Sanity check fetched user data

In order to properly process incoming notes we need
to be able to map the key id back to an actor.
Also, check collections actually belong to the same server.

Key ids of Hubzilla and Bridgy samples were updated to what
modern versions of those output. If anything still uses the
old format, we would not be able to verify their posts anyway.

lib/pleroma/object/containment.ex

@@ -101,4 +101,12 @@ def contain_child(%{"object" => %{"id" => id, "attributedTo" => _} = object}),
     do: contain_origin(id, object)
 
   def contain_child(_), do: :ok
+
+  @doc "Checks whether two URIs belong to the same domain"
+  def same_origin(id1, id2) do
+    uri1 = URI.parse(id1)
+    uri2 = URI.parse(id2)
+
+    compare_uris(uri1, uri2)
+  end
 end

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -22,6 +22,7 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
   alias Pleroma.Upload
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.MRF
+  alias Pleroma.Web.ActivityPub.ObjectValidators.UserValidator
   alias Pleroma.Web.ActivityPub.Transmogrifier
   alias Pleroma.Web.Streamer
   alias Pleroma.Web.WebFinger
@@ -1722,6 +1723,7 @@ def user_data_from_user_object(data, additional \\ []) do
 
   def fetch_and_prepare_user_from_ap_id(ap_id, additional \\ []) do
     with {:ok, data} <- Fetcher.fetch_and_contain_remote_object_from_id(ap_id),
+         {:valid, {:ok, _, _}} <- {:valid, UserValidator.validate(data, [])},
          {:ok, data} <- user_data_from_user_object(data, additional) do
       {:ok, maybe_update_follow_information(data)}
     else
@@ -1734,6 +1736,10 @@ def fetch_and_prepare_user_from_ap_id(ap_id, additional \\ []) do
         Logger.debug("Rejected user #{ap_id}: #{inspect(reason)}")
         {:error, e}
 
+      {:valid, reason} ->
+        Logger.debug("Data is not a valid user #{ap_id}: #{inspect(reason)}")
+        {:error, "Not a user"}
+
       {:error, e} ->
         Logger.error("Could not decode user at fetch #{ap_id}, #{inspect(e)}")
         {:error, e}

lib/pleroma/web/activity_pub/object_validators/user_validator.ex

@@ -0,0 +1,92 @@
+# Akkoma: Magically expressive social media
+# Copyright © 2024 Akkoma Authors <https://akkoma.dev/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.ObjectValidators.UserValidator do
+  @moduledoc """
+  Checks whether ActivityPub data represents a valid user
+
+  Users don't go through the same ingest pipeline like activities or other objects.
+  To ensure this can only match a user and no users match in the other pipeline,
+  this is a separate from the generic ObjectValidator.
+  """
+
+  @behaviour Pleroma.Web.ActivityPub.ObjectValidator.Validating
+
+  alias Pleroma.Object.Containment
+  alias Pleroma.Signature
+
+  @impl true
+  def validate(object, meta)
+
+  def validate(%{"type" => type, "id" => _id} = data, meta)
+      when type in ["Person", "Organization", "Group", "Application"] do
+    with :ok <- validate_pubkey(data),
+         :ok <- validate_inbox(data),
+         :ok <- contain_collection_origin(data) do
+      {:ok, data, meta}
+    else
+      {:error, e} -> {:error, e}
+      e -> {:error, e}
+    end
+  end
+
+  def validate(_, _), do: {:error, "Not a user object"}
+
+  defp mabye_validate_owner(nil, _actor), do: :ok
+  defp mabye_validate_owner(actor, actor), do: :ok
+  defp mabye_validate_owner(_owner, _actor), do: :error
+
+  defp validate_pubkey(
+         %{"id" => id, "publicKey" => %{"id" => pk_id, "publicKeyPem" => _key}} = data
+       )
+       when id != nil do
+    with {_, {:ok, kactor}} <- {:key, Signature.key_id_to_actor_id(pk_id)},
+         true <- id == kactor,
+         :ok <- mabye_validate_owner(Map.get(data, "owner"), id) do
+      :ok
+    else
+      {:key, _} ->
+        {:error, "Unable to determine actor id from key id"}
+
+      false ->
+        {:error, "Key id does not relate to user id"}
+
+      _ ->
+        {:error, "Actor does not own its public key"}
+    end
+  end
+
+  # pubkey is optional atm
+  defp validate_pubkey(_data), do: :ok
+
+  defp validate_inbox(%{"id" => id, "inbox" => inbox}) do
+    case Containment.same_origin(id, inbox) do
+      :ok -> :ok
+      :error -> {:error, "Inbox on different doamin"}
+    end
+  end
+
+  defp validate_inbox(_), do: {:error, "No inbox"}
+
+  defp check_field_value(%{"id" => id} = _data, value) do
+    Containment.same_origin(id, value)
+  end
+
+  defp maybe_check_field(data, field) do
+    with val when val != nil <- data[field],
+         :ok <- check_field_value(data, val) do
+      :ok
+    else
+      nil -> :ok
+      _ -> {:error, "#{field} on different domain"}
+    end
+  end
+
+  defp contain_collection_origin(data) do
+    Enum.reduce(["followers", "following", "featured"], :ok, fn
+      field, :ok -> maybe_check_field(data, field)
+      _, error -> error
+    end)
+  end
+end

test/fixtures/bridgy/actor.json

@@ -70,7 +70,7 @@
   "preferredUsername": "jk.nipponalba.scot",
   "summary": "",
   "publicKey": {
-    "id": "jk.nipponalba.scot",
+    "id": "https://fed.brid.gy/jk.nipponalba.scot#key",
     "publicKeyPem": "-----BEGIN PUBLIC KEY-----\nMIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDdarxwzxnNbJ2hneWOYHkYJowk\npyigQtxlUd0VjgSQHwxU9kWqfbrHBVADyTtcqi/4dAzQd3UnCI1TPNnn4LPZY9PW\noiWd3Zl1/EfLFxO7LU9GS7fcSLQkyj5JNhSlN3I8QPudZbybrgRDVZYooDe1D+52\n5KLGqC2ajrIVOiDRTQIDAQAB\n-----END PUBLIC KEY-----"
   },
   "inbox": "https://fed.brid.gy/jk.nipponalba.scot/inbox",

test/fixtures/tesla_mock/https___osada.macgirvin.com_channel_mike.json

@@ -37,7 +37,7 @@
         "sharedInbox": "https://osada.macgirvin.com/inbox"
     },
     "publicKey": {
-        "id": "https://osada.macgirvin.com/channel/mike/public_key_pem",
+        "id": "https://osada.macgirvin.com/channel/mike",
         "owner": "https://osada.macgirvin.com/channel/mike",
         "publicKeyPem": "-----BEGIN PUBLIC KEY-----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\nnJhQF8udPLcXLaj6GW75JacCAwEAAQ==\n-----END PUBLIC KEY-----\n"
     },

test/fixtures/tesla_mock/kaniini@hubzilla.example.org.json

@@ -1 +1 @@
-{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1","https://hubzilla.example.org/apschema/v1.2"],"type":"Person","id":"https://hubzilla.example.org/channel/kaniini","preferredUsername":"kaniini","name":"kaniini","icon":{"type":"Image","mediaType":"image/jpeg","url":"https://hubzilla.example.org/photo/profile/l/281","height":300,"width":300},"url":{"type":"Link","mediaType":"text/html","href":"https://hubzilla.example.org/channel/kaniini"},"inbox":"https://hubzilla.example.org/inbox/kaniini","outbox":"https://hubzilla.example.org/outbox/kaniini","followers":"https://hubzilla.example.org/followers/kaniini","following":"https://hubzilla.example.org/following/kaniini","endpoints":{"sharedInbox":"https://hubzilla.example.org/inbox"},"publicKey":{"id":"https://hubzilla.example.org/channel/kaniini/public_key_pem","owner":"https://hubzilla.example.org/channel/kaniini","publicKeyPem":"-----BEGIN PUBLIC KEY-----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\nDropXWaOfy7Lac+G4qlfSgsCAwEAAQ==\n-----END PUBLIC KEY-----\n"},"nomadicLocations":[{"id":"https://hubzilla.example.org/locs/kaniini","type":"nomadicLocation","locationAddress":"acct:kaniini@hubzilla.example.org","locationPrimary":true,"locationDeleted":false}],"signature":{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1"],"type":"RsaSignature2017","nonce":"6b981a2f3bdcffc20252e3b131d4a4569fd2dea9fac543e5196136302f492694","creator":"https://hubzilla.example.org/channel/kaniini/public_key_pem","created":"2018-05-19T08:19:13Z","signatureValue":"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"}}
+{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1","https://hubzilla.example.org/apschema/v1.2"],"type":"Person","id":"https://hubzilla.example.org/channel/kaniini","preferredUsername":"kaniini","name":"kaniini","icon":{"type":"Image","mediaType":"image/jpeg","url":"https://hubzilla.example.org/photo/profile/l/281","height":300,"width":300},"url":{"type":"Link","mediaType":"text/html","href":"https://hubzilla.example.org/channel/kaniini"},"inbox":"https://hubzilla.example.org/inbox/kaniini","outbox":"https://hubzilla.example.org/outbox/kaniini","followers":"https://hubzilla.example.org/followers/kaniini","following":"https://hubzilla.example.org/following/kaniini","endpoints":{"sharedInbox":"https://hubzilla.example.org/inbox"},"publicKey":{"id":"https://hubzilla.example.org/channel/kaniini","owner":"https://hubzilla.example.org/channel/kaniini","publicKeyPem":"-----BEGIN PUBLIC KEY-----\nMIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAvXCDkQPw+1N8B2CUd5s2\nbYvjHt+t7soMNfUiRy0qGbgW46S45k5lCq1KpbFIX3sgGZ4OWjnXVbvjCJi4kl5M\nfm5DBXzpuu05AmjVl8hqk4GejajiE/1Nq0uWHPiOSFWispUjCzzCu65V+IsiE5JU\nvcL6WEf/pYNRq7gYqyT693F7+cO5/rVv9OScx5UOxbIuU1VXYhdHCqAMDJWadC89\nhePrcD3HOQKl06W2tDxHcWk6QjrdsUQGbNOgK/QIN9gSxA+rCFEvH5O0HAhI0aXq\ncOB+vysJUFLeQOAqmAKvKS5V6RqE1GqqT0pDWHack4EmQi0gkgVzo+45xoP6wfDl\nWwG88w21LNxGvGHuN4I8mg6cEoApqKQBSOj086UtfDfSlPC1B+PRD2phE5etucHd\nF/RIWN3SxVzU9BKIiaDm2gwOpvI8QuorQb6HDtZFO5NsSN3PnMnSywPe7kXl/469\nuQRYXrseqyOVIi6WjhvXkyWVKVE5CBz+S8wXHfKph+9YOyUcJeAVMijp9wrjBlMc\noSzOGu79oM7tpMSq/Xo6ePJ/glNOwZR+OKrg92Qp9BGTKDNwGrxuxP/9KwWtGLNf\nOMTtIkxtC3ubhxL3lBxOd7l+Bmum0UJV2f8ogkCgvTpIz05jMoyU8qWl6kkWNQlY\nDropXWaOfy7Lac+G4qlfSgsCAwEAAQ==\n-----END PUBLIC KEY-----\n"},"nomadicLocations":[{"id":"https://hubzilla.example.org/locs/kaniini","type":"nomadicLocation","locationAddress":"acct:kaniini@hubzilla.example.org","locationPrimary":true,"locationDeleted":false}],"signature":{"@context":["https://www.w3.org/ns/activitystreams","https://w3id.org/security/v1"],"type":"RsaSignature2017","nonce":"6b981a2f3bdcffc20252e3b131d4a4569fd2dea9fac543e5196136302f492694","creator":"https://hubzilla.example.org/channel","created":"2018-05-19T08:19:13Z","signatureValue":"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"}}