usb: Allow configuration 5 after verifying it is actualy usable

VMware on macOS somehow exposes a bad configuration 5 for iDevices. Trying
to use it breaks things and can end up in a kernel panic on the device. The
code change introduced with this commit tries its best to make sure the USB
configuration 5 is not 'bad' before switching to it, and otherwise falling
back to configuration 4.

1 files changed, 25 insertions, 1 deletions

diff --git a/src/usb.c b/src/usb.c
index 39917ef..571a822 100644
--- a/src/usb.c
+++ b/src/usb.c
@@ -395,7 +395,31 @@ static int usb_device_add(libusb_device* dev)
 
         int desired_config = devdesc.bNumConfigurations;
         if (desired_config > 4) {
-                desired_config = 4;
+                if (desired_config > 5) {
+                        usbmuxd_log(LL_ERROR, "Device %d-%d has more than 5 configurations, but usbmuxd doesn't support that. Choosing configuration 5 instead.", bus, address);
+                        desired_config = 5;
+                }
+                /* verify if the configuration 5 is actually usable */
+                do {
+                        struct libusb_config_descriptor *config;
+                        const struct libusb_interface_descriptor *intf;
+                        if (libusb_get_config_descriptor_by_value(dev, 5, &config) != 0) {
+                                usbmuxd_log(LL_WARNING, "Device %d-%d: Failed to get config descriptor for configuration 5, choosing configuration 4 instead.", bus, address);
+                                desired_config = 4;
+                                break;
+                        }
+                        if (config->bNumInterfaces != 3) {
+                                usbmuxd_log(LL_WARNING, "Device %d-%d: Ignoring possibly bad configuration 5, choosing configuration 4 instead.", bus, address);
+                                desired_config = 4;
+                                break;
+                        }
+                        intf = &config->interface[2].altsetting[0];
+                        if (intf->bInterfaceClass != 0xFF || intf->bInterfaceSubClass != 0x2A || intf->bInterfaceProtocol != 0xFF) {
+                                usbmuxd_log(LL_WARNING, "Device %d-%d: Ignoring possibly bad configuration 5, choosing configuration 4 instead.", bus, address);
+                                desired_config = 4;
+                                break;
+                        }
+                } while (0);
         }
         int current_config = 0;
         if((res = libusb_get_configuration(handle, &current_config)) != 0) {