[RFC]How else could a malicious device sabotage endpoints for usbnet

[Oliver Neukum <oneukum@xxxxxxxx>]

Hi,

I have checked for type, direction and number of endpoints.
But I keep thinking that I have overlooked a way to make broken
endpoint descriptors. Any suggestions?

    Regards
        Oliver

>From 853e421630f82fb3b7005ad0b294c091a064ac39 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxxx>
Date: Thu, 18 Nov 2021 18:15:03 +0100
Subject: [PATCH] usbnet: sanity check for endpoint types

A malicious device can pretend to be a device with a known
configuration of endpoints yet present endpoints of the wrong type
or too few or none at all.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
---
 drivers/net/usb/usbnet.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index 9a6450f796dc..b1f93810a6f3 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -91,6 +91,31 @@ static const char * const usbnet_event_names[] = {
 	[EVENT_NO_IP_ALIGN]	   = "EVENT_NO_IP_ALIGN",
 };
 
+bool usbnet_validate_endpoints(struct usbnet *dev, struct usb_interface *intf, const struct driver_info *info)
+{
+	struct usb_host_interface *alt = intf->cur_altsetting;
+	struct usb_host_endpoint *e;
+	int num_endpoints = alt->desc.bNumEndpoints;
+
+	if (info->in > num_endpoints)
+		return false;
+	e = alt->endpoint + info->in;
+	if (!e)
+		return false;
+	if (!usb_endpoint_is_bulk_in(&e->desc))
+		return false;
+
+	if (info->out > num_endpoints)
+		return false;
+	e = alt->endpoint + info->out;
+	if (!e)
+		return false;
+	if (!usb_endpoint_is_bulk_out(&e->desc))
+		return false;
+
+	return true;
+}
+
 /* handles CDC Ethernet and many other network "bulk data" interfaces */
 int usbnet_get_endpoints(struct usbnet *dev, struct usb_interface *intf)
 {
@@ -1772,6 +1797,8 @@ usbnet_probe (struct usb_interface *udev, const struct usb_device_id *prod)
 	} else if (!info->in || !info->out)
 		status = usbnet_get_endpoints (dev, udev);
 	else {
+		if (!usbnet_validate_endpoints(dev, udev, info))
+			goto out3;
 		dev->in = usb_rcvbulkpipe (xdev, info->in);
 		dev->out = usb_sndbulkpipe (xdev, info->out);
 		if (!(info->flags & FLAG_NO_SETINT))
-- 
2.26.2