[PATCH 2/2] HID: multitouch: Check to ensure report responses match the request

[Lee Jones <lee@kernel.org>]

It is possible for a malicious (or clumsy) device to respond to a
specific report's feature request using a completely different report
ID.  This can cause confusion in the HID core resulting in nasty
side-effects such as OOB writes.

Add a check to ensure that the report ID in the response, matches the
one that was requested.  If it doesn't, omit reporting the raw event and
return early.

Signed-off-by: Lee Jones <lee@kernel.org>
---
 drivers/hid/hid-multitouch.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
index b1c3ef129058..834c1a334887 100644
--- a/drivers/hid/hid-multitouch.c
+++ b/drivers/hid/hid-multitouch.c
@@ -499,12 +499,19 @@ static void mt_get_feature(struct hid_device *hdev, struct hid_report *report)
 		dev_warn(&hdev->dev, "failed to fetch feature %d\n",
 			 report->id);
 	} else {
+		/* The report ID in the request and the response should match */
+		if (report->id != buf[0]) {
+			hid_err(hdev, "Returned feature report did not match the request\n");
+			goto free;
+		}
+
 		ret = hid_report_raw_event(hdev, HID_FEATURE_REPORT, buf,
 					   size, 0);
 		if (ret)
 			dev_warn(&hdev->dev, "failed to report feature\n");
 	}
 
+free:
 	kfree(buf);
 }
 
-- 
2.53.0.473.g4a7958ca14-goog