Re: [PATCH v2] hwmon: (pmbus/max20730) Remove strlcpy occurences

From: Guenter Roeck
Date: Sat Jul 15 2023 - 12:56:31 EST

On Wed, Jul 12, 2023 at 09:43:07PM +0000, Azeem Shaikh wrote:
> strlcpy() reads the entire source buffer first.
> This read may exceed the destination size limit.
> This is both inefficient and can lead to linear read
> overflows if a source string is not NUL-terminated [1].
> In an effort to remove strlcpy() completely [2], replace
> strlcpy() here with direct assignment.
>
> strlcpy in this file is used to copy fixed-length strings which can be
> completely avoided by direct assignment and is safe to do so. strlen()
> is used to return the length of @tbuf.
>
> [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#strlcpy
> [2] https://github.com/KSPP/linux/issues/89
>
> Signed-off-by: Azeem Shaikh <azeemshaikh38@xxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Applied.

Thanks,
Guenter

> ---
> v2:
> * Includes driver name in commit header.
> * Removes unrelated change tbuf{ 0 } -> tbuf{}.
> * Fixes bug where @tbuf was being passed instead of @result.
>
> v1:
> * https://lore.kernel.org/all/20230712144429.2845940-1-azeemshaikh38@xxxxxxxxx/
>
> drivers/hwmon/pmbus/max20730.c | 64 +++++++++++++++++++++--------------------
> 1 file changed, 33 insertions(+), 31 deletions(-)
>
> --
> 2.41.0.255.g8b1d071c50-goog
>
> diff --git a/drivers/hwmon/pmbus/max20730.c b/drivers/hwmon/pmbus/max20730.c
> index 7bcf27995033..1de34da177c9 100644
> --- a/drivers/hwmon/pmbus/max20730.c
> +++ b/drivers/hwmon/pmbus/max20730.c
> @@ -114,6 +114,7 @@ static ssize_t max20730_debugfs_read(struct file *file, char __user *buf,
> const struct pmbus_driver_info *info;
> const struct max20730_data *data;
> char tbuf[DEBUG_FS_DATA_MAX] = { 0 };
> + char *result = tbuf;
> u16 val;
>
> info = pmbus_get_driver_info(psu->client);
> @@ -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);
> + result = "2000\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "125\n", DEBUG_FS_DATA_MAX);
> + result = "125\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "62.5\n", DEBUG_FS_DATA_MAX);
> + result = "62.5\n";
> else
> - len = strlcpy(tbuf, "32\n", DEBUG_FS_DATA_MAX);
> + result = "32\n";
> 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);
> + result = "0.8\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "3.2\n", DEBUG_FS_DATA_MAX);
> + result = "3.2\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "1.6\n", DEBUG_FS_DATA_MAX);
> + result = "1.6\n";
> else
> - len = strlcpy(tbuf, "6.4\n", DEBUG_FS_DATA_MAX);
> + result = "6.4\n";
> } else if (data->id == max20730 || data->id == max20710) {
> /* AN6042 or AN6140 */
> if (val == 0)
> - len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
> + result = "0.9\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
> + result = "3.6\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
> + result = "1.8\n";
> else
> - len = strlcpy(tbuf, "7.2\n", DEBUG_FS_DATA_MAX);
> + result = "7.2\n";
> } else if (data->id == max20743) {
> /* AN6042 */
> if (val == 0)
> - len = strlcpy(tbuf, "0.45\n", DEBUG_FS_DATA_MAX);
> + result = "0.45\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "1.8\n", DEBUG_FS_DATA_MAX);
> + result = "1.8\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "0.9\n", DEBUG_FS_DATA_MAX);
> + result = "0.9\n";
> else
> - len = strlcpy(tbuf, "3.6\n", DEBUG_FS_DATA_MAX);
> + result = "3.6\n";
> } else {
> - len = strlcpy(tbuf, "Not supported\n", DEBUG_FS_DATA_MAX);
> + result = "Not supported\n";
> }
> 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);
> + result = "0.6484\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "0.8984\n", DEBUG_FS_DATA_MAX);
> + result = "0.8984\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "1.0\n", DEBUG_FS_DATA_MAX);
> + result = "1.0\n";
> else
> - len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
> + result = "Invalid\n";
> 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);
> + result = "4\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "2\n", DEBUG_FS_DATA_MAX);
> + result = "2\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "1\n", DEBUG_FS_DATA_MAX);
> + result = "1\n";
> else
> - len = strlcpy(tbuf, "Invalid\n", DEBUG_FS_DATA_MAX);
> + result = "Invalid\n";
> 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);
> + result = "0.75\n";
> else if (val == 1)
> - len = strlcpy(tbuf, "1.5\n", DEBUG_FS_DATA_MAX);
> + result = "1.5\n";
> else if (val == 2)
> - len = strlcpy(tbuf, "3\n", DEBUG_FS_DATA_MAX);
> + result = "3\n";
> else
> - len = strlcpy(tbuf, "6\n", DEBUG_FS_DATA_MAX);
> + result = "6\n";
> break;
> case MAX20730_DEBUGFS_IMAX:
> ret = (data->mfr_devset2 & MAX20730_MFR_DEVSET2_IMAX_MASK)
> @@ -287,10 +288,11 @@ 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);
> + result = "Invalid\n";
> }
>
> - return simple_read_from_buffer(buf, count, ppos, tbuf, len);
> + len = strlen(result);
> + return simple_read_from_buffer(buf, count, ppos, result, len);
> }
>
> static const struct file_operations max20730_fops = {