[PATCH v2] drivers: misc: ti-st: replace deprecated strncpy with strscpy

[PATCH v2] drivers: misc: ti-st: replace deprecated strncpy with strscpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect both `kim_data->dev_name` and `kim_gdata->dev_name` to be
NUL-terminated.

`kim_data->dev_name` seems to not require NUL-padding.

`kim_gdata` is already zero-allocated and as such does not require
NUL-padding:
|       kim_gdata = kzalloc(sizeof(struct kim_data_s), GFP_KERNEL);

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Let's also opt to use the more idiomatic strscpy usage of:
strscpy(dest, src, sizeof(dest))

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- use sizeof(dest) (thanks Kees)
- rebase onto mainline cbf3a2cb156a2c91
- Link to v1: https://lore.kernel.org/r/20230927-strncpy-drivers-misc-ti-st-st_kim-c-v1-1-29bbdeed1a2c@google.com
---
Note: build-tested only.
---
 drivers/misc/ti-st/st_kim.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/ti-st/st_kim.c b/drivers/misc/ti-st/st_kim.c
index fe682e0553b2..4b1be0bb6ac0 100644
--- a/drivers/misc/ti-st/st_kim.c
+++ b/drivers/misc/ti-st/st_kim.c
@@ -590,7 +590,7 @@ static ssize_t store_dev_name(struct device *dev,
 {
 	struct kim_data_s *kim_data = dev_get_drvdata(dev);
 	pr_debug("storing dev name >%s<", buf);
-	strncpy(kim_data->dev_name, buf, count);
+	strscpy(kim_data->dev_name, buf, sizeof(kim_data->dev_name));
 	pr_debug("stored dev name >%s<", kim_data->dev_name);
 	return count;
 }
@@ -751,7 +751,8 @@ static int kim_probe(struct platform_device *pdev)
 	}
 
 	/* copying platform data */
-	strncpy(kim_gdata->dev_name, pdata->dev_name, UART_DEV_NAME_LEN);
+	strscpy(kim_gdata->dev_name, pdata->dev_name,
+		sizeof(kim_gdata->dev_name));
 	kim_gdata->flow_cntrl = pdata->flow_cntrl;
 	kim_gdata->baud_rate = pdata->baud_rate;
 	pr_info("sysfs entries created\n");

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20230927-strncpy-drivers-misc-ti-st-st_kim-c-e1663a211a0c

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH v2] drivers: misc: ti-st: replace deprecated strncpy with strscpy

[Kees Cook]

On Tue, Oct 03, 2023 at 10:23:07PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> We expect both `kim_data->dev_name` and `kim_gdata->dev_name` to be
> NUL-terminated.
> 
> `kim_data->dev_name` seems to not require NUL-padding.
> 
> `kim_gdata` is already zero-allocated and as such does not require
> NUL-padding:
> |       kim_gdata = kzalloc(sizeof(struct kim_data_s), GFP_KERNEL);
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Let's also opt to use the more idiomatic strscpy usage of:
> strscpy(dest, src, sizeof(dest))
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Thanks for the adjustment. This looks right to me now.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook