {
 		path = lua_tostring(L, 1);
-		CHECK_SECURE_PATH(L, path);
+		CHECK_SECURE_PATH_INTERNAL(L, path, false, NULL);
 	}
 
 	if (!safeLoadFile(L, path)) {
@@ -529,7 +554,16 @@ int ScriptApiSecurity::sl_io_open(lua_State *L)
 
 	luaL_checktype(L, 1, LUA_TSTRING);
 	const char *path = lua_tostring(L, 1);
-	CHECK_SECURE_PATH(L, path);
+
+	bool write_requested = false;
+	if (with_mode) {
+		luaL_checktype(L, 2, LUA_TSTRING);
+		const char *mode = lua_tostring(L, 2);
+		write_requested = strchr(mode, 'w') != NULL ||
+			strchr(mode, '+') != NULL ||
+			strchr(mode, 'a') != NULL;
+	}
+	CHECK_SECURE_PATH_INTERNAL(L, path, write_requested, NULL);
 
 	push_original(L, "io", "open");
 	lua_pushvalue(L, 1);
@@ -546,7 +580,7 @@ int ScriptApiSecurity::sl_io_input(lua_State *L)
 {
 	if (lua_isstring(L, 1)) {
 		const char *path = lua_tostring(L, 1);
-		CHECK_SECURE_PATH(L, path);
+		CHECK_SECURE_PATH_INTERNAL(L, path, false, NULL);
 	}
 
 	push_original(L, "io", "input");
@@ -560,7 +594,7 @@ int ScriptApiSecurity::sl_io_output(lua_State *L)
 {
 	if (lua_isstring(L, 1)) {
 		const char *path = lua_tostring(L, 1);
-		CHECK_SECURE_PATH(L, path);
+		CHECK_SECURE_PATH_INTERNAL(L, path, true, NULL);
 	}
 
 	push_original(L, "io", "output");
@@ -574,7 +608,7 @@ int ScriptApiSecurity::sl_io_lines(lua_State *L)
 {
 	if (lua_isstring(L, 1)) {
 		const char *path = lua_tostring(L, 1);
-		CHECK_SECURE_PATH(L, path);
+		CHECK_SECURE_PATH_INTERNAL(L, path, false, NULL);
 	}
 
 	int top_precall = lua_gettop(L);
@@ -591,11 +625,11 @@ int ScriptApiSecurity::sl_os_rename(lua_State *L)
 {
 	luaL_checktype(L, 1, LUA_TSTRING);
 	const char *path1 = lua_tostring(L, 1);
-	CHECK_SECURE_PATH(L, path1);
+	CHECK_SECURE_PATH_INTERNAL(L, path1, true, NULL);
 
 	luaL_checktype(L, 2, LUA_TSTRING);
 	const char *path2 = lua_tostring(L, 2);
-	CHECK_SECURE_PATH(L, path2);
+	CHECK_SECURE_PATH_INTERNAL(L, path2, true, NULL);
 
 	push_original(L, "os", "rename");
 	lua_pushvalue(L, 1);
@@ -609,7 +643,7 @@ int ScriptApiSecurity::sl_os_remove(lua_State *L)
 {
 	luaL_checktype(L, 1, LUA_TSTRING);
 	const char *path = lua_tostring(L, 1);
-	CHECK_SECURE_PATH(L, path);
+	CHECK_SECURE_PATH_INTERNAL(L, path, true, NULL);
 
 	push_original(L, "os", "remove");
 	lua_pushvalue(L, 1);

src/script/cpp_api/s_security.h

@@ -23,14 +23,18 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "cpp_api/s_base.h"
 
 
-#define CHECK_SECURE_PATH(L, path) \
-	if (!ScriptApiSecurity::checkPath(L, path)) { \
-		throw LuaError(std::string("Attempt to access external file ") + \
-					path + " with mod security on."); \
+#define CHECK_SECURE_PATH_INTERNAL(L, path, write_required, ptr) \
+	if (!ScriptApiSecurity::checkPath(L, path, write_required, ptr)) { \
+		throw LuaError(std::string("Mod security: Blocked attempted ") + \
+				(write_required ? "write to " : "read from ") + path); \
 	}
-#define CHECK_SECURE_PATH_OPTIONAL(L, path) \
+#define CHECK_SECURE_PATH(L, path, write_required) \
 	if (ScriptApiSecurity::isSecure(L)) { \
-		CHECK_SECURE_PATH(L, path); \
+		CHECK_SECURE_PATH_INTERNAL(L, path, write_required, NULL); \
+	}
+#define CHECK_SECURE_PATH_POSSIBLE_WRITE(L, path, ptr) \
+	if (ScriptApiSecurity::isSecure(L)) { \
+		CHECK_SECURE_PATH_INTERNAL(L, path, false, ptr); \
 	}
 
 
@@ -43,8 +47,9 @@ public:
 	static bool isSecure(lua_State *L);
 	// Loads a file as Lua code safely (doesn't allow bytecode).
 	static bool safeLoadFile(lua_State *L, const char *path);
-	// Checks if mods are allowed to read and write to the path
-	static bool checkPath(lua_State *L, const char *path);
+	// Checks if mods are allowed to read (and optionally write) to the path
+	static bool checkPath(lua_State *L, const char *path, bool write_required,
+			bool *write_allowed=NULL);
 
 private:
 	// Syntax: "sl_" <Library name or 'g' (global)> '_' <Function name>

src/script/lua_api/l_areastore.cpp

@@ -263,7 +263,7 @@ int LuaAreaStore::l_to_file(lua_State *L)
 	AreaStore *ast = o->as;
 
 	const char *filename = luaL_checkstring(L, 2);
-	CHECK_SECURE_PATH_OPTIONAL(L, filename);
+	CHECK_SECURE_PATH(L, filename, true);
 
 	std::ostringstream os(std::ios_base::binary);
 	ast->serialize(os);
@@ -294,7 +294,7 @@ int LuaAreaStore::l_from_file(lua_State *L)
 	LuaAreaStore *o = checkobject(L, 1);
 
 	const char *filename = luaL_checkstring(L, 2);
-	CHECK_SECURE_PATH_OPTIONAL(L, filename);
+	CHECK_SECURE_PATH(L, filename, false);
 
 	std::ifstream is(filename, std::ios::binary);
 	return deserialization_helper(L, o->as, is);

src/script/lua_api/l_mapgen.cpp

@@ -1295,7 +1295,7 @@ int ModApiMapgen::l_create_schematic(lua_State *L)
 	INodeDefManager *ndef = getServer(L)->getNodeDefManager();
 
 	const char *filename = luaL_checkstring(L, 4);
-	CHECK_SECURE_PATH_OPTIONAL(L, filename);
+	CHECK_SECURE_PATH(L, filename, true);
 
 	Map *map = &(getEnv(L)->getMap());
 	Schematic schem;

src/script/lua_api/l_settings.cpp

@@ -118,6 +118,11 @@ int LuaSettings::l_write(lua_State* L)
 	NO_MAP_LOCK_REQUIRED;
 	LuaSettings* o = checkobject(L, 1);
 
+	if (!o->m_write_allowed) {
+		throw LuaError("Settings: writing " + o->m_filename +
+				" not allowed with mod security on.");
+	}
+
 	bool success = o->m_settings->updateConfigFile(o->m_filename.c_str());
 	lua_pushboolean(L, success);
 
@@ -142,8 +147,9 @@ int LuaSettings::l_to_table(lua_State* L)
 	return 1;
 }
 
-LuaSettings::LuaSettings(const char* filename)
+LuaSettings::LuaSettings(const char* filename, bool write_allowed)
 {
+	m_write_allowed = write_allowed;
 	m_filename = std::string(filename);
 
 	m_settings = new Settings();
@@ -188,9 +194,10 @@ void LuaSettings::Register(lua_State* L)
 int LuaSettings::create_object(lua_State* L)
 {
 	NO_MAP_LOCK_REQUIRED;
+	bool write_allowed;
 	const char* filename = luaL_checkstring(L, 1);
-	CHECK_SECURE_PATH_OPTIONAL(L, filename);
-	LuaSettings* o = new LuaSettings(filename);
+	CHECK_SECURE_PATH_POSSIBLE_WRITE(L, filename, &write_allowed);
+	LuaSettings* o = new LuaSettings(filename, write_allowed);
 	*(void **)(lua_newuserdata(L, sizeof(void *))) = o;
 	luaL_getmetatable(L, className);
 	lua_setmetatable(L, -2);

src/script/lua_api/l_settings.h

@@ -53,11 +53,12 @@ private:
 	// to_table(self) -> {[key1]=value1,...}
 	static int l_to_table(lua_State* L);
 
+	bool m_write_allowed;
 	Settings* m_settings;
 	std::string m_filename;
 
 public:
-	LuaSettings(const char* filename);
+	LuaSettings(const char* filename, bool write_allowed);
 	~LuaSettings();
 
 	// LuaSettings(filename)

src/script/lua_api/l_util.cpp

@@ -388,7 +388,7 @@ int ModApiUtil::l_mkdir(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
 	const char *path = luaL_checkstring(L, 1);
-	CHECK_SECURE_PATH_OPTIONAL(L, path);
+	CHECK_SECURE_PATH(L, path, true);
 	lua_pushboolean(L, fs::CreateAllDirs(path));
 	return 1;
 }
@@ -400,7 +400,7 @@ int ModApiUtil::l_get_dir_list(lua_State *L)
 	const char *path = luaL_checkstring(L, 1);
 	short is_dir = lua_isboolean(L, 2) ? lua_toboolean(L, 2) : -1;
 
-	CHECK_SECURE_PATH_OPTIONAL(L, path);
+	CHECK_SECURE_PATH(L, path, false);
 
 	std::vector<fs::DirListNode> list = fs::GetDirListing(path);
 

src/server.h

@@ -298,6 +298,7 @@ public:
 	IWritableNodeDefManager* getWritableNodeDefManager();
 	IWritableCraftDefManager* getWritableCraftDefManager();
 
+	const std::vector<ModSpec> &getMods() const { return m_mods; }
 	const ModSpec* getModSpec(const std::string &modname) const;
 	void getModNames(std::vector<std::string> &modlist);
 	std::string getBuiltinLuaPath();