[PATCH v2] Input: cros_ec_keyb - Fix an invalid memory access

[Tzung-Bi Shih <tzungbi@kernel.org>]

If cros_ec_keyb_register_matrix() isn't called (due to
`buttons_switches_only`) in cros_ec_keyb_probe(), `ckdev->idev` remains
NULL.  An invalid memory access is observed in cros_ec_keyb_process()
when receiving an EC_MKBP_EVENT_KEY_MATRIX event in cros_ec_keyb_work()
in such case.

  Unable to handle kernel read from unreadable memory at virtual address 0000000000000028
  ...
  x3 : 0000000000000000 x2 : 0000000000000000
  x1 : 0000000000000000 x0 : 0000000000000000
  Call trace:
  input_event
  cros_ec_keyb_work
  blocking_notifier_call_chain
  ec_irq_thread

It's still unknown about why the kernel receives such malformed event,
in any cases, the kernel shouldn't access `ckdev->idev` and friends if
the driver doesn't intend to initialize them.

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
v2:
- dev_info() -> dev_warn_once().

v1: https://lore.kernel.org/chrome-platform/20251104064353.3072727-1-tzungbi@kernel.org

 drivers/input/keyboard/cros_ec_keyb.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/input/keyboard/cros_ec_keyb.c b/drivers/input/keyboard/cros_ec_keyb.c
index f7209c8ebbcc..324c98b1cb52 100644
--- a/drivers/input/keyboard/cros_ec_keyb.c
+++ b/drivers/input/keyboard/cros_ec_keyb.c
@@ -261,6 +261,11 @@ static int cros_ec_keyb_work(struct notifier_block *nb,
 	case EC_MKBP_EVENT_KEY_MATRIX:
 		pm_wakeup_event(ckdev->dev, 0);
 
+		if (!ckdev->idev) {
+			dev_warn_once(ckdev->dev, "No key matrix\n");
+			return NOTIFY_OK;
+		}
+
 		if (ckdev->ec->event_size != ckdev->cols) {
 			dev_err(ckdev->dev,
 				"Discarded incomplete key matrix event.\n");
-- 
2.51.2.997.g839fc31de9-goog