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 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 (6): blk-mq: export two symbols to get request by tag nbd: convert to use blk_mq_find_and_get_req() 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 block/blk-mq-tag.c | 5 +++-- block/blk-mq.c | 1 + drivers/block/nbd.c | 46 +++++++++++++++++++++++++++++++++++------- include/linux/blk-mq.h | 3 +++ 4 files changed, 46 insertions(+), 9 deletions(-) -- 2.31.1
