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Date: Mon, 10 Jul 2017 21:20:39 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] handle whitespace before %% in scanf

On Sun, Jul 09, 2017 at 11:00:18PM +0200, Bartosz Brachaczek wrote:
> this is mandated by C and POSIX standards and is in accordance with
> glibc behavior.
> ---
>  src/stdio/vfscanf.c  | 10 +++++++---
>  src/stdio/vfwscanf.c |  8 ++++++--
>  2 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/src/stdio/vfscanf.c b/src/stdio/vfscanf.c
> index d4d2454b..9e030fc4 100644
> --- a/src/stdio/vfscanf.c
> +++ b/src/stdio/vfscanf.c
> @@ -89,15 +89,19 @@ int vfscanf(FILE *restrict f, const char *restrict fmt, va_list ap)
>  			continue;
>  		}
>  		if (*p != '%' || p[1] == '%') {
> -			p += *p=='%';
>  			shlim(f, 0);
> -			c = shgetc(f);
> +			if (*p == '%') {
> +				p++;
> +				while (isspace((c=shgetc(f))));
> +			} else {
> +				c = shgetc(f);
> +			}
>  			if (c!=*p) {
>  				shunget(f);
>  				if (c<0) goto input_fail;
>  				goto match_fail;
>  			}
> -			pos++;
> +			pos += shcnt(f);
>  			continue;
>  		}

Assuming your interpretation is correct, I have no objection to going
forward with the change, but I don't think this is the right way to do
it. The only reason %% was handled in the code that handles literal
characters is because I assumed it behaves like one, but if it
doesn't, it should just be handled as a format specifier that consumes
space where it can use the existing code that does that, rather than
complicting the code for literals and adding a duplicate of the
space-skipping code to it.

Rich

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