linux-kernel - Re: [PATCH] FS-Cache: print hexadecimal value for special cookies type

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Date:   Fri, 21 Apr 2017 22:41:54 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jérémy Lefaure <jeremy.lefaure@....epita.fr>
Cc:     David Howells <dhowells@...hat.com>, linux-cachefs@...hat.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] FS-Cache: print hexadecimal value for special cookies type

On Wed, Apr 19, 2017 at 11:38 PM, Jérémy Lefaure
<jeremy.lefaure@....epita.fr> wrote:
> When building object-list.o, gcc 6 raises a warning on the sprintf call
> in fscache_objlist_show:
>
>   CC      fs/fscache/object-list.o
> fs/fscache/object-list.c: In function ‘fscache_objlist_show’:
> fs/fscache/object-list.c:265:19: warning: ‘sprintf’ may write a
> terminating nul past the end of the destination [-Wformat-overflow=]
>     sprintf(_type, "%02u", cookie->def->type);
>                    ^~~~~~
> fs/fscache/object-list.c:265:4: note: ‘sprintf’ output between 3 and 4
> bytes into a destination of size 3
>     sprintf(_type, "%02u", cookie->def->type);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Moreover, the documentation says that we should have an hex value for
> special cookies (see Documentation/filesystems/caching/fscache.txt).
>
> Printing hexadecimal value for special cookies fixes the overflow
> warning and complies with the documentation.

If this is used by some user space tool the safest fix is to print in
BCD and fix documentation.

> Signed-off-by: Jérémy Lefaure <jeremy.lefaure@....epita.fr>
> ---
>  fs/fscache/object-list.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/fscache/object-list.c b/fs/fscache/object-list.c
> index 67f940892ef8..d51303124889 100644
> --- a/fs/fscache/object-list.c
> +++ b/fs/fscache/object-list.c
> @@ -262,7 +262,7 @@ static int fscache_objlist_show(struct seq_file *m, void *v)
>                         type = "DT";
>                         break;
>                 default:
> -                       sprintf(_type, "%02u", cookie->def->type);
> +                       sprintf(_type, "%02x", cookie->def->type);
>                         type = _type;
>                         break;
>                 }
> --
> 2.12.2
>



-- 
With Best Regards,
Andy Shevchenko