linux-kernel - Re: [PATCH v2 3/4] block: add IOC_PR_READ

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Message-ID: <20251201064016.GC19461@lst.de>
Date: Mon, 1 Dec 2025 07:40:16 +0100
From: Christoph Hellwig <hch@....de>
To: Stefan Hajnoczi <stefanha@...hat.com>
Cc: linux-block@...r.kernel.org, Keith Busch <kbusch@...nel.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	linux-kernel@...r.kernel.org,
	"James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
	Christoph Hellwig <hch@....de>,
	Mike Christie <michael.christie@...cle.com>,
	linux-nvme@...ts.infradead.org, Jens Axboe <axboe@...nel.dk>,
	linux-scsi@...r.kernel.org, Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH v2 3/4] block: add IOC_PR_READ_KEYS ioctl

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?