Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 11.2 \(3445.5.20\))
Subject: Re: usercopy whitelist woe in scsi_sense_cache
From:   Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <0fbf2b13-8bae-c7c5-d930-ebaafdc72202@kernel.dk>
Date:   Wed, 18 Apr 2018 11:08:45 +0200
Cc:     Kees Cook <keescook@chromium.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
Content-Transfer-Encoding: quoted-printable
Message-Id: <011EF7D1-B095-4B8D-AD2A-993048932C49@linaro.org>
References: <10360653.ov98egbaqx@natalenko.name>
 <2864697.7uzmEJovl2@natalenko.name>
 <CAGXu5jLSmJv9AstzsgSscrv-wA7FwfrxAKRxj-FVBmihQvnj1g@mail.gmail.com>
 <CAGXu5j+dh1zm32iBjRVh0s+3gLJYgjwt+z1aBJmrK2Cr8XPWnA@mail.gmail.com>
 <CAGXu5jLhnWnUiscP9B=kTEFNyRw9jgFn7Zr5FxhZrO20553+1Q@mail.gmail.com>
 <CAGXu5jKuZwicyyXH2gB3vp-OjtS+MkG+hqxV1cq1jaG9vAAO=g@mail.gmail.com>
 <CAGXu5jLQuzpjFcfjpT=MvgOxBizFNMjnfmY+E7eCHkDAV5swHg@mail.gmail.com>
 <CAGXu5jJTMqbXia7TmN2yEW11SM+XC3pkMt=bb+xBrY7-OOf=tw@mail.gmail.com>
 <CAGXu5j+xX3kDDS_sPY44hPVb=8isMX-evYzPx3ur=rge1rL5JQ@mail.gmail.com>
 <CAGXu5jJmvKcANUSsCz3fjGSv-tv1hceNd3rOpT4WTfYRb65RRA@mail.gmail.com>
 <8473f909-2123-0cfc-43b1-beba0b1aef9b@kernel.dk>
 <CAGXu5jL9miO3OXpjAxm9t8v=f_f5StB=Tk=aV8BVRdEj-Y-PDA@mail.gmail.com>
 <CAGXu5jKVPQi0cdTbe5Y1DNHdiJ6-kEFRBTNv7znuqT9w5eifGg@mail.gmail.com>
 <07f263ff-cea6-ac3c-944b-0f36fee8ba25@kernel.dk>
 <CAGXu5j+kHipvoyFWjGp8M6+83zbd6yHOzwxQ-2LNBQbD5-jS9w@mail.gmail.com>
 <8b32e079-d4e6-3fea-a89d-ff856e4e13b1@kernel.dk>
 <0fbf2b13-8bae-c7c5-d930-ebaafdc72202@kernel.dk>
To:     Jens Axboe <axboe@kernel.dk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Il giorno 18 apr 2018, alle ore 00:57, Jens Axboe <axboe@kernel.dk> ha =
scritto:
>=20
> 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?
>>>>>=20
>>>>> Got it. This fixes it for me:
>>>>>=20
>>>>> 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,
>>>>>=20
>>>>>        rq =3D blk_mq_rq_ctx_init(data, tag, op);
>>>>>        if (!op_is_flush(op)) {
>>>>> -               rq->elv.icq =3D 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 =3D NULL;
>>>>> +                       memset(&rq->elv, 0, sizeof(rq->elv));
>>>>>                }
>>>>>        }
>>>>=20
>>>> 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 =3D=3D =
NULL.
>>>=20
>>> I sent the patch anyway, since it's kind of a robustness =
improvement,
>>> I'd hope. If you fix BFQ also, please add:
>>=20
>> 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.
>=20

Hi,
I'm very sorry for tuning in very late, but, at the same time, very
glad to find the problem probably already solved ;) (in this respect, I =
swear,
my delay was not intentional)

> Does this fix it?
>=20
> 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 =3D false;
> 	bool bfqq_already_existing =3D false, split =3D false;
>=20
> -	if (!rq->elv.icq)
> +	if (!rq->elv.icq) {
> +		rq->elv.priv[0] =3D rq->elv.priv[1] =3D NULL;
> 		return;
> +	}
> +

This does solve the problem at hand.  But it also arouses a question,
related to a possible subtle bug.

For BFQ, !rq->elv.icq basically means "this request is not for me, as
I am an icq-based scheduler".  But, IIUC the main points in this
thread, then this assumption is false.  If it is actually false, then
I hope that all requests with !rq->elv.icq that are sent to BFQ do
verify the condition (at_head || blk_rq_is_passthrough(rq)).  In fact,
requests that do not verify that condition are those that BFQ must put
in a bfq_queue.  So, even if this patch makes the crash disappear, we
drive BFQ completely crazy (and we may expect other strange failures)
if we send BFQ a request with !((at_head || blk_rq_is_passthrough(rq))
and !rq->elv.icq.  BFQ has to put that rq into a bfq_queue, but simply
cannot.

Jens, or any other, could you please shed a light on this, and explain
how things are exactly?

Thanks,
Paolo

> 	bic =3D icq_to_bic(rq->elv.icq);
>=20
> 	spin_lock_irq(&bfqd->lock);
>=20
> --=20
> Jens Axboe