Raise error on path traversal in UploadsRewriter

changelogs/unreleased/security-path-traversal-master.yml

+---
+title: Fix UploadRewriter Path Traversal vulnerability
+merge_request:
+author:
+type: security

lib/gitlab/gfm/uploads_rewriter.rb

@@ -22,6 +22,8 @@ module Gitlab
         return @text unless needs_rewrite?
 
         @text.gsub(@pattern) do |markdown|
+          Gitlab::Utils.check_path_traversal!($~[:file])
+
           file = find_file(@source_project, $~[:secret], $~[:file])
           break markdown unless file.try(:exists?)
 

spec/lib/gitlab/gfm/uploads_rewriter_spec.rb

@@ -68,6 +68,16 @@ describe Gitlab::Gfm::UploadsRewriter do
       expect(moved_text.scan(/\A\[.*?\]/).count).to eq(1)
     end
 
+    context 'path traversal in file name' do
+      let(:text) do
+        "![a](/uploads/11111111111111111111111111111111/../../../../../../../../../../../../../../etc/passwd)"
+      end
+
+      it 'throw an error' do
+        expect { rewriter.rewrite(new_project) }.to raise_error(an_instance_of(StandardError).and having_attributes(message: "Invalid path"))
+      end
+    end
+
     context "file are stored locally" do
       include_examples "files are accessible"
     end