linux-kernel - Re: [PATCH v2] sscanf: implement basic character sets

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Date:	Tue, 23 Feb 2016 12:56:32 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Jessica Yu <jeyu@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sscanf: implement basic character sets

On Mon, 2016-02-22 at 16:24 -0500, Jessica Yu wrote:
> Implement basic character sets for the '%[]' conversion specifier.
> 
> The '%[]' conversion specifier matches a nonempty sequence of
> characters
> from the specified set of accepted (or with '^', rejected) characters
> between the brackets. The substring matched is to be made up of
> characters
> in (or not in) the set. This implementation differs from its glibc
> counterpart in that it does not support character ranges (e.g., 'a-z' 
> or
> '0-9'), the hyphen '-' is *not* a special character, and the brackets
> themselves cannot be matched.
> 
> Signed-off-by: Jessica Yu <jeyu@...hat.com>
> ---
> Patch based on linux-next-20160222.
> 
> v2:
>  - Use kstrndup() to copy the character set from fmt instead of using
> a
>    statically allocated array
>  
>  lib/vsprintf.c | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 525c8e1..93a6f52 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2714,6 +2714,45 @@ int vsscanf(const char *buf, const char *fmt,
> va_list args)
>  			num++;
>  		}
>  		continue;
> +		case '[':
> +		{
> +			char *s = (char *)va_arg(args, char *);
> +			char *set;
> +			size_t (*op)(const char *str, const char
> *set);
> +			size_t len = 0;
> +			bool negate = (*(fmt) == '^');
> +
> +			if (field_width == -1)
> +				field_width = SHRT_MAX;

I'm not sure if it's needed here. It will count down till 0 in any
case.

> +
> +			op = negate ? &strcspn : &strspn;
> +			if (negate)
> +				fmt++;

> +
> +			len = strcspn(fmt, "]");
> +			/* invalid format; stop here */
> +			if (!len)
> +				return num;
> +
> +			set = kstrndup(fmt, len, GFP_KERNEL);
> +			if (!set)
> +				return num;
> +
> +			/* advance fmt past ']' */
> +			fmt += len + 1;
> +
> +			len = (*op)(str, set);

Can we use just normal form:
 op();
?

> +			/* no matches */
> +			if (!len)

Memory leak here.

> +				return num;
> +
> +			while (*str && len-- && field_width--)
> +				*s++ = *str++;

Looks like strcpy() variant. First of all, is it possible to have *str
== '\0' when len != 0?

> +			*s = '\0';
> +			kfree(set);
> +			num++;
> +		}
> +		continue;
>  		case 'o':
>  			base = 8;
>  			break;

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy