Prevent String.to_atom/1 calls

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## v0.4.4 (TBA)
+
+* [`PowAssent.Plug`] Now uses `String.to_existing_atom/1` in `PowAssent.Plug.providers_for_current_user/1`
+* [`PowAssent.Plug`] Fixed security issue by removing `String.to_atom/1` for user provided binary in `PowAssent.Plug.authorize_url/3` and `PowAssent.Plug.callback/4`
+* [`PowAssent.Config`] `PowAssent.Config.get_provider_config/2` now accepts binary provider
+
 ## v0.4.3 (2019-11-20)
 
 * Removed `:phoenix_html` dependency requirement

lib/pow_assent/config.ex

@@ -50,15 +50,27 @@ defmodule PowAssent.Config do
   @doc """
   Gets the provider configuration from the provided configuration.
   """
-  @spec get_provider_config(t(), atom()) :: t() | no_return
+  @spec get_provider_config(t(), atom() | binary()) :: t() | no_return
   def get_provider_config(config, provider) do
     config
     |> get_providers()
-    |> get(provider)
+    |> get_for_provider(provider)
     |> Kernel.||(raise_error("No provider configuration available for #{provider}."))
     |> add_global_config(config)
   end
 
+  defp get_for_provider(providers_config, provider) when is_atom(provider) do
+    get(providers_config, provider)
+  end
+  defp get_for_provider(providers_config, provider) when is_binary(provider) do
+    Enum.find_value(providers_config, fn {key, value} ->
+      case Atom.to_string(key) do
+        ^provider -> value
+        _any      -> false
+      end
+    end)
+  end
+
   defp add_global_config(provider_config, config) do
     [
       :http_adapter,

lib/pow_assent/plug.ex

@@ -197,7 +197,7 @@ defmodule PowAssent.Plug do
     conn
     |> Pow.Plug.current_user()
     |> get_all_providers_for_user(config)
-    |> Enum.map(&String.to_atom(&1.provider))
+    |> Enum.map(&String.to_existing_atom(&1.provider))
   end
 
   defp get_all_providers_for_user(nil, _config), do: []
@@ -232,7 +232,6 @@ defmodule PowAssent.Plug do
     |> get_provider_config(provider, redirect_uri)
   end
   defp get_provider_config(config, provider, redirect_uri) do
-    provider        = String.to_atom(provider)
     config          = Config.get_provider_config(config, provider)
     strategy        = config[:strategy]
     provider_config =

test/pow_assent/config_test.exs

@@ -28,4 +28,14 @@ defmodule PowAssent.ConfigTest do
     assert Config.get_provider_config([http_adapter: HTTPAdapater, json_adapter: JSONAdapter, jwt_adapter: JWTAdapter], :provider1) ==
       [http_adapter: HTTPAdapater, json_adapter: JSONAdapter, jwt_adapter: JWTAdapter, a: 1]
   end
+
+  test "get_provider_config/2 with binary provider" do
+    config = [providers: [provider1: [a: 1], provider2: [b: 2]]]
+
+    assert Config.get_provider_config(config, "provider1") == [a: 1]
+
+    assert_raise PowAssent.Config.ConfigError, "No provider configuration available for non_existent.", fn ->
+      refute Config.get_provider_config(config, "non_existent")
+    end
+  end
 end