Re: [PATCH 1/5] [v2] test_hexdump: avoid string truncation warning

[Justin Stitt]

On Tue, Apr 09, 2024 at 04:00:54PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> gcc can warn when a string is too long to fit into the strncpy()
> destination buffer, as it is here depending on the function
> arguments:
> 
>     inlined from 'test_hexdump_prepare_test.constprop' at /home/arnd/arm-soc/lib/test_hexdump.c:116:3:
> include/linux/fortify-string.h:108:33: error: '__builtin_strncpy' output truncated copying between 0 and 32 bytes from a string of length 32 [-Werror=stringop-truncation]
>   108 | #define __underlying_strncpy    __builtin_strncpy
>       |                                 ^
> include/linux/fortify-string.h:187:16: note: in expansion of macro '__underlying_strncpy'
>   187 |         return __underlying_strncpy(p, q, size);
>       |                ^~~~~~~~~~~~~~~~~~~~
> 
> The intention here is to copy exactly 'l' bytes without any padding or
> NUL-termination, so the most logical change is to use memcpy(), just as
> a previous change adapted the other output from strncpy() to memcpy().
> 
> Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

This looks better than the previous strscpy() usage.

Acked-by: Justin Stitt <justinstitt@xxxxxxxxxx>

> ---
> ---
>  lib/test_hexdump.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/test_hexdump.c b/lib/test_hexdump.c
> index b916801f23a8..fe2682bb21e6 100644
> --- a/lib/test_hexdump.c
> +++ b/lib/test_hexdump.c
> @@ -113,7 +113,7 @@ static void __init test_hexdump_prepare_test(size_t len, int rowsize,
>  			*p++ = ' ';
>  		} while (p < test + rs * 2 + rs / gs + 1);
>  
> -		strncpy(p, data_a, l);
> +		memcpy(p, data_a, l);
>  		p += l;
>  	}
>  
> -- 
> 2.39.2
>