Re: [PATCH v2 2/4] md/raid10: fix overflow in safe_delay_store

[Yu Kuai]

Hi,

在 2023/05/06 9:23, linan666@xxxxxxxxxxxxxxx 写道:
> From: Li Nan <linan122@xxxxxxxxxx>
>
> There is no input check when echo md/safe_mode_delay, and overflow will
> occur. There is risk of overflow in strict_strtoul_scaled(), too. Fix it
> by using kstrtoul instead of parsing word one by one.

Other than some nits below, this patch looks good to me,
feel free to add:

Reviewed-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> Fixes: 72e02075a33f ("md: factor out parsing of fixed-point numbers")
> Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> ---
>   drivers/md/md.c | 70 ++++++++++++++++++++++++++++++++-----------------
>   1 file changed, 46 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 8e344b4b3444..fd5c3babcd6d 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -3767,52 +3767,74 @@ static int analyze_sbs(struct mddev *mddev)
>    */
>   int strict_strtoul_scaled(const char *cp, unsigned long *res, int scale)
>   {
> -	unsigned long result = 0;
> -	long decimals = -1;
> -	while (isdigit(*cp) || (*cp == '.' && decimals < 0)) {
> -		if (*cp == '.')
> -			decimals = 0;
> -		else if (decimals < scale) {
> -			unsigned int value;
> -			value = *cp - '0';
> -			result = result * 10 + value;
> -			if (decimals >= 0)
> -				decimals++;
> -		}
> -		cp++;
> -	}
> -	if (*cp == '\n')
> -		cp++;
> -	if (*cp)
> +	unsigned long result = 0, decimals = 0;
> +	char *pos, *str;
> +	int rv;
> +
> +	str = kmemdup_nul(cp, strlen(cp), GFP_KERNEL);
> +	if (!str)
> +		return -ENOMEM;
> +	pos = strchr(str, '.');
> +	if (pos) {
> +		int cnt = scale;
> +
> +		*pos = '\0';
> +		while (isdigit(*(++pos))) {
> +			if (cnt) {
> +				decimals = decimals * 10 + *pos - '0';
> +				cnt--;
> +			}
> +		}
> +		if (*pos == '\n')
> +			pos++;
> +		if (*pos) {
> +			kfree(str);
> +			return -EINVAL;
> +		}
> +		decimals *= int_pow(10, cnt);
> +	}
> +
> +	rv = kstrtoul(str, 10, &result);
> +	kfree(str);
> +	if (rv)
> +		return rv;
> +
> +	if (result > (ULONG_MAX - decimals) / (unsigned int)int_pow(10, scale))

This is correct, I guess the reason to use unsigned int is that u64/u64
will compile error in some 32-bit architecture. It's better to use
div64_u64() here.

>   		return -EINVAL;
> -	if (decimals < 0)
> -		decimals = 0;
> -	*res = result * int_pow(10, scale - decimals);
> -	return 0;
> +	*res = result * int_pow(10, scale) + decimals;
> +
> +	return rv;
>   }
>   
>   static ssize_t
>   safe_delay_show(struct mddev *mddev, char *page)
>   {
> -	int msec = (mddev->safemode_delay*1000)/HZ;
> -	return sprintf(page, "%d.%03d\n", msec/1000, msec%1000);
> +	unsigned int msec = ((unsigned long)mddev->safemode_delay*1000)/HZ;
> +
> +	return sprintf(page, "%u.%03u\n", msec/1000, msec%1000);
>   }
>   static ssize_t
>   safe_delay_store(struct mddev *mddev, const char *cbuf, size_t len)
>   {
>   	unsigned long msec;
> +	int ret;
>   
>   	if (mddev_is_clustered(mddev)) {
>   		pr_warn("md: Safemode is disabled for clustered mode\n");
>   		return -EINVAL;
>   	}
>   
> -	if (strict_strtoul_scaled(cbuf, &msec, 3) < 0)
> +	ret = strict_strtoul_scaled(cbuf, &msec, 3);
> +	if (ret < 0)
> +		return ret;
> +	if (msec > UINT_MAX)
>   		return -EINVAL;
> +
>   	if (msec == 0)
>   		mddev->safemode_delay = 0;
>   	else {
>   		unsigned long old_delay = mddev->safemode_delay;
> +		/* HZ <= 1000, so new_delay < UINT_MAX, too */

new_delay <= UNIT_MAX

>   		unsigned long new_delay = (msec*HZ)/1000;

There is no need do declare them as 'unsigned long', you can use
'unsigned int' directly now.

And you can also use DIV64_U64_ROUND_UP() directly here.

Thanks,
Kuai
>   
>   		if (new_delay == 0)