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Refactor ScriptApiSecurity for cleaner separation of concerns

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This commit is contained in:
sfan5 2024-11-03 14:24:35 +01:00
parent 4c44942a39
commit 1fd4e0b82d
11 changed files with 229 additions and 135 deletions
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10
src/script/common/c_internal.cpp
View File

@ -3,6 +3,7 @@
// Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
#include "common/c_internal.h"
#include "cpp_api/s_security.h"
#include "util/numeric.h"
#include "debug.h"
#include "log.h"
@ -184,12 +185,9 @@ void log_deprecated(lua_State *L, std::string_view message, int stack_depth, boo
void call_string_dump(lua_State *L, int idx)
{
// Retrieve string.dump from insecure env to avoid it being tampered with
lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
if (!lua_isnil(L, -1))
lua_getfield(L, -1, "string");
else
lua_getglobal(L, "string");
// Retrieve string.dump from untampered env
ScriptApiSecurity::getGlobalsBackup(L);
lua_getfield(L, -1, "string");
lua_getfield(L, -1, "dump");
lua_remove(L, -2); // remove _G
lua_remove(L, -2); // remove 'string' table

1
src/script/common/c_internal.h
View File

@ -39,6 +39,7 @@ enum {
#endif
CUSTOM_RIDX_SCRIPTAPI,
/// @warning don't use directly, `ScriptApiSecurity` has wrappers
CUSTOM_RIDX_GLOBALS_BACKUP,
CUSTOM_RIDX_CURRENT_MOD_NAME,
CUSTOM_RIDX_ERROR_HANDLER,

8
src/script/cpp_api/s_async.h
View File

@ -50,11 +50,17 @@ class AsyncWorkerThread : public Thread,
public:
virtual ~AsyncWorkerThread();
void *run();
void *run() override;
protected:
AsyncWorkerThread(AsyncEngine* jobDispatcher, const std::string &name);
bool checkPathInternal(const std::string &abs_path, bool write_required,
bool *write_allowed) override {
return ScriptApiSecurity::checkPathWithGamedef(getStack(),
abs_path, write_required, write_allowed);
};
private:
AsyncEngine *jobDispatcher = nullptr;
bool isErrored = false;

33
src/script/cpp_api/s_base.cpp
View File

@ -225,37 +225,6 @@ std::string ScriptApiBase::getCurrentModNameInsecure(lua_State *L)
return ret;
}
std::string ScriptApiBase::getCurrentModName(lua_State *L)
{
auto script = ModApiBase::getScriptApiBase(L);
if (script->getType() == ScriptingType::Async ||
script->getType() == ScriptingType::Emerge)
{
// As a precaution never return a "secure" mod name in the async and
// emerge environment, because these currently do not track mod origins
// in a spoof-safe way (see l_register_async_dofile and l_register_mapgen_script).
return "";
}
// We have to make sure that this function is being called directly by
// a mod, otherwise a malicious mod could override a function and
// steal its return value. (e.g. request_insecure_environment)
lua_Debug info;
// Make sure there's only one item below this function on the stack...
if (lua_getstack(L, 2, &info))
return "";
FATAL_ERROR_IF(!lua_getstack(L, 1, &info), "lua_getstack() failed");
FATAL_ERROR_IF(!lua_getinfo(L, "S", &info), "lua_getinfo() failed");
// ...and that that item is the main file scope.
if (strcmp(info.what, "main") != 0)
return "";
// at this point we can trust this value:
return getCurrentModNameInsecure(L);
}
void ScriptApiBase::loadMod(const std::string &script_path,
const std::string &mod_name)
{
@ -273,7 +242,7 @@ void ScriptApiBase::loadScript(const std::string &script_path)
int error_handler = PUSH_ERROR_HANDLER(L);
bool ok;
if (m_secure) {
if (ScriptApiSecurity::isSecure(L)) {
ok = ScriptApiSecurity::safeLoadFile(L, script_path.c_str());
} else {
ok = !luaL_loadfile(L, script_path.c_str());

20
src/script/cpp_api/s_base.h
View File

@ -101,17 +101,15 @@ public:
void setOriginDirect(const char *origin);
void setOriginFromTableRaw(int index, const char *fxn);
// Returns the currently running mod, only during init time.
// The reason this is "insecure" is that mods can mess with each others code,
// so the boundary of who is responsible is fuzzy.
// Note: checking this against BUILTIN_MOD_NAME is always safe (not spoofable).
// returns "" on error
/**
* Returns the currently running mod, only during init time.
* The reason this is insecure is that mods can mess with each others code,
* so the boundary of who is responsible is fuzzy.
* @note Checking this against BUILTIN_MOD_NAME is always safe (not spoofable).
* @note See ScriptApiSecurity::getCurrentModName() for the secure equivalent.
* @return mod name or "" on error
*/
static std::string getCurrentModNameInsecure(lua_State *L);
// Returns the currently running mod, only during init time.
// This checks the Lua stack to only permit direct calls in the file
// scope. That way it is assured that it's really the mod it claims to be.
// returns "" on error
static std::string getCurrentModName(lua_State *L);
#if !CHECK_CLIENT_BUILD()
inline void clientOpenLibs(lua_State *L) { assert(false); }
@ -171,7 +169,7 @@ protected:
std::recursive_mutex m_luastackmutex;
std::string m_last_run_mod;
bool m_secure = false;
#ifdef SCRIPTAPI_LOCK_DEBUG
int m_lock_recursion_count{};
std::thread::id m_owning_thread;

183
src/script/cpp_api/s_security.cpp
View File

@ -260,6 +260,8 @@ void ScriptApiSecurity::initializeSecurity()
lua_pop(L, 1); // Pop empty string
}
#if CHECK_CLIENT_BUILD()
void ScriptApiSecurity::initializeSecurityClient()
{
static const char *whitelist[] = {
@ -375,6 +377,8 @@ void ScriptApiSecurity::initializeSecurityClient()
setLuaEnv(L, thread);
}
#endif
int ScriptApiSecurity::getThread(lua_State *L)
{
#if LUA_VERSION_NUM <= 501
@ -408,19 +412,24 @@ void ScriptApiSecurity::setLuaEnv(lua_State *L, int thread)
bool ScriptApiSecurity::isSecure(lua_State *L)
{
#if CHECK_CLIENT_BUILD()
auto script = ModApiBase::getScriptApiBase(L);
// CSM keeps no globals backup but is always secure
if (script->getType() == ScriptingType::Client)
return true;
#endif
lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
bool secure = !lua_isnil(L, -1);
lua_pop(L, 1);
return secure;
auto *script = ModApiBase::getScriptApiBase(L);
if (auto *sec = dynamic_cast<ScriptApiSecurity*>(script))
return sec->m_secure;
return false;
}
bool ScriptApiSecurity::safeLoadString(lua_State *L, const std::string &code, const char *chunk_name)
void ScriptApiSecurity::getGlobalsBackup(lua_State *L)
{
if (!ScriptApiSecurity::isSecure(L)) {
lua_getglobal(L, "_G");
return;
}
lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
// We cannot fulfill the callers wish securely if they don't exist.
FATAL_ERROR_IF(lua_isnil(L, -1), "Globals backup requested, but it is not available. Cannot proceed securely.");
}
bool ScriptApiSecurity::safeLoadString(lua_State *L, std::string_view code, const char *chunk_name)
{
if (code.size() > 0 && code[0] == LUA_SIGNATURE[0]) {
lua_pushliteral(L, "Bytecode prohibited when mod security is enabled.");
@ -441,7 +450,7 @@ bool ScriptApiSecurity::safeLoadFile(lua_State *L, const char *path, const char
fp = stdin;
chunk_name = const_cast<char *>("=stdin");
} else {
fp = fopen(path, "rb");
fp = std::fopen(path, "rb");
if (!fp) {
lua_pushfstring(L, "%s: %s", path, strerror(errno));
return false;
@ -500,7 +509,35 @@ bool ScriptApiSecurity::safeLoadFile(lua_State *L, const char *path, const char
}
bool checkModNameWhitelisted(const std::string &mod_name, const std::string &setting)
std::string ScriptApiSecurity::getCurrentModName(lua_State *L)
{
auto *script = ModApiBase::getScriptApiBase(L);
auto *sec = dynamic_cast<ScriptApiSecurity*>(script);
if (sec && !sec->modNamesAreTrusted())
return "";
// We have to make sure that this function is being called directly by
// a mod, otherwise a malicious mod could override a function and
// steal its return value. (e.g. request_insecure_environment)
lua_Debug info;
// Make sure there's only one item below this function on the stack...
if (lua_getstack(L, 2, &info))
return "";
FATAL_ERROR_IF(!lua_getstack(L, 1, &info), "lua_getstack() failed");
FATAL_ERROR_IF(!lua_getinfo(L, "S", &info), "lua_getinfo() failed");
// ...and that that item is the main file scope.
if (strcmp(info.what, "main") != 0)
return "";
// at this point we can trust this value:
return getCurrentModNameInsecure(L);
}
static bool checkModNameWhitelisted(const std::string &mod_name, const std::string &setting)
{
assert(str_starts_with(setting, "secure."));
@ -517,7 +554,7 @@ bool checkModNameWhitelisted(const std::string &mod_name, const std::string &set
bool ScriptApiSecurity::checkWhitelisted(lua_State *L, const std::string &setting)
{
std::string mod_name = ScriptApiBase::getCurrentModName(L);
std::string mod_name = getCurrentModName(L);
return checkModNameWhitelisted(mod_name, setting);
}
@ -528,16 +565,8 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
if (write_allowed)
*write_allowed = false;
std::string str; // Transient
std::string abs_path = fs::AbsolutePath(path);
if (!abs_path.empty()) {
// Don't allow accessing the settings file
str = fs::AbsolutePath(g_settings_path);
if (str == abs_path) return false;
}
// If we couldn't find the absolute path (path doesn't exist) then
// try removing the last components until it works (to allow
// non-existent files/folders for mkdir).
@ -560,61 +589,84 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
}
if (abs_path.empty())
return false;
// Add the removed parts back so that you can't, eg, create a
// Add the removed parts back so that you can e.g. create a
// directory in worldmods if worldmods doesn't exist.
if (!removed.empty())
abs_path += DIR_DELIM + removed;
// Get gamedef from registry
ScriptApiBase *script = ModApiBase::getScriptApiBase(L);
const IGameDef *gamedef = script->getGameDef();
tracestream << "ScriptApiSecurity: path \"" << path << "\" resolved to \""
<< abs_path << "\"" << std::endl;
// Ask the environment-specific implementation
auto *sec = ModApiBase::getScriptApi<ScriptApiSecurity>(L);
return sec->checkPathInternal(abs_path, write_required, write_allowed);
}
bool ScriptApiSecurity::checkPathWithGamedef(lua_State *L,
const std::string &abs_path, bool write_required, bool *write_allowed)
{
const auto &set_write_allowed = [&] (bool v) {
if (write_allowed)
*write_allowed = v;
};
std::string str; // Transient
auto *gamedef = ModApiBase::getGameDef(L);
if (!gamedef)
return false;
if (!abs_path.empty()) {
// Don't allow accessing the settings file
str = fs::AbsolutePath(g_settings_path);
if (str == abs_path)
return false;
}
// Get mod name
std::string mod_name = ScriptApiBase::getCurrentModNameInsecure(L);
if (!mod_name.empty()) {
// Builtin can access anything
if (mod_name == BUILTIN_MOD_NAME) {
if (write_allowed) *write_allowed = true;
set_write_allowed(true);
return true;
}
}
// Allow paths in mod path
// Don't bother if write access isn't important, since it will be handled later
if (write_required || write_allowed != NULL) {
const ModSpec *mod = gamedef->getModSpec(mod_name);
if (mod) {
str = fs::AbsolutePath(mod->path);
if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
// `mod_name` cannot be trusted here, so we catch the scenarios where this becomes a problem:
bool is_trusted = checkModNameWhitelisted(mod_name, "secure.trusted_mods") ||
checkModNameWhitelisted(mod_name, "secure.http_mods");
std::string filename = lowercase(fs::GetFilenameFromPath(abs_path.c_str()));
// By writing to any of these a malicious mod could turn itself into
// an existing trusted mod by renaming or becoming a modpack.
bool is_dangerous_file = filename == "mod.conf" ||
filename == "modpack.conf" ||
filename == "modpack.txt";
if (write_required) {
if (is_trusted) {
throw LuaError(
"Unable to write to a trusted or http mod's directory. "
"For data storage consider minetest.get_mod_data_path() or minetest.get_worldpath() instead.");
} else if (is_dangerous_file) {
throw LuaError(
"Unable to write to special file for security reasons");
} else {
const char *message =
"Writing to mod directories is deprecated, as any changes "
"will be overwritten when updating content. "
"For data storage consider minetest.get_mod_data_path() or minetest.get_worldpath() instead.";
log_deprecated(L, message, 1);
}
// Allow paths in mod path
// Don't bother if write access isn't important, since it will be handled later
if (write_required || write_allowed) {
const ModSpec *mod = gamedef->getModSpec(mod_name);
if (mod) {
str = fs::AbsolutePath(mod->path);
if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
// `mod_name` cannot be trusted here, so we catch the scenarios where this becomes a problem:
bool is_trusted = checkModNameWhitelisted(mod_name, "secure.trusted_mods") ||
checkModNameWhitelisted(mod_name, "secure.http_mods");
std::string filename = lowercase(fs::GetFilenameFromPath(abs_path.c_str()));
// By writing to any of these a malicious mod could turn itself into
// an existing trusted mod by renaming or becoming a modpack.
bool is_dangerous_file = filename == "mod.conf" ||
filename == "modpack.conf" ||
filename == "modpack.txt";
if (write_required) {
if (is_trusted) {
throw LuaError(
"Unable to write to a trusted or http mod's directory. "
"For data storage consider minetest.get_mod_data_path() or minetest.get_worldpath() instead.");
} else if (is_dangerous_file) {
throw LuaError(
"Unable to write to special file for security reasons");
} else {
const char *message =
"Writing to mod directories is deprecated, as any changes "
"will be overwritten when updating content. "
"For data storage consider minetest.get_mod_data_path() or minetest.get_worldpath() instead.";
log_deprecated(L, message, 1);
}
if (write_allowed) *write_allowed = !is_trusted && !is_dangerous_file;
return true;
}
set_write_allowed(!is_trusted && !is_dangerous_file);
return true;
}
}
}
@ -624,9 +676,8 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
const SubgameSpec *game_spec = gamedef->getGameSpec();
if (game_spec && !game_spec->path.empty()) {
str = fs::AbsolutePath(game_spec->path);
if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
if (!str.empty() && fs::PathStartsWith(abs_path, str))
return true;
}
}
}
@ -635,16 +686,15 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
const std::vector<ModSpec> &mods = gamedef->getMods();
for (const ModSpec &mod : mods) {
str = fs::AbsolutePath(mod.path);
if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
if (!str.empty() && fs::PathStartsWith(abs_path, str))
return true;
}
}
}
// Allow read/write access to all mod common dirs
str = fs::AbsolutePath(gamedef->getModDataPath());
if (!str.empty() && fs::PathStartsWith(abs_path, str)) {
if (write_allowed) *write_allowed = true;
set_write_allowed(true);
return true;
}
@ -662,12 +712,11 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path,
}
// Allow all other paths in world path
if (fs::PathStartsWith(abs_path, str)) {
if (write_allowed) *write_allowed = true;
set_write_allowed(true);
return true;
}
}
// Default to disallowing
return false;
}

68
src/script/cpp_api/s_security.h
View File

@ -12,10 +12,12 @@
throw LuaError(std::string("Mod security: Blocked attempted ") + \
(write_required ? "write to " : "read from ") + path); \
}
#define CHECK_SECURE_PATH(L, path, write_required) \
if (ScriptApiSecurity::isSecure(L)) { \
CHECK_SECURE_PATH_INTERNAL(L, path, write_required, NULL); \
CHECK_SECURE_PATH_INTERNAL(L, path, write_required, nullptr); \
}
#define CHECK_SECURE_PATH_POSSIBLE_WRITE(L, path, ptr) \
if (ScriptApiSecurity::isSecure(L)) { \
CHECK_SECURE_PATH_INTERNAL(L, path, false, ptr); \
@ -27,19 +29,65 @@ class ScriptApiSecurity : virtual public ScriptApiBase
public:
// Sets up security on the ScriptApi's Lua state
void initializeSecurity();
#if CHECK_CLIENT_BUILD()
void initializeSecurityClient();
#else
inline void initializeSecurityClient() { assert(0); }
#endif
// Checks if the Lua state has been secured
static bool isSecure(lua_State *L);
// Loads a string as Lua code safely (doesn't allow bytecode).
static bool safeLoadString(lua_State *L, const std::string &code, const char *chunk_name);
// Loads a file as Lua code safely (doesn't allow bytecode).
static bool safeLoadFile(lua_State *L, const char *path, const char *display_name = NULL);
// Check if mod is whitelisted in the given setting
// This additionally checks that the mod's main file scope is executing.
// Leaves the untampered globals (table) on top of the stack
static void getGlobalsBackup(lua_State *L);
/// Loads a string as Lua code safely (doesn't allow bytecode).
static bool safeLoadString(lua_State *L, std::string_view code, const char *chunk_name);
/// Loads a file as Lua code safely (doesn't allow bytecode).
/// @warning path is not validated in any way
static bool safeLoadFile(lua_State *L, const char *path, const char *display_name = nullptr);
/**
* Returns the currently running mod, only during init time.
* This checks the Lua stack to only permit direct calls in the file
* scope. That way it is assured that it's really the mod it claims to be.
* @return mod name or "" on error
*/
static std::string getCurrentModName(lua_State *L);
/// Check if mod is whitelisted in the given setting.
/// This additionally does main scope checks (see above method).
/// @note check is performed even in non-secured Lua state
static bool checkWhitelisted(lua_State *L, const std::string &setting);
// Checks if mods are allowed to read (and optionally write) to the path
/// Checks if mods are allowed to read (and optionally write) to the path
/// @note invalid to call in non-secured Lua state
static bool checkPath(lua_State *L, const char *path, bool write_required,
bool *write_allowed=NULL);
bool *write_allowed = nullptr);
protected:
// To be implemented by descendants:
/**
* Specify if the mod names during init time(!) can be trusted.
* It needs to be assured that no tampering happens before any call to `loadMod()`.
* @note disabling this implies that mod whitelisting never works
* @return boolean value
*/
virtual bool modNamesAreTrusted() { return false; }
/**
* Should check if the given path may be accessed.
* If `write_required` is true test for write access, if false test for read access.
* @param abs_path absolute file/directory path, may not exist
* @param write_required was write access requested?
* @param write_allowed output parameter (nullable): set to true if writing is allowed
* @return true if access is allowed
*/
virtual bool checkPathInternal(const std::string &abs_path, bool write_required,
bool *write_allowed) = 0;
// Ready-made implementation of `checkPathInternal` suitable for server-related uses
static bool checkPathWithGamedef(lua_State *L, const std::string &abs_path,
bool write_required, bool *write_allowed);
private:
int getThread(lua_State *L);
@ -48,6 +96,8 @@ private:
// creates an empty Lua environment
void createEmptyEnv(lua_State *L);
bool m_secure = false;
// Syntax: "sl_" <Library name or 'g' (global)> '_' <Function name>
// (sl stands for Secure Lua)

13
src/script/lua_api/l_util.cpp
View File

@ -494,18 +494,13 @@ int ModApiUtil::l_request_insecure_environment(lua_State *L)
{
NO_MAP_LOCK_REQUIRED;
// Just return _G if security is disabled
if (!ScriptApiSecurity::isSecure(L)) {
lua_getglobal(L, "_G");
return 1;
}
if (!ScriptApiSecurity::checkWhitelisted(L, "secure.trusted_mods")) {
return 0;
if (ScriptApiSecurity::isSecure(L)) {
if (!ScriptApiSecurity::checkWhitelisted(L, "secure.trusted_mods"))
return 0;
}
// Push insecure environment
lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
ScriptApiSecurity::getGlobalsBackup(L);
return 1;
}

12
src/script/scripting_client.h
View File

@ -5,6 +5,8 @@
#pragma once
#include <cassert>
#include "cpp_api/s_base.h"
#include "cpp_api/s_client.h"
#include "cpp_api/s_modchannels.h"
@ -27,6 +29,16 @@ public:
void on_camera_ready(Camera *camera);
void on_minimap_ready(Minimap *minimap);
protected:
// from ScriptApiSecurity:
bool checkPathInternal(const std::string &abs_path, bool write_required,
bool *write_allowed) override {
warningstream << "IO API called in client scripting" << std::endl;
assert(0);
return false;
}
bool modNamesAreTrusted() override { return true; }
private:
virtual void InitializeModApi(lua_State *L, int top);
};

7
src/script/scripting_emerge.h
View File

@ -17,6 +17,13 @@ class EmergeScripting:
public:
EmergeScripting(EmergeThread *parent);
protected:
bool checkPathInternal(const std::string &abs_path, bool write_required,
bool *write_allowed) override {
return ScriptApiSecurity::checkPathWithGamedef(getStack(),
abs_path, write_required, write_allowed);
};
private:
void InitializeModApi(lua_State *L, int top);
};

9
src/script/scripting_server.h
View File

@ -50,6 +50,15 @@ public:
u32 queueAsync(std::string &&serialized_func,
PackedValue *param, const std::string &mod_origin);
protected:
// from ScriptApiSecurity:
bool checkPathInternal(const std::string &abs_path, bool write_required,
bool *write_allowed) override {
return ScriptApiSecurity::checkPathWithGamedef(getStack(),
abs_path, write_required, write_allowed);
}
bool modNamesAreTrusted() override { return true; }
private:
void InitializeModApi(lua_State *L, int top);