Add restrictions for open registration (#2402)

* Add restrications for open registration

* Make enable open registration a parameter

* Enable registration for CI

* Update error message

* Shuffle things around a bit

* Add a warning at every startup just to be extra annoying

* Ignore shared secret when warning about open registration, since it's not strictly required when it is set if registration is otherwise enabled

* Make CI happy?

* Add missing parameter; try new parameter in upgrade-test

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

3 files changed, 33 insertions, 3 deletions

diff --git a/setup/base/base.go b/setup/base/base.go
index 7091c6ba..4b771aa3 100644
--- a/setup/base/base.go
+++ b/setup/base/base.go
@@ -126,6 +126,10 @@ func NewBaseDendrite(cfg *config.Dendrite, componentName string, options ...Base
 
 	logrus.Infof("Dendrite version %s", internal.VersionString())
 
+	if !cfg.ClientAPI.RegistrationDisabled && cfg.ClientAPI.OpenRegistrationWithoutVerificationEnabled {
+		logrus.Warn("Open registration is enabled")
+	}
+
 	closer, err := cfg.SetupTracing("Dendrite" + componentName)
 	if err != nil {
 		logrus.WithError(err).Panicf("failed to start opentracing")
diff --git a/setup/config/config_clientapi.go b/setup/config/config_clientapi.go
index 4590e752..6104ed8b 100644
--- a/setup/config/config_clientapi.go
+++ b/setup/config/config_clientapi.go
@@ -15,6 +15,12 @@ type ClientAPI struct {
 	// If set disables new users from registering (except via shared
 	// secrets)
 	RegistrationDisabled bool `yaml:"registration_disabled"`
+
+	// Enable registration without captcha verification or shared secret.
+	// This option is populated by the -really-enable-open-registration
+	// command line parameter as it is not recommended.
+	OpenRegistrationWithoutVerificationEnabled bool `yaml:"-"`
+
 	// If set, allows registration by anyone who also has the shared
 	// secret, even if registration is otherwise disabled.
 	RegistrationSharedSecret string `yaml:"registration_shared_secret"`
@@ -55,7 +61,8 @@ func (c *ClientAPI) Defaults(generate bool) {
 	c.RecaptchaEnabled = false
 	c.RecaptchaBypassSecret = ""
 	c.RecaptchaSiteVerifyAPI = ""
-	c.RegistrationDisabled = false
+	c.RegistrationDisabled = true
+	c.OpenRegistrationWithoutVerificationEnabled = false
 	c.RateLimiting.Defaults()
 }
 
@@ -72,6 +79,20 @@ func (c *ClientAPI) Verify(configErrs *ConfigErrors, isMonolith bool) {
 	}
 	c.TURN.Verify(configErrs)
 	c.RateLimiting.Verify(configErrs)
+
+	// Ensure there is any spam counter measure when enabling registration
+	if !c.RegistrationDisabled && !c.OpenRegistrationWithoutVerificationEnabled {
+		if !c.RecaptchaEnabled {
+			configErrs.Add(
+				"You have tried to enable open registration without any secondary verification methods " +
+					"(such as reCAPTCHA). By enabling open registration, you are SIGNIFICANTLY " +
+					"increasing the risk that your server will be used to send spam or abuse, and may result in " +
+					"your server being banned from some rooms. If you are ABSOLUTELY CERTAIN you want to do this, " +
+					"start Dendrite with the -really-enable-open-registration command line flag. Otherwise, you " +
+					"should set the registration_disabled option in your Dendrite config.",
+			)
+		}
+	}
 }
 
 type TURN struct {
diff --git a/setup/flags.go b/setup/flags.go
index 281cf339..a9dac61a 100644
--- a/setup/flags.go
+++ b/setup/flags.go
@@ -25,8 +25,9 @@ import (
 )
 
 var (
-	configPath = flag.String("config", "dendrite.yaml", "The path to the config file. For more information, see the config file in this repository.")
-	version    = flag.Bool("version", false, "Shows the current version and exits immediately.")
+	configPath                            = flag.String("config", "dendrite.yaml", "The path to the config file. For more information, see the config file in this repository.")
+	version                               = flag.Bool("version", false, "Shows the current version and exits immediately.")
+	enableRegistrationWithoutVerification = flag.Bool("really-enable-open-registration", false, "This allows open registration without secondary verification (reCAPTCHA). This is NOT RECOMMENDED and will SIGNIFICANTLY increase the risk that your server will be used to send spam or conduct attacks, which may result in your server being banned from rooms.")
 )
 
 // ParseFlags parses the commandline flags and uses them to create a config.
@@ -48,5 +49,9 @@ func ParseFlags(monolith bool) *config.Dendrite {
 		logrus.Fatalf("Invalid config file: %s", err)
 	}
 
+	if *enableRegistrationWithoutVerification {
+		cfg.ClientAPI.OpenRegistrationWithoutVerificationEnabled = true
+	}
+
 	return cfg
 }