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PacketFu::Packet

Packet is the parent class of EthPacket, IPPacket, UDPPacket, TCPPacket, and all other packets. It acts as both a singleton class, so things like Packet.parse can happen, and as an abstract class to provide subclasses some structure.

Attributes

flavor[R]
headers[RW]
iface[RW]
inspect_style[RW]

Public Class Methods

can_parse?(str) click to toggle source

Packet subclasses must override this, since the Packet superclass can't actually parse anything.

# File lib/packetfu/packet.rb, line 281
def self.can_parse?(str)
        false
end
force_binary(str) click to toggle source

Force strings into binary.

# File lib/packetfu/packet.rb, line 21
def self.force_binary(str)
        str.force_encoding Encoding::BINARY if str.respond_to? :force_encoding
end
inherited(subclass) click to toggle source

Register subclasses in PacketFu.packet_class to do all kinds of neat things that obviates those long if/else trees for parsing. It's pretty sweet.

# File lib/packetfu/packet.rb, line 16
def self.inherited(subclass)
        PacketFu.add_packet_class(subclass)
end
layer() click to toggle source

Defines the layer this packet type lives at, based on the number of headers it requires. Note that this has little to do with the OSI model, since TCP/IP doesn't really have Session and Presentation layers.

Ethernet and the like are layer 1, IP, IPv6, and ARP are layer 2, TCP, UDP, and other transport protocols are layer 3, and application protocols are at layer 4 or higher. InvalidPackets have an arbitrary layer 0 to distinguish them.

Because these don't change much, it's cheaper just to case through them, and only resort to counting headers if we don't have a match -- this makes adding protocols somewhat easier, but of course you can just override this method over there, too. This is merely optimized for the most likely protocols you see on the Internet.

# File lib/packetfu/packet.rb, line 250
def self.layer
        case self.name # Lol ran into case's fancy treatment of classes
        when /InvalidPacket$/; 0
        when /EthPacket$/; 1
        when /IPPacket$/, /ARPPacket$/, /LLDPPacket$/, /IPv6Packet$/; 2
        when /TCPPacket$/, /UDPPacket$/, /ICMPPacket$/; 3
        when /HSRPPacket$/; 4
        else; self.new.headers.size
        end
end
layer_symbol() click to toggle source
# File lib/packetfu/packet.rb, line 265
def self.layer_symbol
        case self.layer
        when 0; :invalid
        when 1; :link
        when 2; :internet
        when 3; :transport
        else; :application
        end
end
new(args={}) click to toggle source

the Packet class should not be instantiated directly, since it's an abstract class that real packet types inherit from. Sadly, this makes the Packet class more difficult to test directly.

# File lib/packetfu/packet.rb, line 466
def initialize(args={})
        if self.class.name =~ /(::|^)PacketFu::Packet$/
                raise NoMethodError, "method `new' called for abstract class #{self.class.name}"
        end
        @inspect_style = args[:inspect_style] || PacketFu.inspect_style || :dissect
        if args[:config]
                args[:config].each_pair do |k,v|
                        case k
                        when :eth_daddr; @eth_header.eth_daddr=v if @eth_header
                        when :eth_saddr; @eth_header.eth_saddr=v if @eth_header
                        when :ip_saddr; @ip_header.ip_saddr=v               if @ip_header
                        when :iface; @iface = v
                        end
                end
        end
end
parse(packet=nil,args={}) click to toggle source

Parse() creates the correct packet type based on the data, and returns the apporpiate Packet subclass object.

There is an assumption here that all incoming packets are either EthPacket or InvalidPacket types. This will be addressed pretty soon.

If application-layer parsing is /not/ desired, that should be indicated explicitly with an argument of :parse_app => false. Otherwise, app-layer parsing will happen.

It is no longer neccisary to manually add packet types here.

# File lib/packetfu/packet.rb, line 35
def self.parse(packet=nil,args={})
        parse_app = true if(args[:parse_app].nil? or args[:parse_app])
        force_binary(packet)
        if parse_app
                classes = PacketFu.packet_classes.select {|pclass| pclass.can_parse? packet}
        else
                classes = PacketFu.packet_classes.select {|pclass| pclass.can_parse? packet}.reject {|pclass| pclass.layer_symbol == :application}
        end
        p = classes.sort {|x,y| x.layer <=> y.layer}.last.new
        parsed_packet = p.read(packet,args)
end

Public Instance Methods

==(other) click to toggle source

If two packets are represented as the same binary string, and they're both actually PacketFu packets of the same sort, they're equal.

The intuitive result is that a packet of a higher layer (like DNSPacket) can be equal to a packet of a lower level (like UDPPacket) as long as the bytes are equal (this can come up if a transport-layer packet has a hand-crafted payload that is identical to what would have been created by using an application layer packet)

# File lib/packetfu/packet.rb, line 188
def ==(other)
        return false unless other.kind_of? self.class
        return false unless other.respond_to? :to_s
        self.to_s == other.to_s
end
clone() click to toggle source

Packets are bundles of lots of objects, so copying them is a little complicated -- a dup of a packet is actually full of pass-by-reference stuff in the @headers, so if you change one, you're changing all this copies, too.

Normally, this doesn't seem to be a big deal, and it's a pretty decent performance tradeoff. But, if you're going to be creating a template packet to base a bunch of slightly different ones off of (like a fuzzer might), you'll want to use clone()

# File lib/packetfu/packet.rb, line 176
def clone
        Packet.parse(self.to_s)
end
dissect() click to toggle source

Renders the dissection_table suitable for screen printing. Can take one or two arguments. If just the one, only that layer will be displayed take either a range or a number -- if a range, only protos within that range will be rendered. If an integer, only that proto will be rendered.

# File lib/packetfu/packet.rb, line 359
def dissect
        dtable = self.dissection_table
        hex_body = nil
        if dtable.last.kind_of?(Array) and dtable.last.first == :body
                body = dtable.pop 
                hex_body = hexify(body[1])
        end
        elem_widths = [0,0,0]
        dtable.each do |proto_table|
                proto_table[1].each do |elems|
                        elems.each_with_index do |e,i|
                                width = e.size
                                elem_widths[i] = width if width > elem_widths[i]
                        end
                end
        end
        total_width = elem_widths.inject(0) {|sum,x| sum+x} 
        table = ""
        dtable.each do |proto|
                table << "--"
                table << proto[0] 
                if total_width > proto[0].size
                        table << ("-" * (total_width - proto[0].size + 2))
                else
                        table << ("-" * (total_width + 2))
                end
                table << "\n"
                proto[1].each do |elems|
                        table << "  "
                        elems_table = []
                        (0..2).each do |i|
                                elems_table << ("%-#{elem_widths[i]}s" % elems[i])
                        end
                        table << elems_table.join("\s")
                        table << "\n"
                end
        end
        if hex_body && !hex_body.empty?
                table << "-" * 66
                table << "\n"
                table << "00-01-02-03-04-05-06-07-08-09-0a-0b-0c-0d-0e-0f---0123456789abcdef\n"
                table << "-" * 66
                table << "\n"
                table << hex_body
        end
        table
end
dissection_table() click to toggle source
# File lib/packetfu/packet.rb, line 327
def dissection_table
        table = []
        @headers.each_with_index do |header,table_idx|
                proto = header.class.name.sub(/^.*::/,"")
                table << [proto,[]]
                header.class.members.each do |elem|
                        elem_sym = elem.to_sym # to_sym needed for 1.8
                        next if elem_sym == :body 
                        elem_type_value = []
                        elem_type_value[0] = elem
                        readable_element = "#{elem}_readable"
                        if header.respond_to? readable_element
                                elem_type_value[1] = header.send(readable_element)
                        else
                                elem_type_value[1] = header.send(elem)
                        end
                        elem_type_value[2] = header[elem.to_sym].class.name 
                        table[table_idx][1] << elem_type_value
                end
        end
        table
        if @headers.last.members.map {|x| x.to_sym }.include? :body
                body_part = [:body, self.payload, @headers.last.body.class.name]
        end
        table << body_part
end
handle_is_identity(ptype) click to toggle source
# File lib/packetfu/packet.rb, line 47
def handle_is_identity(ptype)
        idx = PacketFu.packet_prefixes.index(ptype.to_s.downcase)
        if idx
                self.kind_of? PacketFu.packet_classes[idx]
        else
                raise NoMethodError, "Undefined method `is_#{ptype}?' for #{self.class}."
        end
end
hexify(str) click to toggle source

Hexify provides a neatly-formatted dump of binary data, familar to hex readers.

# File lib/packetfu/packet.rb, line 286
def hexify(str)
        str.force_encoding(Encoding::BINARY) if str.respond_to? :force_encoding
        hexascii_lines = str.to_s.unpack("H*")[0].scan(/.{1,32}/)
        regex = Regexp.new('[\x00-\x1f\x7f-\xff]', nil, 'n')
        chars = str.to_s.gsub(regex,'.')
        chars_lines = chars.scan(/.{1,16}/)
        ret = []
        hexascii_lines.size.times {|i| ret << "%-48s  %s" % [hexascii_lines[i].gsub(/(.{2})/,"\\1 "),chars_lines[i]]}
        ret.join("\n")
end
inspect() click to toggle source

For packets, inspect is overloaded as inspect_hex(0). Not sure if this is a great idea yet, but it sure makes the irb output more sane.

If you hate this, you can run PacketFu.toggle_inspect to return to the typical (and often unreadable) Object#inspect format.

# File lib/packetfu/packet.rb, line 428
def inspect
        case @inspect_style
        when :dissect
                self.dissect
        when :hex
                self.proto.join("|") + "\n" + self.inspect_hex
        else
                super
        end
end
inspect_hex(arg=0) click to toggle source

If @inspect_style is :default (or :ugly), the inspect output is the usual inspect.

If @inspect_style is :hex (or :pretty), the inspect output is a much more compact hexdump-style, with a shortened set of packet header names at the top.

If @inspect_style is :dissect (or :verbose), the inspect output is the longer, but more readable, dissection of the packet. This is the default.

TODO: Have an option for colors. Everyone loves colorized irb output.

# File lib/packetfu/packet.rb, line 308
def inspect_hex(arg=0)
        case arg
        when :layers
                ret = []
                @headers.size.times do |i|
                        ret << hexify(@headers[i])
                end
                ret
        when (0..9)
                if @headers[arg]
                        hexify(@headers[arg])
                else
                        nil
                end
        when :all
                inspect_hex(0)
        end
end
inspect_style=() click to toggle source

Delegate to PacketFu's inspect_style, since the class variable name is the same. Yay for namespace pollution!

# File lib/packetfu/packet.rb, line 486
def inspect_style=()
        PacketFu.inspect_style(arg)
end
kind_of?(klass) click to toggle source
# File lib/packetfu/packet.rb, line 409
def kind_of?(klass)
        return true if orig_kind_of? klass
        packet_types = proto.map {|p| PacketFu.const_get("#{p}Packet")}
        match = false
        packet_types.each do |p|
                if p.ancestors.include? klass
                        match =  true
                        break
                end
        end
        return match
end
Also aliased as: orig_kind_of?
layer() click to toggle source
# File lib/packetfu/packet.rb, line 261
def layer
        self.class.layer
end
layer_symbol() click to toggle source
# File lib/packetfu/packet.rb, line 275
def layer_symbol
        self.class.layer_symbol
end
length() click to toggle source
Alias for: size
method_missing(sym, *args, &block) click to toggle source

method_missing() delegates protocol-specific field actions to the apporpraite class variable (which contains the associated packet type) This register-of-protocols style switch will work for the forseeable future (there aren't /that/ many packet types), and it's a handy way to know at a glance what packet types are supported.

# File lib/packetfu/packet.rb, line 495
def method_missing(sym, *args, &block)
        case sym.to_s
        when /^is_([a-zA-Z0-9]+)\?/
                ptype = $1
                if PacketFu.packet_prefixes.index(ptype)
                        self.send(:handle_is_identity, $1)
                else
                        super
                end
        when /^([a-zA-Z0-9]+)_.+/
                ptype = $1
                if PacketFu.packet_prefixes.index(ptype)
                        self.instance_variable_get("@#{ptype}_header").send(sym,*args, &block)
                else
                        super
                end
        else
                super
        end
end
orig_kind_of?(klass) click to toggle source
Alias for: kind_of?
payload() click to toggle source

Get the outermost payload (body) of the packet; this is why all packet headers should have a body type.

# File lib/packetfu/packet.rb, line 68
def payload
        @headers.last.body
end
payload=(args) click to toggle source

Set the outermost payload (body) of the packet.

# File lib/packetfu/packet.rb, line 73
def payload=(args)
        @headers.last.body=(args)
end
peek(args={}) click to toggle source

Peek provides summary data on packet contents.

Each packet type should provide a peek_format.

# File lib/packetfu/packet.rb, line 197
def peek(args={})
        idx = @headers.reverse.map {|h| h.respond_to? peek_format}.index(true)
        if idx
                @headers.reverse[idx].peek_format
        else
                peek_format
        end
end
peek_format() click to toggle source

The peek_format is used to display a single line of packet data useful for eyeballing. It should not exceed 80 characters. The Packet superclass defines an example peek_format, but it should hardly ever be triggered, since peek traverses the @header list in reverse to find a suitable format.

Format

* A one or two character protocol initial. It should be unique
* The packet size
* Useful data in a human-usable form.

Ideally, related peek_formats will all line up with each other when printed to the screen.

Example

tcp_packet.peek
#=> "T  1054 10.10.10.105:55000   ->   192.168.145.105:80 [......] S:adc7155b|I:8dd0"
tcp_packet.peek.size
#=> 79
# File lib/packetfu/packet.rb, line 229
def peek_format
        peek_data = ["?  "]
        peek_data << "%-5d" % self.to_s.size
        peek_data << "%68s" % self.to_s[0,34].unpack("H*")[0]
        peek_data.join
end
proto() click to toggle source

Returns an array of protocols contained in this packet. For example:

t = PacketFu::TCPPacket.new
=> 00 1a c5 00 00 00 00 1a c5 00 00 00 08 00 45 00   ..............E.
00 28 3c ab 00 00 ff 06 7f 25 00 00 00 00 00 00   .(<......%......
00 00 93 5e 00 00 ad 4f e4 a4 00 00 00 00 50 00   ...^...O......P.
40 00 4a 92 00 00                                 @.J...
t.proto
=> ["Eth", "IP", "TCP"]
# File lib/packetfu/packet.rb, line 454
def proto
        type_array = []
        self.headers.each {|header| type_array << header.class.to_s.split('::').last.gsub(/Header$/,'')}
        type_array
end
Also aliased as: protocol
protocol() click to toggle source
Alias for: proto
read(args={}) click to toggle source

Read() takes (and trusts) the io input and shoves it all into a well-formed Packet. Note that read is a destructive process, so any existing data will be lost.

A note on the :strip => true argument: If :strip is set, defined lengths of data will be believed, and any trailers (such as frame check sequences) will be chopped off. This helps to ensure well-formed packets, at the cost of losing perhaps important FCS data.

If :strip is false, header lengths are /not/ believed, and all data will be piped in. When capturing from the wire, this is usually fine, but recalculating the length before saving or re-transmitting will absolutely change the data payload; FCS data will become part of the TCP data as far as tcp_len is concerned. Some effort has been made to preserve the "real" payload for the purposes of checksums, but currently, it's impossible to seperate new payload data from old trailers, so things like pkt.payload += "some data" will not work correctly.

So, to summarize; if you intend to alter the data, use :strip. If you don't, don't. Also, this is a horrid hack. Stripping is useful (and fun!), but the default behavior really should be to create payloads correctly, and /not/ treat extra FCS data as a payload.

Finally, packet subclasses should take two arguments: the string that is the data to be transmuted into a packet, as well as args. This superclass method is merely concerned with handling args common to many packet formats (namely, fixing packets on the fly)

# File lib/packetfu/packet.rb, line 158
def read(args={})
        if args[:fix] || args[:recalc]
                ip_recalc(:ip_sum) if self.is_ip?
                recalc(:tcp) if self.is_tcp?
                recalc(:udp) if self.is_udp?
        end
end
recalc(arg=:all) click to toggle source

Recalculates all the calcuated fields for all headers in the packet. This is important since read() wipes out all the calculated fields such as length and checksum and what all.

# File lib/packetfu/packet.rb, line 114
def recalc(arg=:all)
        case arg
        when :ip
                ip_recalc(:all)
        when :icmp
                icmp_recalc(:all)
        when :udp
                udp_recalc(:all)
        when :tcp
                tcp_recalc(:all)
        when :all
                ip_recalc(:all) if @ip_header
                icmp_recalc(:all) if @icmp_header
                udp_recalc(:all) if @udp_header
                tcp_recalc(:all) if @tcp_header
        else
                raise ArgumentError, "Recalculating `#{arg}' unsupported. Try :all"
        end
        @headers[0]
end
respond_to?(sym, include_private = false) click to toggle source
# File lib/packetfu/packet.rb, line 516
def respond_to?(sym, include_private = false)
        if sym.to_s =~ /^(invalid|eth|arp|ip|icmp|udp|hsrp|tcp|ipv6)_/
                self.instance_variable_get("@#{$1}_header").respond_to? sym
        elsif sym.to_s =~ /^is_([a-zA-Z0-9]+)\?/
                if PacketFu.packet_prefixes.index($1)
                        true
                else
                        super
                end
        else
                super
        end
end
size() click to toggle source

Returns the size of the packet (as a binary string)

# File lib/packetfu/packet.rb, line 440
def size
        self.to_s.size
end
Also aliased as: length
to_f(filename=nil,mode='w') click to toggle source

Put the entire packet into a libpcap file. XXX: this is a hack for now just to confirm that packets are getting created correctly. Now with append! XXX: Document this!

# File lib/packetfu/packet.rb, line 89
def to_f(filename=nil,mode='w')
        filename ||= 'out.pcap'
        mode = mode.to_s[0,1] + "b"
        raise ArgumentError, "Unknown mode: #{mode.to_s}" unless mode =~ /^[wa]/
        if(mode == 'w' || !(File.exists?(filename)))
                data = [PcapHeader.new, self.to_pcap].map {|x| x.to_s}.join
        else
                data = self.to_pcap
        end
        File.open(filename, mode) {|f| f.write data}
        return [filename, 1, data.size]
end
to_pcap(args={}) click to toggle source

Converts a packet to libpcap format. Bit of a hack?

# File lib/packetfu/packet.rb, line 78
def to_pcap(args={})
        p = PcapPacket.new(:endian => args[:endian],
                                                                                :timestamp => Timestamp.new.to_s,
                                                                                :incl_len => self.to_s.size,
                                                                                :orig_len => self.to_s.size,
                                                                                :data => self)
end
to_s() click to toggle source

Get the binary string of the entire packet.

# File lib/packetfu/packet.rb, line 57
def to_s
        @headers[0].to_s
end
to_w(iface=nil) click to toggle source

Put the entire packet on the wire by creating a temporary PacketFu::Inject object. TODO: Do something with auto-checksumming?

# File lib/packetfu/packet.rb, line 104
def to_w(iface=nil)
        iface = (iface || self.iface || PacketFu::Config.new.config[:iface]).to_s
        inj = PacketFu::Inject.new(:iface => iface)
        inj.array = [@headers[0].to_s]
        inj.inject
end
write(io) click to toggle source

In the event of no proper decoding, at least send it to the inner-most header.

# File lib/packetfu/packet.rb, line 62
def write(io)
        @headers[0].write(io)
end

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