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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 17 Apr 2018 16:06:28 -0700
Message-ID: <CAGXu5jK2qwHLN+ormmCpeVPTMwojYELPOfEYsB60LwZ7pQcpcg@mail.gmail.com>
Subject: Re: usercopy whitelist woe in scsi_sense_cache
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Paolo Valente <paolo.valente@linaro.org>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        Bart Van Assche <bart.vanassche@wdc.com>,
        David Windsor <dave@nullcore.net>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Hannes Reinecke <hare@suse.com>,
        Johannes Thumshirn <jthumshirn@suse.de>,
        linux-block@vger.kernel.org
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On Tue, Apr 17, 2018 at 3:57 PM, Jens Axboe <axboe@kernel.dk> wrote:
> On 4/17/18 3:48 PM, Jens Axboe wrote:
>> On 4/17/18 3:47 PM, Kees Cook wrote:
>>> On Tue, Apr 17, 2018 at 2:39 PM, Jens Axboe <axboe@kernel.dk> wrote:
>>>> On 4/17/18 3:25 PM, Kees Cook wrote:
>>>>> On Tue, Apr 17, 2018 at 1:46 PM, Kees Cook <keescook@chromium.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.
>
> Does this fix it?
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index f0ecd98509d8..d883469a1582 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -4934,8 +4934,11 @@ static void bfq_prepare_request(struct request *rq, struct bio *bio)
>         bool new_queue = false;
>         bool bfqq_already_existing = false, split = false;
>
> -       if (!rq->elv.icq)
> +       if (!rq->elv.icq) {
> +               rq->elv.priv[0] = rq->elv.priv[1] = NULL;
>                 return;
> +       }
> +
>         bic = icq_to_bic(rq->elv.icq);
>
>         spin_lock_irq(&bfqd->lock);

It does! Excellent. :)

-Kees

-- 
Kees Cook
Pixel Security