Allow pinned device certs without a registered CA

Fixes #838

We were previously requiring that the signer CA to be registered even if the
device certificate was already pinned, which was incorrect. This fixes that to
skip the check if we're being presented with a signer CA so that validation of the
device certificate can happen.

If the device cert is pinned, the check will pass. If not, it will go through the
normal validation flow and fail due to an expired, unregistered signer CA anyway

apps/nerves_hub_device/lib/nerves_hub_device/ssl.ex

@@ -43,33 +43,23 @@ defmodule NervesHubDevice.SSL do
   # This can happen if the Signer CA is not included in the request
   # and only the device cert/key is. Or if some other unknown CA
   # was included.
-  def verify_fun(otp_cert, {:bad_cert, :unknown_ca}, state) do
+  def verify_fun(otp_cert, {:bad_cert, err}, state) when err in [:unknown_ca, :cert_expired] do
     aki = Certificate.get_aki(otp_cert)
     ski = Certificate.get_ski(otp_cert)
 
     if aki == ski do
       # Because Signer CAs are required to be registered first, we don't
-      # really care about it coming in here
+      # really care about it coming in here. Likewise, if this is an
+      # unregistered CA, we can just move on so that the device can
+      # still attempt to present it's certificate to check if it has been
+      # pinned or not. Veririfcation will fail there if the device cert
+      # and it's signer CA is unknown
       {:valid, state}
     else
       do_verify(otp_cert, state)
     end
   end
 
-  def verify_fun(otp_cert, {:bad_cert, :cert_expired}, state) do
-    # If the CA is expired but already registered then we should
-    # still allow it in the request. If this is a device attempting
-    # to register, the validation will fail later on due to the expired.
-    #
-    # If this is an existing device presenting an expired cert in the chain
-    # then allowing the expired CA cert prevents the request from being
-    # terminating prematurely
-    case check_known_ca(otp_cert) do
-      {:ok, _ca} -> {:valid, state}
-      _unknown_ca -> :cert_expired
-    end
-  end
-
   def verify_fun(_certificate, {:extension, _}, state) do
     {:valid, state}
   end

apps/nerves_hub_device/test/nerves_hub_device_web/channels/websocket_test.exs

@@ -118,6 +118,70 @@ defmodule NervesHubDeviceWeb.WebsocketTest do
       refute_receive({"presence_diff", _})
       Socket.stop(socket)
     end
+
+    test "already registered expired certificate without signer CA can connect", %{user: user} do
+      org = Fixtures.org_fixture(user, %{name: "custom_ca_test"})
+      {device, _firmware} = device_fixture(user, %{identifier: @valid_serial}, org)
+
+      ca_key = X509.PrivateKey.new_ec(:secp256r1)
+      ca = X509.Certificate.self_signed(ca_key, "CN=#{org.name}", template: :root_ca)
+      serial = NervesHubWebCore.Certificate.get_serial_number(ca)
+
+      # Ensure this signer CA does not exist in the DB
+      assert {:error, :not_found} = Devices.get_ca_certificate_by_serial(serial)
+
+      key = X509.PrivateKey.new_ec(:secp256r1)
+
+      not_before = Timex.now() |> Timex.shift(days: -2)
+      not_after = Timex.now() |> Timex.shift(days: -1)
+
+      cert =
+        key
+        |> X509.PublicKey.derive()
+        |> X509.Certificate.new("CN=#{device.identifier}", ca, ca_key,
+          validity: X509.Certificate.Validity.new(not_before, not_after)
+        )
+
+      # Verify our cert is indeed expired
+      assert {:error, {:bad_cert, :cert_expired}} =
+               :public_key.pkix_path_validation(
+                 X509.Certificate.to_der(ca),
+                 [X509.Certificate.to_der(cert)],
+                 []
+               )
+
+      _ = Fixtures.device_certificate_fixture(device, cert)
+
+      nerves_hub_ca_cert =
+        Path.expand("../../test/fixtures/ssl/ca.pem")
+        |> File.read!()
+        |> X509.Certificate.from_pem!()
+
+      opts = [
+        url: "wss://127.0.0.1:#{@device_port}/socket/websocket",
+        serializer: Jason,
+        ssl_verify: :verify_peer,
+        transport_opts: [
+          socket_opts: [
+            cert: X509.Certificate.to_der(cert),
+            key: {:ECPrivateKey, X509.PrivateKey.to_der(key)},
+            cacerts: [X509.Certificate.to_der(ca), X509.Certificate.to_der(nerves_hub_ca_cert)],
+            server_name_indication: 'device.nerves-hub.org'
+          ]
+        ]
+      ]
+
+      {:ok, socket} = Socket.start_link(opts)
+      wait_for_socket(socket)
+      {:ok, _reply, _channel} = Channel.join(socket, "device")
+
+      device =
+        NervesHubWebCore.Repo.get(Device, device.id)
+        |> NervesHubWebCore.Repo.preload(:org)
+
+      assert Presence.device_status(device) == "online"
+      refute_receive({"presence_diff", _})
+    end
   end
 
   describe "firmware update" do