Detect and prevent image bombs, max. processable dimension 4096^2 (#7229)

1 files changed, 29 insertions, 3 deletions

diff --git a/app/models/concerns/attachmentable.rb b/app/models/concerns/attachmentable.rb
index 90ce88463..6f8489b89 100644
--- a/app/models/concerns/attachmentable.rb
+++ b/app/models/concerns/attachmentable.rb
@@ -1,10 +1,15 @@
 # frozen_string_literal: true
 
+require 'mime/types'
+
 module Attachmentable
   extend ActiveSupport::Concern
 
+  MAX_MATRIX_LIMIT = 16_777_216 # 4096x4096px or approx. 16MB
+
   included do
     before_post_process :set_file_extensions
+    before_post_process :check_image_dimensions
   end
 
   private
@@ -12,10 +17,31 @@ module Attachmentable
   def set_file_extensions
     self.class.attachment_definitions.each_key do |attachment_name|
       attachment = send(attachment_name)
+
       next if attachment.blank?
-      extension = Paperclip::Interpolations.content_type_extension(attachment, :original)
-      basename  = Paperclip::Interpolations.basename(attachment, :original)
-      attachment.instance_write :file_name, [basename, extension].delete_if(&:blank?).join('.')
+
+      attachment.instance_write :file_name, [Paperclip::Interpolations.basename(attachment, :original), appropriate_extension(attachment)].delete_if(&:blank?).join('.')
+    end
+  end
+
+  def check_image_dimensions
+    self.class.attachment_definitions.each_key do |attachment_name|
+      attachment = send(attachment_name)
+
+      next if attachment.blank? || !attachment.content_type.match?(/image.*/) || attachment.queued_for_write[:original].blank?
+
+      width, height = FastImage.size(attachment.queued_for_write[:original].path)
+
+      raise Mastodon::DimensionsValidationError, "#{width}x#{height} images are not supported" if width.present? && height.present? && (width * height >= MAX_MATRIX_LIMIT)
     end
   end
+
+  def appropriate_extension(attachment)
+    mime_type = MIME::Types[attachment.content_type]
+
+    extensions_for_mime_type = mime_type.empty? ? [] : mime_type.first.extensions
+    original_extension       = Paperclip::Interpolations.extension(attachment, :original)
+
+    extensions_for_mime_type.include?(original_extension) ? original_extension : extensions_for_mime_type.first
+  end
 end