[PATCH] fix %*s%n in sscanf

[PATCH] fix %*s%n in sscanf

[Andy Spencer]

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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.

Please CC me in replies.


Signed-off-by: Andy Spencer <andy753421@gmail.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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Re: [PATCH] fix %*s%n in sscanf

[Américo Wang]

On Fri, Sep 25, 2009 at 2:27 PM, Andy Spencer <andy753421@gmail.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@gmail.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@gmail.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++;
>

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

[Andy Spencer]

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> >   int end;
> >   char buf[] = "hello    world";
> >   sscanf(buf, "%*s%n", &end);
> >   printf("%d\n", end);
> 
> Yeah, seems reasonable. So, without your patch, sscanf() in kernel
> will ignore everything after '*', right?

Currently it ignores everything between '*' and whitespace. So '%*s%n'
does not work, but '%*s %n' will correctly return the start of "world".

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