[PATCH] auxdisplay: panel: refactor deprecated strncpy

[Justin Stitt <justinstitt@google.com>]

`strncpy` is deprecated and as such we should prefer more robust and
less ambiguous interfaces.

In this case, all of `press_str`, `repeat_str` and `release_str` are
explicitly marked as nonstring:
|   struct {	/* valid when type == INPUT_TYPE_KBD */
|           char press_str[sizeof(void *) + sizeof(int)] __nonstring;
|           char repeat_str[sizeof(void *) + sizeof(int)] __nonstring;
|           char release_str[sizeof(void *) + sizeof(int)] __nonstring;
|   } kbd;

... which makes `strtomem_pad` a suitable replacement as it is
functionally the same whilst being more obvious about its behavior.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested
---
 drivers/auxdisplay/panel.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/auxdisplay/panel.c b/drivers/auxdisplay/panel.c
index eba04c0de7eb..e20d35bdf5fe 100644
--- a/drivers/auxdisplay/panel.c
+++ b/drivers/auxdisplay/panel.c
@@ -1449,10 +1449,9 @@ static struct logical_input *panel_bind_key(const char *name, const char *press,
 	key->rise_time = 1;
 	key->fall_time = 1;
 
-	strncpy(key->u.kbd.press_str, press, sizeof(key->u.kbd.press_str));
-	strncpy(key->u.kbd.repeat_str, repeat, sizeof(key->u.kbd.repeat_str));
-	strncpy(key->u.kbd.release_str, release,
-		sizeof(key->u.kbd.release_str));
+	strtomem_pad(key->u.kbd.press_str, press, '\0');
+	strtomem_pad(key->u.kbd.repeat_str, repeat, '\0');
+	strtomem_pad(key->u.kbd.release_str, release, '\0');
 	list_add(&key->list, &logical_inputs);
 	return key;
 }

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230911-strncpy-drivers-auxdisplay-panel-c-83bce51f32cb

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