Lua: always load built-in Lua scripts from default data-dir

The Lua modules `pandoc` and `pandoc.List` are now always loaded from the
system's default data directory. Loading from a different directory by
overriding the default path, e.g. via `--data-dir`, is no longer supported to
avoid unexpected behavior and to address security concerns.

4 files changed, 44 insertions, 46 deletions

diff --git a/src/Text/Pandoc/Lua/Init.hs b/src/Text/Pandoc/Lua/Init.hs
index 0a5ce85cb..baa6f0295 100644
--- a/src/Text/Pandoc/Lua/Init.hs
+++ b/src/Text/Pandoc/Lua/Init.hs
@@ -12,17 +12,18 @@ module Text.Pandoc.Lua.Init
   ( runLua
   ) where
 
+import Control.Monad (when)
 import Control.Monad.Catch (try)
 import Control.Monad.Trans (MonadIO (..))
 import Data.Data (Data, dataTypeConstrs, dataTypeOf, showConstr)
 import Foreign.Lua (Lua)
 import GHC.IO.Encoding (getForeignEncoding, setForeignEncoding, utf8)
+import Text.Pandoc.Class.PandocMonad (readDataFile)
 import Text.Pandoc.Class.PandocIO (PandocIO)
 import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Packages (installPandocPackageSearcher)
-import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua,
-                                  loadScriptFromDataDir, runPandocLua)
-
+import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua, runPandocLua)
+import Text.Pandoc.Lua.Util (throwTopMessageAsError')
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Definition as Pandoc
 import qualified Text.Pandoc.Lua.Module.Pandoc as ModulePandoc
@@ -44,7 +45,7 @@ initLuaState = do
   liftPandocLua Lua.openlibs
   installPandocPackageSearcher
   initPandocModule
-  loadScriptFromDataDir "init.lua"
+  loadInitScript "init.lua"
  where
   initPandocModule :: PandocLua ()
   initPandocModule = do
@@ -61,6 +62,15 @@ initLuaState = do
     -- assign module to global variable
     liftPandocLua $ Lua.setglobal "pandoc"
 
+  loadInitScript :: FilePath -> PandocLua ()
+  loadInitScript scriptFile = do
+    script <- readDataFile scriptFile
+    status <- liftPandocLua $ Lua.dostring script
+    when (status /= Lua.OK) . liftPandocLua $
+      throwTopMessageAsError'
+      (("Couldn't load '" ++ scriptFile ++ "'.\n") ++)
+
+
 -- | AST elements are marshaled via normal constructor functions in the
 -- @pandoc@ module. However, accessing Lua globals from Haskell is
 -- expensive (due to error handling). Accessing the Lua registry is much
diff --git a/src/Text/Pandoc/Lua/Module/Pandoc.hs b/src/Text/Pandoc/Lua/Module/Pandoc.hs
index a9ce3866d..a8afecd2e 100644
--- a/src/Text/Pandoc/Lua/Module/Pandoc.hs
+++ b/src/Text/Pandoc/Lua/Module/Pandoc.hs
@@ -25,7 +25,7 @@ import Text.Pandoc.Definition (Block, Inline)
 import Text.Pandoc.Lua.Filter (walkInlines, walkBlocks, LuaFilter, SingletonsList (..))
 import Text.Pandoc.Lua.Marshaling ()
 import Text.Pandoc.Lua.PandocLua (PandocLua, addFunction, liftPandocLua,
-                                  loadScriptFromDataDir)
+                                  loadDefaultModule)
 import Text.Pandoc.Walk (Walkable)
 import Text.Pandoc.Options (ReaderOptions (readerExtensions))
 import Text.Pandoc.Process (pipeProcess)
@@ -38,11 +38,11 @@ import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 import Text.Pandoc.Error
 
--- | Push the "pandoc" on the lua stack. Requires the `list` module to be
--- loaded.
+-- | Push the "pandoc" package to the Lua stack. Requires the `List`
+-- module to be loadable.
 pushModule :: PandocLua NumResults
 pushModule = do
-  loadScriptFromDataDir "pandoc.lua"
+  loadDefaultModule "pandoc"
   addFunction "read" readDoc
   addFunction "pipe" pipeFn
   addFunction "walk_block" walkBlock
diff --git a/src/Text/Pandoc/Lua/Packages.hs b/src/Text/Pandoc/Lua/Packages.hs
index d62fb725d..5949a1a7d 100644
--- a/src/Text/Pandoc/Lua/Packages.hs
+++ b/src/Text/Pandoc/Lua/Packages.hs
@@ -1,6 +1,3 @@
-{-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE LambdaCase #-}
-{-# LANGUAGE ScopedTypeVariables #-}
 {- |
    Module      : Text.Pandoc.Lua.Packages
    Copyright   : Copyright © 2017-2021 Albert Krewinkel
@@ -15,13 +12,9 @@ module Text.Pandoc.Lua.Packages
   ( installPandocPackageSearcher
   ) where
 
-import Control.Monad.Catch (try)
 import Control.Monad (forM_)
-import Data.ByteString (ByteString)
-import Foreign.Lua (Lua, NumResults)
-import Text.Pandoc.Error (PandocError)
-import Text.Pandoc.Class.PandocMonad (readDataFile)
-import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua)
+import Foreign.Lua (NumResults)
+import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua, loadDefaultModule)
 
 import qualified Foreign.Lua as Lua
 import qualified Foreign.Lua.Module.Text as Text
@@ -54,24 +47,12 @@ pandocPackageSearcher pkgName =
     "pandoc.types"    -> pushWrappedHsFun Types.pushModule
     "pandoc.utils"    -> pushWrappedHsFun Utils.pushModule
     "text"            -> pushWrappedHsFun Text.pushModule
-    _                 -> searchPureLuaLoader
+    "pandoc.List"     -> pushWrappedHsFun (loadDefaultModule pkgName)
+    _                 -> reportPandocSearcherFailure
  where
   pushWrappedHsFun f = liftPandocLua $ do
     Lua.pushHaskellFunction f
     return 1
-  searchPureLuaLoader = do
-    let filename = pkgName ++ ".lua"
-    try (readDataFile filename) >>= \case
-      Right script -> pushWrappedHsFun (loadStringAsPackage pkgName script)
-      Left (_ :: PandocError) -> liftPandocLua $ do
-        Lua.push ("\n\tno file '" ++ filename ++ "' in pandoc's datadir")
-        return (1 :: NumResults)
-
-loadStringAsPackage :: String -> ByteString -> Lua NumResults
-loadStringAsPackage pkgName script = do
-  status <- Lua.dostring script
-  if status == Lua.OK
-    then return (1 :: NumResults)
-    else do
-      msg <- Lua.popValue
-      Lua.raiseError ("Error while loading `" <> pkgName <> "`.\n" <> msg)
+  reportPandocSearcherFailure = liftPandocLua $ do
+    Lua.push ("\n\t" <> pkgName <> "is not one of pandoc's default packages")
+    return (1 :: NumResults)
diff --git a/src/Text/Pandoc/Lua/PandocLua.hs b/src/Text/Pandoc/Lua/PandocLua.hs
index 4beac22b7..750e019b6 100644
--- a/src/Text/Pandoc/Lua/PandocLua.hs
+++ b/src/Text/Pandoc/Lua/PandocLua.hs
@@ -23,24 +23,23 @@ module Text.Pandoc.Lua.PandocLua
   , runPandocLua
   , liftPandocLua
   , addFunction
-  , loadScriptFromDataDir
+  , loadDefaultModule
   ) where
 
-import Control.Monad (when)
 import Control.Monad.Catch (MonadCatch, MonadMask, MonadThrow)
 import Control.Monad.Except (MonadError (catchError, throwError))
 import Control.Monad.IO.Class (MonadIO (liftIO))
 import Foreign.Lua (Lua (..), NumResults, Pushable, ToHaskellFunction)
 import Text.Pandoc.Class.PandocIO (PandocIO)
-import Text.Pandoc.Class.PandocMonad (PandocMonad (..), readDataFile)
-import Text.Pandoc.Error (PandocError)
+import Text.Pandoc.Class.PandocMonad (PandocMonad (..), readDefaultDataFile)
+import Text.Pandoc.Error (PandocError (PandocLuaError))
 import Text.Pandoc.Lua.Global (Global (..), setGlobals)
 import Text.Pandoc.Lua.ErrorConversion (errorConversion)
 
 import qualified Control.Monad.Catch as Catch
+import qualified Data.Text as T
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Class.IO as IO
-import qualified Text.Pandoc.Lua.Util as LuaUtil
 
 -- | Type providing access to both, pandoc and Lua operations.
 newtype PandocLua a = PandocLua { unPandocLua :: Lua a }
@@ -86,14 +85,22 @@ addFunction name fn = liftPandocLua $ do
   Lua.pushHaskellFunction fn
   Lua.rawset (-3)
 
--- | Load a file from pandoc's data directory.
-loadScriptFromDataDir :: FilePath -> PandocLua ()
-loadScriptFromDataDir scriptFile = do
-  script <- readDataFile scriptFile
+-- | Load a pure Lua module included with pandoc. Leaves the result on
+-- the stack and returns @NumResults 1@.
+--
+-- The script is loaded from the default data directory. We do not load
+-- from data directories supplied via command line, as this could cause
+-- scripts to be executed even though they had not been passed explicitly.
+loadDefaultModule :: String -> PandocLua NumResults
+loadDefaultModule name = do
+  script <- readDefaultDataFile (name <> ".lua")
   status <- liftPandocLua $ Lua.dostring script
-  when (status /= Lua.OK) . liftPandocLua $
-    LuaUtil.throwTopMessageAsError'
-      (("Couldn't load '" ++ scriptFile ++ "'.\n") ++)
+  if status == Lua.OK
+    then return (1 :: NumResults)
+    else do
+      msg <- liftPandocLua Lua.popValue
+      let err = "Error while loading `" <> name <> "`.\n" <> msg
+      throwError $ PandocLuaError (T.pack err)
 
 -- | Global variables which should always be set.
 defaultGlobals :: PandocIO [Global]