RE: [PATCH v3 3/4] vsscanf(): do not skip spaces

[David Laight <David.Laight@xxxxxxxxxx>]

From: Demi Marie Obenour
> Sent: 10 June 2023 21:41
> 
> Passing spaces before e.g. an integer is usually
> not intended.  This was suggested by Christoph in
> https://lore.kernel.org/lkml/ZIQrohcizoj4bZWx@xxxxxxxxxxxxx/.

This is contrary to libc scanf and could easily affect userspace
writing fixed width values into sysctl nodes (etc).

IIRC strtoul() (etc) are also expected to strip leading spaces.
Removing the sign in sscanf() may lead to "-    12" being
valid - which may not be desired.

        David

> 
> Suggested-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Demi Marie Obenour <demi@xxxxxxxxxxxxxxxxxxxxxx>
> ---
>  lib/vsprintf.c | 8 +-------
>  1 file changed, 1 insertion(+), 7 deletions(-)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 
> 9e53355c35b1d6260631868228ede1d178fe3325..665f6197f8313d653f67d7886b12c43942e058dd
>  100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -3551,8 +3551,6 @@ int vsscanf(const char *buf, const char *fmt, va_list 
> args)
>                       char *s = (char *)va_arg(args, char *);
>                       if (field_width == -1)
>                               field_width = SHRT_MAX;
> -                     /* first, skip leading white space in buffer */
> -                     str = skip_spaces(str);
> 
>                       /* now copy until next white space */
>                       while (*str && !isspace(*str) && field_width--)
> @@ -3639,11 +3637,7 @@ int vsscanf(const char *buf, const char *fmt, va_list 
> args)
>                       return num;
>               }
> 
> -             /* have some sort of integer conversion.
> -              * first, skip white space in buffer.
> -              */
> -             str = skip_spaces(str);
> -
> +             /* have some sort of integer conversion. */
>               digit = *str;
>               if (is_sign && digit == '-') {
>                       if (field_width == 1)
> --
> Sincerely,
> Demi Marie Obenour (she/her/hers)
> Invisible Things Lab

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