staging: gigaset: fix general protection fault on probe

Fix a general protection fault when accessing the endpoint descriptors
which could be triggered by a malicious device due to missing sanity
checks on the number of endpoints.

Reported-by: syzbot+35b1c403a14f5c89eba7@syzkaller.appspotmail.com
Fixes: 07dc1f9 ("[PATCH] isdn4linux: Siemens Gigaset drivers - M105 USB DECT adapter")
Cc: stable <stable@vger.kernel.org>     # 2.6.17
Cc: Hansjoerg Lipp <hjlipp@web.de>
Cc: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20191202085610.12719-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/isdn/gigaset/usb-gigaset.c

@@ -685,6 +685,11 @@ static int gigaset_probe(struct usb_interface *interface,
 		return -ENODEV;
 	}
 
+	if (hostif->desc.bNumEndpoints < 2) {
+		dev_err(&interface->dev, "missing endpoints\n");
+		return -ENODEV;
+	}
+
 	dev_info(&udev->dev, "%s: Device matched ... !\n", __func__);
 
 	/* allocate memory for our device state and initialize it */