linux-kernel - Re: [PATCH 1/3] [v2] staging: rts5208: replace weird strncpy() with memcpy()

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Date: Tue, 9 Apr 2024 09:23:45 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Justin Stitt <justinstitt@...gle.com>,
	Arnd Bergmann <arnd@...db.de>, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] [v2] staging: rts5208: replace weird strncpy() with
 memcpy()

On Mon, Apr 08, 2024 at 09:48:09PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> When -Wstringop-truncation is enabled, gcc finds a function that
> always does a short copy:
> 
> In function 'inquiry',
>     inlined from 'rtsx_scsi_handler' at drivers/staging/rts5208/rtsx_scsi.c:3210:12:
> drivers/staging/rts5208/rtsx_scsi.c:526:17: error: 'strncpy' output truncated copying between 1 and 28 bytes from a string of length 28 [-Werror=stringop-truncation]
>   526 |                 strncpy(buf + 8, inquiry_string, sendbytes - 8);
>       |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The code originally had a memcpy() that would overread the source string,
> and commit 88a5b39b69ab ("staging/rts5208: Fix read overflow in memcpy")
> fixed this but introduced the warning about truncation in the process.
> 
> As Dan points out, the final space in the inquiry_string always gets
> cut off, so remove it here for clarity, leaving exactly the 28 non-NUL
> characters that can get copied into the output. In the 'pro_formatter_flag'
> this is followed by another 20 bytes from the 'formatter_inquiry_str'
> array, but there the output never contains a NUL-termination, and the
> length is known, so memcpy() is the more logical choice.
> 
> Cc: Dan Carpenter <dan.carpenter@...aro.org>
> Link: https://lore.kernel.org/lkml/695be581-548f-4e5e-a211-5f3b95568e77@moroto.mountain/
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> v2: remove unneeded space byte from input string for clarity,
>     rework changelog text

Reviewed-by: Dan Carpenter <dan.carpenter@...aro.org>

regards,
dan carpenter