linux-kernel - Re: [PATCH 2/2] mm, cma: use literal printf format string

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Message-ID: <CAPTztWauUVnA+ZRytPadKv7oHaRb1xmf_MneiiNXrD1j_1N9xw@mail.gmail.com>
Date: Mon, 24 Feb 2025 09:02:17 -0800
From: Frank van der Linden <fvdl@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Nathan Chancellor <nathan@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH 2/2] mm, cma: use literal printf format string

On Mon, Feb 24, 2025 at 6:11 AM Arnd Bergmann <arnd@...nel.org> wrote:
>
> From: Arnd Bergmann <arnd@...db.de>
>
> Using a variable string as a printf format can be a security issue
> that clang warns about when extra warnings are enabled:
>
> mm/cma.c:239:37: error: format string is not a string literal (potentially insecure) [-Werror,-Wformat-security]
>   239 |                 snprintf(cma->name, CMA_MAX_NAME, name);
>       |                                                   ^~~~
>
> This one does not appear to be a security issue since the string is
> not user controlled, but it's better to avoid the warning.
> Use "%s" as the format instead and just pass the name as the argument.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  mm/cma.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index ef0206c0f16d..09322b8284bd 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -236,7 +236,7 @@ static int __init cma_new_area(const char *name, phys_addr_t size,
>         cma_area_count++;
>
>         if (name)
> -               snprintf(cma->name, CMA_MAX_NAME, name);
> +               snprintf(cma->name, CMA_MAX_NAME, "%s", name);
>         else
>                 snprintf(cma->name, CMA_MAX_NAME,  "cma%d\n", cma_area_count);
>
> --
> 2.39.5
>

Yes, thanks - not sure why I didn't use "%s" there.

Reviewed-by: Frank van der Linden <fvdl@...gle.com>