linux-kernel - Re: [PATCH 07/14] lib/vsprintf.c: slightly refactor vscnprintf()

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Message-ID: <CAHp75Vdbj3CteSFq931hT6ruLyGwifTLo3hPptAxDGO7eB9RqA@mail.gmail.com>
Date:	Tue, 24 Nov 2015 00:39:16 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/14] lib/vsprintf.c: slightly refactor vscnprintf()

On Mon, Nov 23, 2015 at 11:29 PM, Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> If we're given a size of 0, the vsnprintf() won't have any side
> effects, and neither "i < size" or "size != 0" will trigger. So we
> might as well return 0 immediately.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---
>  lib/vsprintf.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 8af5535fd738..e22a6189548f 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2036,13 +2036,14 @@ int vscnprintf(char *buf, size_t size, const char *fmt, va_list args)
>  {
>         int i;
>
> +       if (unlikely(!size))
> +               return 0;
> +

Might it potentially shadow any issue when run vsnprintf(buf, 0, fmt,
args); with certain arguments?
I can imagine something like %pV with unstable pointer.

>         i = vsnprintf(buf, size, fmt, args);
>
>         if (likely(i < size))
>                 return i;
> -       if (size != 0)
> -               return size - 1;
> -       return 0;
> +       return size - 1;
>  }
>  EXPORT_SYMBOL(vscnprintf);
>
> --
> 2.6.1
>
> --
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-- 
With Best Regards,
Andy Shevchenko
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