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: 7fc4da6a304b ("ublk: scan partition in async way") Reported-by: Ruikai Peng Signed-off-by: Ming Lei --- drivers/block/ublk_drv.c | 37 ++++++++++++++++++++++--------------- 1 file changed, 22 insertions(+), 15 deletions(-) diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c index 837fedb02e0d..f6e5a0766721 100644 --- a/drivers/block/ublk_drv.c +++ b/drivers/block/ublk_drv.c @@ -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); } -- 2.47.1