[PATCH v4 3/6] HID: wacom: add NULL input guards to wacom_intuos_irq() and its helpers

[Jinmo Yang <jinmo44.yang@gmail.com>]

wacom_intuos_irq() assigns pen_input to a local variable and
dereferences it in a dev_dbg() before any NULL check.  Its helpers
wacom_intuos_inout() and wacom_intuos_general() also dereference
pen_input unconditionally.  Add a pen_input NULL guard at the top of
wacom_intuos_irq() to protect them all.

wacom_intuos_pad() uses pad_input throughout, but pad_input can be NULL
when wacom_setup_pad_input_capabilities() returns -ENODEV during a
successful probe.  Add a NULL guard after the report-ID check.

Adopt the same return convention as wacom_intuos_inout() and
wacom_intuos_general(): return 1 for "handled, don't sync" and 2 for
"handled, sync".  Update wacom_intuos_irq() to apply the matching
"result - 1" transform so that the NULL-guard path (return 1) suppresses
the spurious input_sync() that the old "return 1" would have triggered
via wacom_wac_irq().

Fixes: 10059cdc0ad0 ("Input: wacom - split out the pad device for Intuos/Cintiq")
Signed-off-by: Jinmo Yang <jinmo44.yang@gmail.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 drivers/hid/wacom_wac.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index bec8dbec5bc3..c38fbec114e4 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -581,6 +581,12 @@ static int wacom_intuos_pad(struct wacom_wac *wacom)
 	      data[0] == WACOM_REPORT_CINTIQPAD))
 		return 0;
 
+	if (!input) {
+		dev_warn_once(&container_of(wacom, struct wacom, wacom_wac)->hdev->dev,
+			      "%s: pad_input is NULL\n", __func__);
+		return 1; /* handled; the -1 in wacom_intuos_irq() suppresses sync */
+	}
+
 	if (features->type >= INTUOS4S && features->type <= INTUOS4L) {
 		buttons = (data[3] << 1) | (data[2] & 0x01);
 		ring1 = data[1];
@@ -716,7 +722,7 @@ static int wacom_intuos_pad(struct wacom_wac *wacom)
 
 	input_event(input, EV_MSC, MSC_SERIAL, 0xffffffff);
 
-	return 1;
+	return 2;
 }
 
 static int wacom_intuos_id_mangle(int tool_id)
@@ -1073,6 +1079,12 @@ static int wacom_intuos_irq(struct wacom_wac *wacom)
 	struct input_dev *input = wacom->pen_input;
 	int result;
 
+	if (!input) {
+		dev_warn_once(&container_of(wacom, struct wacom, wacom_wac)->hdev->dev,
+			      "%s: pen_input is NULL\n", __func__);
+		return 0;
+	}
+
 	if (data[0] != WACOM_REPORT_PENABLED &&
 	    data[0] != WACOM_REPORT_INTUOS_ID1 &&
 	    data[0] != WACOM_REPORT_INTUOS_ID2 &&
@@ -1089,7 +1101,7 @@ static int wacom_intuos_irq(struct wacom_wac *wacom)
 	/* process pad events */
 	result = wacom_intuos_pad(wacom);
 	if (result)
-		return result;
+		return result - 1;
 
 	/* process in/out prox events */
 	result = wacom_intuos_inout(wacom);
-- 
2.53.0