Re: [PATCH v6 2/8] iio: core: add fixed point parsing with 64-bit parts

[Andy Shevchenko]

On Fri, Jan 30, 2026 at 10:06:43AM +0000, Rodrigo Alencar via B4 Relay wrote:

> Add iio_str_to_fixpoint64() function that leverages simple_strtoull()
> to parse numbers from a string.
> A helper function __iio_str_to_fixpoint64() replaces
> __iio_str_to_fixpoint() implementation, extending its usage for
> 64-bit fixed-point parsing.

...

> +/**
> + * iio_safe_strntou64() - Parse u64 from string checking for overflow safety
> + * @str: The string to parse
> + * @endp: output pointer to the end parsing position
> + * @result: parsed value
> + * @max_chars: maximum number of digit characters to read
> + *
> + * This function is used in fixed-point parsing and it iterates over a const
> + * char array. It might duplicate behavior of simple_strtoull() or kstrtoull(),
> + * but those have their own limitations:
> + * - simple_strtoull() is not overflow-safe and its usage is discouraged;
> + * - kstrtoull() is safe, but requires termination and it would required a copy
> + *   of the string to a temporary buffer.
> + *
> + * The implementation of this function is similar to _parse_integer_limit()
> + * available in lib/kstrtox.h, but that header/function is not available to be
> + * used in kernel modules. Hence, this implementation may need to change or
> + * removed to reuse a new suitable helper that is properly exposed.
> + *
> + * Returns:
> + * number of parsed characters on success, -ERANGE on overflow
> + */
> +static ssize_t iio_safe_strntou64(const char *str, const char **endp,
> +				  u64 *result, size_t max_chars)
> +{
> +	u64 digit, acc = 0;
> +	ssize_t idx = 0;
> +
> +	while (isdigit(str[idx]) && idx < max_chars) {
> +		digit = str[idx] - '0';
> +		if (unlikely(acc & (~0ull << 60))) {
> +			if (check_mul_overflow(acc, 10, &acc) ||
> +			    check_add_overflow(acc, digit, &acc))
> +				return -ERANGE;
> +		} else {
> +			acc = acc * 10 + digit;
> +		}
> +		idx++;
> +	}
> +
> +	*endp = str + idx;
> +	*result = acc;
> +	return idx;
> +}

There is a development in the parse_integer in the lib/. I reviewed that series
and hopefully it will go in. With that done, we better reuse the lib/ function.

https://lore.kernel.org/linux-hardening/20260202115451.290173-1-dmantipov@xxxxxxxxx/

-- 
With Best Regards,
Andy Shevchenko