Re: [PATCH v2] scsi: sd: Set a default optimal IO size if one is not defined

[Bart Van Assche <bvanassche@acm.org>]

On 6/11/25 5:29 AM, Damien Le Moal wrote:
> +static void sd_set_io_opt(struct scsi_disk *sdkp, unsigned int dev_max,
> +			  struct queue_limits *lim)
> +{
> +	struct scsi_device *sdp = sdkp->device;
> +	struct Scsi_Host *shost = sdp->host;
> +
> +	lim->io_opt = shost->opt_sectors << SECTOR_SHIFT;
> +	if (sd_validate_opt_xfer_size(sdkp, dev_max))
> +		lim->io_opt = min_not_zero(lim->io_opt,
> +				logical_to_bytes(sdp, sdkp->opt_xfer_blocks));
> +	if (!lim->io_opt) {
> +		lim->io_opt = ALIGN_DOWN(lim->max_sectors << SECTOR_SHIFT,
> +					 sdkp->physical_block_size - 1);
> +		sd_first_printk(KERN_INFO, sdkp,
> +			"Using default optimal transfer size of %u bytes\n",
> +			lim->io_opt);
> +	}
> +}

shost->opt_sectors and lim->max_sectors both have type unsigned int so
when shifting these left there is a risk of overflow. As an example,
from the scsi_debug driver:

	.max_sectors =		-1U,

Shouldn't integer overflows be prevented instead of letting these
happen?

Thanks,

Bart.