linux-kernel - Re: [PATCH 2/2] lib: vsprintf.c remove macros defining strict string functions

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Date:	Thu, 8 May 2008 00:09:09 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Harvey Harrison <harvey.harrison@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] lib: vsprintf.c remove macros defining strict
	string functions

On Wed, May 07, 2008 at 11:25:29AM -0700, Harvey Harrison wrote:
> Directly code the strict string conversion functions rather than using
> defining macros.  Pull out a small helper to check the strict conditions
> required at the end of a string (nul-terminated or newline).

> Add additional checks in strict_strtol and strict_strtoll for numeric
> overflow of the signed types.

C interer ranges are asymmetric.

These "strict_" functions are a farce. No amount of afterchecking will
save you if there is trivial wraparound in core function.

	Alexey "kstrtonum" Dobriyan


> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -128,6 +128,18 @@ long long simple_strtoll(const char *cp, char **endp, unsigned int base)
>  	return simple_strtoull(cp, endp, base);
>  }
>  
> +/*
> + * Strictly check that the string is nul terminated or has a newline
> + * immediately following len chars.
> + */
> +static int strict_checktail(size_t len, const char *cp, const char *tail)

Name simply sucks.

> +{
> +	if ((*tail == '\0') ||
> +	    ((len == (size_t)(tail - cp) + 1) && (*tail == '\n')))
> +		return 1;
> +	else
> +		return 0;
> +}

> @@ -165,7 +196,29 @@ int strict_strtoul(const char *cp, unsigned int base, unsigned long *res);
>   * It returns 0 if conversion is successful and *res is set to the converted
>   * value, otherwise it returns -EINVAL and *res is set to 0.
>   */
> -int strict_strtol(const char *cp, unsigned int base, long *res);
> +int strict_strtol(const char *cp, unsigned int base, long *res)
> +{
> +	int ret;
> +	unsigned long tmp;
> +
> +	if (*cp == '-')
> +		ret = strict_strtoul(cp + 1, base, &tmp);
> +	else
> +		ret = strict_strtoul(cp, base, &tmp);
> +
> +	if (!ret || tmp > LONG_MAX) {
> +		*res = 0;
> +		return -EINVAL;
> +	}
> +
> +	if (*cp == '-')
> +		*res = -tmp;
> +	else
> +		*res = tmp;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(strict_strtol);
>  
>  /**
>   * strict_strtoull - convert a string to an unsigned long long strictly

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