add support for login throttling

Makefile

 	python3 ./gencapdefs.py | diff - ${capdef_file}
 	cd irc && go test . && go vet .
 	cd irc/caps && go test . && go vet .
+	cd irc/connection_limits && go test . && go vet .
 	cd irc/history && go test . && go vet .
 	cd irc/isupport && go test . && go vet .
 	cd irc/modes && go test . && go vet .

irc/client.go

 	"github.com/goshuirc/irc-go/ircmsg"
 	ident "github.com/oragono/go-ident"
 	"github.com/oragono/oragono/irc/caps"
+	"github.com/oragono/oragono/irc/connection_limits"
 	"github.com/oragono/oragono/irc/history"
 	"github.com/oragono/oragono/irc/modes"
 	"github.com/oragono/oragono/irc/sno"
 	isDestroyed        bool
 	isQuitting         bool
 	languages          []string
+	loginThrottle      connection_limits.GenericThrottle
 	maxlenTags         uint32
 	maxlenRest         uint32
 	nick               string
 	fullLineLenLimit := config.Limits.LineLen.Tags + config.Limits.LineLen.Rest
 	socket := NewSocket(conn, fullLineLenLimit*2, config.Server.MaxSendQBytes)
 	client := &Client{
-		atime:          now,
-		authorized:     server.Password() == nil,
-		capabilities:   caps.NewSet(),
-		capState:       caps.NoneState,
-		capVersion:     caps.Cap301,
-		channels:       make(ChannelSet),
-		ctime:          now,
-		flags:          modes.NewModeSet(),
+		atime:        now,
+		authorized:   server.Password() == nil,
+		capabilities: caps.NewSet(),
+		capState:     caps.NoneState,
+		capVersion:   caps.Cap301,
+		channels:     make(ChannelSet),
+		ctime:        now,
+		flags:        modes.NewModeSet(),
+		loginThrottle: connection_limits.GenericThrottle{
+			Duration: config.Accounts.LoginThrottling.Duration,
+			Limit:    config.Accounts.LoginThrottling.MaxAttempts,
+		},
 		server:         server,
 		socket:         socket,
 		accountName:    "*",

irc/config.go

 
 type AccountConfig struct {
 	Registration          AccountRegistrationConfig
-	AuthenticationEnabled bool                  `yaml:"authentication-enabled"`
-	SkipServerPassword    bool                  `yaml:"skip-server-password"`
-	NickReservation       NickReservationConfig `yaml:"nick-reservation"`
-	VHosts                VHostConfig
+	AuthenticationEnabled bool `yaml:"authentication-enabled"`
+	LoginThrottling       struct {
+		Enabled     bool
+		Duration    time.Duration
+		MaxAttempts int `yaml:"max-attempts"`
+	} `yaml:"login-throttling"`
+	SkipServerPassword bool                  `yaml:"skip-server-password"`
+	NickReservation    NickReservationConfig `yaml:"nick-reservation"`
+	VHosts             VHostConfig
 }
 
 // AccountRegistrationConfig controls account registration.
 		config.Accounts.VHosts.ValidRegexp = defaultValidVhostRegex
 	}
 
+	if !config.Accounts.LoginThrottling.Enabled {
+		config.Accounts.LoginThrottling.MaxAttempts = 0 // limit of 0 means disabled
+	}
+
 	maxSendQBytes, err := bytefmt.ToBytes(config.Server.MaxSendQString)
 	if err != nil {
 		return nil, fmt.Errorf("Could not parse maximum SendQ size (make sure it only contains whole numbers): %s", err.Error())

irc/connection_limits/throttler.go

 
 // ThrottleDetails holds the connection-throttling details for a subnet/IP.
 type ThrottleDetails struct {
-	Start       time.Time
-	ClientCount int
+	Start time.Time
+	Count int
+}
+
+// GenericThrottle allows enforcing limits of the form
+// "at most X events per time window of duration Y"
+type GenericThrottle struct {
+	ThrottleDetails // variable state: what events have been seen
+	// these are constant after creation:
+	Duration time.Duration // window length to consider
+	Limit    int           // number of events allowed per window
+}
+
+// Touch checks whether an additional event is allowed:
+// it either denies it (by returning false) or allows it (by returning true)
+// and records it
+func (g *GenericThrottle) Touch() (throttled bool, remainingTime time.Duration) {
+	return g.touch(time.Now())
+}
+
+func (g *GenericThrottle) touch(now time.Time) (throttled bool, remainingTime time.Duration) {
+	if g.Limit == 0 {
+		return // limit of 0 disables throttling
+	}
+
+	elapsed := now.Sub(g.Start)
+	if elapsed > g.Duration {
+		// reset window, record the operation
+		g.Start = now
+		g.Count = 1
+		return false, 0
+	} else if g.Count >= g.Limit {
+		// we are throttled
+		return true, g.Start.Add(g.Duration).Sub(now)
+	} else {
+		// we are not throttled, record the operation
+		g.Count += 1
+		return false, 0
+	}
 }
 
 // Throttler manages automated client connection throttling.
 	ct.maskAddr(addr)
 	addrString := addr.String()
 
-	details, exists := ct.population[addrString]
-	if !exists || details.Start.Add(ct.duration).Before(time.Now()) {
-		details = ThrottleDetails{
-			Start: time.Now(),
-		}
+	details := ct.population[addrString] // retrieve mutable throttle state from the map
+	// add in constant state to process the limiting operation
+	g := GenericThrottle{
+		ThrottleDetails: details,
+		Duration:        ct.duration,
+		Limit:           ct.subnetLimit,
 	}
+	throttled, _ := g.Touch()                     // actually check the limit
+	ct.population[addrString] = g.ThrottleDetails // store modified mutable state
 
-	if details.ClientCount+1 > ct.subnetLimit {
+	if throttled {
 		return errTooManyClients
+	} else {
+		return nil
 	}
-
-	details.ClientCount++
-	ct.population[addrString] = details
-
-	return nil
 }
 
 func (ct *Throttler) BanDuration() time.Duration {

irc/connection_limits/throttler_test.go

+// Copyright (c) 2018 Shivaram Lingamneni
+// released under the MIT license
+
+package connection_limits
+
+import (
+	"net"
+	"reflect"
+	"testing"
+	"time"
+)
+
+func assertEqual(supplied, expected interface{}, t *testing.T) {
+	if !reflect.DeepEqual(supplied, expected) {
+		t.Errorf("expected %v but got %v", expected, supplied)
+	}
+}
+
+func TestGenericThrottle(t *testing.T) {
+	minute, _ := time.ParseDuration("1m")
+	second, _ := time.ParseDuration("1s")
+	zero, _ := time.ParseDuration("0s")
+
+	throttler := GenericThrottle{
+		Duration: minute,
+		Limit:    2,
+	}
+
+	now := time.Now()
+	throttled, remaining := throttler.touch(now)
+	assertEqual(throttled, false, t)
+	assertEqual(remaining, zero, t)
+
+	now = now.Add(second)
+	throttled, remaining = throttler.touch(now)
+	assertEqual(throttled, false, t)
+	assertEqual(remaining, zero, t)
+
+	now = now.Add(second)
+	throttled, remaining = throttler.touch(now)
+	assertEqual(throttled, true, t)
+	assertEqual(remaining, 58*second, t)
+
+	now = now.Add(minute)
+	throttled, remaining = throttler.touch(now)
+	assertEqual(throttled, false, t)
+	assertEqual(remaining, zero, t)
+}
+
+func TestGenericThrottleDisabled(t *testing.T) {
+	minute, _ := time.ParseDuration("1m")
+	throttler := GenericThrottle{
+		Duration: minute,
+		Limit:    0,
+	}
+
+	for i := 0; i < 1024; i += 1 {
+		throttled, _ := throttler.Touch()
+		if throttled {
+			t.Error("disabled throttler should not throttle")
+		}
+	}
+}
+
+func TestConnectionThrottle(t *testing.T) {
+	minute, _ := time.ParseDuration("1m")
+	maxConnections := 3
+	config := ThrottlerConfig{
+		Enabled:            true,
+		CidrLenIPv4:        32,
+		CidrLenIPv6:        64,
+		ConnectionsPerCidr: maxConnections,
+		Duration:           minute,
+	}
+	throttler := NewThrottler()
+	throttler.ApplyConfig(config)
+
+	addr := net.ParseIP("8.8.8.8")
+
+	for i := 0; i < maxConnections; i += 1 {
+		err := throttler.AddClient(addr)
+		assertEqual(err, nil, t)
+	}
+	err := throttler.AddClient(addr)
+	assertEqual(err, errTooManyClients, t)
+}

irc/handlers.go

 
 // ACC REGISTER <accountname> [callback_namespace:]<callback> [cred_type] :<credential>
 func accRegisterHandler(server *Server, client *Client, msg ircmsg.IrcMessage, rb *ResponseBuffer) bool {
+	nick := client.Nick()
 	// clients can't reg new accounts if they're already logged in
 	if client.LoggedIntoAccount() {
-		rb.Add(nil, server.name, ERR_REG_UNSPECIFIED_ERROR, client.nick, "*", client.t("You're already logged into an account"))
+		rb.Add(nil, server.name, ERR_REG_UNSPECIFIED_ERROR, nick, "*", client.t("You're already logged into an account"))
 		return false
 	}
 
 	casefoldedAccount, err := CasefoldName(account)
 	// probably don't need explicit check for "*" here... but let's do it anyway just to make sure
 	if err != nil || msg.Params[1] == "*" {
-		rb.Add(nil, server.name, ERR_REG_UNSPECIFIED_ERROR, client.nick, account, client.t("Account name is not valid"))
+		rb.Add(nil, server.name, ERR_REG_UNSPECIFIED_ERROR, nick, account, client.t("Account name is not valid"))
 		return false
 	}
 
 	if len(msg.Params) < 4 {
-		rb.Add(nil, server.name, ERR_NEEDMOREPARAMS, client.nick, msg.Command, client.t("Not enough parameters"))
+		rb.Add(nil, server.name, ERR_NEEDMOREPARAMS, nick, msg.Command, client.t("Not enough parameters"))
 		return false
 	}
 
 	callbackNamespace, callbackValue := parseCallback(callbackSpec, server.AccountConfig())
 
 	if callbackNamespace == "" {
-		rb.Add(nil, server.name, ERR_REG_INVALID_CALLBACK, client.nick, account, callbackSpec, client.t("Callback namespace is not supported"))
+		rb.Add(nil, server.name, ERR_REG_INVALID_CALLBACK, nick, account, callbackSpec, client.t("Callback namespace is not supported"))
 		return false
 	}
 
 		}
 	}
 	if credentialType == "certfp" && client.certfp == "" {
-		rb.Add(nil, server.name, ERR_REG_INVALID_CRED_TYPE, client.nick, credentialType, callbackNamespace, client.t("You are not using a TLS certificate"))
+		rb.Add(nil, server.name, ERR_REG_INVALID_CRED_TYPE, nick, credentialType, callbackNamespace, client.t("You are not using a TLS certificate"))
 		return false
 	}
 
 	if !credentialValid {
-		rb.Add(nil, server.name, ERR_REG_INVALID_CRED_TYPE, client.nick, credentialType, callbackNamespace, client.t("Credential type is not supported"))
+		rb.Add(nil, server.name, ERR_REG_INVALID_CRED_TYPE, nick, credentialType, callbackNamespace, client.t("Credential type is not supported"))
 		return false
 	}
 
 	} else if credentialType == "passphrase" {
 		passphrase = credentialValue
 	}
+
+	throttled, remainingTime := client.loginThrottle.Touch()
+	if throttled {
+		rb.Add(nil, server.name, ERR_REG_UNSPECIFIED_ERROR, nick, fmt.Sprintf(client.t("Please wait at least %v and try again"), remainingTime))
+		return false
+	}
+
 	err = server.accounts.Register(client, account, callbackNamespace, callbackValue, passphrase, certfp)
 	if err != nil {
 		msg := "Unknown"
 		if err == errAccountAlreadyRegistered || err == errAccountCreation || err == errCertfpAlreadyExists {
 			msg = err.Error()
 		}
-		rb.Add(nil, server.name, code, client.nick, "ACC", "REGISTER", client.t(msg))
+		rb.Add(nil, server.name, code, nick, "ACC", "REGISTER", client.t(msg))
 		return false
 	}
 
 	} else {
 		messageTemplate := client.t("Account created, pending verification; verification code has been sent to %s:%s")
 		message := fmt.Sprintf(messageTemplate, callbackNamespace, callbackValue)
-		rb.Add(nil, server.name, RPL_REG_VERIFICATION_REQUIRED, client.nick, casefoldedAccount, message)
+		rb.Add(nil, server.name, RPL_REG_VERIFICATION_REQUIRED, nick, casefoldedAccount, message)
 	}
 
 	return false
 
 	var accountKey, authzid string
 
+	nick := client.Nick()
+
 	if len(splitValue) == 3 {
 		accountKey = string(splitValue[0])
 		authzid = string(splitValue[1])
 		if accountKey == "" {
 			accountKey = authzid
 		} else if accountKey != authzid {
-			rb.Add(nil, server.name, ERR_SASLFAIL, client.nick, client.t("SASL authentication failed: authcid and authzid should be the same"))
+			rb.Add(nil, server.name, ERR_SASLFAIL, nick, client.t("SASL authentication failed: authcid and authzid should be the same"))
 			return false
 		}
 	} else {
-		rb.Add(nil, server.name, ERR_SASLFAIL, client.nick, client.t("SASL authentication failed: Invalid auth blob"))
+		rb.Add(nil, server.name, ERR_SASLFAIL, nick, client.t("SASL authentication failed: Invalid auth blob"))
+		return false
+	}
+
+	throttled, remainingTime := client.loginThrottle.Touch()
+	if throttled {
+		rb.Add(nil, server.name, ERR_SASLFAIL, nick, fmt.Sprintf(client.t("Please wait at least %v and try again"), remainingTime))
 		return false
 	}
 
 	err := server.accounts.AuthenticateByPassphrase(client, accountKey, password)
 	if err != nil {
 		msg := authErrorToMessage(server, err)
-		rb.Add(nil, server.name, ERR_SASLFAIL, client.nick, fmt.Sprintf("%s: %s", client.t("SASL authentication failed"), client.t(msg)))
+		rb.Add(nil, server.name, ERR_SASLFAIL, nick, fmt.Sprintf("%s: %s", client.t("SASL authentication failed"), client.t(msg)))
 		return false
 	}
 

irc/nickserv.go

 	}
 }
 
+func nsLoginThrottleCheck(client *Client, rb *ResponseBuffer) (success bool) {
+	throttled, remainingTime := client.loginThrottle.Touch()
+	if throttled {
+		nsNotice(rb, fmt.Sprintf(client.t("Please wait at least %v and try again"), remainingTime))
+		return false
+	}
+	return true
+}
+
 func nsIdentifyHandler(server *Server, client *Client, command, params string, rb *ResponseBuffer) {
 	loginSuccessful := false
 
 
 	// try passphrase
 	if username != "" && passphrase != "" {
+		if !nsLoginThrottleCheck(client, rb) {
+			return
+		}
 		err := server.accounts.AuthenticateByPassphrase(client, username, passphrase)
 		loginSuccessful = (err == nil)
 	}
 	var newPassword string
 	var errorMessage string
 
+	hasPrivs := client.HasRoleCapabs("accreg")
+	if !hasPrivs && !nsLoginThrottleCheck(client, rb) {
+		return
+	}
+
 	fields := strings.Fields(params)
 	switch len(fields) {
 	case 2:
-		if !client.HasRoleCapabs("accreg") {
+		if !hasPrivs {
 			errorMessage = "Insufficient privileges"
 		} else {
 			target, newPassword = fields[0], fields[1]

oragono.yaml

     # is account authentication enabled?
     authentication-enabled: true
 
+    # throttle account login attempts (to prevent either password guessing, or DoS
+    # attacks on the server aimed at forcing repeated expensive bcrypt computations)
+    login-throttling:
+        enabled: true
+
+        # window
+        duration:  1m
+
+        # number of attempts allowed within the window
+        max-attempts: 3
+
     # some clients (notably Pidgin and Hexchat) offer only a single password field,
     # which makes it impossible to specify a separate server password (for the PASS
     # command) and SASL password. if this option is set to true, a client that