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
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
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>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231018-strncpy-drivers-net-wireless-ti-wl18xx-main-c-v2-1-ab828a491ce5@google.com

diff --git a/drivers/net/wireless/ti/wl18xx/main.c b/drivers/net/wireless/ti/wl18xx/main.c
index d4a8940..20d9181 100644 (file)
--- a/drivers/net/wireless/ti/wl18xx/main.c
+++ b/drivers/net/wireless/ti/wl18xx/main.c
@@ -1516,12 +1516,9 @@ static int wl18xx_handle_static_data(struct wl1271 *wl,
        struct wl18xx_static_data_priv *static_data_priv =
                (struct wl18xx_static_data_priv *) static_data->priv;
 
-       strncpy(wl->chip.phy_fw_ver_str, static_data_priv->phy_version,
+       strscpy(wl->chip.phy_fw_ver_str, static_data_priv->phy_version,
                sizeof(wl->chip.phy_fw_ver_str));
 
-       /* make sure the string is NULL-terminated */
-       wl->chip.phy_fw_ver_str[sizeof(wl->chip.phy_fw_ver_str) - 1] = '\0';
-
        wl1271_info("PHY firmware version: %s", static_data_priv->phy_version);
 
        return 0;