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    SubjectRe: [patch v8 0/7] handle unexpected message from server
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    On 2021/09/16 17:33, Yu Kuai wrote:

    Hi, jens

    Any interest to apply this series?

    Thanks,
    Kuai
    > 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.
    >
    > Yu Kuai (7):
    > nbd: don't handle response without a corresponding request message
    > nbd: make sure request completion won't concurrent
    > nbd: check sock index in nbd_read_stat()
    > nbd: don't start request if nbd_queue_rq() failed
    > nbd: clean up return value checking of sock_xmit()
    > nbd: partition nbd_read_stat() into nbd_read_reply() and
    > nbd_handle_reply()
    > nbd: fix uaf in nbd_handle_reply()
    >
    > drivers/block/nbd.c | 135 +++++++++++++++++++++++++++++++-------------
    > 1 file changed, 96 insertions(+), 39 deletions(-)
    >

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