From 7d94476dd6e46071cf5b8662055a109f9ef904ef Mon Sep 17 00:00:00 2001
From: "Haelwenn (lanodan) Monnier" <contact@hacktivis.me>
Date: Tue, 20 Feb 2024 08:45:48 +0100
Subject: [PATCH 1/2] StealEmojiPolicy: Sanitize shortcodes

Closes: https://git.pleroma.social/pleroma/pleroma/-/issues/3245
---
 .../activity_pub/mrf/steal_emoji_policy.ex    |  2 ++
 .../mrf/steal_emoji_policy_test.exs           | 26 +++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex b/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
index 45b2d4ca7..3e1dc7d43 100644
--- a/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
@@ -34,6 +34,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.StealEmojiPolicy do
           |> Path.basename()
           |> Path.extname()
 
+        shortcode = Path.basename(shortcode)
         file_path = Path.join(emoji_dir_path, shortcode <> (extension || ".png"))
 
         case File.write(file_path, response.body) do
@@ -76,6 +77,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.StealEmojiPolicy do
       new_emojis =
         foreign_emojis
         |> Enum.reject(fn {shortcode, _url} -> shortcode in installed_emoji end)
+        |> Enum.reject(fn {shortcode, _url} -> String.contains?(shortcode, ["/", "\\"]) end)
         |> Enum.filter(fn {shortcode, _url} ->
           reject_emoji? =
             [:mrf_steal_emoji, :rejected_shortcodes]
diff --git a/test/pleroma/web/activity_pub/mrf/steal_emoji_policy_test.exs b/test/pleroma/web/activity_pub/mrf/steal_emoji_policy_test.exs
index b0a7e8993..59baa3a43 100644
--- a/test/pleroma/web/activity_pub/mrf/steal_emoji_policy_test.exs
+++ b/test/pleroma/web/activity_pub/mrf/steal_emoji_policy_test.exs
@@ -60,6 +60,32 @@ defmodule Pleroma.Web.ActivityPub.MRF.StealEmojiPolicyTest do
            |> File.exists?()
   end
 
+  test "rejects invalid shortcodes", %{path: path} do
+    message = %{
+      "type" => "Create",
+      "object" => %{
+        "emoji" => [{"fired/fox", "https://example.org/emoji/firedfox"}],
+        "actor" => "https://example.org/users/admin"
+      }
+    }
+
+    fullpath = Path.join(path, "fired/fox.png")
+
+    Tesla.Mock.mock(fn %{method: :get, url: "https://example.org/emoji/firedfox"} ->
+      %Tesla.Env{status: 200, body: File.read!("test/fixtures/image.jpg")}
+    end)
+
+    clear_config(:mrf_steal_emoji, hosts: ["example.org"], size_limit: 284_468)
+
+    refute "firedfox" in installed()
+    refute File.exists?(path)
+
+    assert {:ok, _message} = StealEmojiPolicy.filter(message)
+
+    refute "fired/fox" in installed()
+    refute File.exists?(fullpath)
+  end
+
   test "reject regex shortcode", %{message: message} do
     refute "firedfox" in installed()
 

From b387f4a1c1ff02573f16de0b25403cf501afc3b4 Mon Sep 17 00:00:00 2001
From: Erin Shepherd <erin.shepherd@e43.eu>
Date: Tue, 20 Feb 2024 11:31:29 +0100
Subject: [PATCH 2/2] Don't steal emoji who's shortcodes have dots or colons in
 their name

Mastodon at the very least seems to prevent the creation of emoji with
dots in their name (and refuses to accept them in federation). It feels
like being cautious in what we accept is reasonable here.

Colons are the emoji separator and so obviously should be blocked.

Perhaps instead of filtering out things like this we should just
do a regex match on `[a-zA-Z0-9_-]`? But that's plausibly a decision
for another day

    Perhaps we should also have a centralised "is this a valid emoji shortcode?"
    function
---
 lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex b/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
index 3e1dc7d43..6c43afa58 100644
--- a/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/steal_emoji_policy.ex
@@ -77,7 +77,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.StealEmojiPolicy do
       new_emojis =
         foreign_emojis
         |> Enum.reject(fn {shortcode, _url} -> shortcode in installed_emoji end)
-        |> Enum.reject(fn {shortcode, _url} -> String.contains?(shortcode, ["/", "\\"]) end)
+        |> Enum.reject(fn {shortcode, _url} -> String.contains?(shortcode, ["/", "\\", ".", ":"]) end)
         |> Enum.filter(fn {shortcode, _url} ->
           reject_emoji? =
             [:mrf_steal_emoji, :rejected_shortcodes]