Always insert Dedupe upload filter

This actually was already intended before to eradict all future
path-traversal-style exploits and to fix issues with some
characters like akkoma#610 in 0b2ec0ccee. However, Dedupe and
AnonymizeFilename got mixed up. The latter only anonymises the name
in Content-Disposition headers GET parameters (with link_name),
_not_ the upload path.

Even without Dedupe, the upload path is prefixed by an UUID,
so it _should_ already be hard to guess for attackers. But now
we actually can be sure no path shenanigangs occur, uploads
reliably work and save some disk space.

While this makes the final path predictable, this prediction is
not exploitable. Insertion of a back-reference to the upload
itself requires pulling off a successfull preimage attack against
SHA-256, which is deemed infeasible for the foreseeable futures.

Dedupe was already included in the default list in config.exs
since 28cfb2c37a, but this will get overridde by whatever the
config generated by the "pleroma.instance gen" task chose.

Upload+delete tests running in parallel using Dedupe might be flaky, but
this was already true before and needs its own commit to fix eventually.

CHANGELOG.md

@@ -11,6 +11,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ## Changed
 - `Pleroma.Upload, :base_url` now MUST be configured explicitly;
   use of the same domain as the instance is **strongly** discouraged
+- The `Dedupe` upload filter is now always active;
+  `AnonymizeFilenames` is again opt-in
 
 ## Fixed
 - Critical security issue allowing Akkoma to be used as a vector for

config/config.exs

@@ -61,7 +61,7 @@
 # Upload configuration
 config :pleroma, Pleroma.Upload,
   uploader: Pleroma.Uploaders.Local,
-  filters: [Pleroma.Upload.Filter.Dedupe],
+  filters: [],
   link_name: false,
   proxy_remote: false,
   filename_display_max_length: 30,

docs/docs/configuration/cheatsheet.md

@@ -597,7 +597,7 @@ the source code is here: [kocaptcha](https://github.com/koto-bank/kocaptcha). Th
 
 * `uploader`: Which one of the [uploaders](#uploaders) to use.
 * `filters`: List of [upload filters](#upload-filters) to use.
-* `link_name`: When enabled Akkoma will add a `name` parameter to the url of the upload, for example `https://instance.tld/media/corndog.png?name=corndog.png`. This is needed to provide the correct filename in Content-Disposition headers when using filters like `Pleroma.Upload.Filter.Dedupe`
+* `link_name`: When enabled Akkoma will add a `name` parameter to the url of the upload, for example `https://instance.tld/media/corndog.png?name=corndog.png`. This is needed to provide the correct filename in Content-Disposition headers
 * `base_url`: The base URL to access a user-uploaded file; MUST be configured explicitly.
   Using a (sub)domain distinct from the instance endpoint is **strongly** recommended.
 * `proxy_remote`: If you're using a remote uploader, Akkoma will proxy media requests instead of redirecting to it.
@@ -639,17 +639,18 @@ config :ex_aws, :s3,
 
 ### Upload filters
 
-#### Pleroma.Upload.Filter.AnonymizeFilename
-
-This filter replaces the filename (not the path) of an upload. For complete obfuscation, add
-`Pleroma.Upload.Filter.Dedupe` before AnonymizeFilename.
-
-* `text`: Text to replace filenames in links. If empty, `{random}.extension` will be used. You can get the original filename extension by using `{extension}`, for example `custom-file-name.{extension}`.
-
 #### Pleroma.Upload.Filter.Dedupe
 
+**Always** active; cannot be turned off.
+Renames files to their hash and prevents duplicate files filling up the disk.
 No specific configuration.
 
+#### Pleroma.Upload.Filter.AnonymizeFilename
+
+This filter replaces the declared filename (not the path) of an upload.
+
+* `text`: Text to replace filenames in links. If empty, `{random}.extension` will be used. You can get the original filename extension by using `{extension}`, for example `custom-file-name.{extension}`.
+
 #### Pleroma.Upload.Filter.Exiftool
 
 This filter only strips the GPS and location metadata with Exiftool leaving color profiles and attributes intact.

lib/mix/tasks/pleroma/instance.ex

@@ -36,8 +36,7 @@ def run(["gen" | rest]) do
           listen_ip: :string,
           listen_port: :string,
           strip_uploads: :string,
-          anonymize_uploads: :string,
-          dedupe_uploads: :string
+          anonymize_uploads: :string
         ],
         aliases: [
           o: :output,
@@ -195,14 +194,6 @@ def run(["gen" | rest]) do
           "n"
         ) === "y"
 
-      dedupe_uploads =
-        get_option(
-          options,
-          :dedupe_uploads,
-          "Do you want to deduplicate uploaded files? (y/n)",
-          "n"
-        ) === "y"
-
       Config.put([:instance, :static_dir], static_dir)
 
       secret = :crypto.strong_rand_bytes(64) |> Base.encode64() |> binary_part(0, 64)
@@ -240,8 +231,7 @@ def run(["gen" | rest]) do
           upload_filters:
             upload_filters(%{
               strip: strip_uploads,
-              anonymize: anonymize_uploads,
-              dedupe: dedupe_uploads
+              anonymize: anonymize_uploads
             })
         )
 
@@ -329,13 +319,6 @@ defp upload_filters(filters) when is_map(filters) do
         enabled_filters
       end
 
-    enabled_filters =
-      if filters.dedupe do
-        enabled_filters ++ [Pleroma.Upload.Filter.Dedupe]
-      else
-        enabled_filters
-      end
-
     enabled_filters
   end
 end

lib/pleroma/upload.ex

@@ -66,7 +66,7 @@ defmodule Pleroma.Upload do
           path: String.t()
         }
 
-  @always_enabled_filters [Pleroma.Upload.Filter.AnonymizeFilename]
+  @always_enabled_filters [Pleroma.Upload.Filter.Dedupe]
 
   defstruct [:id, :name, :tempfile, :content_type, :width, :height, :blurhash, :path]
 

test/mix/tasks/pleroma/instance_test.exs

@@ -71,8 +71,6 @@ test "running gen" do
         "./test/../test/instance/static/",
         "--strip-uploads",
         "y",
-        "--dedupe-uploads",
-        "n",
         "--anonymize-uploads",
         "n"
       ])

test/mix/tasks/pleroma/uploads_test.exs

@@ -16,7 +16,6 @@ defmodule Mix.Tasks.Pleroma.UploadsTest do
       Mix.shell(Mix.Shell.IO)
     end)
 
-    File.mkdir_p!("test/uploads")
     :ok
   end
 

test/pleroma/object_test.exs

@@ -22,6 +22,13 @@ defmodule Pleroma.ObjectTest do
     :ok
   end
 
+  # Only works for a single attachment but that's all we need here
+  defp get_attachment_filepath(note, uploads_dir) do
+    %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} = note
+    filename = href |> Path.basename()
+    "#{uploads_dir}/#{filename}"
+  end
+
   test "returns an object by it's AP id" do
     object = insert(:note)
     found_object = Object.get_by_ap_id(object.data["id"])
@@ -95,14 +102,13 @@ test "Disabled via config" do
       {:ok, %Object{} = attachment} =
         Pleroma.Web.ActivityPub.ActivityPub.upload(file, actor: user.ap_id)
 
-      %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} =
-        note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
+      note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
 
       uploads_dir = Pleroma.Config.get!([Pleroma.Uploaders.Local, :uploads])
 
-      path = href |> Path.dirname() |> Path.basename()
+      path = get_attachment_filepath(note, uploads_dir)
 
-      assert {:ok, ["an_image.jpg"]} == File.ls("#{uploads_dir}/#{path}")
+      assert File.exists?("#{path}")
 
       Object.delete(note)
 
@@ -111,7 +117,7 @@ test "Disabled via config" do
       assert Object.get_by_id(note.id).data["deleted"]
       refute Object.get_by_id(attachment.id) == nil
 
-      assert {:ok, ["an_image.jpg"]} == File.ls("#{uploads_dir}/#{path}")
+      assert File.exists?("#{path}")
     end
 
     test "in subdirectories" do
@@ -129,14 +135,13 @@ test "in subdirectories" do
       {:ok, %Object{} = attachment} =
         Pleroma.Web.ActivityPub.ActivityPub.upload(file, actor: user.ap_id)
 
-      %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} =
-        note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
+      note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
 
       uploads_dir = Pleroma.Config.get!([Pleroma.Uploaders.Local, :uploads])
 
-      path = href |> Path.dirname() |> Path.basename()
+      path = get_attachment_filepath(note, uploads_dir)
 
-      assert {:ok, ["an_image.jpg"]} == File.ls("#{uploads_dir}/#{path}")
+      assert File.exists?("#{path}")
 
       Object.delete(note)
 
@@ -145,7 +150,7 @@ test "in subdirectories" do
       assert Object.get_by_id(note.id).data["deleted"]
       assert Object.get_by_id(attachment.id) == nil
 
-      assert {:ok, []} == File.ls("#{uploads_dir}/#{path}")
+      refute File.exists?("#{path}")
     end
 
     test "with dedupe enabled" do
@@ -168,13 +173,11 @@ test "with dedupe enabled" do
       {:ok, %Object{} = attachment} =
         Pleroma.Web.ActivityPub.ActivityPub.upload(file, actor: user.ap_id)
 
-      %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} =
-        note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
+      note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
 
-      filename = Path.basename(href)
+      path = get_attachment_filepath(note, uploads_dir)
 
-      assert {:ok, files} = File.ls(uploads_dir)
-      assert filename in files
+      assert File.exists?("#{path}")
 
       Object.delete(note)
 
@@ -182,8 +185,8 @@ test "with dedupe enabled" do
 
       assert Object.get_by_id(note.id).data["deleted"]
       assert Object.get_by_id(attachment.id) == nil
-      assert {:ok, files} = File.ls(uploads_dir)
-      refute filename in files
+      # what if another test runs concurrently using the same image file?
+      refute File.exists?("#{path}")
     end
 
     test "with objects that have legacy data.url attribute" do
@@ -203,14 +206,13 @@ test "with objects that have legacy data.url attribute" do
 
       {:ok, %Object{}} = Object.create(%{url: "https://google.com", actor: user.ap_id})
 
-      %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} =
-        note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
+      note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
 
       uploads_dir = Pleroma.Config.get!([Pleroma.Uploaders.Local, :uploads])
 
-      path = href |> Path.dirname() |> Path.basename()
+      path = get_attachment_filepath(note, uploads_dir)
 
-      assert {:ok, ["an_image.jpg"]} == File.ls("#{uploads_dir}/#{path}")
+      assert File.exists?("#{path}")
 
       Object.delete(note)
 
@@ -219,7 +221,7 @@ test "with objects that have legacy data.url attribute" do
       assert Object.get_by_id(note.id).data["deleted"]
       assert Object.get_by_id(attachment.id) == nil
 
-      assert {:ok, []} == File.ls("#{uploads_dir}/#{path}")
+      refute File.exists?("#{path}")
     end
 
     test "With custom base_url" do
@@ -238,14 +240,13 @@ test "With custom base_url" do
       {:ok, %Object{} = attachment} =
         Pleroma.Web.ActivityPub.ActivityPub.upload(file, actor: user.ap_id)
 
-      %{data: %{"attachment" => [%{"url" => [%{"href" => href}]}]}} =
-        note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
+      note = insert(:note, %{user: user, data: %{"attachment" => [attachment.data]}})
 
       uploads_dir = Pleroma.Config.get!([Pleroma.Uploaders.Local, :uploads])
 
-      path = href |> Path.dirname() |> Path.basename()
+      path = get_attachment_filepath(note, uploads_dir)
 
-      assert {:ok, ["an_image.jpg"]} == File.ls("#{uploads_dir}/#{path}")
+      assert File.exists?("#{path}")
 
       Object.delete(note)
 
@@ -254,7 +255,7 @@ test "With custom base_url" do
       assert Object.get_by_id(note.id).data["deleted"]
       assert Object.get_by_id(attachment.id) == nil
 
-      assert {:ok, []} == File.ls("#{uploads_dir}/#{path}")
+      refute File.exists?("#{path}")
     end
   end
 

test/pleroma/upload_test.exs

@@ -188,7 +188,7 @@ test "copies the file to the configured folder with anonymizing filename" do
       refute data["name"] == "an [image.jpg"
     end
 
-    test "escapes invalid characters in url" do
+    test "mangles the filename" do
       File.cp!("test/fixtures/image.jpg", "test/fixtures/image_tmp.jpg")
 
       file = %Plug.Upload{
@@ -200,23 +200,8 @@ test "escapes invalid characters in url" do
       {:ok, data} = Upload.store(file)
       [attachment_url | _] = data["url"]
 
-      assert Path.basename(attachment_url["href"]) == "an%E2%80%A6%20image.jpg"
-    end
-
-    test "escapes reserved uri characters" do
-      File.cp!("test/fixtures/image.jpg", "test/fixtures/image_tmp.jpg")
-
-      file = %Plug.Upload{
-        content_type: "image/jpeg",
-        path: Path.absname("test/fixtures/image_tmp.jpg"),
-        filename: ":?#[]@!$&\\'()*+,;=.jpg"
-      }
-
-      {:ok, data} = Upload.store(file)
-      [attachment_url | _] = data["url"]
-
-      assert Path.basename(attachment_url["href"]) ==
-               "%3A%3F%23%5B%5D%40%21%24%26%5C%27%28%29%2A%2B%2C%3B%3D.jpg"
+      refute Path.basename(attachment_url["href"]) == "an%E2%80%A6%20image.jpg"
+      refute Path.basename(attachment_url["href"]) == "an… image.jpg"
     end
   end
 

test/pleroma/web/activity_pub/activity_pub_test.exs

@@ -1304,14 +1304,6 @@ test "returns reblogs for users for whom reblogs have not been muted" do
       %{test_file: test_file}
     end
 
-    test "strips / from filename", %{test_file: file} do
-      file = %Plug.Upload{file | filename: "../../../../../nested/bad.jpg"}
-      {:ok, %Object{} = object} = ActivityPub.upload(file)
-      [%{"href" => href}] = object.data["url"]
-      assert Regex.match?(~r"/bad.jpg$", href)
-      refute Regex.match?(~r"/nested/", href)
-    end
-
     test "sets a description if given", %{test_file: file} do
       {:ok, %Object{} = object} = ActivityPub.upload(file, description: "a cool file")
       assert object.data["name"] == "a cool file"

test/pleroma/web/pleroma_api/controllers/mascot_controller_test.exs

@@ -64,6 +64,10 @@ test "mascot retrieving" do
 
     assert json_response_and_validate_schema(ret_conn, 200)
 
+    %{"url" => uploaded_url} = Jason.decode!(ret_conn.resp_body)
+
+    assert uploaded_url != nil and is_binary(uploaded_url)
+
     user = User.get_cached_by_id(user.id)
 
     conn =
@@ -72,6 +76,6 @@ test "mascot retrieving" do
       |> get("/api/v1/pleroma/mascot")
 
     assert %{"url" => url, "type" => "image"} = json_response_and_validate_schema(conn, 200)
-    assert url =~ "an_image"
+    assert url == uploaded_url
   end
 end

test/test_helper.exs

@@ -9,6 +9,10 @@
 
 {:ok, _} = Application.ensure_all_started(:ex_machina)
 
+# Prepare and later automatically cleanup upload dir
+uploads_dir = Pleroma.Config.get([Pleroma.Uploaders.Local, :uploads], "test/uploads")
+File.mkdir_p!(uploads_dir)
+
 ExUnit.after_suite(fn _results ->
   uploads = Pleroma.Config.get([Pleroma.Uploaders.Local, :uploads], "test/uploads")
   File.rm_rf!(uploads)