[PATCH v2] HID: wacom: validate report length in wacom_intuos_pro2_bt_irq

[Ibrahim Hashimov <security@auditcode.ai>]

wacom_intuos_pro2_bt_irq() receives the wire report length in `len`
but never consults it before parsing. After the report-id gate it
unconditionally calls wacom_intuos_pro2_bt_pen() and then, selected by
features.type, a fixed chain of sub-parsers, none of which receive
`len`:

	wacom_intuos_pro2_bt_pen(wacom);
	if (type == INTUOSP2_BT || type == INTUOSP2S_BT) {
		wacom_intuos_pro2_bt_touch(wacom);
		wacom_intuos_pro2_bt_pad(wacom);
		wacom_intuos_pro2_bt_battery(wacom);
	} else {
		wacom_intuos_gen3_bt_pad(wacom);
		wacom_intuos_gen3_bt_battery(wacom);
	}

Each sub-parser dereferences wacom->data at fixed offsets. The furthest
byte touched on each branch is:

  INTUOSP2_BT / INTUOSP2S_BT: wacom_intuos_pro2_bt_pad() reads data[285]
	(the touchring byte), so the report must be at least 286 bytes;
  INTUOSHT3_BT ("gen3"): wacom_intuos_gen3_bt_battery() reads data[45],
	so the report must be at least 46 bytes.

features.type is selected from the VID/PID id_table entry and
wacom_setup_device_quirks() force-registers the pen/pad/touch inputs
for that type independent of the report descriptor, so a malicious or
malfunctioning paired/spoofed Bluetooth peripheral can advertise that
VID/PID and send an undersized report that still satisfies the
data[0] == 0x80/0x81 gate. The driver then reads past the received
report and forwards the bytes to userspace via evdev (MSC_SERIAL /
ABS_MISC / ABS_WHEEL on the pen and pad input nodes), an out-of-bounds
read with a concrete userspace read-back channel, and a true
out-of-bounds read on transports whose backing buffer is sized to the
(small) report descriptor rather than a fixed-size staging buffer.

This is the same class of bug commit 2f1763f62909 ("HID: wacom: fix
out-of-bounds read in wacom_intuos_bt_irq") already hardened in the
sibling wacom_intuos_bt_irq(), which guards each report id against its
minimum length before parsing.

Guard wacom_intuos_pro2_bt_irq() the same way: before parsing, reject
reports shorter than the furthest offset the selected branch actually
dereferences, warn, and bail out. Because the whole pen/touch/pad/
battery chain runs unconditionally per branch, a single up-front check
against the maximum offset (286 bytes for INTUOSP2_BT/INTUOSP2S_BT,
46 bytes for the gen3 branch) bounds every sub-parser. Returning 0 on
a short report also skips those calls for the same malformed report,
which is the safe, conservative behavior.

Fixes: 4922cd26f03c ("HID: wacom: Support 2nd-gen Intuos Pro's Bluetooth classic interface")
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
---
v2: the v1 check (len < 109 / len < 43) only bounded
    wacom_intuos_pro2_bt_pen(). As sashiko-bot pointed out, the
    unconditional touch/pad/battery calls read much further --
    wacom_intuos_pro2_bt_pad() up to data[285] and
    wacom_intuos_gen3_bt_battery() up to data[45] -- so a report in the
    gap (109..285 / 43..45) passed the guard yet still over-read. Raise
    the minimums to the furthest offset each branch dereferences
    (286 / 46) so the guard actually bounds the whole call chain.

 drivers/hid/wacom_wac.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index da1f0ea85625..89a191cf1924 100644
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1548,6 +1548,19 @@ static int wacom_intuos_pro2_bt_irq(struct wacom_wac *wacom, size_t len)
 		return 0;
 	}
 
+	if (wacom->features.type == INTUOSP2_BT ||
+	    wacom->features.type == INTUOSP2S_BT) {
+		if (len < 286) {
+			dev_warn(wacom->pen_input->dev.parent,
+				 "Pro2 BT report too short: %zu bytes\n", len);
+			return 0;
+		}
+	} else if (len < 46) {
+		dev_warn(wacom->pen_input->dev.parent,
+			 "Pro2 BT report too short: %zu bytes\n", len);
+		return 0;
+	}
+
 	wacom_intuos_pro2_bt_pen(wacom);
 	if (wacom->features.type == INTUOSP2_BT ||
 	    wacom->features.type == INTUOSP2S_BT) {
-- 
2.50.1 (Apple Git-155)