ssh: allow to bind to a hostname in remote forwarding To avoid breaking backwards compatibility, we fix Listen, which receives the address as a string, while ListenTCP can still only be used with IP addresses. Fixes golang/go#33227 Fixes golang/go#37239 Change-Id: I4d45b40fdcb0d6012ed8da59a02149fa37e7db50 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/599995 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Junyang Shao <shaojunyang@google.com> Reviewed-by: Bishakh Ghosh <ghoshbishakh@gmail.com> Reviewed-by: Filippo Valsorda <filippo@golang.org> Auto-Submit: Nicola Murino <nicola.murino@gmail.com> Reviewed-by: Michael Pratt <mpratt@google.com>
diff --git a/ssh/streamlocal.go b/ssh/streamlocal.go index b171b33..152470f 100644 --- a/ssh/streamlocal.go +++ b/ssh/streamlocal.go
@@ -44,7 +44,7 @@ if !ok { return nil, errors.New("ssh: streamlocal-forward@openssh.com request denied by peer") } - ch := c.forwards.add(&net.UnixAddr{Name: socketPath, Net: "unix"}) + ch := c.forwards.add("unix", socketPath) return &unixListener{socketPath, c, ch}, nil } @@ -96,7 +96,7 @@ // Close closes the listener. func (l *unixListener) Close() error { // this also closes the listener. - l.conn.forwards.remove(&net.UnixAddr{Name: l.socketPath, Net: "unix"}) + l.conn.forwards.remove("unix", l.socketPath) m := streamLocalChannelForwardMsg{ l.socketPath, }
diff --git a/ssh/tcpip.go b/ssh/tcpip.go index 93d844f..78c41fe 100644 --- a/ssh/tcpip.go +++ b/ssh/tcpip.go
@@ -11,6 +11,7 @@ "io" "math/rand" "net" + "net/netip" "strconv" "strings" "sync" @@ -22,14 +23,21 @@ // the returned net.Listener. The listener must be serviced, or the // SSH connection may hang. // N must be "tcp", "tcp4", "tcp6", or "unix". +// +// If the address is a hostname, it is sent to the remote peer as-is, without +// being resolved locally, and the Listener Addr method will return a zero IP. func (c *Client) Listen(n, addr string) (net.Listener, error) { switch n { case "tcp", "tcp4", "tcp6": - laddr, err := net.ResolveTCPAddr(n, addr) + host, portStr, err := net.SplitHostPort(addr) if err != nil { return nil, err } - return c.ListenTCP(laddr) + port, err := strconv.ParseInt(portStr, 10, 32) + if err != nil { + return nil, err + } + return c.listenTCPInternal(host, int(port)) case "unix": return c.ListenUnix(addr) default: @@ -102,15 +110,24 @@ // ListenTCP requests the remote peer open a listening socket // on laddr. Incoming connections will be available by calling // Accept on the returned net.Listener. +// +// ListenTCP accepts an IP address, to provide a hostname use [Client.Listen] +// with "tcp", "tcp4", or "tcp6" network instead. func (c *Client) ListenTCP(laddr *net.TCPAddr) (net.Listener, error) { c.handleForwardsOnce.Do(c.handleForwards) if laddr.Port == 0 && isBrokenOpenSSHVersion(string(c.ServerVersion())) { return c.autoPortListenWorkaround(laddr) } + return c.listenTCPInternal(laddr.IP.String(), laddr.Port) +} + +func (c *Client) listenTCPInternal(host string, port int) (net.Listener, error) { + c.handleForwardsOnce.Do(c.handleForwards) + m := channelForwardMsg{ - laddr.IP.String(), - uint32(laddr.Port), + host, + uint32(port), } // send message ok, resp, err := c.SendRequest("tcpip-forward", true, Marshal(&m)) @@ -123,20 +140,33 @@ // If the original port was 0, then the remote side will // supply a real port number in the response. - if laddr.Port == 0 { + if port == 0 { var p struct { Port uint32 } if err := Unmarshal(resp, &p); err != nil { return nil, err } - laddr.Port = int(p.Port) + port = int(p.Port) } + // Construct a local address placeholder for the remote listener. If the + // original host is an IP address, preserve it so that Listener.Addr() + // reports the same IP. If the host is a hostname or cannot be parsed as an + // IP, fall back to IPv4zero. The port field is always set, even if the + // original port was 0, because in that case the remote server will assign + // one, allowing callers to determine which port was selected. + ip := net.IPv4zero + if parsed, err := netip.ParseAddr(host); err == nil { + ip = net.IP(parsed.AsSlice()) + } + laddr := &net.TCPAddr{ + IP: ip, + Port: port, + } + addr := net.JoinHostPort(host, strconv.FormatInt(int64(port), 10)) + ch := c.forwards.add("tcp", addr) - // Register this forward, using the port number we obtained. - ch := c.forwards.add(laddr) - - return &tcpListener{laddr, c, ch}, nil + return &tcpListener{laddr, addr, c, ch}, nil } // forwardList stores a mapping between remote @@ -149,8 +179,9 @@ // forwardEntry represents an established mapping of a laddr on a // remote ssh server to a channel connected to a tcpListener. type forwardEntry struct { - laddr net.Addr - c chan forward + addr string // host:port or socket path + network string // tcp or unix + c chan forward } // forward represents an incoming forwarded tcpip connection. The @@ -161,12 +192,13 @@ raddr net.Addr // the raddr of the incoming connection } -func (l *forwardList) add(addr net.Addr) chan forward { +func (l *forwardList) add(n, addr string) chan forward { l.Lock() defer l.Unlock() f := forwardEntry{ - laddr: addr, - c: make(chan forward, 1), + addr: addr, + network: n, + c: make(chan forward, 1), } l.entries = append(l.entries, f) return f.c @@ -185,19 +217,20 @@ if port == 0 || port > 65535 { return nil, fmt.Errorf("ssh: port number out of range: %d", port) } - ip := net.ParseIP(string(addr)) - if ip == nil { + ip, err := netip.ParseAddr(addr) + if err != nil { return nil, fmt.Errorf("ssh: cannot parse IP address %q", addr) } - return &net.TCPAddr{IP: ip, Port: int(port)}, nil + return &net.TCPAddr{IP: net.IP(ip.AsSlice()), Port: int(port)}, nil } func (l *forwardList) handleChannels(in <-chan NewChannel) { for ch := range in { var ( - laddr net.Addr - raddr net.Addr - err error + addr string + network string + raddr net.Addr + err error ) switch channelType := ch.ChannelType(); channelType { case "forwarded-tcpip": @@ -207,40 +240,34 @@ continue } - // RFC 4254 section 7.2 specifies that incoming - // addresses should list the address, in string - // format. It is implied that this should be an IP - // address, as it would be impossible to connect to it - // otherwise. - laddr, err = parseTCPAddr(payload.Addr, payload.Port) - if err != nil { - ch.Reject(ConnectionFailed, err.Error()) - continue - } + // RFC 4254 section 7.2 specifies that incoming addresses should + // list the address that was connected, in string format. It is the + // same address used in the tcpip-forward request. The originator + // address is an IP address instead. + addr = net.JoinHostPort(payload.Addr, strconv.FormatUint(uint64(payload.Port), 10)) + raddr, err = parseTCPAddr(payload.OriginAddr, payload.OriginPort) if err != nil { ch.Reject(ConnectionFailed, err.Error()) continue } - + network = "tcp" case "forwarded-streamlocal@openssh.com": var payload forwardedStreamLocalPayload if err = Unmarshal(ch.ExtraData(), &payload); err != nil { ch.Reject(ConnectionFailed, "could not parse forwarded-streamlocal@openssh.com payload: "+err.Error()) continue } - laddr = &net.UnixAddr{ - Name: payload.SocketPath, - Net: "unix", - } + addr = payload.SocketPath raddr = &net.UnixAddr{ Name: "@", Net: "unix", } + network = "unix" default: panic(fmt.Errorf("ssh: unknown channel type %s", channelType)) } - if ok := l.forward(laddr, raddr, ch); !ok { + if ok := l.forward(network, addr, raddr, ch); !ok { // Section 7.2, implementations MUST reject spurious incoming // connections. ch.Reject(Prohibited, "no forward for address") @@ -252,11 +279,11 @@ // remove removes the forward entry, and the channel feeding its // listener. -func (l *forwardList) remove(addr net.Addr) { +func (l *forwardList) remove(n, addr string) { l.Lock() defer l.Unlock() for i, f := range l.entries { - if addr.Network() == f.laddr.Network() && addr.String() == f.laddr.String() { + if n == f.network && addr == f.addr { l.entries = append(l.entries[:i], l.entries[i+1:]...) close(f.c) return @@ -274,11 +301,11 @@ l.entries = nil } -func (l *forwardList) forward(laddr, raddr net.Addr, ch NewChannel) bool { +func (l *forwardList) forward(n, addr string, raddr net.Addr, ch NewChannel) bool { l.Lock() defer l.Unlock() for _, f := range l.entries { - if laddr.Network() == f.laddr.Network() && laddr.String() == f.laddr.String() { + if n == f.network && addr == f.addr { f.c <- forward{newCh: ch, raddr: raddr} return true } @@ -288,6 +315,7 @@ type tcpListener struct { laddr *net.TCPAddr + addr string conn *Client in <-chan forward @@ -314,13 +342,21 @@ // Close closes the listener. func (l *tcpListener) Close() error { + host, port, err := net.SplitHostPort(l.addr) + if err != nil { + return err + } + rport, err := strconv.ParseUint(port, 10, 32) + if err != nil { + return err + } m := channelForwardMsg{ - l.laddr.IP.String(), - uint32(l.laddr.Port), + host, + uint32(rport), } // this also closes the listener. - l.conn.forwards.remove(l.laddr) + l.conn.forwards.remove("tcp", l.addr) ok, _, err := l.conn.SendRequest("cancel-tcpip-forward", true, Marshal(&m)) if err == nil && !ok { err = errors.New("ssh: cancel-tcpip-forward failed")
diff --git a/ssh/test/forward_unix_test.go b/ssh/test/forward_unix_test.go index c10d1d0..549d46c 100644 --- a/ssh/test/forward_unix_test.go +++ b/ssh/test/forward_unix_test.go
@@ -51,6 +51,8 @@ } }() + // The forwarded address match the listen address because we run the tests + // on the same host. forwardedAddr := sshListener.Addr().String() netConn, err := net.Dial(n, forwardedAddr) if err != nil { @@ -111,6 +113,8 @@ } func TestPortForwardTCP(t *testing.T) { + testPortForward(t, "tcp", ":0") + testPortForward(t, "tcp", "[::]:0") testPortForward(t, "tcp", "localhost:0") }