[PATCH v3] HID: betop: fix slab-out-of-bounds Write in betop_probe

["F.A.Sulaiman" <asha.16@itfac.mrt.ac.lk>]

Syzbot reported slab-out-of-bounds Write bug in hid-betopff driver.
The problem is the driver assumes the device must have an input report but
some malicious devices violate this assumption.

So this patch checks hid_device's input is non empty before it's been used.

Reported-by: syzbot+07efed3bc5a1407bd742@syzkaller.appspotmail.com
Signed-off-by: F.A. SULAIMAN <asha.16@itfac.mrt.ac.lk>
---
 drivers/hid/hid-betopff.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/hid-betopff.c b/drivers/hid/hid-betopff.c
index 0790fbd3fc9a..467d789f9bc2 100644
--- a/drivers/hid/hid-betopff.c
+++ b/drivers/hid/hid-betopff.c
@@ -56,15 +56,22 @@ static int betopff_init(struct hid_device *hid)
 {
 	struct betopff_device *betopff;
 	struct hid_report *report;
-	struct hid_input *hidinput =
-			list_first_entry(&hid->inputs, struct hid_input, list);
+	struct hid_input *hidinput;
 	struct list_head *report_list =
 			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
-	struct input_dev *dev = hidinput->input;
+	struct input_dev *dev;
 	int field_count = 0;
 	int error;
 	int i, j;
 
+	if (list_empty(&hid->inputs)) {
+		hid_err(hid, "no inputs found\n");
+		return -ENODEV;
+	}
+
+	hidinput = list_first_entry(&hid->inputs, struct hid_input, list);
+	dev = hidinput->input;
+
 	if (list_empty(report_list)) {
 		hid_err(hid, "no output reports found\n");
 		return -ENODEV;
-- 
2.17.1