Replace Lua loadfile/dofile with execfile()

src/controllers/plugins/ApiChatterino.cpp

@@ -13,6 +13,9 @@
 #    include "lauxlib.h"
 #    include "lua.h"
 #    include "lualib.h"
+
+#    include <QFileInfo>
+#    include <QTextCodec>
 namespace chatterino::lua::api {
 
 int c2_register_command(lua_State *L)
@@ -135,9 +138,78 @@ int g_load(lua_State *L)
     }
 
     lua_call(L, countArgs, LUA_MULTRET);
-    qCDebug(chatterinoLua) << "FDM " << lua_gettop(L);
 
     return lua_gettop(L);
 }
+
+int g_dofile(lua_State *L)
+{
+    auto countArgs = lua_gettop(L);
+    // Lua allows dofile() which loads from stdin, but this is very useless in our case
+    if (countArgs == 0)
+    {
+        lua_pushnil(L);
+        // NOLINTNEXTLINE
+        luaL_error(L, "it is not allowed to call dofile() without arguments");
+        return 1;
+    }
+
+    auto *pl = getApp()->plugins->getPluginByStatePtr(L);
+    QString fname;
+    if (!lua::pop(L, &fname))
+    {
+        lua_pushnil(L);
+        // NOLINTNEXTLINE
+        luaL_error(L, "chatterino g_dofile: expected a string for a filename");
+        return 1;
+    }
+    auto dir = QUrl(pl->loadDirectory().canonicalPath() + "/");
+    auto file = dir.resolved(fname);
+
+    qCDebug(chatterinoLua) << "plugin" << pl->codename << "is trying to load"
+                           << file << "(its dir is" << dir << ")";
+    if (!dir.isParentOf(file))
+    {
+        lua_pushnil(L);
+        // NOLINTNEXTLINE
+        luaL_error(L, "chatterino g_dofile: filename must be inside of the "
+                      "plugin directory");
+        return 1;
+    }
+
+    auto path = file.path(QUrl::FullyDecoded);
+    // validate utf-8 to block bytecode exploits
+    QFile qf(path);
+    qf.open(QIODevice::ReadOnly);
+    if (qf.size() > 10'000'000)
+    {
+        lua_pushnil(L);
+        // NOLINTNEXTLINE
+        luaL_error(L, "chatterino g_dofile: size limit of 10MB exceeded, what "
+                      "the hell are you doing");
+        return 1;
+    }
+    auto data = qf.readAll();
+    auto *utf8 = QTextCodec::codecForName("UTF-8");
+    QTextCodec::ConverterState state;
+    utf8->toUnicode(data.constData(), data.size(), &state);
+    if (state.invalidChars != 0)
+    {
+        lua_pushnil(L);
+        // NOLINTNEXTLINE
+        luaL_error(L, "invalid utf-8 in dofile() target (%s) is not allowed",
+                   fname.toStdString().c_str());
+        return 1;
+    }
+
+    // fetch dofile and call it
+    lua_getfield(L, LUA_REGISTRYINDEX, "real_dofile");
+    // maybe data race here if symlink was swapped?
+    lua::push(L, path);
+    lua_call(L, 1, LUA_MULTRET);
+
+    return lua_gettop(L);
+}
+
 }  // namespace chatterino::lua::api
 #endif

src/controllers/plugins/ApiChatterino.hpp

@@ -10,6 +10,7 @@ int c2_send_msg(lua_State *L);          // NOLINT(readability-identifier-naming)
 int c2_system_msg(lua_State *L);        // NOLINT(readability-identifier-naming)
 
 int g_load(lua_State *L);    // NOLINT(readability-identifier-naming)
+int g_dofile(lua_State *L);  // NOLINT(readability-identifier-naming)
 
 }  // namespace chatterino::lua::api
 

src/controllers/plugins/Plugin.hpp

@@ -72,6 +72,11 @@ public:
 
     std::set<QString> listRegisteredCommands();
 
+    const QDir &loadDirectory() const
+    {
+        return this->loadDirectory_;
+    }
+
 private:
     QDir loadDirectory_;
     lua_State *state_;

src/controllers/plugins/PluginController.cpp

@@ -165,13 +165,25 @@ void PluginController::openLibrariesFor(lua_State *L,
     // possibly randomize this name at runtime to prevent some attacks?
     lua_setfield(L, LUA_REGISTRYINDEX, "real_load");
 
+    lua_getfield(L, gtable, "dofile");
+    lua_setfield(L, LUA_REGISTRYINDEX, "real_dofile");
+
     // NOLINTNEXTLINE
     static const luaL_Reg replacementFuncs[] = {
         {"load", lua::api::g_load},
+
+        // chatterino dofile is way more similar to require() than dofile()
+        {"execfile", lua::api::g_dofile},
         {nullptr, nullptr},
     };
     luaL_setfuncs(L, replacementFuncs, 0);
 
+    lua_pushnil(L);
+    lua_setfield(L, gtable, "loadfile");
+
+    lua_pushnil(L);
+    lua_setfield(L, gtable, "dofile");
+
     lua_pop(L, 1);
 }