Avoid deadlock on unknown user channel

gumble/gumble/handlers.go

@@ -660,7 +660,7 @@ func (c *Client) handleUserState(buffer []byte) error {
 			}
 			newChannel := c.Channels[*packet.ChannelId]
 			if newChannel == nil {
-				c.volatile.Lock()
+				c.volatile.Unlock()
 				return errInvalidProtobuf
 			}
 			if newChannel != user.Channel {

gumble/gumble/handlers_regression_test.go

@@ -0,0 +1,28 @@
+package gumble
+
+import (
+	"testing"
+	"time"
+
+	"git.stormux.org/storm/barnard/gumble/gumble/MumbleProto"
+	"google.golang.org/protobuf/proto"
+)
+
+// Regression: an out-of-order user move to an unknown channel used to lock
+// volatile twice, permanently deadlocking subsequent protocol handling.
+func TestUserStateUnknownChannelDoesNotDeadlock(t *testing.T) {
+	c := &Client{Config: NewConfig(), Users: make(Users), Channels: make(Channels)}
+	c.Users.create(1)
+	id, channel := uint32(1), uint32(99)
+	data, _ := proto.Marshal(&MumbleProto.UserState{Session: &id, ChannelId: &channel})
+	if err := c.handleUserState(data); err != errInvalidProtobuf {
+		t.Fatalf("got %v", err)
+	}
+	locked := make(chan struct{})
+	go func() { c.volatile.Lock(); c.volatile.Unlock(); close(locked) }()
+	select {
+	case <-locked:
+	case <-time.After(time.Second):
+		t.Fatal("volatile lock was left locked")
+	}
+}