Prevent defining globals in config.

1 files changed, 20 insertions, 14 deletions

diff --git a/mkelf.lua b/mkelf.lua
index 5869a6a..1140be2 100644
--- a/mkelf.lua
+++ b/mkelf.lua
@@ -17,21 +17,27 @@ local function loadconfig(fn)
     local header_mt = { __index = elf.header }
     local segments_mt = { __index = elf.segment }
     local sections_mt = { __index = elf.section }
-    local env = {
-        -- Keep in sync with types/elf.d.lua
-        Class = elf.Class,
-        Endian = elf.Endian,
-        Osabi = elf.Osabi,
-        Type = elf.Type,
-        Machine = elf.Machine,
-        SegmentType = elf.SegmentType,
-        SegmentFlags = elf.SegmentFlags,
-        ELFVERSION = elf.VERSION,
+    local env = setmetatable({}, {
+        __index = {
+            -- Keep in sync with types/elf.d.lua
+            Class = elf.Class,
+            Endian = elf.Endian,
+            Osabi = elf.Osabi,
+            Type = elf.Type,
+            Machine = elf.Machine,
+            SegmentType = elf.SegmentType,
+            SegmentFlags = elf.SegmentFlags,
+            ELFVERSION = elf.VERSION,
 
-        header = function(t) header = setmetatable(t, header_mt) end,
-        segments = function(t) segments = setmetatable(t, segments_mt) end,
-        sections = function(t) sections = setmetatable(t, sections_mt) end,
-    }
+            header = function(t) header = setmetatable(t, header_mt) end,
+            segments = function(t) segments = setmetatable(t, segments_mt) end,
+            sections = function(t) sections = setmetatable(t, sections_mt) end,
+        },
+        __newindex = function(_, name)
+            error(("may not define global %q"):format(name), 2)
+        end,
+        __metatable = false,
+    })
     -- TODO error check for multiple headers
     local chunk, err = loadfile(fn, "t", env)
     if not chunk then die("%s", err) end