linux-kernel - Re: usercopy whitelist woe in scsi_sense

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Message-ID: <CAGXu5j+kHipvoyFWjGp8M6+83zbd6yHOzwxQ-2LNBQbD5-jS9w@mail.gmail.com>
Date:   Tue, 17 Apr 2018 14:47:00 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jens Axboe <axboe@...nel.dk>
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 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:

Reported-by: Oleksandr Natalenko <oleksandr@...alenko.name>
Root-caused-by: Kees Cook <keescook@...omium.org>

:) I gotta task-switch to other things!

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

-Kees

-- 
Kees Cook
Pixel Security