linux-kernel - Re: usercopy whitelist woe in scsi_sense

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Date:   Tue, 17 Apr 2018 15:48:19 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Paolo Valente <paolo.valente@...aro.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Bart Van Assche <bart.vanassche@....com>,
        David Windsor <dave@...lcore.net>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>,
        Hannes Reinecke <hare@...e.com>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        linux-block@...r.kernel.org
Subject: Re: usercopy whitelist woe in scsi_sense_cache

On 4/17/18 3:47 PM, Kees Cook wrote:
> On Tue, Apr 17, 2018 at 2:39 PM, Jens Axboe <axboe@...nel.dk> wrote:
>> On 4/17/18 3:25 PM, Kees Cook wrote:
>>> On Tue, Apr 17, 2018 at 1:46 PM, Kees Cook <keescook@...omium.org> 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:

It's also a memset() in the hot path, would prefer to avoid that...
The issue here is really the convoluted bfq usage of insert/prepare,
I'm sure Paolo can take it from here.

-- 
Jens Axboe