[v2] wifi: wl18xx: 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.

wl->chip.phy_fw_ver_str is obviously intended to be NUL-terminated by
the deliberate comment telling us as much. Furthermore, its only use is
drivers/net/wireless/ti/wlcore/debugfs.c shows us it should be
NUL-terminated since its used in scnprintf:
492 | DRIVER_STATE_PRINT_STR(chip.phy_fw_ver_str);
which is defined as:
| #define DRIVER_STATE_PRINT_STR(x)  DRIVER_STATE_PRINT(x, "%s")
...
| #define DRIVER_STATE_PRINT(x, fmt)   \
| 	(res += scnprintf(buf + res, DRIVER_STATE_BUF_LEN - res,\
| 			  #x " = " fmt "\n", wl->x))

We can also see that NUL-padding is not required.

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.

The very fact that a plain-english comment had to be made alongside a
manual NUL-byte assignment for such a simple purpose shows why strncpy
is faulty. It has non-obvious behavior that has to be clarified every
time it is used (and if it isn't then the reader suffers).

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:
- add wifi: to subject (thanks Jeff)
- Link to v1: https://lore.kernel.org/r/20231017-strncpy-drivers-net-wireless-ti-wl18xx-main-c-v1-1-ed5322ec8068@google.com
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/net/wireless/ti/wl18xx/main.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)


---
base-commit: 58720809f52779dc0f08e53e54b014209d13eebb
change-id: 20231017-strncpy-drivers-net-wireless-ti-wl18xx-main-c-356a0272bab4

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

On Wed, Oct 18, 2023 at 09:18:24PM +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.
> 
> wl->chip.phy_fw_ver_str is obviously intended to be NUL-terminated by
> the deliberate comment telling us as much. Furthermore, its only use is
> drivers/net/wireless/ti/wlcore/debugfs.c shows us it should be
> NUL-terminated since its used in scnprintf:
> 492 | DRIVER_STATE_PRINT_STR(chip.phy_fw_ver_str);
> which is defined as:
> | #define DRIVER_STATE_PRINT_STR(x)  DRIVER_STATE_PRINT(x, "%s")
> ...
> | #define DRIVER_STATE_PRINT(x, fmt)   \
> | 	(res += scnprintf(buf + res, DRIVER_STATE_BUF_LEN - res,\
> | 			  #x " = " fmt "\n", wl->x))
> 
> We can also see that NUL-padding is not required.
> 
> 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.
> 
> The very fact that a plain-english comment had to be made alongside a
> manual NUL-byte assignment for such a simple purpose shows why strncpy
> is faulty. It has non-obvious behavior that has to be clarified every
> time it is used (and if it isn't then the reader suffers).
> 
> 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>

Yup, a clear case for strscpy.

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

Justin Stitt <justinstitt@google.com> 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.
> 
> wl->chip.phy_fw_ver_str is obviously intended to be NUL-terminated by
> the deliberate comment telling us as much. Furthermore, its only use is
> drivers/net/wireless/ti/wlcore/debugfs.c shows us it should be
> NUL-terminated since its used in scnprintf:
> 492 | DRIVER_STATE_PRINT_STR(chip.phy_fw_ver_str);
> which is defined as:
> | #define DRIVER_STATE_PRINT_STR(x)  DRIVER_STATE_PRINT(x, "%s")
> ...
> | #define DRIVER_STATE_PRINT(x, fmt)   \
> | 	(res += scnprintf(buf + res, DRIVER_STATE_BUF_LEN - res,\
> | 			  #x " = " fmt "\n", wl->x))
> 
> We can also see that NUL-padding is not required.
> 
> 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.
> 
> The very fact that a plain-english comment had to be made alongside a
> manual NUL-byte assignment for such a simple purpose shows why strncpy
> is faulty. It has non-obvious behavior that has to be clarified every
> time it is used (and if it isn't then the reader suffers).
> 
> 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>
> Reviewed-by: Kees Cook <keescook@chromium.org>

Patch applied to wireless-next.git, thanks.

fb329e8b1d88 wifi: wl18xx: replace deprecated strncpy with strscpy