From 6b0b04f1b265c429bd19d6c99c9e7e2921723601 Mon Sep 17 00:00:00 2001
From: "Meir Shpilraien (Spielrein)" <meir@redis.com>
Date: Sun, 28 Nov 2021 11:59:39 +0200
Subject: [PATCH] Clean Lua stack before parsing call reply to avoid crash on a
 call with many arguments (#9809)

This commit 0f8b634cd (CVE-2021-32626 released in 6.2.6, 6.0.16, 5.0.14)
fixes an invalid memory write issue by using `lua_checkstack` API to make
sure the Lua stack is not overflow. This fix was added on 3 places:
1. `luaReplyToRedisReply`
2. `ldbRedis`
3. `redisProtocolToLuaType`

On the first 2 functions, `lua_checkstack` is handled gracefully while the
last is handled with an assert and a statement that this situation can
not happened (only with misbehave module):

> the Redis reply might be deep enough to explode the LUA stack (notice
that currently there is no such command in Redis that returns such a nested
reply, but modules might do it)

The issue that was discovered is that user arguments is also considered part
of the stack, and so the following script (for example) make the assertion reachable:
```
local a = {}
for i=1,7999 do
    a[i] = 1
end
return redis.call("lpush", "l", unpack(a))
```

This is a regression because such a script would have worked before and now
its crashing Redis. The solution is to clear the function arguments from the Lua
stack which makes the original assumption true and the assertion unreachable.
---
 src/scripting.c          |  4 ++++
 tests/unit/scripting.tcl | 10 ++++++++++
 2 files changed, 14 insertions(+)

diff --git a/src/scripting.c b/src/scripting.c
index 7880d1b0e..3fc804a96 100644
--- a/src/scripting.c
+++ b/src/scripting.c
@@ -790,6 +790,10 @@ int luaRedisGenericCommand(lua_State *lua, int raise_error) {
         return raise_error ? luaRaiseError(lua) : 1;
     }
 
+    /* Pop all arguments from the stack, we do not need them anymore
+     * and this way we guaranty we will have room on the stack for the result. */
+    lua_pop(lua, argc);
+
     /* Setup our fake client for command execution */
     c->argv = argv;
     c->argc = argc;
diff --git a/tests/unit/scripting.tcl b/tests/unit/scripting.tcl
index 9fbf7e41d..be7147d35 100644
--- a/tests/unit/scripting.tcl
+++ b/tests/unit/scripting.tcl
@@ -622,6 +622,16 @@ start_server {tags {"scripting"}} {
         # make sure the connection is still valid
         assert_equal [r ping] {PONG}
     }
+
+    test {Script check unpack with massive arguments} {
+        r eval {
+            local a = {}
+            for i=1,7999 do
+                a[i] = 1
+            end 
+            return redis.call("lpush", "l", unpack(a))
+        } 0
+    } {7999}
 }
 
 # Start a new server since the last test in this stanza will kill the