[PATCH v2] ubi: block: Fix cleanup handling

[Zhihao Cheng]

在 2023/6/9 11:16, Zhihao Cheng 写道:
> 在 2023/6/7 17:25, Vincent Whitchurch 写道:
>> ubiblock's remove handling has a couple of problems:
>>
>>   - It uses the gendisk after put_disk(), resulting in a use-after-free.
>>
>>   - There is a circular locking dependency between disk->open_mutex (used
>>     from del_gendisk() and blkdev_open()) and dev->dev_mutex (used from
>>     ubiblock_open() and ubiblock_remove()).
>>
>> Fix these by implementing ->free_disk() and moving the final cleanup
>> there.
>>
>> Signed-off-by: Vincent Whitchurch <vincent.whitchurch at axis.com>
>> ---
>> Changes in v2:
>> - Combine and rework patches to implement and use ->free_disk().
>> - Link to v1: 
>> https://lore.kernel.org/r/20230523-ubiblock-remove-v1-0-240bed75849b@axis.com 
>>
>> ---
>>   drivers/mtd/ubi/block.c | 27 ++++++++++++++++++++-------
>>   1 file changed, 20 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/mtd/ubi/block.c b/drivers/mtd/ubi/block.c
>> index 3711d7f74600..570e660673ad 100644
>> --- a/drivers/mtd/ubi/block.c
>> +++ b/drivers/mtd/ubi/block.c
>> @@ -293,11 +293,23 @@ static int ubiblock_getgeo(struct block_device 
>> *bdev, struct hd_geometry *geo)
>>       return 0;
>>   }
>> +static void ubiblock_free_disk(struct gendisk *disk)
>> +{
>> +    struct ubiblock *dev = disk->private_data;
>> +
>> +    mutex_lock(&devices_mutex);
>> +    idr_remove(&ubiblock_minor_idr, disk->first_minor);
>> +    mutex_unlock(&devices_mutex);
>> +
>> +    kfree(dev);
>> +}
>> +
>>   static const struct block_device_operations ubiblock_ops = {
>>       .owner = THIS_MODULE,
>>       .open = ubiblock_open,
>>       .release = ubiblock_release,
>>       .getgeo    = ubiblock_getgeo,
>> +    .free_disk = ubiblock_free_disk,
>>   };
>>   static blk_status_t ubiblock_queue_rq(struct blk_mq_hw_ctx *hctx,
>> @@ -452,9 +464,8 @@ static void ubiblock_cleanup(struct ubiblock *dev)
>>       del_gendisk(dev->gd);
>>       /* Finally destroy the blk queue */
>>       dev_info(disk_to_dev(dev->gd), "released");
>> -    put_disk(dev->gd);
>>       blk_mq_free_tag_set(&dev->tag_set);
>> -    idr_remove(&ubiblock_minor_idr, dev->gd->first_minor);
>> +    put_disk(dev->gd);
> 
> I thought it's better to do put_disk() first then do 
> blk_mq_free_tag_set(), likes nbd, loop does. Will 
> put_disk->disk_release->blk_mq_exit_queue->blk_mq_exit_hw_queues access 
> tag_set which has been freed by blk_mq_free_tag_set()?
> 

All right, just ignore this comment. The nbd doesn't implement 
'->free_disk'. The 'ubiblock' will be freed in '->free_disk' invoked 
from put_disk, so 'blk_mq_free_tag_set(&dev->tag_set)' should be 
executed before put_disk.

>>   }
>>   int ubiblock_remove(struct ubi_volume_info *vi)
>> @@ -478,11 +489,11 @@ int ubiblock_remove(struct ubi_volume_info *vi)
>>       /* Remove from device list */
>>       list_del(&dev->list);
>> -    ubiblock_cleanup(dev);
>>       mutex_unlock(&dev->dev_mutex);
>>       mutex_unlock(&devices_mutex);
>> -    kfree(dev);
>> +    ubiblock_cleanup(dev);
>> +
>>       return 0;
>>   out_unlock_dev:
>> @@ -623,17 +634,19 @@ static void ubiblock_remove_all(void)
>>   {
>>       struct ubiblock *next;
>>       struct ubiblock *dev;
>> +    LIST_HEAD(list);
>>       mutex_lock(&devices_mutex);
>> -    list_for_each_entry_safe(dev, next, &ubiblock_devices, list) {
>> +    list_splice_init(&ubiblock_devices, &list);
>> +    mutex_unlock(&devices_mutex);
>> +
>> +    list_for_each_entry_safe(dev, next, &list, list) {
>>           /* The module is being forcefully removed */
>>           WARN_ON(dev->desc);
>>           /* Remove from device list */
>>           list_del(&dev->list);
>>           ubiblock_cleanup(dev);
>> -        kfree(dev);
>>       }
>> -    mutex_unlock(&devices_mutex);
>>   }
>>   int __init ubiblock_init(void)
>>
>> ---
>> base-commit: 44c026a73be8038f03dbdeef028b642880cf1511
>> change-id: 20230523-ubiblock-remove-eab61cf683f0
>>
>> Best regards,
>>
> 
> 
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