linux-kernel - Re: [PATCH] fix %*s%n in sscanf

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Date:	Fri, 25 Sep 2009 15:02:35 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	Andy Spencer <andy753421@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fix %*s%n in sscanf

On Fri, Sep 25, 2009 at 2:27 PM, Andy Spencer <andy753421@...il.com> wrote:
> When using %*s, sscanf should honor conversion specifiers immediately following
> the %*s. For example, the following code should find the position of the end of
> the string "hello".
>
>  int end;
>  char buf[] = "hello    world";
>  sscanf(buf, "%*s%n", &end);
>  printf("%d\n", end);
>
> Ideally, sscanf would advance the fmt and str pointers the same as it would
> without the *, but the code for that is rather complicated and is not included
> in the patch.


Yeah, seems reasonable. So, without your patch, sscanf() in kernel
will ignore everything after '*', right?


>
> Please CC me in replies.
>
>
> Signed-off-by: Andy Spencer <andy753421@...il.com>


Fortunately, a quick grep shows no one uses '%*' in sscanf()
in kernel space:

% grep 'sscanf(.*\".*%\*.*\".*)' -nr ./

For completeness,

Acked-by: WANG Cong <xiyou.wangcong@...il.com>

>
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 73a14b8..da2daf2 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1766,7 +1766,7 @@ int vsscanf(const char * buf, const char * fmt, va_list args)
>                 * advance both strings to next white space
>                 */
>                if (*fmt == '*') {
> -                       while (!isspace(*fmt) && *fmt)
> +                       while (!isspace(*fmt) && *fmt != '%' && *fmt)
>                                fmt++;
>                        while (!isspace(*str) && *str)
>                                str++;
>
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