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Commit 89736653 authored by Jan Kara's avatar Jan Kara Committed by Jens Axboe
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genhd: Fix use after free in __blkdev_get() 



When two blkdev_open() calls race with device removal and recreation,
__blkdev_get() can use looked up gendisk after it is freed:

CPU0				CPU1			CPU2
							del_gendisk(disk);
							  bdev_unhash_inode(inode);
blkdev_open()			blkdev_open()
  bdev = bd_acquire(inode);
    - creates and returns new inode
				  bdev = bd_acquire(inode);
				    - returns the same inode
  __blkdev_get(devt)		  __blkdev_get(devt)
    disk = get_gendisk(devt);
      - got structure of device going away
							<finish device removal>
							<new device gets
							 created under the same
							 device number>
				  disk = get_gendisk(devt);
				    - got new device structure
				  if (!bdev->bd_openers) {
				    does the first open
				  }
    if (!bdev->bd_openers)
      - false
    } else {
      put_disk_and_module(disk)
        - remember this was old device - this was last ref and disk is
          now freed
    }
    disk_unblock_events(disk); -> oops

Fix the problem by making sure we drop reference to disk in
__blkdev_get() only after we are really done with it.

Reported-by: default avatarHou Tao <houtao1@huawei.com>
Tested-by: default avatarHou Tao <houtao1@huawei.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9df6c299

fs/block_dev.c

+5 −2
Original line number Original line Diff line number Diff line
@@ -1409,6 +1409,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) 
	int ret;

	int ret;

	int partno;

	int partno;

	int perm = 0;

	int perm = 0;

	bool first_open = false;





	if (mode & FMODE_READ)

	if (mode & FMODE_READ)

		perm |= MAY_READ;

		perm |= MAY_READ;
@@ -1435,6 +1436,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) 
	disk_block_events(disk);

	disk_block_events(disk);

	mutex_lock_nested(&bdev->bd_mutex, for_part);

	mutex_lock_nested(&bdev->bd_mutex, for_part);

	if (!bdev->bd_openers) {

	if (!bdev->bd_openers) {

		first_open = true;

		bdev->bd_disk = disk;

		bdev->bd_disk = disk;

		bdev->bd_queue = disk->queue;

		bdev->bd_queue = disk->queue;

		bdev->bd_contains = bdev;

		bdev->bd_contains = bdev;
@@ -1520,14 +1522,15 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part) 
			if (ret)

			if (ret)

				goto out_unlock_bdev;

				goto out_unlock_bdev;

		}

		}

		/* only one opener holds refs to the module and disk */

		put_disk_and_module(disk);

	}

	}

	bdev->bd_openers++;

	bdev->bd_openers++;

	if (for_part)

	if (for_part)

		bdev->bd_part_count++;

		bdev->bd_part_count++;

	mutex_unlock(&bdev->bd_mutex);

	mutex_unlock(&bdev->bd_mutex);

	disk_unblock_events(disk);

	disk_unblock_events(disk);

	/* only one opener holds refs to the module and disk */

	if (!first_open)

		put_disk_and_module(disk);

	return 0;

	return 0;





 out_clear:

 out_clear: