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Date: Fri, 9 Feb 2024 23:06:10 -0800
From: Kees Cook <keescook@chromium.org>
To: Lee Jones <lee@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	linux-scsi@vger.kernel.org
Subject: Re: [PATCH 06/10] scsi: aha1542: Replace snprintf() with the safer
 scnprintf() variant
Message-ID: <202402092303.F5F31A17@keescook>
References: <20240208084512.3803250-1-lee@kernel.org>
 <20240208084512.3803250-7-lee@kernel.org>
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In-Reply-To: <20240208084512.3803250-7-lee@kernel.org>

On Thu, Feb 08, 2024 at 08:44:18AM +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.

It may be better to do a global replace of snprintf() where the return
value is not used.

$ git grep '\bsnprintf\b' | grep -v = | wc -l
6400

There's plenty of work to do to remove just the ones taking the result:

$ git grep ' = snprintf\b' | wc -l
764

Regardless,

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> 
> Link: https://lwn.net/Articles/69419/
> Link: https://github.com/KSPP/linux/issues/105
> Signed-off-by: Lee Jones <lee@kernel.org>
> ---
> Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
> Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
> Cc: linux-scsi@vger.kernel.org
> ---
>  drivers/scsi/aha1542.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/aha1542.c b/drivers/scsi/aha1542.c
> index 9503996c63256..b5ec7887801a5 100644
> --- a/drivers/scsi/aha1542.c
> +++ b/drivers/scsi/aha1542.c
> @@ -772,7 +772,7 @@ static struct Scsi_Host *aha1542_hw_init(const struct scsi_host_template *tpnt,
>  		goto unregister;
>  
>  	if (sh->dma_channel != 0xFF)
> -		snprintf(dma_info, sizeof(dma_info), "DMA %d", sh->dma_channel);
> +		scnprintf(dma_info, sizeof(dma_info), "DMA %d", sh->dma_channel);
>  	shost_printk(KERN_INFO, sh, "Adaptec AHA-1542 (SCSI-ID %d) at IO 0x%x, IRQ %d, %s\n",
>  				sh->this_id, base_io, sh->irq, dma_info);
>  	if (aha1542->bios_translation == BIOS_TRANSLATION_25563)
> -- 
> 2.43.0.594.gd9cf4e227d-goog
> 
> 

-- 
Kees Cook