Allow RelativeLinkFilter to go up multiple directories

lib/gitlab/markdown/relative_link_filter.rb

@@ -91,8 +91,7 @@ module Gitlab
         parts = request_path.split('/')
         parts.pop if path_type(request_path) != 'tree'
 
-        # Allow for going up one directory
-        if parts.length > 1 && path.start_with?('../')
+        while parts.length > 1 && path.start_with?('../')
           parts.pop
           path.sub!('../', '')
         end

spec/lib/gitlab/markdown/relative_link_filter_spec.rb

@@ -85,6 +85,14 @@ module Gitlab::Markdown
           to eq "/#{project_path}/blob/#{ref}/doc/api/README.md"
       end
 
+      it 'rebuilds relative URL for a file in the repo up multiple directories' do
+        relative_link = link('../../../api/README.md')
+        doc = filter(relative_link, requested_path: 'doc/foo/bar/baz/README.md')
+
+        expect(doc.at_css('a')['href']).
+          to eq "/#{project_path}/blob/#{ref}/doc/api/README.md"
+      end
+
       it 'rebuilds relative URL for a file in the repo with an anchor' do
         doc = filter(link('README.md#section'))
         expect(doc.at_css('a')['href']).