From 166bbfd00dce82ed8a7f119310d26d97578853be Mon Sep 17 00:00:00 2001 From: Pradeep P V K Date: Mon, 14 Sep 2020 12:57:53 +0530 Subject: [PATCH] block: Fix use-after-free issue while accessing ioscheduler lock Observes below crash while accessing (use-after-free) lock member of bfq data. context#1 context#2 process_one_work() kthread() blk_mq_run_work_fn() worker_thread() ->__blk_mq_run_hw_queue() process_one_work() ->blk_mq_sched_dispatch_requests() __blk_release_queue() ->blk_mq_do_dispatch_sched() ->__elevator_exit() ->blk_mq_exit_sched() ->exit_sched() ->kfree() ->bfq_dispatch_request() ->spin_unlock_irq(&bfqd->lock) This is because of the kblockd delayed work that might got scheduled around blk_release_queue() and accessed use-after-free member of bfq_data. 240.212359: <2> Unable to handle kernel paging request at virtual address ffffffee2e33ad70 ... 240.212637: <2> Workqueue: kblockd blk_mq_run_work_fn 240.212649: <2> pstate: 00c00085 (nzcv daIf +PAN +UAO) 240.212666: <2> pc : queued_spin_lock_slowpath+0x10c/0x2e0 240.212677: <2> lr : queued_spin_lock_slowpath+0x84/0x2e0 ... Call trace: 240.212865: <2> queued_spin_lock_slowpath+0x10c/0x2e0 240.212876: <2> do_raw_spin_lock+0xf0/0xf4 240.212890: <2> _raw_spin_lock_irq+0x74/0x94 240.212906: <2> bfq_dispatch_request+0x4c/0xd60 240.212918: <2> blk_mq_do_dispatch_sched+0xe0/0x1f0 240.212927: <2> blk_mq_sched_dispatch_requests+0x130/0x194 240.212940: <2> __blk_mq_run_hw_queue+0x100/0x158 240.212950: <2> blk_mq_run_work_fn+0x1c/0x28 240.212963: <2> process_one_work+0x280/0x460 240.212973: <2> worker_thread+0x27c/0x4dc 240.212986: <2> kthread+0x160/0x170 Fix this by cancelling the delayed work if any before elevator exits. Change-Id: If015576983e328aa726bac90a7a8de824d6532f0 Signed-off-by: Pradeep P V K --- block/blk-mq-sysfs.c | 1 - block/blk-sysfs.c | 8 ++++++-- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c index a09ab0c3d074..28c9921c756f 100644 --- a/block/blk-mq-sysfs.c +++ b/block/blk-mq-sysfs.c @@ -36,7 +36,6 @@ static void blk_mq_hw_sysfs_release(struct kobject *kobj) struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx, kobj); - cancel_delayed_work_sync(&hctx->run_work); if (hctx->flags & BLK_MQ_F_BLOCKING) cleanup_srcu_struct(hctx->srcu); diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 46f5198be017..0bd8ff7b356c 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -891,9 +891,13 @@ static void __blk_release_queue(struct work_struct *work) blk_free_queue_stats(q->stats); - if (queue_is_mq(q)) + if (queue_is_mq(q)) { + struct blk_mq_hw_ctx *hctx; + int i; cancel_delayed_work_sync(&q->requeue_work); - + queue_for_each_hw_ctx(q, hctx, i) + cancel_delayed_work_sync(&hctx->run_work); + } blk_exit_queue(q); blk_queue_free_zone_bitmaps(q);