linux-kernel - Re: [PATCH v2 1/4] scsi: sd: reject invalid pr_read_keys() num

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Message-ID: <20251201063413.GA19461@lst.de>
Date: Mon, 1 Dec 2025 07:34:13 +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 1/4] scsi: sd: reject invalid pr_read_keys()
 num_keys values

On Thu, Nov 27, 2025 at 10:54:21AM -0500, Stefan Hajnoczi wrote:
> +	/*
> +	 * Each reservation key takes 8 bytes and there is an 8-byte header
> +	 * before the reservation key list. The total size must fit into the
> +	 * 16-bit ALLOCATION LENGTH field.
> +	 */
> +	if (num_keys > (USHRT_MAX / 8) - 1)
> +		return -EINVAL;
> +
> +	data_len = num_keys * 8 + 8;

Having the same arithmerics express here in two different ways is a bit
odd.

I'd expected this to be something like:

	if (check_mul_overflow(num_keys, 8, &data_len) || data_len > USHRT_MAX)
		return -EINVAL;