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diff --git a/content/posts/2022-02-25-relaxed-csp-for-go-coverage.md b/content/posts/2022-02-25-relaxed-csp-for-go-coverage.md new file mode 100644 index 0000000..bf5dcfe --- /dev/null +++ b/content/posts/2022-02-25-relaxed-csp-for-go-coverage.md @@ -0,0 +1,98 @@ +--- +slug: relaxed-csp-for-go-coverage +title: "Relaxed Content-Security-Policy for Go Code Coverage Reports" +date: "2022-02-25T01:36:14-04:00" +--- +There is a conflict between [my strict +`Content-Security-Policy`][my-csp] and the [CSS][] and [JavaScript][js] +embedded in the [HTML][] [code coverage][] reports generated by [`go +cover`][go-cover]. + +I tested a couple of methods of overriding the base +[`Content-Security-Policy`][csp], without success: + +1. Add a relaxed [`<meta http-equiv='Content-Security-Policy' + content='...'>`][meta-http-equiv] element. +2. Embed the script and style as [`data:` URLs][data-url]. + +(Aside: I'm glad browsers don't allow these workarounds, because they +would be potential security holes). + +In any case, the my solution was to relax the policy for a specific +location via the [Apache][] config: + +```apache +# +# Relax style-src and script-src content security policies for content +# in the "/coverage-reports" directory so that the HTML coverage reports +# generated by `go cover` work as expected. +# +# Specifically the relaxed constraints allow: +# +# 1. The inline `<script>` element at the end of the generated HTML. +# 2. `style='display: none'` attributes on hidden elements. +# +# Notes: +# +# * You *have* to use `Header set` rather than `Header append` to +# replace rather than append to the existing header. +# * Ideally we'd use `style-src-elem` and `script-src-elem`, but neither +# are currently supported by Firefox. +# +<Location /coverage-reports> + Header set "Content-Security-Policy" "default-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'self' 'unsafe-inline'" +</Location> +``` + + +The situation could be improved by making the following changes to the +[go cover HTML report source code][go-cover-html-src]: + +1. Replace `style="display: none"` attribute on elements with + `class=hide`. +2. Add `.hide { display: none }` to the inline `<style>` element. +2. Hash the inner content of the inline `<style>` element. +3. Hash the inner content of the inline `<script>` element. +4. Add a [`<meta http-equiv ...>`][meta-http-equiv] element to the + header, using the hashes from the previous two steps. + +Example: + +```html +<meta + http-equiv="content-security-policy" + content="default-src 'self'; script-src 'self' 'sha256-a43KCehRqYcFBGPJxgYD6a15e6CRFwVvwuDAe8rGbkM='; style-src 'self' 'sha256-8OTC92xYkW7CWPJGhRvqCR0U1CR6L8PhhpRGGxgW4Ts='" +/> +``` + + +Bonus: These reports would automatically set a reasonable policy even in +the absense of a more restrictive server policy. + +Counter-argument to this post: These coverage reports are meant to be +simple and only used locally. More elaborate or more secure coverage +reports should be generated by a separate tool rather than complicating +the default one. + +[my-csp]: {{< ref "2021-10-25-the-nuclear-option-no-more-unsafe-inline" >}} + "My strict Content-Security-Policy setting." +[go-cover]: https://go.dev/blog/cover + "Go code coverage HTML reports." +[code coverage]: https://en.wikipedia.org/wiki/Code_coverage + "Test suite code coverage." +[css]: https://en.wikipedia.org/wiki/CSS + "Cascading Style Sheets" +[js]: https://en.wikipedia.org/wiki/JavaScript + "JavaScript programming language." +[html]: https://en.wikipedia.org/wiki/HTML + "HyperText Markup Language" +[meta-http-equiv]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/meta + "The <meta http-equiv ...> element." +[csp]: https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP + "Content-Security-Policy HTTP response header." +[data-url]: https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs + "Data URL." +[apache]: https://httpd.apache.org/ + "Apache web server." +[go-cover-html-src]: https://cs.opensource.google/go/go/+/master:src/cmd/cover/html.go + "Source code for the HTML code coverage reports generated by go cover." |