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diff --git a/contrib/pf/man/pf.os.5 b/contrib/pf/man/pf.os.5 new file mode 100644 index 0000000..485f69a --- /dev/null +++ b/contrib/pf/man/pf.os.5 @@ -0,0 +1,242 @@ +.\" $OpenBSD: pf.os.5,v 1.4 2003/08/28 09:41:23 jmc Exp $ +.\" +.\" Copyright (c) 2003 Mike Frantzen <frantzen@w4g.org> +.\" +.\" Permission to use, copy, modify, and distribute this software for any +.\" purpose with or without fee is hereby granted, provided that the above +.\" copyright notice and this permission notice appear in all copies. +.\" +.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES +.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF +.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR +.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES +.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN +.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF +.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. +.Dd August 18, 2003 +.Dt PF.OS 5 +.Os +.Sh NAME +.Nm pf.os +.Nd format of the operating system fingerprints file +.Sh DESCRIPTION +The +.Xr pf 4 +firewall and the +.Xr tcpdump 8 +program can both fingerprint the operating system of hosts that +originate an IPv4 TCP connection. +The file consists of newline-separated records, one per fingerprint, +containing nine colon +.Pq Ql \&: +separated fields. +These fields are as follows: +.Pp +.Bl -tag -width Description -offset indent -compact +.It window +The TCP window size. +.It TTL +The IP time to live. +.It df +The presence of the IPv4 don't fragment bit. +.It packet size +The size of the initial TCP packet. +.It TCP options +An ordered list of the TCP options. +.It class +The class of operating system. +.It version +The version of the operating system. +.It subtype +The subtype of patchlevel of the operating system. +.It description +The overall textual description of the operating system, version and subtype. +.El +.Pp +The +.Ar window +field corresponds to the th->th_win field in the TCP header and is the +source host's advertised TCP window size. +It may be between zero and 65,535 inclusive. +The window size may be given as a multiple of a constant by prepending +the size with a percent sign +.Sq % +and the value will be used as a modulus. +Three special values may be used for the window size: +.Pp +.Bl -tag -width xxx -offset indent -compact +.It * +An asterisk will wildcard the value so any window size will match. +.It S +Allow any window size which is a multiple of the maximum segment size (MSS). +.It T +Allow any window size which is a multiple of the maximum transmission unit +(MTU). +.El +.Pp +The +.Ar ttl +value is the initial time to live in the IP header. +The fingerprint code will account for the volatility of the packets's TTL +as it traverses a network. +.Pp +The +.Ar df +bit corresponds to the Don't Fragment bit in an IPv4 header. +It tells intermediate routers not to fragment the packet and is used for +path MTU discovery. +It may be either a zero or a one. +.Pp +The +.Ar packet size +is the literal size of the full IP packet and is a function of all of +the IP and TCP options. +.Pp +The +.Ar TCP options +field is an ordered list of the individual TCP options that appear in the +SYN packet. +Each option is described by a single character separated by a comma and +certain ones may include a value. +The options are: +.Pp +.Bl -tag -width Description -offset indent -compact +.It Mnnn +maximum segment size (MSS) option. +The value is the maximum packet size of the network link which may +include the +.Sq % +modulus or match all MSSes with the +.Sq * +value. +.It N +the NOP option (NO Operation). +.It T[0] +the timestamp option. +Certain operating systems always start with a zero timestamp in which +case a zero value is added to the option; otherwise no value is appended. +.It S +the Selective ACKnowledgement OK (SACKOK) option. +.It Wnnn +window scaling option. +The value is the size of the window scaling which may include the +.Sq % +modulus or match all window scalings with the +.Sq * +value. +.El +.Pp +No TCP options in the fingerprint may be given with a single dot +.Sq \&. . +.Pp +An example of OpenBSD's TCP options are: +.Pp +.Dl M*,N,N,S,N,W0,N,N,T +.Pp +The first option +.Ar M* +is the MSS option and will match all values. +The second and third options +.Ar N +will match two NOPs. +The fourth option +.Ar S +will match the SACKOK option. +The fifth +.Ar N +will match another NOP. +The sixth +.Ar W0 +will match a window scaling option with a zero scaling size. +The seventh and eighth +.Ar N +options will match two NOPs. +And the ninth and final option +.Ar T +will match the timestamp option with any time value. +.Pp +The TCP options in a fingerprint will only match packets with the +exact same TCP options in the same order. +.Pp +The +.Ar class +field is the class, genre or vender of the operating system. +.Pp +The +.Ar version +is the version of the operating system. +It is used to distinguish between different fingerprints of operating +systems of the same class but different versions. +.Pp +The +.Ar subtype +is the subtype or patch level of the operating system version. +It is used to distinguish between different fingerprints of operating +systems of the same class and same version but slightly different +patches or tweaking. +.Pp +The +.Ar description +is a general description of the operating system, its version, +patchlevel and any further useful details. +.Sh EXAMPLES +The fingerprint of a plain +.Ox 3.3 +host is: +.Bd -literal + 16384:64:1:64:M*,N,N,S,N,W0,N,N,T:OpenBSD:3.3::OpenBSD 3.3 +.Ed +.Pp +The fingerprint of an +.Ox 3.3 +host behind a PF scrubbing firewall with a no-df rule would be: +.Bd -literal + 16384:64:0:64:M*,N,N,S,N,W0,N,N,T:OpenBSD:3.3:!df:OpenBSD 3.3 scrub no-df +.Ed +.Pp +An absolutely braindead embedded operating system fingerprint could be: +.Bd -literal + 65535:255:0:40:.:DUMMY:1.1:p3:Dummy embedded OS v1.1p3 +.Ed +.Pp +The +.Xr tcpdump 8 +output of +.Bd -literal + # tcpdump -s128 -c1 -nv 'tcp[13] == 2' + 03:13:48.118526 10.0.0.1.3377 > 10.0.0.0.2: S [tcp sum ok] \e + 534596083:534596083(0) win 57344 <mss 1460> (DF) [tos 0x10] \e + (ttl 64, id 11315) +.Ed +.Pp +almost translates into the following fingerprint +.Bd -literal + 57344:64:1:44:M1460: exampleOS:1.0::exampleOS 1.0 +.Ed +.Pp +.Xr tcpdump 8 +does not explicitly give the packet length. +But it can usually be derived by adding the size of the IPv4 header to +the size of the TCP header to the size of the TCP options. +The size of both headers is typically twenty each and the usual +sizes of the TCP options are: +.Pp +.Bl -tag -width timestamp -offset indent -compact +.It mss +four bytes. +.It nop +1 byte. +.It sackOK +two bytes. +.It timestamp +ten bytes. +.It wscale +three bytes. +.El +.Pp +In the above example, the packet size comes out to 44 bytes. +.Sh SEE ALSO +.Xr pf 4 , +.Xr pf.conf 5 , +.Xr pfctl 8 , +.Xr tcpdump 8 |
