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

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Message-ID: <a8173918-f0d2-42c7-82d8-3fa6ff944d5f@suse.de>
Date: Thu, 27 Nov 2025 07:59:38 +0100
From: Hannes Reinecke <hare@...e.de>
To: Stefan Hajnoczi <stefanha@...hat.com>, linux-block@...r.kernel.org
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>,
 linux-kernel@...r.kernel.org,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 Mike Christie <michael.christie@...cle.com>, Jens Axboe <axboe@...nel.dk>,
 linux-nvme@...ts.infradead.org, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>, linux-scsi@...r.kernel.org,
 Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/4] scsi: sd: reject invalid pr_read_keys() num_keys
 values

On 11/26/25 17:35, 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@...hat.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..d65646f35f453 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 > (65536 - 8) / 8)

Odd coding. Maybe (USHRT_MAX / 8) - 1 ?

> +		return -EINVAL;
> +
> +	data_len = num_keys * 8 + 8;
>   	data = kzalloc(data_len, GFP_KERNEL);
>   	if (!data)
>   		return -ENOMEM;

Cheers,

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