[PATCH] HID: wacom: Access shared touch input by rcu_dereference()

[Ping Cheng <pinglinux@gmail.com>]

Allow the __rcu-annotated wacom_wac->shared->touch_input to be accessed
inside an RCU read-side critical section by using rcu_dereference().

Cc: stable@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202610180015.KsRqmoTE-lkp@intel.com/
Fixes: 9183319a5ba4 ("Input: wacom - Setup SW_MUTE_DEVICE according to the order of input registration")
Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Ping Cheng <ping.cheng@wacom.com>
---
The patch is based on for-7.4/wacom branch
---
 drivers/hid/wacom_wac.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index cf459c16b39a..ef6480338b2c 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -4414,7 +4414,7 @@ int wacom_setup_pad_input_capabilities(struct input_dev *input_dev,
 		break;
 
 	case HID_GENERIC:
-		if (wacom_wac->shared) {
+		if (wacom_wac->shared && wacom_wac->has_mute_touch_switch) {
 			/*
 			 * The setup of touch switch capability can only be done
 			 * here for those devices, such as Cintiq Pro 13 and 16,
@@ -4425,11 +4425,12 @@ int wacom_setup_pad_input_capabilities(struct input_dev *input_dev,
 			 * stylus first or touch first. This path covers the touch
 			 * input first case.
 			 */
-			if (wacom_wac->has_mute_touch_switch &&
-			    wacom_wac->shared->touch_input) {
-				input_set_capability(wacom_wac->shared->touch_input,
-				    EV_SW, SW_MUTE_DEVICE);
-			}
+                        struct input_dev *touch_input;
+
+                        guard(rcu)();
+                        touch_input = rcu_dereference(wacom_wac->shared->touch_input);
+			if (touch_input)
+				input_set_capability(touch_input, EV_SW, SW_MUTE_DEVICE);
 		}
 		break;
 
-- 
2.56.0