Fix WebFinger for split-domain set ups

Signed-off-by: nicole mikołajczyk <git@mkljczk.pl>

lib/pleroma/web/web_finger.ex

@@ -194,8 +194,8 @@ defmodule Pleroma.Web.WebFinger do
 
   defp get_address_from_domain(_, _), do: {:error, :webfinger_no_domain}
 
-  @spec finger(String.t()) :: {:ok, map()} | {:error, any()}
-  def finger(account) do
+  @spec finger(String.t(), boolean()) :: {:ok, map()} | {:error, any()}
+  def finger(account, follow_redirects \\ true) do
     account = String.trim_leading(account, "@")
 
     domain =
@@ -229,8 +229,15 @@ defmodule Pleroma.Web.WebFinger do
           {:error, {:content_type, nil}}
       end
       |> case do
-        {:ok, data} -> validate_webfinger(address, data)
-        error -> error
+        {:ok, data} ->
+          if follow_redirects do
+            validate_webfinger(address, data)
+          else
+            {:ok, data}
+          end
+
+        error ->
+          error
       end
     else
       error ->
@@ -241,10 +248,8 @@ defmodule Pleroma.Web.WebFinger do
 
   defp validate_webfinger(request_url, %{"subject" => "acct:" <> acct = subject} = data) do
     with [_name, acct_host] <- String.split(acct, "@"),
-         {_, url} <- {:address, get_address_from_domain(acct_host, subject)},
-         %URI{host: request_host} <- URI.parse(request_url),
-         %URI{host: acct_host} <- URI.parse(url),
-         {_, true} <- {:hosts_match, acct_host == request_host} do
+         {_, resolved_url} <- {:address, get_address_from_domain(acct_host, subject)},
+         {_, true} <- {:url_match, resolved_webfinger_matches?(request_url, resolved_url, data)} do
       {:ok, data}
     else
       _ -> {:error, {:webfinger_invalid, request_url, data}}
@@ -252,4 +257,17 @@ defmodule Pleroma.Web.WebFinger do
   end
 
   defp validate_webfinger(url, data), do: {:error, {:webfinger_invalid, url, data}}
+
+  defp resolved_webfinger_matches?(request_url, resolved_url, _data)
+       when request_url == resolved_url do
+    true
+  end
+
+  defp resolved_webfinger_matches?(_request_url, _resolved_url, %{"subject" => "acct:" <> acct}) do
+    with {:ok, %{"subject" => "acct:" <> new_acct}} <- finger(acct, false) do
+      acct == new_acct
+    else
+      _ -> false
+    end
+  end
 end

test/pleroma/web/web_finger_test.exs

@@ -93,7 +93,7 @@ defmodule Pleroma.Web.WebFingerTest do
       {:ok, _data} = WebFinger.finger(user)
     end
 
-    test "it work for AP-only user" do
+    test "it works for AP-only user" do
       user = "kpherox@mstdn.jp"
 
       {:ok, data} = WebFinger.finger(user)
@@ -224,24 +224,36 @@ defmodule Pleroma.Web.WebFingerTest do
              status: 200,
              body: File.read!("test/fixtures/tesla_mock/gleasonator.com_host_meta")
            }}
+
+        %{url: "https://whitehouse.gov/.well-known/webfinger?resource=acct:trump@whitehouse.gov"} ->
+          {:ok, %Tesla.Env{status: 404}}
       end)
 
       {:error, _data} = WebFinger.finger("alex@gleasonator.com")
     end
-  end
 
-  test "prevents forgeries" do
-    Tesla.Mock.mock(fn
-      %{url: "https://fba.ryona.agency/.well-known/webfinger?resource=acct:graf@fba.ryona.agency"} ->
-        fake_webfinger =
-          File.read!("test/fixtures/webfinger/graf-imposter-webfinger.json") |> Jason.decode!()
+    test "prevents forgeries" do
+      Tesla.Mock.mock(fn
+        %{url: "https://fba.ryona.agency/.well-known/webfinger?resource=acct:graf@fba.ryona.agency"} ->
+          fake_webfinger =
+            File.read!("test/fixtures/webfinger/graf-imposter-webfinger.json") |> Jason.decode!()
 
-        Tesla.Mock.json(fake_webfinger)
+          Tesla.Mock.json(fake_webfinger)
 
-      %{url: "https://fba.ryona.agency/.well-known/host-meta"} ->
-        {:ok, %Tesla.Env{status: 404}}
-    end)
+        %{url: url}
+        when url in [
+                "https://poa.st/.well-known/webfinger?resource=acct:graf@poa.st",
+                "https://fba.ryona.agency/.well-known/host-meta"
+              ] ->
+          {:ok, %Tesla.Env{status: 404}}
+      end)
 
-    assert {:error, _} = WebFinger.finger("graf@fba.ryona.agency")
+      assert {:error, _} = WebFinger.finger("graf@fba.ryona.agency")
+    end
+
+    test "works for correctly set up split-domain instances" do
+      {:ok, _data} = WebFinger.finger("a@mastodon.example")
+      {:ok, _data} = WebFinger.finger("a@sub.mastodon.example")
+    end
   end
 end

test/support/http_request_mock.ex

@@ -1229,7 +1229,8 @@ defmodule HttpRequestMock do
     {:ok, %Tesla.Env{status: 404, body: ""}}
   end
 
-  def get("https://mstdn.jp/.well-known/webfinger?resource=acct:kpherox@mstdn.jp", _, _, _) do
+  def get("https://mstdn.jp/.well-known/webfinger?resource=acct:" <> acct, _, _, _)
+      when acct in ["kpherox@mstdn.jp", "kPherox@mstdn.jp"] do
     {:ok,
      %Tesla.Env{
        status: 200,