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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 17 Apr 2018 09:42:42 -0700
Message-ID: <CAGXu5jLsX+nmc8hRSdOa28js7=ggPSGkUuTHbc3DUEcKSpEDbw@mail.gmail.com>
Subject: Re: usercopy whitelist woe in scsi_sense_cache
To:     Oleksandr Natalenko <oleksandr@natalenko.name>,
        Jens Axboe <axboe@kernel.dk>,
        Bart Van Assche <bart.vanassche@wdc.com>,
        Paolo Valente <paolo.valente@linaro.org>
Cc:     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 Mon, Apr 16, 2018 at 8:12 PM, Kees Cook <keescook@chromium.org> wrote:
> With a hardware watchpoint, I've isolated the corruption to here:
>
> bfq_dispatch_request+0x2be/0x1610:
> __bfq_dispatch_request at block/bfq-iosched.c:3902
> 3900            if (rq) {
> 3901    inc_in_driver_start_rq:
> 3902                    bfqd->rq_in_driver++;
> 3903    start_rq:
> 3904                    rq->rq_flags |= RQF_STARTED;
> 3905            }

FWIW, the stacktrace here (removing the ? lines) is:

[   34.311980] RIP: 0010:bfq_dispatch_request+0x2be/0x1610
[   34.452491]  blk_mq_do_dispatch_sched+0x1d9/0x260
[   34.454561]  blk_mq_sched_dispatch_requests+0x3da/0x4b0
[   34.458789]  __blk_mq_run_hw_queue+0xae/0x130
[   34.460001]  __blk_mq_delay_run_hw_queue+0x192/0x280
[   34.460823]  blk_mq_run_hw_queue+0x10b/0x1b0
[   34.463240]  blk_mq_sched_insert_request+0x3bd/0x4d0
[   34.467342]  blk_execute_rq+0xcf/0x140
[   34.468483]  sg_io+0x2f7/0x730

Can anyone tell me more about the memory allocation layout of the
various variables here? It looks like struct request is a header in
front of struct scsi_request? How do struct elevator_queue, struct
blk_mq_ctx, and struct blk_mq_hw_ctx overlap these?

Regardless, I'll check for elevator data changing too...

-Kees

-- 
Kees Cook
Pixel Security