When LUA call our C code, by default, the LUA stack has room for 10
elements. In most cases, this is more than enough but sometimes it's not
and the caller must verify the LUA stack size before he pushes elements.
On 3 places in the code, there was no verification of the LUA stack size.
On specific inputs this missing verification could have lead to invalid
memory write:
1. On 'luaReplyToRedisReply', one might return a nested reply that will
explode the LUA stack.
2. On 'redisProtocolToLuaType', 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)
3. On 'ldbRedis', one might give a command with enough arguments to
explode the LUA stack (all the arguments will be pushed to the LUA
stack)
This commit is solving all those 3 issues by calling 'lua_checkstack' and
verify that there is enough room in the LUA stack to push elements. In
case 'lua_checkstack' returns an error (there is not enough room in the
LUA stack and it's not possible to increase the stack), we will do the
following:
1. On 'luaReplyToRedisReply', we will return an error to the user.
2. On 'redisProtocolToLuaType' we will exit with panic (we assume this
scenario is rare because it can only happen with a module).
3. On 'ldbRedis', we return an error.
0f8b634cd5