module Net::SSH::Transport::PacketStream

A module that builds additional functionality onto the Net::SSH::BufferedIo module. It adds SSH encryption, compression, and packet validation, as per the SSH2 protocol. It also adds an abstraction for polling packets, to allow for both blocking and non-blocking reads.

Constants

PROXY_COMMAND_HOST_IP

Attributes

client[R]

The client state object, which encapsulates the algorithms used to build packets to send to the server.

hints[R]

The map of “hints” that can be used to modify the behavior of the packet stream. For instance, when authentication succeeds, an “authenticated” hint is set, which is used to determine whether or not to compress the data when using the “delayed” compression algorithm.

server[R]

The server state object, which encapsulates the algorithms used to interpret packets coming from the server.

Public Class Methods

extended(object) click to toggle source

# File lib/net/ssh/transport/packet_stream.rb, line 22
def self.extended(object)
  object.__send__(:initialize_ssh)
end

Public Instance Methods

available_for_read?() click to toggle source

Returns true if the IO is available for reading, and false otherwise.

# File lib/net/ssh/transport/packet_stream.rb, line 75
def available_for_read?
  result = IO.select([self], nil, nil, 0)
  result && result.first.any?
end

cleanup() click to toggle source

Performs any pending cleanup necessary on the IO and its associated state objects. (See Net::SSH::Transport::State#cleanup).

# File lib/net/ssh/transport/packet_stream.rb, line 186
def cleanup
  client.cleanup
  server.cleanup
end

client_name() click to toggle source

The name of the client (local) end of the socket, as reported by the socket.

# File lib/net/ssh/transport/packet_stream.rb, line 42
def client_name
  @client_name ||= begin
    sockaddr = getsockname
    begin
      Socket.getnameinfo(sockaddr, Socket::NI_NAMEREQD).first
    rescue StandardError
      begin
        Socket.getnameinfo(sockaddr).first
      rescue StandardError
        begin
          Socket.gethostbyname(Socket.gethostname).first
        rescue StandardError
          lwarn { "the client ipaddr/name could not be determined" }
          "unknown"
        end
      end
    end
  end
end

enqueue_packet(payload) click to toggle source

Enqueues a packet to be sent, but does not immediately send the packet. The given payload is pre-processed according to the algorithms specified in the client state (compression, cipher, and hmac).

# File lib/net/ssh/transport/packet_stream.rb, line 128
def enqueue_packet(payload)
  # try to compress the packet
  payload = client.compress(payload)

  # the length of the packet, minus the padding
  actual_length = (client.hmac.etm ? 0 : 4) + payload.bytesize + 1

  # compute the padding length
  padding_length = client.block_size - (actual_length % client.block_size)
  padding_length += client.block_size if padding_length < 4

  # compute the packet length (sans the length field itself)
  packet_length = payload.bytesize + padding_length + 1

  if packet_length < 16
    padding_length += client.block_size
    packet_length = payload.bytesize + padding_length + 1
  end

  padding = Array.new(padding_length) { rand(256) }.pack("C*")

  if client.hmac.etm
    debug { "using encrypt-then-mac" }

    # Encrypt padding_length, payload, and padding. Take MAC
    # from the unencrypted packet_lenght and the encrypted
    # data.
    length_data = [packet_length].pack("N")

    unencrypted_data = [padding_length, payload, padding].pack("CA*A*")

    encrypted_data = client.update_cipher(unencrypted_data) << client.final_cipher

    mac_data = length_data + encrypted_data

    mac = client.hmac.digest([client.sequence_number, mac_data].pack("NA*"))

    message = mac_data + mac
  else
    unencrypted_data = [packet_length, padding_length, payload, padding].pack("NCA*A*")

    mac = client.hmac.digest([client.sequence_number, unencrypted_data].pack("NA*"))

    encrypted_data = client.update_cipher(unencrypted_data) << client.final_cipher

    message = encrypted_data + mac
  end

  debug { "queueing packet nr #{client.sequence_number} type #{payload.getbyte(0)} len #{packet_length}" }
  enqueue(message)

  client.increment(packet_length)

  self
end

if_needs_rekey?() { || ... } click to toggle source

If the IO object requires a rekey operation (as indicated by either its client or server state objects, see Net::SSH::Transport::State#needs_rekey?), this will yield. Otherwise, this does nothing.

# File lib/net/ssh/transport/packet_stream.rb, line 194
def if_needs_rekey?
  if client.needs_rekey? || server.needs_rekey?
    yield
    client.reset! if client.needs_rekey?
    server.reset! if server.needs_rekey?
  end
end

next_packet(mode=:nonblock, timeout=nil) click to toggle source

Returns the next full packet. If the mode parameter is :nonblock (the default), then this will return immediately, whether a packet is available or not, and will return nil if there is no packet ready to be returned. If the mode parameter is :block, then this method will block until a packet is available or timeout seconds have passed.

# File lib/net/ssh/transport/packet_stream.rb, line 85
def next_packet(mode=:nonblock, timeout=nil)
  case mode
  when :nonblock then
    packet = poll_next_packet
    return packet if packet

    if available_for_read?
      if fill <= 0
        result = poll_next_packet
        if result.nil?
          raise Net::SSH::Disconnect, "connection closed by remote host"
        else
          return result
        end
      end
    end
    poll_next_packet

  when :block then
    loop do
      packet = poll_next_packet
      return packet if packet

      result = IO.select([self], nil, nil, timeout)
      raise Net::SSH::ConnectionTimeout, "timeout waiting for next packet" unless result
      raise Net::SSH::Disconnect, "connection closed by remote host" if fill <= 0
    end

  else
    raise ArgumentError, "expected :block or :nonblock, got #{mode.inspect}"
  end
end

peer_ip() click to toggle source

The IP address of the peer (remote) end of the socket, as reported by the socket.

# File lib/net/ssh/transport/packet_stream.rb, line 64
def peer_ip
  @peer_ip ||=
    if respond_to?(:getpeername)
      addr = getpeername
      Socket.getnameinfo(addr, Socket::NI_NUMERICHOST | Socket::NI_NUMERICSERV).first
    else
      PROXY_COMMAND_HOST_IP
    end
end

send_packet(payload) click to toggle source

Enqueues a packet to be sent, and blocks until the entire packet is sent.

# File lib/net/ssh/transport/packet_stream.rb, line 120
def send_packet(payload)
  enqueue_packet(payload)
  wait_for_pending_sends
end

Protected Instance Methods

initialize_ssh() click to toggle source

Called when this module is used to extend an object. It initializes the states and generally prepares the object for use as a packet stream.

# File lib/net/ssh/transport/packet_stream.rb, line 206
def initialize_ssh
  @hints  = {}
  @server = State.new(self, :server)
  @client = State.new(self, :client)
  @packet = nil
  initialize_buffered_io
end

poll_next_packet() click to toggle source

Tries to read the next packet. If there is insufficient data to read an entire packet, this returns immediately, otherwise the packet is read, post-processed according to the cipher, hmac, and compression algorithms specified in the server state object, and returned as a new Packet object.

# File lib/net/ssh/transport/packet_stream.rb, line 219
def poll_next_packet
  aad_length = server.hmac.etm ? 4 : 0

  if @packet.nil?
    minimum = server.block_size < 4 ? 4 : server.block_size
    return nil if available < minimum
    data = read_available(minimum + aad_length)

    # decipher it
    if server.hmac.etm
      @packet_length = data.unpack("N").first
      @mac_data = data
      @packet = Net::SSH::Buffer.new(server.update_cipher(data[aad_length..-1]))
    else
      @packet = Net::SSH::Buffer.new(server.update_cipher(data))
      @packet_length = @packet.read_long
    end
  end

  need = @packet_length + 4 - aad_length - server.block_size
  raise Net::SSH::Exception, "padding error, need #{need} block #{server.block_size}" if need % server.block_size != 0

  return nil if available < need + server.hmac.mac_length

  if need > 0
    # read the remainder of the packet and decrypt it.
    data = read_available(need)
    @mac_data += data if server.hmac.etm
    @packet.append(server.update_cipher(data))
  end

  # get the hmac from the tail of the packet (if one exists), and
  # then validate it.
  real_hmac = read_available(server.hmac.mac_length) || ""

  @packet.append(server.final_cipher)
  padding_length = @packet.read_byte

  payload = @packet.read(@packet_length - padding_length - 1)

  my_computed_hmac = if server.hmac.etm
                       server.hmac.digest([server.sequence_number, @mac_data].pack("NA*"))
                     else
                       server.hmac.digest([server.sequence_number, @packet.content].pack("NA*"))
                     end
  raise Net::SSH::Exception, "corrupted hmac detected" if real_hmac != my_computed_hmac

  # try to decompress the payload, in case compression is active
  payload = server.decompress(payload)

  debug { "received packet nr #{server.sequence_number} type #{payload.getbyte(0)} len #{@packet_length}" }

  server.increment(@packet_length)
  @packet = nil

  return Packet.new(payload)
end