Re: [PATCH v2 3/4] block: add IOC_PR_READ_KEYS ioctl

[Christoph Hellwig <hch@lst.de>]

On Thu, Nov 27, 2025 at 10:54:23AM -0500, Stefan Hajnoczi wrote:
> +static int blkdev_pr_read_keys(struct block_device *bdev, blk_mode_t mode,
> +		struct pr_read_keys __user *arg)
> +{
> +	const struct pr_ops *ops = bdev->bd_disk->fops->pr_ops;
> +	struct pr_keys *keys_info __free(kfree) = NULL;

Please avoid the use of the __free mess and write readable and maintainable
code instead.

> +	struct pr_read_keys inout;

Inout is not a very good variable name, as it doesn't really have much
of meaning.  

> +	if (copy_from_user(&inout, arg, sizeof(inout)))
> +		return -EFAULT;
> +
> +	/*
> +	 * 64-bit hosts could handle more keys than 32-bit hosts, but this
> +	 * limit is more than enough in practice.
> +	 */
> +	if (inout.num_keys > (U32_MAX - sizeof(*keys_info)) /
> +	                     sizeof(keys_info->keys[0]))
> +		return -EINVAL;
> +
> +	keys_info_len = struct_size(keys_info, keys, inout.num_keys);

Do the size check on the calculate len here?

> +		return ret;
> +
> +	/* Copy out individual keys */
> +	keys_ptr = u64_to_user_ptr(inout.keys_ptr);
> +	num_copy_keys = min(inout.num_keys, keys_info->num_keys);
> +	keys_copy_len = num_copy_keys * sizeof(keys_info->keys[0]);

num_copy_keys is only used once, so maybe drop it?