linux-kernel - Re: [PATCH 05/10] scsi: aacraid: linit: Replace snprintf() with the safer scnprintf() variant

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Message-ID: <202402092301.5097145A@keescook>
Date: Fri, 9 Feb 2024 23:03:26 -0800
From: Kees Cook <keescook@...omium.org>
To: Lee Jones <lee@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	Adaptec OEM Raid Solutions <aacraid@...rosemi.com>,
	"James E.J. Bottomley" <jejb@...ux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	"PMC-Sierra, Inc" <aacraid@...-sierra.com>,
	linux-scsi@...r.kernel.org
Subject: Re: [PATCH 05/10] scsi: aacraid: linit: Replace snprintf() with the
 safer scnprintf() variant

On Thu, Feb 08, 2024 at 08:44:17AM +0000, Lee Jones wrote:
> There is a general misunderstanding amongst engineers that {v}snprintf()
> returns the length of the data *actually* encoded into the destination
> array.  However, as per the C99 standard {v}snprintf() really returns
> the length of the data that *would have been* written if there were
> enough space for it.  This misunderstanding has led to buffer-overruns
> in the past.  It's generally considered safer to use the {v}scnprintf()
> variants in their place (or even sprintf() in simple cases).  So let's
> do that.
> 
> Link: https://lwn.net/Articles/69419/
> Link: https://github.com/KSPP/linux/issues/105
> Signed-off-by: Lee Jones <lee@...nel.org>
> ---
> Cc: Adaptec OEM Raid Solutions <aacraid@...rosemi.com>
> Cc: "James E.J. Bottomley" <jejb@...ux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@...cle.com>
> Cc: "PMC-Sierra, Inc" <aacraid@...-sierra.com>
> Cc: linux-scsi@...r.kernel.org
> ---
>  drivers/scsi/aacraid/linit.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/aacraid/linit.c b/drivers/scsi/aacraid/linit.c
> index 69526e2bd2e78..0e47d9c4cff23 100644
> --- a/drivers/scsi/aacraid/linit.c
> +++ b/drivers/scsi/aacraid/linit.c
> @@ -583,7 +583,7 @@ static ssize_t aac_show_unique_id(struct device *dev,
>  	if (sdev_channel(sdev) == CONTAINER_CHANNEL)
>  		memcpy(sn, aac->fsa_dev[sdev_id(sdev)].identifier, sizeof(sn));
>  
> -	return snprintf(buf, 16 * 2 + 2,
> +	return scnprintf(buf, 16 * 2 + 2,
>  		"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X\n",
>  		sn[0], sn[1], sn[2], sn[3],
>  		sn[4], sn[5], sn[6], sn[7],

I'm confused about this conversion and the original size argument. Isn't
this also a sysfs entry? Size should be PAGE_SIZE, or it should be
replaced with sysfs_emit().

-Kees

> @@ -1302,13 +1302,13 @@ static ssize_t aac_show_serial_number(struct device *device,
>  	int len = 0;
>  
>  	if (le32_to_cpu(dev->adapter_info.serial[0]) != 0xBAD0)
> -		len = snprintf(buf, 16, "%06X\n",
> +		len = scnprintf(buf, 16, "%06X\n",
>  		  le32_to_cpu(dev->adapter_info.serial[0]));
>  	if (len &&
>  	  !memcmp(&dev->supplement_adapter_info.mfg_pcba_serial_no[
>  	    sizeof(dev->supplement_adapter_info.mfg_pcba_serial_no)-len],
>  	  buf, len-1))
> -		len = snprintf(buf, 16, "%.*s\n",
> +		len = scnprintf(buf, 16, "%.*s\n",
>  		  (int)sizeof(dev->supplement_adapter_info.mfg_pcba_serial_no),
>  		  dev->supplement_adapter_info.mfg_pcba_serial_no);
>  
> -- 
> 2.43.0.594.gd9cf4e227d-goog
> 
> 

-- 
Kees Cook