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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Jessica Yu <jeyu@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] sscanf: implement basic character sets
Organization: D03
References: <1456518059-7472-1-git-send-email-jeyu@redhat.com>
Date: Thu, 03 Mar 2016 00:49:53 +0100
In-Reply-To: <1456518059-7472-1-git-send-email-jeyu@redhat.com> (Jessica Yu's
	message of "Fri, 26 Feb 2016 15:20:59 -0500")
Message-ID: <87r3fs4ezi.fsf@rasmusvillemoes.dk>
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On Fri, Feb 26 2016, Jessica Yu <jeyu@redhat.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