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@xxxxxxxxxxxxxx> to the series. Sorry Jens, this one slipped through the cracks. Thanks, Josef
