The pr_read_keys() interface has a u32 num_keys parameter. The SCSI
PERSISTENT RESERVE IN command has a maximum READ KEYS service action
size of 65536 bytes. Reject num_keys values that are too large to fit
into the SCSI command.

This will become important when pr_read_keys() is exposed to untrusted
userspace via an <linux/pr.h> ioctl.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 drivers/scsi/sd.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 0252d3f6bed17..e436ed977cdb4 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -1974,9 +1974,18 @@ static int sd_pr_read_keys(struct block_device *bdev, struct pr_keys *keys_info)
 {
 	int result, i, data_offset, num_copy_keys;
 	u32 num_keys = keys_info->num_keys;
-	int data_len = num_keys * 8 + 8;
+	int data_len;
 	u8 *data;
 
+	/*
+	 * 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;
 	data = kzalloc(data_len, GFP_KERNEL);
 	if (!data)
 		return -ENOMEM;
-- 
2.52.0

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;

On Mon, Dec 01, 2025 at 07:34:13AM +0100, Christoph Hellwig wrote:
> 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;

Will fix, thanks.

Stefan

On Mon, Dec 01, 2025 at 07:34:13AM +0100, Christoph Hellwig wrote:
> 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;

Thanks, will fix.

Stefan

On 11/27/25 16:54, Stefan Hajnoczi wrote:
> The pr_read_keys() interface has a u32 num_keys parameter. The SCSI
> PERSISTENT RESERVE IN command has a maximum READ KEYS service action
> size of 65536 bytes. Reject num_keys values that are too large to fit
> into the SCSI command.
> 
> This will become important when pr_read_keys() is exposed to untrusted
> userspace via an <linux/pr.h> ioctl.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   drivers/scsi/sd.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich