Add back media proxy for resources pictures

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/web/controllers/media_proxy_controller.ex

@@ -0,0 +1,33 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Mobilizon.Web.MediaProxyController do
+  use Mobilizon.Web, :controller
+
+  alias Mobilizon.Config
+  alias Mobilizon.Web.{MediaProxy, ReverseProxy}
+  alias Plug.Conn
+
+  # sobelow_skip ["XSS.SendResp"]
+  def remote(conn, %{"sig" => sig64, "url" => url64}) do
+    with {_, true} <- {:enabled, MediaProxy.enabled?()},
+         {:ok, url} <- MediaProxy.decode_url(sig64, url64),
+         :ok <- MediaProxy.verify_request_path_and_url(conn, url) do
+      ReverseProxy.call(conn, url, media_proxy_opts())
+    else
+      {:enabled, false} ->
+        send_resp(conn, 404, Conn.Status.reason_phrase(404))
+
+      {:error, :invalid_signature} ->
+        send_resp(conn, 403, Conn.Status.reason_phrase(403))
+
+      {:wrong_filename, filename} ->
+        redirect(conn, external: MediaProxy.build_url(sig64, url64, filename))
+    end
+  end
+
+  defp media_proxy_opts do
+    Config.get([:media_proxy, :proxy_opts], [])
+  end
+end

lib/web/media_proxy.ex

@@ -0,0 +1,115 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Mobilizon.Web.MediaProxy do
+  @moduledoc """
+  Module to proxify remote media
+  """
+  alias Mobilizon.Config
+  alias Mobilizon.Web
+
+  @base64_opts [padding: false]
+
+  def url(url) when is_nil(url) or url == "", do: nil
+  def url("/" <> _ = url), do: url
+
+  def url(url) do
+    if enabled?() and url_proxiable?(url) do
+      encode_url(url)
+    else
+      url
+    end
+  end
+
+  @spec url_proxiable?(String.t()) :: boolean()
+  def url_proxiable?(url) do
+    not local?(url)
+  end
+
+  def enabled?, do: Config.get([:media_proxy, :enabled], false)
+
+  # Note: media proxy must be enabled for media preview proxy in order to load all
+  #   non-local non-whitelisted URLs through it and be sure that body size constraint is preserved.
+  def preview_enabled?, do: enabled?() and !!Config.get([:media_preview_proxy, :enabled])
+
+  def local?(url), do: String.starts_with?(url, Web.Endpoint.url())
+
+  defp base64_sig64(url) do
+    base64 = Base.url_encode64(url, @base64_opts)
+
+    sig64 =
+      base64
+      |> signed_url()
+      |> Base.url_encode64(@base64_opts)
+
+    {base64, sig64}
+  end
+
+  def encode_url(url) do
+    {base64, sig64} = base64_sig64(url)
+
+    build_url(sig64, base64, filename(url))
+  end
+
+  def decode_url(sig, url) do
+    with {:ok, sig} <- Base.url_decode64(sig, @base64_opts),
+         signature when signature == sig <- signed_url(url) do
+      {:ok, Base.url_decode64!(url, @base64_opts)}
+    else
+      _ -> {:error, :invalid_signature}
+    end
+  end
+
+  defp signed_url(url) do
+    :crypto.hmac(:sha, Config.get([Web.Endpoint, :secret_key_base]), url)
+  end
+
+  def filename(url_or_path) do
+    if path = URI.parse(url_or_path).path, do: Path.basename(path)
+  end
+
+  def base_url do
+    Web.Endpoint.url()
+  end
+
+  defp proxy_url(path, sig_base64, url_base64, filename) do
+    [
+      base_url(),
+      path,
+      sig_base64,
+      url_base64,
+      filename
+    ]
+    |> Enum.filter(& &1)
+    |> Path.join()
+  end
+
+  def build_url(sig_base64, url_base64, filename \\ nil) do
+    proxy_url("proxy", sig_base64, url_base64, filename)
+  end
+
+  def verify_request_path_and_url(
+        %Plug.Conn{params: %{"filename" => _}, request_path: request_path},
+        url
+      ) do
+    verify_request_path_and_url(request_path, url)
+  end
+
+  def verify_request_path_and_url(request_path, url) when is_binary(request_path) do
+    filename = filename(url)
+
+    if filename && not basename_matches?(request_path, filename) do
+      {:wrong_filename, filename}
+    else
+      :ok
+    end
+  end
+
+  def verify_request_path_and_url(_, _), do: :ok
+
+  defp basename_matches?(path, filename) do
+    basename = Path.basename(path)
+    basename == filename or URI.decode(basename) == filename or URI.encode(basename) == filename
+  end
+end

lib/web/proxy/reverse_proxy.ex

@@ -4,17 +4,22 @@
 # Upstream: https://git.pleroma.social/pleroma/pleroma/blob/develop/lib/pleroma/reverse_proxy.ex
 
 defmodule Mobilizon.Web.ReverseProxy do
-  @keep_req_headers ~w(accept user-agent accept-encoding cache-control
-    if-modified-since if-unmodified-since if-none-match if-range range)
-  @resp_cache_headers ~w(etag date last-modified cache-control)
-  @keep_resp_headers @resp_cache_headers ++ ~w(content-type content-disposition
-    content-encoding content-range accept-ranges vary)
+  @range_headers ~w(range if-range)
+  @keep_req_headers ~w(accept user-agent accept-encoding cache-control if-modified-since) ++
+                      ~w(if-unmodified-since if-none-match) ++ @range_headers
+  @resp_cache_headers ~w(etag date last-modified)
+  @keep_resp_headers @resp_cache_headers ++
+                       ~w(content-length content-type content-disposition content-encoding) ++
+                       ~w(content-range accept-ranges vary)
   @default_cache_control_header "public, max-age=1209600"
   @valid_resp_codes [200, 206, 304]
   @max_read_duration :timer.seconds(30)
   @max_body_length :infinity
   @methods ~w(GET HEAD)
 
+  def max_read_duration_default, do: @max_read_duration
+  def default_cache_control_header, do: @default_cache_control_header
+
   @moduledoc """
   A reverse proxy.
 

lib/web/router.ex

@@ -163,6 +163,11 @@ defmodule Mobilizon.Web.Router do
     post("/auth/:provider/callback", AuthController, :callback)
   end
 
+  scope "/proxy/", Mobilizon.Web do
+    get("/:sig/:url", MediaProxyController, :remote)
+    get("/:sig/:url/:filename", MediaProxyController, :remote)
+  end
+
   if Application.fetch_env!(:mobilizon, :env) in [:dev, :e2e] do
     # If using Phoenix
     forward("/sent_emails", Bamboo.SentEmailViewerPlug)