Bugfix: validate nicknames in server JOIN messages (Thanks Cauchy)

ircserver/server_commands.go

@@ -641,6 +641,18 @@ func (i *IRCServer) cmdServerJoin(s *Session, reply *Replyctx, msg *irc.Message)
			})
			continue
		}

		nick := NickToLower(msg.Prefix.Name)
		if _, ok := i.nicks[nick]; !ok {
			i.sendServices(reply, &irc.Message{
				Prefix:   i.ServerPrefix,
				Command:  irc.ERR_NOSUCHNICK,
				Params:   []string{msg.Prefix.Name, channelname},
				Trailing: "No such nick/channel",
			})
			continue
		}

		// TODO(secure): reduce code duplication with cmdJoin()
		c, ok := i.channels[ChanToLower(channelname)]
		if !ok {
@@ -650,11 +662,11 @@ func (i *IRCServer) cmdServerJoin(s *Session, reply *Replyctx, msg *irc.Message)
			}
			i.channels[ChanToLower(channelname)] = c
		}
		c.nicks[NickToLower(msg.Prefix.Name)] = &[maxChanMemberStatus]bool{}
		c.nicks[nick] = &[maxChanMemberStatus]bool{}
		// If the channel did not exist before, the first joining user becomes a
		// channel operator.
		if !ok {
			c.nicks[NickToLower(msg.Prefix.Name)][chanop] = true
			c.nicks[nick][chanop] = true
		}
		s.Channels[ChanToLower(channelname)] = true