Re: usercopy whitelist woe in scsi_sense_cache

[Kees Cook]

On Tue, Apr 17, 2018 at 2:39 PM, Jens Axboe <axboe@xxxxxxxxx> wrote:
> On 4/17/18 3:25 PM, Kees Cook wrote:
>> On Tue, Apr 17, 2018 at 1:46 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> I see elv.priv[1] assignments made in a few places -- is it possible
>>> there is some kind of uninitialized-but-not-NULL state that can leak
>>> in there?
>>
>> Got it. This fixes it for me:
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 0dc9e341c2a7..859df3160303 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -363,7 +363,7 @@ static struct request *blk_mq_get_request(struct
>> request_queue *q,
>>
>>         rq = blk_mq_rq_ctx_init(data, tag, op);
>>         if (!op_is_flush(op)) {
>> -               rq->elv.icq = NULL;
>> +               memset(&rq->elv, 0, sizeof(rq->elv));
>>                 if (e && e->type->ops.mq.prepare_request) {
>>                         if (e->type->icq_cache && rq_ioc(bio))
>>                                 blk_mq_sched_assign_ioc(rq, bio);
>> @@ -461,7 +461,7 @@ void blk_mq_free_request(struct request *rq)
>>                         e->type->ops.mq.finish_request(rq);
>>                 if (rq->elv.icq) {
>>                         put_io_context(rq->elv.icq->ioc);
>> -                       rq->elv.icq = NULL;
>> +                       memset(&rq->elv, 0, sizeof(rq->elv));
>>                 }
>>         }
>
> This looks like a BFQ problem, this should not be necessary. Paolo,
> you're calling your own prepare request handler from the insert
> as well, and your prepare request does nothing if rq->elv.icq == NULL.

I sent the patch anyway, since it's kind of a robustness improvement,
I'd hope. If you fix BFQ also, please add:

Reported-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Root-caused-by: Kees Cook <keescook@xxxxxxxxxxxx>

:) I gotta task-switch to other things!

Thanks for the pointers, and thank you Oleksandr for providing the reproducer!

-Kees

-- 
Kees Cook
Pixel Security