linux-kernel - Re: usercopy whitelist woe in scsi_sense

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Date:   Tue, 17 Apr 2018 15:39:44 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Kees Cook <keescook@...omium.org>,
        Paolo Valente <paolo.valente@...aro.org>
Cc:     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 3:25 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.

-- 
Jens Axboe