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Date: Wed, 10 Apr 2024 21:04:54 +0000
From: Justin Stitt <justinstitt@google.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: linux-kbuild@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>, 
	Richard Russon <ldm@flatcap.org>, Jens Axboe <axboe@kernel.dk>, 
	Robert Moore <robert.moore@intel.com>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, 
	Len Brown <lenb@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, 
	Masami Hiramatsu <mhiramat@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Masahiro Yamada <masahiroy@kernel.org>, 
	Nathan Chancellor <nathan@kernel.org>, Nicolas Schier <nicolas@fjasle.eu>, 
	Lin Ming <ming.m.lin@intel.com>, Alexey Starikovskiy <astarikovskiy@suse.de>, 
	linux-ntfs-dev@lists.sourceforge.net, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-acpi@vger.kernel.org, acpica-devel@lists.linux.dev, linux-trace-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] [v2] test_hexdump: avoid string truncation warning
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References: <20240409140059.3806717-1-arnd@kernel.org>
 <20240409140059.3806717-2-arnd@kernel.org>
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On Tue, Apr 09, 2024 at 04:00:54PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> 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@google.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

This looks better than the previous strscpy() usage.

Acked-by: Justin Stitt <justinstitt@google.com>

> ---
> ---
>  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
>