Globals protection global() function modified for speed and correctness.

[redis.git] / src / scripting.c

diff --git a/src/scripting.c b/src/scripting.c
index 0f876961a221cf4c200d1c4c76edba0615585a9e..44ceb1e284ccd03f690b6fa3cc7eeeea94f6696f 100644 (file)
--- a/src/scripting.c
+++ b/src/scripting.c
@@ -412,6 +412,61 @@ void luaLoadLibraries(lua_State *lua) {
 #endif
 }
 
+/* This function installs metamethods in the global table _G that prevent
+ * the creation of globals accidentally.
+ *
+ * It should be the last to be called in the scripting engine initialization
+ * sequence, because it may interact with creation of globals.
+ * Note that the function is designed to be called multiple times if needed
+ * without issues, because it is possible to enabled/disable globals protection
+ * at runtime with CONFIG SET. */
+void scriptingEnableGlobalsProtection(lua_State *lua) {
+    char *s[32];
+    sds code = sdsempty();
+    int j = 0;
+
+    /* strict.lua from: http://metalua.luaforge.net/src/lib/strict.lua.html.
+     * Modified to be adapted to Redis. */
+    s[j++]="local mt = {}\n";
+    s[j++]="setmetatable(_G, mt)\n";
+    s[j++]="mt.declared = {}\n";
+    s[j++]="mt.__newindex = function (t, n, v)\n";
+    s[j++]="  if not mt.declared[n] and debug.getinfo(2) then\n";
+    s[j++]="    local w = debug.getinfo(2, \"S\").what\n";
+    s[j++]="    if w ~= \"main\" and w ~= \"C\" then\n";
+    s[j++]="      error(\"assignment to undeclared global variable '\"..n..\"'\", 2)\n";
+    s[j++]="    end\n";
+    s[j++]="    mt.declared[n] = true\n";
+    s[j++]="  end\n";
+    s[j++]="  rawset(t, n, v)\n";
+    s[j++]="end\n";
+    s[j++]="mt.__index = function (t, n)\n";
+    s[j++]="  if debug.getinfo(2) and not mt.declared[n] and debug.getinfo(2, \"S\").what ~= \"C\" then\n";
+    s[j++]="    error(\"global variable '\"..n..\"' is not declared\", 2)\n";
+    s[j++]="  end\n";
+    s[j++]="  return rawget(t, n)\n";
+    s[j++]="end\n";
+    s[j++]="function global(...)\n";
+    s[j++]="  local nargs = select(\"#\",...)\n";
+    s[j++]="  for i = 1, nargs do\n";
+    s[j++]="    local v = select(i,...)\n";
+    s[j++]="    mt.declared[v] = true\n";
+    s[j++]="  end\n";
+    s[j++]="end\n";
+    s[j++]=NULL;
+
+    for (j = 0; s[j] != NULL; j++) code = sdscatlen(code,s[j],strlen(s[j]));
+    luaL_loadbuffer(lua,code,sdslen(code),"enable_strict_lua");
+    lua_pcall(lua,0,0,0);
+    sdsfree(code);
+}
+
+void scriptingDisableGlobalsProtection(lua_State *lua) {
+    char *s = "setmetatable(_G, nil)\n";
+    luaL_loadbuffer(lua,s,strlen(s),"disable_strict_lua");
+    lua_pcall(lua,0,0,0);
+}
+
 /* Initialize the scripting environment.
  * It is possible to call this function to reset the scripting environment
  * assuming that we call scriptingRelease() before.
@@ -501,6 +556,12 @@ void scriptingInit(void) {
         server.lua_client->flags |= REDIS_LUA_CLIENT;
     }
 
+    /* Lua beginners ofter don't use "local", this is likely to introduce
+     * subtle bugs in their code. To prevent problems we protect accesses
+     * to global variables. */
+    if (server.lua_protect_globals)
+        scriptingEnableGlobalsProtection(lua);
+
     server.lua = lua;
 }