Commit f0d385f6 authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

ublk: fix use-after-free in ublk_partition_scan_work 



A race condition exists between the async partition scan work and device
teardown that can lead to a use-after-free of ub->ub_disk:

1. ublk_ctrl_start_dev() schedules partition_scan_work after add_disk()
2. ublk_stop_dev() calls ublk_stop_dev_unlocked() which does:
   - del_gendisk(ub->ub_disk)
   - ublk_detach_disk() sets ub->ub_disk = NULL
   - put_disk() which may free the disk
3. The worker ublk_partition_scan_work() then dereferences ub->ub_disk
   leading to UAF

Fix this by using ublk_get_disk()/ublk_put_disk() in the worker to hold
a reference to the disk during the partition scan. The spinlock in
ublk_get_disk() synchronizes with ublk_detach_disk() ensuring the worker
either gets a valid reference or sees NULL and exits early.

Also change flush_work() to cancel_work_sync() to avoid running the
partition scan work unnecessarily when the disk is already detached.

Fixes: 7fc4da6a ("ublk: scan partition in async way")
Reported-by: default avatarRuikai Peng <ruikai@pwno.io>
Signed-off-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9670db22

drivers/block/ublk_drv.c

+22 −15
Original line number Diff line number Diff line
@@ -255,20 +255,6 @@ static inline struct request *__ublk_check_and_get_req(struct ublk_device *ub, 
		u16 q_id, u16 tag, struct ublk_io *io, size_t offset);

static inline unsigned int ublk_req_build_flags(struct request *req);



static void ublk_partition_scan_work(struct work_struct *work)

{

	struct ublk_device *ub =

		container_of(work, struct ublk_device, partition_scan_work);



	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,

					     &ub->ub_disk->state)))

		return;



	mutex_lock(&ub->ub_disk->open_mutex);

	bdev_disk_changed(ub->ub_disk, false);

	mutex_unlock(&ub->ub_disk->open_mutex);

}



static inline struct ublksrv_io_desc *

ublk_get_iod(const struct ublk_queue *ubq, unsigned tag)

{
@@ -1597,6 +1583,27 @@ static void ublk_put_disk(struct gendisk *disk) 
		put_device(disk_to_dev(disk));

}



static void ublk_partition_scan_work(struct work_struct *work)

{

	struct ublk_device *ub =

		container_of(work, struct ublk_device, partition_scan_work);

	/* Hold disk reference to prevent UAF during concurrent teardown */

	struct gendisk *disk = ublk_get_disk(ub);



	if (!disk)

		return;



	if (WARN_ON_ONCE(!test_and_clear_bit(GD_SUPPRESS_PART_SCAN,

					     &disk->state)))

		goto out;



	mutex_lock(&disk->open_mutex);

	bdev_disk_changed(disk, false);

	mutex_unlock(&disk->open_mutex);

out:

	ublk_put_disk(disk);

}



/*

 * Use this function to ensure that ->canceling is consistently set for

 * the device and all queues. Do not set these flags directly.
@@ -2041,7 +2048,7 @@ static void ublk_stop_dev(struct ublk_device *ub) 
	mutex_lock(&ub->mutex);

	ublk_stop_dev_unlocked(ub);

	mutex_unlock(&ub->mutex);

	flush_work(&ub->partition_scan_work);

	cancel_work_sync(&ub->partition_scan_work);

	ublk_cancel_dev(ub);

}