improve security properties of INVITE

See #1171.

default.yaml

@@ -556,6 +556,10 @@ channels:
     # than this value will get an empty response to /LIST (a time period of 0 disables)
     list-delay: 0s
 
+    # INVITE to an invite-only channel expires after this amount of time
+    # (0 or omit for no expiration):
+    invite-expiration: 24h
+
 # operator classes
 oper-classes:
     # local operator

irc/channel.go

@@ -677,6 +677,7 @@ func (channel *Channel) Join(client *Client, key string, isSajoin bool, rb *Resp
 	chname := channel.name
 	chcfname := channel.nameCasefolded
 	founder := channel.registeredFounder
+	createdAt := channel.createdTime
 	chkey := channel.key
 	limit := channel.userLimit
 	chcount := len(channel.members)
@@ -695,7 +696,7 @@ func (channel *Channel) Join(client *Client, key string, isSajoin bool, rb *Resp
 	// 3. people invited with INVITE can join
 	hasPrivs := isSajoin || (founder != "" && founder == details.account) ||
 		(persistentMode != 0 && persistentMode != modes.Voice) ||
-		client.CheckInvited(chcfname)
+		client.CheckInvited(chcfname, createdAt)
 	if !hasPrivs {
 		if limit != 0 && chcount >= limit {
 			return errLimitExceeded
@@ -1475,23 +1476,33 @@ func (channel *Channel) Kick(client *Client, target *Client, comment string, rb
 
 // Invite invites the given client to the channel, if the inviter can do so.
 func (channel *Channel) Invite(invitee *Client, inviter *Client, rb *ResponseBuffer) {
-	chname := channel.Name()
-	if channel.flags.HasMode(modes.InviteOnly) && !channel.ClientIsAtLeast(inviter, modes.ChannelOperator) {
-		rb.Add(nil, inviter.server.name, ERR_CHANOPRIVSNEEDED, inviter.Nick(), chname, inviter.t("You're not a channel operator"))
-		return
-	}
+	channel.stateMutex.RLock()
+	chname := channel.name
+	chcfname := channel.nameCasefolded
+	createdAt := channel.createdTime
+	_, inviterPresent := channel.members[inviter]
+	_, inviteePresent := channel.members[invitee]
+	channel.stateMutex.RUnlock()
 
-	if !channel.hasClient(inviter) {
+	if !inviterPresent {
 		rb.Add(nil, inviter.server.name, ERR_NOTONCHANNEL, inviter.Nick(), chname, inviter.t("You're not on that channel"))
 		return
 	}
 
-	if channel.hasClient(invitee) {
+	inviteOnly := channel.flags.HasMode(modes.InviteOnly)
+	if inviteOnly && !channel.ClientIsAtLeast(inviter, modes.ChannelOperator) {
+		rb.Add(nil, inviter.server.name, ERR_CHANOPRIVSNEEDED, inviter.Nick(), chname, inviter.t("You're not a channel operator"))
+		return
+	}
+
+	if inviteePresent {
 		rb.Add(nil, inviter.server.name, ERR_USERONCHANNEL, inviter.Nick(), invitee.Nick(), chname, inviter.t("User is already on that channel"))
 		return
 	}
 
-	invitee.Invite(channel.NameCasefolded())
+	if inviteOnly {
+		invitee.Invite(chcfname, createdAt)
+	}
 
 	for _, member := range channel.Members() {
 		if member == inviter || member == invitee || !channel.ClientIsAtLeast(member, modes.Halfop) {

irc/client.go

@@ -84,7 +84,7 @@ type Client struct {
 	destroyed          bool
 	modes              modes.ModeSet
 	hostname           string
-	invitedTo          utils.StringSet
+	invitedTo          map[string]channelInvite
 	isSTSOnly          bool
 	languages          []string
 	lastActive         time.Time            // last time they sent a command that wasn't PONG or similar
@@ -1764,26 +1764,45 @@ func (client *Client) removeChannel(channel *Channel) {
 	}
 }
 
+type channelInvite struct {
+	channelCreatedAt time.Time
+	invitedAt        time.Time
+}
+
 // Records that the client has been invited to join an invite-only channel
-func (client *Client) Invite(casefoldedChannel string) {
+func (client *Client) Invite(casefoldedChannel string, channelCreatedAt time.Time) {
+	now := time.Now().UTC()
 	client.stateMutex.Lock()
 	defer client.stateMutex.Unlock()
 
 	if client.invitedTo == nil {
-		client.invitedTo = make(utils.StringSet)
+		client.invitedTo = make(map[string]channelInvite)
 	}
 
-	client.invitedTo.Add(casefoldedChannel)
+	client.invitedTo[casefoldedChannel] = channelInvite{
+		channelCreatedAt: channelCreatedAt,
+		invitedAt:        now,
+	}
+
+	return
 }
 
 // Checks that the client was invited to join a given channel
-func (client *Client) CheckInvited(casefoldedChannel string) (invited bool) {
+func (client *Client) CheckInvited(casefoldedChannel string, createdTime time.Time) (invited bool) {
+	config := client.server.Config()
+	expTime := time.Duration(config.Channels.InviteExpiration)
+	now := time.Now().UTC()
+
 	client.stateMutex.Lock()
 	defer client.stateMutex.Unlock()
 
-	invited = client.invitedTo.Has(casefoldedChannel)
-	// joining an invited channel "uses up" your invite, so you can't rejoin on kick
-	delete(client.invitedTo, casefoldedChannel)
+	curInvite, ok := client.invitedTo[casefoldedChannel]
+	if ok {
+		// joining an invited channel "uses up" your invite, so you can't rejoin on kick
+		delete(client.invitedTo, casefoldedChannel)
+	}
+	invited = ok && (expTime == time.Duration(0) || now.Sub(curInvite.invitedAt) < expTime) &&
+		createdTime.Equal(curInvite.channelCreatedAt)
 	return
 }
 

irc/config.go

@@ -574,7 +574,8 @@ type Config struct {
 			OperatorOnly          bool `yaml:"operator-only"`
 			MaxChannelsPerAccount int  `yaml:"max-channels-per-account"`
 		}
-		ListDelay time.Duration `yaml:"list-delay"`
+		ListDelay        time.Duration    `yaml:"list-delay"`
+		InviteExpiration custime.Duration `yaml:"invite-expiration"`
 	}
 
 	OperClasses map[string]*OperClassConfig `yaml:"oper-classes"`

traditional.yaml

@@ -528,6 +528,10 @@ channels:
     # than this value will get an empty response to /LIST (a time period of 0 disables)
     list-delay: 0s
 
+    # INVITE to an invite-only channel expires after this amount of time
+    # (0 or omit for no expiration):
+    invite-expiration: 24h
+
 # operator classes
 oper-classes:
     # local operator