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Date:   Fri, 15 Oct 2021 12:08:31 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, ming.lei@...hat.com, hch@...radead.org,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [patch v8 0/7] handle unexpected message from server

On Thu, Sep 16, 2021 at 05:33:43PM +0800, Yu Kuai wrote:
> This patch set tries to fix that client might oops if nbd server send
> unexpected message to client, for example, our syzkaller report a uaf
> in nbd_read_stat():
> 
> Call trace:
>  dump_backtrace+0x0/0x310 arch/arm64/kernel/time.c:78
>  show_stack+0x28/0x38 arch/arm64/kernel/traps.c:158
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x144/0x1b4 lib/dump_stack.c:118
>  print_address_description+0x68/0x2d0 mm/kasan/report.c:253
>  kasan_report_error mm/kasan/report.c:351 [inline]
>  kasan_report+0x134/0x2f0 mm/kasan/report.c:409
>  check_memory_region_inline mm/kasan/kasan.c:260 [inline]
>  __asan_load4+0x88/0xb0 mm/kasan/kasan.c:699
>  __read_once_size include/linux/compiler.h:193 [inline]
>  blk_mq_rq_state block/blk-mq.h:106 [inline]
>  blk_mq_request_started+0x24/0x40 block/blk-mq.c:644
>  nbd_read_stat drivers/block/nbd.c:670 [inline]
>  recv_work+0x1bc/0x890 drivers/block/nbd.c:749
>  process_one_work+0x3ec/0x9e0 kernel/workqueue.c:2147
>  worker_thread+0x80/0x9d0 kernel/workqueue.c:2302
>  kthread+0x1d8/0x1e0 kernel/kthread.c:255
>  ret_from_fork+0x10/0x18 arch/arm64/kernel/entry.S:1174
> 
> 1) At first, a normal io is submitted and completed with scheduler:
> 
> internel_tag = blk_mq_get_tag -> get tag from sched_tags
>  blk_mq_rq_ctx_init
>   sched_tags->rq[internel_tag] = sched_tag->static_rq[internel_tag]
> ...
> blk_mq_get_driver_tag
>  __blk_mq_get_driver_tag -> get tag from tags
>  tags->rq[tag] = sched_tag->static_rq[internel_tag]
> 
> So, both tags->rq[tag] and sched_tags->rq[internel_tag] are pointing
> to the request: sched_tags->static_rq[internal_tag]. Even if the
> io is finished.
> 
> 2) nbd server send a reply with random tag directly:
> 
> recv_work
>  nbd_read_stat
>   blk_mq_tag_to_rq(tags, tag)
>    rq = tags->rq[tag]
> 
> 3) if the sched_tags->static_rq is freed:
> 
> blk_mq_sched_free_requests
>  blk_mq_free_rqs(q->tag_set, hctx->sched_tags, i)
>   -> step 2) access rq before clearing rq mapping
>   blk_mq_clear_rq_mapping(set, tags, hctx_idx);
>   __free_pages() -> rq is freed here
> 
> 4) Then, nbd continue to use the freed request in nbd_read_stat()
> 
> Changes in v8:
>  - add patch 5 to this series.
>  - modify some words.
> Changes in v7:
>  - instead of exposing blk_queue_exit(), using percpu_ref_put()
>  directly.
>  - drop the ref right after nbd_handle_reply().
> Changes in v6:
>  - don't set cmd->status to error if request is completed before
>  nbd_clear_req().
>  - get 'q_usage_counter' to prevent accessing freed request through
>  blk_mq_tag_to_rq(), instead of using blk_mq_find_and_get_req().
> Changes in v5:
>  - move patch 1 & 2 in v4 (patch 4 & 5 in v5) behind
>  - add some comment in patch 5
> Changes in v4:
>  - change the name of the patchset, since uaf is not the only problem
>  if server send unexpected reply message.
>  - instead of adding new interface, use blk_mq_find_and_get_req().
>  - add patch 5 to this series
> Changes in v3:
>  - v2 can't fix the problem thoroughly, add patch 3-4 to this series.
>  - modify descriptions.
>  - patch 5 is just a cleanup
> Changes in v2:
>  - as Bart suggested, add a new helper function for drivers to get
>  request by tag.
> 

You can add

Reviewed-by: Josef Bacik <josef@...icpanda.com>

to the series.  Sorry Jens, this one slipped through the cracks.  Thanks,

Josef

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