[PATCH] HID: nintendo: fix out-of-bounds read in joycon_ctlr_read_handler()

[Ibrahim Hashimov <security@auditcode.ai>]

joycon_ctlr_read_handler() casts an incoming HID input report to
struct joycon_input_report and parses it, guarding the cast only with a
12-byte length check:

	if (size >= 12) /* make sure it contains the input report */
		joycon_parse_report(ctlr, (struct joycon_input_report *)data);

struct joycon_input_report is 49 bytes: a 13-byte header followed by a
union whose IMU arm is 36 bytes. For an IMU report joycon_parse_report()
-> joycon_parse_imu_report() walks that union (struct offsets 13..48),
so a report of exactly 12 bytes with data[0] == JC_INPUT_IMU_DATA passes
the guard yet is read up to 37 bytes past its declared length. The
over-read bytes are decoded into accelerometer/gyroscope values and
forwarded to userspace through the "(IMU)" input device, leaking
driver-internal memory. data[0] and size are fully controlled by a
malicious or spoofed Joy-Con/Pro Controller.

Receive buffers are sized to the maximum report length, so this is an
over-read within the allocation rather than a slab OOB, but the decoded
bytes still reach userspace.

The sibling subcmd path in joycon_ctlr_handle_event() already bounds the
same cast correctly:

	if (size < sizeof(struct joycon_input_report) ||
	    data[0] != JC_INPUT_SUBCMD_REPLY)
		break;

Use the same sizeof(struct joycon_input_report) bound here.

Fixes: 2af16c1f846b ("HID: nintendo: add nintendo switch controller driver")
Cc: stable@vger.kernel.org
Signed-off-by: Ibrahim Hashimov <security@auditcode.ai>
Assisted-by: AuditCode-AI:2026.07
---
 drivers/hid/hid-nintendo.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
index e7302ec01ff1..11b5fe05acf4 100644
--- a/drivers/hid/hid-nintendo.c
+++ b/drivers/hid/hid-nintendo.c
@@ -2607,7 +2607,12 @@ static int joycon_ctlr_read_handler(struct joycon_ctlr *ctlr, u8 *data,
 {
 	if (data[0] == JC_INPUT_SUBCMD_REPLY || data[0] == JC_INPUT_IMU_DATA ||
 	    data[0] == JC_INPUT_MCU_DATA) {
-		if (size >= 12) /* make sure it contains the input report */
+		/*
+		 * The whole struct is cast and parsed below, including the
+		 * IMU/subcmd union, not just the 12-byte partial header this
+		 * used to check for.
+		 */
+		if (size >= sizeof(struct joycon_input_report))
 			joycon_parse_report(ctlr,
 					    (struct joycon_input_report *)data);
 	}
-- 
2.50.1 (Apple Git-155)