2023-10-03 22:23:29

by Justin Stitt

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

`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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
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 <[email protected]>

2023-10-03 23:47:02

by Kees Cook

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

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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>

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

Reviewed-by: Kees Cook <[email protected]>

--
Kees Cook