[PATCH v3 1/6] HID: wacom: check the input device in the shared report helpers

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

wacom_report_numbered_buttons() and wacom_wac_finger_count_touches() are
reached from several report handlers and use the input device they are
given without checking it.

Both can see a NULL input device on a fully successful probe. The report
handler is selected by features.type from the id table, while the three
input devices are allocated from what the report descriptor declares.
When wacom_setup_{pen,touch,pad}_input_capabilities() returns -ENODEV,
wacom_setup_inputs() frees that input device, sets the pointer to NULL
and still returns 0 - the "no pen in use on this interface" case.
wacom_wac_irq() then still routes reports to a handler that passes the
NULL pointer down.

Reproduced on linux-next 20260925 (x86_64, KASAN) from one /dev/uhid
device plus a single UHID_INPUT2 write:

  BUG: KASAN: null-ptr-deref in range [0x290-0x297]
  RIP: 0010:wacom_report_numbered_buttons+0x37/0x210
   wacom_intuos_irq+0x29e/0x3300
   wacom_wac_irq+0x1b59/0xb3f0
   wacom_raw_event+0x68f/0xb60
   __hid_input_report+0x398/0x4d0
   uhid_char_write+0xa99/0xfc0

Check the pointer in both helpers, following the convention the driver
already uses in wacom_tpc_irq() and wacom_wac_pad_event(). Log a
warning on the first occurrence so the condition is not silently
swallowed.

Fixes: 10059cdc0ad0 ("Input: wacom - split out the pad device for Intuos/Cintiq")
Fixes: 2a6cdbdd4cc0 ("HID: wacom: Introduce new 'touch_input' device")
Cc: stable@vger.kernel.org
Signed-off-by: Jinmo Yang <jinmo44.yang@gmail.com>
---
 drivers/hid/wacom_wac.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index c4cd87b781c4..567b01882eb1 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1263,6 +1263,12 @@ static int wacom_wac_finger_count_touches(struct wacom_wac *wacom)
 	int count = 0;
 	int i;
 
+	if (!input) {
+		dev_warn_once(&container_of(wacom, struct wacom, wacom_wac)->hdev->dev,
+			      "%s: touch_input is NULL\n", __func__);
+		return 0;
+	}
+
 	if (!touch_max)
 		return 0;
 
@@ -4226,9 +4232,16 @@ static void wacom_update_led(struct wacom *wacom, int button_count, int mask,
 static void wacom_report_numbered_buttons(struct input_dev *input_dev,
 				int button_count, int mask)
 {
-	struct wacom *wacom = input_get_drvdata(input_dev);
+	struct wacom *wacom;
 	int i;
 
+	if (!input_dev) {
+		pr_warn_once("%s: input_dev is NULL\n", __func__);
+		return;
+	}
+
+	wacom = input_get_drvdata(input_dev);
+
 	for (i = 0; i < wacom->led.count; i++)
 		wacom_update_led(wacom,  button_count, mask, i);
 
-- 
2.53.0