linux-kernel - Re: [PATCH v3 3/3] vsprintf: Move space out of string literals in fourcc

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Message-ID: <202201261321.34794CCF3@keescook>
Date:   Wed, 26 Jan 2022 13:22:32 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Francis Laniel <laniel_francis@...vacyrequired.com>,
        Petr Mladek <pmladek@...e.com>, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andy@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v3 3/3] vsprintf: Move space out of string literals in
 fourcc_string()

On Wed, Jan 26, 2022 at 04:19:17PM +0200, Andy Shevchenko wrote:
> The literals "big-endian" and "little-endian" may be potentially
> occurred in other places. Dropping space allows linker to
> "compress" them by using only a single copy.
> 
> Rasmus suggested, while at it, replacing strcpy() + strlen() by
> p = stpcpy(), which is done here as well.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Acked-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
> v3: no changes
>  lib/vsprintf.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 4e8f3e9acb99..e2a1d89f1a5c 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1781,8 +1781,8 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
>  		*p++ = isascii(c) && isprint(c) ? c : '.';
>  	}
>  
> -	strcpy(p, orig & BIT(31) ? " big-endian" : " little-endian");
> -	p += strlen(p);
> +	*p++ = ' ';
> +	p = stpcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
>  
>  	*p++ = ' ';
>  	*p++ = '(';

No need for any of the manual construction nor stpcpy():

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d7ad44f2c8f5..aef8bd2789a9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1788,14 +1788,9 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
 		*p++ = isascii(c) && isprint(c) ? c : '.';
 	}
 
-	strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
-	p += strlen(p);
-
-	*p++ = ' ';
-	*p++ = '(';
-	p = special_hex_number(p, output + sizeof(output) - 2, *fourcc, sizeof(u32));
-	*p++ = ')';
-	*p = '\0';
+	snprintf(p, sizeof(output) - sizeof(*fourcc), " %s (0x%x)",
+		*fourcc & BIT(31) ? "big-endian" : " little-endian",
+		*fourcc);
 
 	return string(buf, end, output, spec);
 }


(untested)

-- 
Kees Cook