HID: ft260: skip unexpected HID input reports

The FT260 is not supposed to generate unexpected HID reports. However,
in theory, the unsolicited HID Input reports can be issued by a specially
crafted malicious USB device masquerading as FT260 when the attacker has
physical access to the USB port. In this case, the read_buf pointer points
to the final data portion of the previous I2C Read transfer, and the memcpy
invoked in the ft260_raw_event() will try copying the content of the
unexpected report into the wrong location.

This commit sets the Read buffer pointer to NULL on the I2C Read
transaction completion and checks it in the ft260_raw_event() to detect
and skip the unsolicited Input report.
Reported-by: Enrik Berkhan <Enrik.Berkhan@inka.de>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-ft260.c

@@ -464,7 +464,7 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 			  u16 len, u8 flag)
 {
 	u16 rd_len;
-	int timeout, ret;
+	int timeout, ret = 0;
 	struct ft260_i2c_read_request_report rep;
 	struct hid_device *hdev = dev->hdev;
 
@@ -480,10 +480,6 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 			rd_len = FT260_RD_DATA_MAX;
 		}
 
-		dev->read_idx = 0;
-		dev->read_buf = data;
-		dev->read_len = rd_len;
-
 		rep.report = FT260_I2C_READ_REQ;
 		rep.length = cpu_to_le16(rd_len);
 		rep.address = addr;
@@ -494,22 +490,30 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 
 		reinit_completion(&dev->wait);
 
+		dev->read_idx = 0;
+		dev->read_buf = data;
+		dev->read_len = rd_len;
+
 		ret = ft260_hid_output_report(hdev, (u8 *)&rep, sizeof(rep));
 		if (ret < 0) {
 			hid_err(hdev, "%s: failed with %d\n", __func__, ret);
-			return ret;
+			goto ft260_i2c_read_exit;
 		}
 
 		timeout = msecs_to_jiffies(5000);
 		if (!wait_for_completion_timeout(&dev->wait, timeout)) {
+			ret = -ETIMEDOUT;
 			ft260_i2c_reset(hdev);
-			return -ETIMEDOUT;
+			goto ft260_i2c_read_exit;
 		}
 
+		dev->read_buf = NULL;
+
 		ret = ft260_xfer_status(dev);
 		if (ret < 0) {
+			ret = -EIO;
 			ft260_i2c_reset(hdev);
-			return -EIO;
+			goto ft260_i2c_read_exit;
 		}
 
 		len -= rd_len;
@@ -518,7 +522,9 @@ static int ft260_i2c_read(struct ft260_device *dev, u8 addr, u8 *data,
 
 	} while (len > 0);
 
-	return 0;
+ft260_i2c_read_exit:
+	dev->read_buf = NULL;
+	return ret;
 }
 
 /*
@@ -1036,6 +1042,13 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 		ft260_dbg("i2c resp: rep %#02x len %d\n", xfer->report,
 			  xfer->length);
 
+		if ((dev->read_buf == NULL) ||
+		    (xfer->length > dev->read_len - dev->read_idx)) {
+			hid_err(hdev, "unexpected report %#02x, length %d\n",
+				xfer->report, xfer->length);
+			return -1;
+		}
+
 		memcpy(&dev->read_buf[dev->read_idx], &xfer->data,
 		       xfer->length);
 		dev->read_idx += xfer->length;
@@ -1044,10 +1057,9 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 			complete(&dev->wait);
 
 	} else {
-		hid_err(hdev, "unknown report: %#02x\n", xfer->report);
-		return 0;
+		hid_err(hdev, "unhandled report %#02x\n", xfer->report);
 	}
-	return 1;
+	return 0;
 }
 
 static struct hid_driver ft260_driver = {