[Tarantool-patches] [PATCH] relay: fix use after free in subscribe_f

[Serge Petrenko]

12.05.2021 14:48, Cyrill Gorcunov пишет:
> On Wed, May 12, 2021 at 02:39:07PM +0300, Serge Petrenko wrote:
>> relay_subscribe_f() remembered old recovery pointer, which might be
>> replaced by relay_restart_recovery() if a raft message is delivered during
>> cbus_process() loop in relay_send_is_raft_enabled().
>>
>> Fix the issue by moving variable initialization below
>> relay_send_is_raft_enabled()
>>
>> Closes #6031
>> ---
>> https://github.com/tarantool/tarantool/issues/6031
>> https://github.com/tarantool/tarantool/tree/sp/gh-6031-use-after-free
>>
>>   src/box/relay.cc | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/box/relay.cc b/src/box/relay.cc
>> index ff43c2fc7..32d3a58dd 100644
>> --- a/src/box/relay.cc
>> +++ b/src/box/relay.cc
>> @@ -741,7 +741,6 @@ static int
>>   relay_subscribe_f(va_list ap)
>>   {
>>   	struct relay *relay = va_arg(ap, struct relay *);
>> -	struct recovery *r = relay->r;
>>   
>>   	coio_enable();
>>   	relay_set_cord_name(relay->io.fd);
>> @@ -756,6 +755,8 @@ relay_subscribe_f(va_list ap)
>>   	if (!relay->replica->anon)
>>   		relay_send_is_raft_enabled(relay, &raft_enabler, true);
>>   
>> +	struct recovery *r = relay->r;
> Could you please add a comment why it is important to fetch `relay->r`
> at exactly this stage. Something like
>
> 	/*
> 	 * Fetching relay->r should be done after
> 	 * cbus processing since the pointer may
> 	 * be updated undeneath.
> 	 */
> 	struct recovery *r = relay->r;
>
> Or something like this. Because commits messages are good but we
> read the code in first place and this very nontrivial moment.

Hi! Thanks for the review.
Vlad suggested to inline relay->r. It has only 2 usage places after all.

I agree this was nontrivial. It's better with the inline, I think.

-- 
Serge Petrenko