diff options
| -rw-r--r-- | mod/hmac.cxx | 92 | ||||
| -rw-r--r-- | mod/hmac.hxx | 29 | ||||
| -rw-r--r-- | mod/mod-ci-github.cxx | 110 | ||||
| -rw-r--r-- | mod/module.cli | 6 | ||||
| -rw-r--r-- | web/server/module.hxx | 5 |
5 files changed, 236 insertions, 6 deletions
diff --git a/mod/hmac.cxx b/mod/hmac.cxx new file mode 100644 index 0000000..dc9eca0 --- /dev/null +++ b/mod/hmac.cxx @@ -0,0 +1,92 @@ +#include <mod/hmac.hxx> + +#include <libbutl/openssl.hxx> + +using namespace std; +using namespace butl; + +string brep:: +compute_hmac (const options::openssl_options& o, + const vector<char>& m, + const char* k) +{ + try + { + fdpipe errp (fdopen_pipe ()); // stderr pipe. + + // To compute an HMAC over stdin with the key "secret": + // + // openssl mac -digest SHA256 -macopt "key:secret" HMAC + // + openssl os (path ("-"), // Read message from openssl::out. + path ("-"), // Write output to openssl::in. + process::pipe (errp.in.get (), move (errp.out)), + process_env (o.openssl (), o.openssl_envvar ()), + "mac", o.openssl_option (), + "-digest", "SHA256", + "-macopt", string ("key:") + k, + "HMAC"); + + ifdstream err (move (errp.in)); + + string h; // The HMAC. + try + { + // In case of exception, skip and close input after output. + // + // Note: re-open in/out so that they get automatically closed on + // exception. + // + ifdstream in (os.in.release (), fdstream_mode::skip); + ofdstream out (os.out.release ()); + + // Write the message to openssl's input. + // + out.write (m.data (), m.size ()); + out.close (); + + // Read the HMAC from openssl's output. + // + h = in.read_text (); + in.close (); + } + catch (const io_error& e) + { + // If the process exits with non-zero status, assume the IO error is due + // to that and fall through. + // + if (os.wait ()) + { + throw_generic_error ( + e.code ().value (), + (string ("unable to read/write openssl stdout/stdin: ") + + e.what ()).c_str ()); + } + } + + if (!os.wait ()) + { + string et (err.read_text ()); + throw_generic_error (EINVAL, + ("non-zero openssl exit status: " + et).c_str ()); + } + + err.close (); + + return h; + } + catch (const process_error& e) + { + throw_generic_error ( + e.code ().value (), + (string ("unable to execute openssl: ") + e.what ()).c_str ()); + } + catch (const io_error& e) + { + // Unable to read diagnostics from stderr. + // + throw_generic_error ( + e.code ().value (), + (string ("unable to read openssl stderr : ") + e.what ()).c_str ()); + } +} diff --git a/mod/hmac.hxx b/mod/hmac.hxx new file mode 100644 index 0000000..104b629 --- /dev/null +++ b/mod/hmac.hxx @@ -0,0 +1,29 @@ +#ifndef MOD_HMAC_HXX +#define MOD_HMAC_HXX + +#include <libbrep/types.hxx> +#include <libbrep/utility.hxx> + +#include <mod/module-options.hxx> + +namespace brep +{ + // Compute the HMAC-SHA256 message authentication code over a message using + // the given key. + // + // Return the HMAC or throw std::system_error in case of an error. + // + // Example output: + // + // 5e822587094c68e646db8b916da1db2056d92f1dea4252136a533b4147a30cb7 + // + // Note that although any cryptographic hash function can be used to compute + // an HMAC, this implementation supports only SHA-256. + // + string + compute_hmac (const options::openssl_options&, + const vector<char>& message, + const char* key); +} + +#endif diff --git a/mod/mod-ci-github.cxx b/mod/mod-ci-github.cxx index e19a41b..7cdc01d 100644 --- a/mod/mod-ci-github.cxx +++ b/mod/mod-ci-github.cxx @@ -7,6 +7,7 @@ #include <libbutl/json/parser.hxx> #include <mod/jwt.hxx> +#include <mod/hmac.hxx> #include <mod/module-options.hxx> #include <stdexcept> @@ -64,10 +65,12 @@ namespace brep HANDLER_DIAG; - // @@ TODO: disable service if HMAC is not specified in config. - // - if (false) + if (!options_->ci_github_app_webhook_secret_specified ()) + { + error << "webhook secret not configured"; + throw invalid_request (404, "CI request submission disabled"); + } // Process headers. // @@ -80,15 +83,26 @@ namespace brep // we already do for the most part), and "webhook event" only when // more context would be useful? // - string event; // Webhook event. + string event; // Webhook event. + string r_hmac; // Received HMAC. { bool content_type (false); for (const name_value& h: rq.headers ()) { + // HMAC authenticating this request. Note that it won't be present + // unless a webhook secret has been set in the GitHub app's settings. + // + if (icasecmp (h.name, "x-hub-signature-256") == 0) + { + if (!h.value) + throw invalid_request (400, "missing x-hub-signature-256 value"); + + r_hmac = *h.value; + } // This event's UUID. // - if (icasecmp (h.name, "x-github-delivery") == 0) + else if (icasecmp (h.name, "x-github-delivery") == 0) { // @@ TODO Check that delivery UUID has not been received before // (replay attack). @@ -118,6 +132,21 @@ namespace brep } } + // Parse the x-hub-signature-256 header value. For example: + // + // sha256=5e822587094c68e646db8b916da1db2056d92f1dea4252136a533b4147a30cb7 + // + // Check for the presence of the "sha256=" prefix and then strip it to + // leave only the HMAC. + // + if (r_hmac.find ("sha256=", 0, 7) == string::npos) + { + throw invalid_request (400, + "invalid x-hub-signature-256 value: '" + + r_hmac + '\''); + } + r_hmac = r_hmac.substr (7); + if (!content_type) throw invalid_request (400, "missing content-type header"); @@ -125,6 +154,75 @@ namespace brep throw invalid_request (400, "missing x-github-event header"); } + // Read the entire request body into a buffer because we need to compute + // an HMAC over it and then parse it as JSON. The alternative of reading + // from the stream twice works out to be more complicated and expensive. + // + // @@ TMP Although it is possible (with a bit of work) to rewind the + // request's input stream, in that case we'd have to read from it + // twice (once for the HMAC and once for the JSON parsing) instead + // of just this once, temp buffer(s) would be necessary, and we'd + // still be storing the entire request body in memory anyway (just + // not here). + // + vector<char> body; + { + // Note: buffer=0 disables caching. + // + istream& is (rq.content (64 * 1024, 0 /* buffer */)); + + // Note that istream::read() sets failbit if unable to read the + // requested number of bytes. + // + is.exceptions (istream::badbit); + + try + { + size_t n (0); // Total bytes read. + + while (!eof (is)) + { + body.resize (n + 8192); + is.read (body.data () + n, 8192); + n += is.gcount (); + } + + body.resize (n); + } + catch (const io_error& e) + { + fail << "unable to read request body: " << e; + } + } + + // Verify the received HMAC. + // + // Compute the HMAC over the request body using the configured webhook + // secret as key and compare it to the received HMAC. + // + try + { + string hmac ( + compute_hmac (*options_, + body, + options_->ci_github_app_webhook_secret ().c_str ())); + + // @@ TODO GitHub recommends constant-time comparison (timing attack). + // + if (!icasecmp (hmac, r_hmac)) + { + string m ("computed HMAC does not match received HMAC"); + + error << m; + + throw invalid_request (400, move (m)); + } + } + catch (const system_error& e) + { + fail << "unable to compute request HMAC: " << e; + } + // There is a webhook event (specified in the x-github-event header) and // each event contains a bunch of actions (specified in the JSON request // body). @@ -140,7 +238,7 @@ namespace brep check_suite_event cs; try { - json::parser p (rq.content (64 * 1024), "check_suite event"); + json::parser p (body.data (), body.size (), "check_suite event"); cs = check_suite_event (p); } diff --git a/mod/module.cli b/mod/module.cli index c635689..bec4c2d 100644 --- a/mod/module.cli +++ b/mod/module.cli @@ -832,6 +832,12 @@ namespace brep "The GitHub App ID. Found in the app's settings on GitHub." } + string ci-github-app-webhook-secret + { + "<secret>", + "The GitHub app's configured webhook secret." + } + path ci-github-app-private-key { "<path>", diff --git a/web/server/module.hxx b/web/server/module.hxx index 20f6217..1b067f5 100644 --- a/web/server/module.hxx +++ b/web/server/module.hxx @@ -82,6 +82,11 @@ namespace web using name_values = std::vector<name_value>; using butl::path; + // @@ TODO: Expose the request input stream rewinding support provided by + // web::apache::request::rewind(). Might come in useful in cases + // where more than one thing needs to be done with the request + // body, e.g., compute its MAC and then parse its contents. + // class request { public: |