File bsc1198952-3.patch of Package redis.26564
From b2ce3719afe5440b010ab3f12d9ad35b79cee55a Mon Sep 17 00:00:00 2001
From: meir <meir@redis.com>
Date: Tue, 22 Mar 2022 11:52:20 +0200
Subject: [PATCH] Protect globals of evals scripts.
Use the new `lua_enablereadonlytable` Lua API to protect the global tables of
evals scripts. The implemetation is easy, we simply call `lua_enablereadonlytable`
on the global table to turn it into a readonly table.
---
src/scripting.c | 76 +++++++++++++++++++---------------------
tests/unit/scripting.tcl | 39 ++++++++++++++++++++-
2 files changed, 75 insertions(+), 40 deletions(-)
Index: redis-6.0.14/src/scripting.c
===================================================================
--- redis-6.0.14.orig/src/scripting.c
+++ redis-6.0.14/src/scripting.c
@@ -1068,43 +1068,39 @@ void luaRemoveUnsupportedFunctions(lua_S
lua_setglobal(lua,"dofile");
}
-/* This function installs metamethods in the global table _G that prevent
- * the creation of globals accidentally.
+static int luaProtectedTableError(lua_State *lua) {
+ int argc = lua_gettop(lua);
+ if (argc != 2) {
+ serverLog(LL_WARNING, "malicious code trying to call luaProtectedTableError with wrong arguments");
+ luaL_error(lua, "Wrong number of arguments to luaProtectedTableError");
+ }
+ if (!lua_isstring(lua, -1) && !lua_isnumber(lua, -1)) {
+ luaL_error(lua, "Second argument to luaProtectedTableError must be a string or number");
+ }
+ const char* variable_name = lua_tostring(lua, -1);
+ luaL_error(lua, "Script attempted to access nonexistent global variable '%s'", variable_name);
+ return 0;
+}
+
+/* Set global protection on table on the top of the stack.
+ * After called, it will no longer be possible to set
+ * new items on the table. Any attempt to access a protected
+ * table for write will result in an error. Any attempt to
+ * get a none existing element from a locked table will result
+ * in an error.
*
- * It should be the last to be called in the scripting engine initialization
- * sequence, because it may interact with creation of globals. */
-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 dbg=debug\n";
- s[j++]="local mt = {}\n";
- s[j++]="setmetatable(_G, mt)\n";
- s[j++]="mt.__newindex = function (t, n, v)\n";
- s[j++]=" if dbg.getinfo(2) then\n";
- s[j++]=" local w = dbg.getinfo(2, \"S\").what\n";
- s[j++]=" if w ~= \"C\" then\n";
- s[j++]=" error(\"Script attempted to create global variable '\"..tostring(n)..\"'\", 2)\n";
- s[j++]=" end\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 dbg.getinfo(2) and dbg.getinfo(2, \"S\").what ~= \"C\" then\n";
- s[j++]=" error(\"Script attempted to access nonexistent global variable '\"..tostring(n)..\"'\", 2)\n";
- s[j++]=" end\n";
- s[j++]=" return rawget(t, n)\n";
- s[j++]="end\n";
- s[j++]="debug = nil\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);
+ * The function assumes the Lua stack have a least enough
+ * space to push 2 element, its up to the caller to verify
+ * this before calling this function. */
+void luaSetGlobalProtection(lua_State *lua) {
+ lua_newtable(lua); /* push metatable */
+ lua_pushcfunction(lua, luaProtectedTableError); /* push get error handler */
+ lua_setfield(lua, -2, "__index");
+ lua_enablereadonlytable(lua, -1, 1); /* protect the metatable */
+
+ lua_setmetatable(lua, -2);
+
+ lua_enablereadonlytable(lua, -1, 1);
}
/* Initialize the scripting environment.
@@ -1287,10 +1283,10 @@ void scriptingInit(int setup) {
server.lua_client->flags |= CLIENT_LUA;
}
- /* Lua beginners often don't use "local", this is likely to introduce
- * subtle bugs in their code. To prevent problems we protect accesses
- * to global variables. */
- scriptingEnableGlobalsProtection(lua);
+ /* Lock the global table from any changes */
+ lua_pushvalue(lua, LUA_GLOBALSINDEX);
+ luaSetGlobalProtection(lua);
+ lua_pop(lua, 1);
server.lua = lua;
}
@@ -1318,7 +1314,9 @@ void luaSetGlobalArray(lua_State *lua, c
lua_pushlstring(lua,(char*)elev[j]->ptr,sdslen(elev[j]->ptr));
lua_rawseti(lua,-2,j+1);
}
+ lua_enablereadonlytable(lua, LUA_GLOBALSINDEX, 0);
lua_setglobal(lua,var);
+ lua_enablereadonlytable(lua, LUA_GLOBALSINDEX, 1);
}
/* ---------------------------------------------------------------------------
Index: redis-6.0.14/tests/unit/scripting.tcl
===================================================================
--- redis-6.0.14.orig/tests/unit/scripting.tcl
+++ redis-6.0.14/tests/unit/scripting.tcl
@@ -351,7 +351,7 @@ start_server {tags {"scripting"}} {
test {Globals protection setting an undeclared global*} {
catch {r eval {a=10} 0} e
set e
- } {*ERR*attempted to create global*}
+ } {ERR*Attempt to modify a readonly table*}
test {Test an example script DECR_IF_GT} {
set decr_if_gt {
@@ -557,6 +557,43 @@ start_server {tags {"scripting"}} {
set res [r eval {redis.setresp(2); return redis.call('hgetall', KEYS[1])} 1 hash]
assert_equal $res $expected_list
}
+
+ test "Try trick global protection 1" {
+ catch {
+ r eval {
+ setmetatable(_G, {})
+ } 0
+ } e
+ set _ $e
+ } {*Attempt to modify a readonly table*}
+
+ test "Try trick global protection 2" {
+ catch {
+ r eval {
+ local g = getmetatable(_G)
+ g.__index = {}
+ } 0
+ } e
+ set _ $e
+ } {*Attempt to modify a readonly table*}
+
+ test "Try trick global protection 3" {
+ catch {
+ r eval {
+ redis = function() return 1 end
+ } 0
+ } e
+ set _ $e
+ } {*Attempt to modify a readonly table*}
+
+ test "Try trick global protection 4" {
+ catch {
+ r eval {
+ _G = {}
+ } 0
+ } e
+ set _ $e
+ } {*Attempt to modify a readonly table*}
}
# Start a new server since the last test in this stanza will kill the
