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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH 11/20] hwmon: Manual replacement of the deprecated
 strlcpy() with return values
To:     Romain Perier <romain.perier@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        kernel-hardening@lists.openwall.com
Cc:     linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20210222151231.22572-1-romain.perier@gmail.com>
 <20210222151231.22572-12-romain.perier@gmail.com>
From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <3b8dd556-8c09-9686-dec6-9d523a9762a8@roeck-us.net>
Date:   Mon, 22 Feb 2021 07:46:14 -0800
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In-Reply-To: <20210222151231.22572-12-romain.perier@gmail.com>
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On 2/22/21 7:12 AM, Romain Perier wrote:
> The strlcpy() reads the entire source buffer first, it is dangerous if
> the source buffer lenght is unbounded or possibility non NULL-terminated.

length

> It can lead to linear read overflows, crashes, etc...
> 
Not here. This description is misleading.

> As recommended in the deprecated interfaces [1], it should be replaced
> by strscpy.
> 
> This commit replaces all calls to strlcpy that handle the return values
> by the corresponding strscpy calls with new handling of the return
> values (as it is quite different between the two functions).
> 
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> 
> Signed-off-by: Romain Perier <romain.perier@gmail.com>

This patch just adds pain to injury, as the source 'buffers' are all fixed
strings and their length will never exceed the maximum buffer length.
I really don't see the point of using strscpy() in this situation.

> ---
>  drivers/hwmon/pmbus/max20730.c |   66 +++++++++++++++++++++--------------------

This patch only modifies a single driver and should be tagged as such.

>  1 file changed, 35 insertions(+), 31 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c
> index 9dd3dd79bc18..a384b57b7327 100644
> --- a/drivers/hwmon/pmbus/max20730.c
> +++ b/drivers/hwmon/pmbus/max20730.c
> @@ -107,7 +107,8 @@ struct max20730_debugfs_data {
>  static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  				     size_t count, loff_t *ppos)
>  {
> -	int ret, len;
> +	int ret;
> +	ssize_t len;
>  	int *idxp = file->private_data;
>  	int idx = *idxp;
>  	struct max20730_debugfs_data *psu = to_psu(idxp, idx);
> @@ -148,13 +149,13 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  			>> MAX20730_MFR_DEVSET1_TSTAT_BIT_POS;
>  
>  		if (val == 0)
> -			len = strlcpy(tbuf, "2000\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "2000\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 1)
> -			len = strlcpy(tbuf, "125\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "125\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 2)
> -			len = strlcpy(tbuf, "62.5\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "62.5\n", DEBUG_FS_DATA_MAX);
>  		else
> -			len = strlcpy(tbuf, "32\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "32\n", DEBUG_FS_DATA_MAX);
>  		break;
>  	case MAX20730_DEBUGFS_INTERNAL_GAIN:
>  		val = (data->mfr_devset1 & MAX20730_MFR_DEVSET1_RGAIN_MASK)
> @@ -163,35 +164,35 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  		if (data->id == max20734) {
>  			/* AN6209 */
>  			if (val == 0)
> -				len = strlcpy(tbuf, "0.8\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "0.8\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 1)
> -				len = strlcpy(tbuf, "3.2\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "3.2\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 2)
> -				len = strlcpy(tbuf, "1.6\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "1.6\n", DEBUG_FS_DATA_MAX);
>  			else
> -				len = strlcpy(tbuf, "6.4\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "6.4\n", DEBUG_FS_DATA_MAX);
>  		} else if (data->id == max20730 || data->id == max20710) {
>  			/* AN6042 or AN6140 */
>  			if (val == 0)
> -				len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 1)
> -				len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 2)
> -				len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
>  			else
> -				len = strlcpy(tbuf, "7.2\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "7.2\n", DEBUG_FS_DATA_MAX);
>  		} else if (data->id == max20743) {
>  			/* AN6042 */
>  			if (val == 0)
> -				len = strlcpy(tbuf, "0.45\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "0.45\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 1)
> -				len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
>  			else if (val == 2)
> -				len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
>  			else
> -				len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
> +				len = strscpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
>  		} else {
> -			len = strlcpy(tbuf, "Not supported\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "Not supported\n", DEBUG_FS_DATA_MAX);
>  		}
>  		break;
>  	case MAX20730_DEBUGFS_BOOT_VOLTAGE:
> @@ -199,26 +200,26 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  			>> MAX20730_MFR_DEVSET1_VBOOT_BIT_POS;
>  
>  		if (val == 0)
> -			len = strlcpy(tbuf, "0.6484\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "0.6484\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 1)
> -			len = strlcpy(tbuf, "0.8984\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "0.8984\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 2)
> -			len = strlcpy(tbuf, "1.0\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "1.0\n", DEBUG_FS_DATA_MAX);
>  		else
> -			len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
>  		break;
>  	case MAX20730_DEBUGFS_OUT_V_RAMP_RATE:
>  		val = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_VRATE)
>  			>> MAX20730_MFR_DEVSET2_VRATE_BIT_POS;
>  
>  		if (val == 0)
> -			len = strlcpy(tbuf, "4\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "4\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 1)
> -			len = strlcpy(tbuf, "2\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "2\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 2)
> -			len = strlcpy(tbuf, "1\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "1\n", DEBUG_FS_DATA_MAX);
>  		else
> -			len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
>  		break;
>  	case MAX20730_DEBUGFS_OC_PROTECT_MODE:
>  		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_OCPM_MASK)
> @@ -230,13 +231,13 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  			>> MAX20730_MFR_DEVSET2_SS_BIT_POS;
>  
>  		if (val == 0)
> -			len = strlcpy(tbuf, "0.75\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "0.75\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 1)
> -			len = strlcpy(tbuf, "1.5\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "1.5\n", DEBUG_FS_DATA_MAX);
>  		else if (val == 2)
> -			len = strlcpy(tbuf, "3\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "3\n", DEBUG_FS_DATA_MAX);
>  		else
> -			len = strlcpy(tbuf, "6\n", DEBUG_FS_DATA_MAX);
> +			len = strscpy(tbuf, "6\n", DEBUG_FS_DATA_MAX);
>  		break;
>  	case MAX20730_DEBUGFS_IMAX:
>  		ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_IMAX_MASK)
> @@ -287,9 +288,12 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
>  				"%d.%d\n", ret / 10000, ret % 10000);
>  		break;
>  	default:
> -		len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
> +		len = strscpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
>  	}
>  
> +	if (len == -E2BIG)
> +		return -E2BIG;
> +
>  	return simple_read_from_buffer(buf, count, ppos, tbuf, len);
>  }
>  
>