From 85100c0aaee728a3c254d4feed6ed5d8035bbd4a Mon Sep 17 00:00:00 2001
From: Emmanuel Dreyfus <manu@netbsd.org>
Date: Mon, 12 Nov 2018 15:26:43 +0000
Subject: [PATCH] Prefer hardcoded PN533 descriptors to the real ones

PN533 easily corrupts its USB descriptors. We know that and we
already try to detect and even repair them.

However there are situations where lower software layers get
confused before libnfc can help. On Windows, libusb may set
dev->config to NULL, but we can also have a non NULL dev->config
referencing corrupted data.

In order to get more robust, let us replace the Windows libusb
specific (dev->config == NULL) test by an inconditionnal use of
hardcoded descriptors when they are available.
---
 libnfc/drivers/pn53x_usb.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/libnfc/drivers/pn53x_usb.c b/libnfc/drivers/pn53x_usb.c
index 807e98e..d001408 100644
--- a/libnfc/drivers/pn53x_usb.c
+++ b/libnfc/drivers/pn53x_usb.c
@@ -236,7 +236,7 @@ pn53x_usb_get_device_model(uint16_t vendor_id, uint16_t product_id)
   return UNKNOWN;
 }
 
-static void
+static bool
 pn53x_usb_get_end_points_default(struct usb_device *dev, struct pn53x_usb_data *data)
 {
   for (size_t n = 0; n < sizeof(pn53x_usb_supported_devices) / sizeof(struct pn53x_usb_supported_device); n++) {
@@ -246,13 +246,13 @@ pn53x_usb_get_end_points_default(struct usb_device *dev, struct pn53x_usb_data *
         data->uiEndPointIn = pn53x_usb_supported_devices[n].uiEndPointIn;
         data->uiEndPointOut = pn53x_usb_supported_devices[n].uiEndPointOut;
         data->uiMaxPacketSize = pn53x_usb_supported_devices[n].uiMaxPacketSize;
-      }
 
-      return;
+        return true;
+      }
     }
   }
 
-  return;
+  return false;
 }
 
 int  pn53x_usb_ack(nfc_device *pnd);
@@ -305,13 +305,12 @@ pn53x_usb_scan(const nfc_context *context, nfc_connstring connstrings[], const s
         if ((pn53x_usb_supported_devices[n].vendor_id == dev->descriptor.idVendor) &&
             (pn53x_usb_supported_devices[n].product_id == dev->descriptor.idProduct)) {
           // Make sure there are 2 endpoints available
-          // with libusb-win32 we got some null pointers so be robust before looking at endpoints:
-          if (dev->config == NULL) {
-            // We tolerate null config if we have defaults
-            if (pn53x_usb_supported_devices[n].uiMaxPacketSize == 0)
-              // Nope, we maybe want the next one, let's try to find another
-              continue;
-          } else {
+          // libusb-win32 may return a NULL dev->config,
+          // or the descriptoes may be corrupted, hence
+          // let us assume we will use hardcoded defaults
+          // from n53x_usb_supported_devices if available.
+          // otherwise get data from the descriptors.
+          if (pn53x_usb_supported_devices[n].uiMaxPacketSize == 0) {
             if (dev->config->interface == NULL || dev->config->interface->altsetting == NULL) {
               // Nope, we maybe want the next one, let's try to find another
               continue;
@@ -422,11 +421,9 @@ pn53x_usb_open(const nfc_context *context, const nfc_connstring connstring)
       // Open the USB device
       if ((data.pudh = usb_open(dev)) == NULL)
         continue;
-      // Retrieve end points, using default if dev->config is broken
-      if (dev->config == NULL) {
-        pn53x_usb_get_end_points_default(dev, &data);
-        data.possibly_corrupted_usbdesc = true;
-      } else {
+      // Retrieve end points, using hardcoded defaults if available
+      // or using the descriptors otherwise.
+      if (pn53x_usb_get_end_points_default(dev, &data) == false) {
         pn53x_usb_get_end_points(dev, &data);
       }
       // Set configuration