block2mtd: prevent direct access of bd_inode

All we need is size, and that can be obtained via bdev_nr_bytes()

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Link: https://lore.kernel.org/r/20240411145346.2516848-11-viro@zeniv.linux.org.uk
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: YuKuai-huawei

drivers/mtd/devices/block2mtd.c

@@ -265,6 +265,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
 	struct file *bdev_file;
 	struct block_device *bdev;
 	struct block2mtd_dev *dev;
+	loff_t size;
 	char *name;
 
 	if (!devname)
@@ -291,7 +292,8 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
 		goto err_free_block2mtd;
 	}
 
-	if ((long)bdev->bd_inode->i_size % erase_size) {
+	size = bdev_nr_bytes(bdev);
+	if ((long)size % erase_size) {
 		pr_err("erasesize must be a divisor of device size\n");
 		goto err_free_block2mtd;
 	}
@@ -309,7 +311,7 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size,
 
 	dev->mtd.name = name;
 
-	dev->mtd.size = bdev->bd_inode->i_size & PAGE_MASK;
+	dev->mtd.size = size & PAGE_MASK;
 	dev->mtd.erasesize = erase_size;
 	dev->mtd.writesize = 1;
 	dev->mtd.writebufsize = PAGE_SIZE;