linux-kernel - Re: [PATCH v4] sscanf: implement basic character sets

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Message-ID: <87r3fs4ezi.fsf@rasmusvillemoes.dk>
Date:	Thu, 03 Mar 2016 00:49:53 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Jessica Yu <jeyu@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] sscanf: implement basic character sets

On Fri, Feb 26 2016, Jessica Yu <jeyu@...hat.com> wrote:

> @@ -2714,6 +2718,57 @@ int vsscanf(const char *buf, const char *fmt, va_list args)
>  			num++;
>  		}
>  		continue;
> +		/*
> +		 * Warning: This implementation of the '[' conversion specifier
> +		 * deviates from its glibc counterpart in the following ways:
> +		 * (1) It does NOT support ranges i.e. '-' is NOT a special character
> +		 * (2) It cannot match the closing bracket ']' itself
> +		 * (3) A field width is required
> +		 * (4) '%*[' (discard matching input) is currently not supported
> +		 *
> +		 * Example usage:
> +		 * ret = sscanf("00:0a:95","%2[^:]:%2[^:]:%2[^:]", buf1, buf2, buf3);
> +		 * if (ret < 3)
> +		 *    // etc..
> +		 */
> +		case '[':
> +		{
> +			char *s = (char *)va_arg(args, char *);
> +			DECLARE_BITMAP(set, 256) = {0};
> +			unsigned int len = 0;
> +			bool negate = (*fmt == '^');
> +
> +			/* field width is required */
> +			if (field_width == -1)
> +				return num;
> +
> +			if (negate)
> +				++fmt;
> +
> +			for ( ; *fmt && *fmt != ']'; ++fmt, ++len)
> +				set_bit((u8)*fmt, set);
> +
> +			/* no ']' or no character set found */
> +			if (!*fmt || !len)
> +				return num;
> +			++fmt;
> +

I think it might be useful to be able to do [^] to match any sequence of
characters. If the user passed [] the code below won't match anything,
so we'll return num anyway. In other words, I'd just omit the test for
empty character set. Other than that, LGTM.

Rasmus