GitHub webhooks: check signature (#2493)

CHANGELOG.md

@@ -70,6 +70,7 @@ be deprecated eventually.
 - [#2636](https://github.com/influxdata/telegraf/pull/2636): Add `message_len_max` option to `kafka_consumer` input
 - [#1100](https://github.com/influxdata/telegraf/issues/1100): Add collectd parser
 - [#1820](https://github.com/influxdata/telegraf/issues/1820): easier plugin testing without outputs
+- [#2493](https://github.com/influxdata/telegraf/pull/2493): Check signature in the GitHub webhook plugin
 
 ### Bugfixes
 

etc/telegraf.conf

@@ -2382,6 +2382,7 @@
 #
 #   [inputs.webhooks.github]
 #     path = "/github"
+#     # secret = ""
 #
 #   [inputs.webhooks.mandrill]
 #     path = "/mandrill"

plugins/inputs/webhooks/github/README.md

@@ -2,6 +2,8 @@
 
 You should configure your Organization's Webhooks to point at the `webhooks` service. To do this go to `github.com/{my_organization}` and click `Settings > Webhooks > Add webhook`. In the resulting menu set `Payload URL` to `http://<my_ip>:1619/github`, `Content type` to `application/json` and under the section `Which events would you like to trigger this webhook?` select 'Send me <b>everything</b>'. By default all of the events will write to the `github_webhooks` measurement, this is configurable by setting the `measurement_name` in the config file.
 
+You can also add a secret that will be used by telegraf to verify the authenticity of the requests.
+
 ## Events
 
 The titles of the following sections are links to the full payloads and details for each event. The body contains what information from the event is persisted. The format is as follows:

plugins/inputs/webhooks/github/github_webhooks.go

@@ -1,6 +1,9 @@
 package github
 
 import (
+	"crypto/hmac"
+	"crypto/sha1"
+	"encoding/hex"
 	"encoding/json"
 	"io/ioutil"
 	"log"
@@ -11,8 +14,9 @@ import (
 )
 
 type GithubWebhook struct {
-	Path string
+	Path   string
-	acc  telegraf.Accumulator
+	Secret string
+	acc    telegraf.Accumulator
 }
 
 func (gh *GithubWebhook) Register(router *mux.Router, acc telegraf.Accumulator) {
@@ -23,12 +27,19 @@ func (gh *GithubWebhook) Register(router *mux.Router, acc telegraf.Accumulator)
 
 func (gh *GithubWebhook) eventHandler(w http.ResponseWriter, r *http.Request) {
 	defer r.Body.Close()
-	eventType := r.Header["X-Github-Event"][0]
+	eventType := r.Header.Get("X-Github-Event")
 	data, err := ioutil.ReadAll(r.Body)
 	if err != nil {
 		w.WriteHeader(http.StatusBadRequest)
 		return
 	}
+
+	if gh.Secret != "" && !checkSignature(gh.Secret, data, r.Header.Get("X-Hub-Signature")) {
+		log.Printf("E! Fail to check the github webhook signature\n")
+		w.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
 	e, err := NewEvent(data, eventType)
 	if err != nil {
 		w.WriteHeader(http.StatusBadRequest)
@@ -108,3 +119,14 @@ func NewEvent(data []byte, name string) (Event, error) {
 	}
 	return nil, &newEventError{"Not a recognized event type"}
 }
+
+func checkSignature(secret string, data []byte, signature string) bool {
+	return hmac.Equal([]byte(signature), []byte(generateSignature(secret, data)))
+}
+
+func generateSignature(secret string, data []byte) string {
+	mac := hmac.New(sha1.New, []byte(secret))
+	mac.Write(data)
+	result := mac.Sum(nil)
+	return "sha1=" + hex.EncodeToString(result)
+}

plugins/inputs/webhooks/github/github_webhooks_test.go

@@ -21,6 +21,19 @@ func GithubWebhookRequest(event string, jsonString string, t *testing.T) {
 	}
 }
 
+func GithubWebhookRequestWithSignature(event string, jsonString string, t *testing.T, signature string, expectedStatus int) {
+	var acc testutil.Accumulator
+	gh := &GithubWebhook{Path: "/github", Secret: "signature", acc: &acc}
+	req, _ := http.NewRequest("POST", "/github", strings.NewReader(jsonString))
+	req.Header.Add("X-Github-Event", event)
+	req.Header.Add("X-Hub-Signature", signature)
+	w := httptest.NewRecorder()
+	gh.eventHandler(w, req)
+	if w.Code != expectedStatus {
+		t.Errorf("POST "+event+" returned HTTP status code %v.\nExpected %v", w.Code, expectedStatus)
+	}
+}
+
 func TestCommitCommentEvent(t *testing.T) {
 	GithubWebhookRequest("commit_comment", CommitCommentEventJSON(), t)
 }
@@ -100,3 +113,23 @@ func TestTeamAddEvent(t *testing.T) {
 func TestWatchEvent(t *testing.T) {
 	GithubWebhookRequest("watch", WatchEventJSON(), t)
 }
+
+func TestEventWithSignatureFail(t *testing.T) {
+	GithubWebhookRequestWithSignature("watch", WatchEventJSON(), t, "signature", http.StatusBadRequest)
+}
+
+func TestEventWithSignatureSuccess(t *testing.T) {
+	GithubWebhookRequestWithSignature("watch", WatchEventJSON(), t, generateSignature("signature", []byte(WatchEventJSON())), http.StatusOK)
+}
+
+func TestCheckSignatureSuccess(t *testing.T) {
+	if !checkSignature("my_little_secret", []byte("random-signature-body"), "sha1=3dca279e731c97c38e3019a075dee9ebbd0a99f0") {
+		t.Errorf("check signature failed")
+	}
+}
+
+func TestCheckSignatureFailed(t *testing.T) {
+	if checkSignature("m_little_secret", []byte("random-signature-body"), "sha1=3dca279e731c97c38e3019a075dee9ebbd0a99f0") {
+		t.Errorf("check signature failed")
+	}
+}

plugins/inputs/webhooks/webhooks.go

@@ -47,6 +47,7 @@ func (wb *Webhooks) SampleConfig() string {
 
   [inputs.webhooks.github]
     path = "/github"
+    # secret = ""
 
   [inputs.webhooks.mandrill]
     path = "/mandrill"