linux-kernel - Re: [PATCH] scsi: hpsa: Replace deprecated strncpy() with strscpy()

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Message-Id: <34BB4FDE-062D-4C1B-B246-86CB55F631B8@linux.dev>
Date: Thu, 13 Feb 2025 12:24:33 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Don Brace <don.brace@...rochip.com>,
 "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: linux-hardening@...r.kernel.org,
 Bart Van Assche <bvanassche@....org>,
 storagedev@...rochip.com,
 linux-scsi@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scsi: hpsa: Replace deprecated strncpy() with strscpy()

On 12. Feb 2025, at 23:22, Thorsten Blum wrote:
> strncpy() is deprecated for NUL-terminated destination buffers [1]. Use
> strscpy() instead and remove the manual NUL-termination.
> 
> Use min() to simplify the size calculation.
> 
> Compile-tested only.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> Suggested-by: Bart Van Assche <bvanassche@....org>
> ---
> drivers/scsi/hpsa.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
> index 84d8de07b7ae..9399e101f150 100644
> --- a/drivers/scsi/hpsa.c
> +++ b/drivers/scsi/hpsa.c
> @@ -460,9 +460,8 @@ static ssize_t host_store_hp_ssd_smart_path_status(struct device *dev,
> 
> 	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
> 		return -EACCES;
> -	len = count > sizeof(tmpbuf) - 1 ? sizeof(tmpbuf) - 1 : count;
> -	strncpy(tmpbuf, buf, len);
> -	tmpbuf[len] = '\0';
> +	len = min(count, sizeof(tmpbuf) - 1);
> +	strscpy(tmpbuf, buf, len);

With strscpy() it should probably just be sizeof(tmpbuf) without -1, and
then add +1 to count for the number of copied bytes to be the same as
with strncpy().

Like this:

	len = min(count + 1, sizeof(tmpbuf));

This subtle difference between strncpy() and strscpy() regarding the
number of bytes copied isn't really documented anywhere, is it? The
documentation I came across so far seems to focus mostly on the
different return values of the two functions.

> 	if (sscanf(tmpbuf, "%d", &status) != 1)
> 		return -EINVAL;
> 	h = shost_to_hba(shost);
> @@ -484,9 +483,8 @@ static ssize_t host_store_raid_offload_debug(struct device *dev,
> 
> 	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_RAWIO))
> 		return -EACCES;
> -	len = count > sizeof(tmpbuf) - 1 ? sizeof(tmpbuf) - 1 : count;
> -	strncpy(tmpbuf, buf, len);
> -	tmpbuf[len] = '\0';
> +	len = min(count, sizeof(tmpbuf) - 1);
> +	strscpy(tmpbuf, buf, len);

Same here.

> 	if (sscanf(tmpbuf, "%d", &debug_level) != 1)
> 		return -EINVAL;
> 	if (debug_level < 0)

Maybe someone can confirm my reasoning before I submit a v2?

Thanks,
Thorsten