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-*****************************************************************************
-27 Oct 94
-Hi again!
-So thanx to Brian McGovern , i'v took this piece of code in hands again
-and made some changes:
- 1) Port to FreeBSD 2.0 , so we will not go after time.
- 2) Some minor changes in kernel part to improve speed and such..
- 3) Chane in behaviour: now any recently added firewall definition
- preferred on other matching but older firewalls.
- REMEMBER: in any case universal IP firewall has larger preference
- then special TCP/UDP/ICMP firewalls.
- 4) Cosmetical changes to control programm. Now it is called ipfw.
- 5) Changed ip_firewall.* to ip_fw.* in kernel,and shortened some long
- variable names.
- 6) From now on we have user defined *policy*,which is DENY/ACCEPT for
- every packet which does not matches any of firewalls.I.e.: if any
- firewall defined and packet does not match them you may set it up
- so it will be anyway throwed or anyway accepted.
-Mostly that's all.
-Bye!
-
---
- -= Ugen J.S.Antsilevich =-
- NetVision - Commercial Internet Provider
------------------------------------------------------[C]---
-NetVision - Home of Israeli Commercial Internet
- E-mail: ugen@NetVision.net.il
- HTTP: http://www.NetVision.net.il/~ugen/
- Phone: +972-4-550330 Fax: +972-4-550122
-
-*****************************************************************************
-10 Jul 94
-Hi again...So i sitted and stared at this nice working tool and thought to
-myself that it's nice but something there it needs and have not..
-So i took a piece of file and a keyboard and typed some strings.
-What it was is:
-
-o List facility improved...Now listing of currently installed firewall
- entries does not go through kernel printf's ,which is really unnice to
- one who runs it NOT from console:)
-
-o Really important facility of deleting entries added..Yes , till this
- day you had to remove all entries and then add them one by one again
- to remove actually just one.Now it's over:)
-
-o All this changes documented in this readme,while you will see where i
- added my words just by vast number of mistaces in English.Well,i hope
- you will forgive one Russian guy like me:)
-
-So enjoy this new code and if you think it needs some additions - you
-are welcome to suggest.Also i made some more warnings , while compiling
-this code,i have no a clue where do they come from,however they does not
-make any bad to programm.But if you will find way to remove them,feel free
-to do it and post anywhere(and notify me as i also need this:)
-
- Bye! Ugen J.S.Antsilevich
-
-
-##########################################################################
-# Ugen J.S.Antsilevich NetVision (Israel) System Staff Member #
-#------------------------------------------------------------------------#
-# Email: ugen@NetVision.net.il | Phone: 972-4-550330 #
-# ugen@NetManage.co.il | Fax: 972-4-550122 #
-#------------------------------------------------------------------------#
-# WWW HomePage: http://www.NetVision.net.il/~ugen #
-# Special : Volk@Les.Tambov.SU #
-##########################################################################
-
-
-*****************************************************************************
-8 Jul 94
-OK..so first of all,this is simple port to FreeBSD by Ugen J.S.Antsilevich
-Actually all i had to do is to find appropriate place in kernel source files
-for ipfirewall stuff..so all your thanks should go to the author...
-Anyway i am porting it now to 1.1.5 (not much job though..:) so if you want
-to ask something about write to me:
-
-ugen@NetVision.net.il
-
-That's it and let the --==REAL==-- author speak...
-*****************************************************************************
-
-Here's my ipfirewall facility. I consider it to still be beta quality mostly
-because the various interfaces are pretty crude. Here's some information that
-you'll probably find useful (in roughly the order in which you'll need to know
-it). Some of this will be absurdly simplistic. Better safe than sorry...
-
-This software was written for BSD/386. The current version has been ported
-to BSD/386 v1.1. The context diffs are with respect to that version of
-BSD/386. If you don't have access to BSD/386 v1.1 and can't make sense out of
-the diffs, contact me and I'll send you the entire files (they are copyrighted
-by UC-Berkeley with very 'friendly' conditions).
-
-Speaking of copyrights, here's mine:
-
-/*
- * Copyright (c) 1993 Daniel Boulet
- * Copyright (c) 1994 Ugen J.S.Antsilevich
- *
- * Redistribution and use in source forms, with and without modification,
- * are permitted provided that this entire comment appears intact.
- *
- * Redistribution in binary form may occur without any restrictions.
- * Obviously, it would be nice if you gave credit where credit is due
- * but requiring it would be too onerous.
- *
- * This software is provided ``AS IS'' without any warranties of any kind.
- */
-
-Enough introductory stuff, here we go...
-
- 1) The file IPFIREWALL is the configuration of kernel i use with
- IPFIREWALL and GATEWAY options enabled. You may not find it useful.
- About the only key things are that it enables the IPFIREWALL
- option and the GATEWAY option. IPFIREWALL turns on my
- stuff and GATEWAY turns your machine into an IP router.
-
- There is nothing magical about the name of this file or the
- ident name for the kernel.
-
- 2) The files ip_fw.c and ip_fw.h are new files that should be
- placed into the /usr/src/sys/netinet directory.
-
- 3) The files ip_input.c and raw_ip.c are new patched versions of the
- same files , they made up for version 2.0 of FreeBSD,however it was
- some pre-Beta release we worked on , so to add it to other releases
- just find all parts of code surrounded by:
- #ifdef IPFIREWALL
- ....
- #endif
- and place in the appropriate places in the same files.
- All those files are in /usr/src/sys/netinet directory of corse.
-
- 4) Add the line "netinet/ip_fw.c optional ipfirewall" to the
- file /usr/src/sys/conf/files. This tells the config program to
- include the netinet/ip_fw.c file if the IPFIREWALL option is
- defined for a kernel.
-
- 5) The Makefile and ipfw.c files should go into directory probably
- back in your home directory tree somewhere. If this ever becomes a
- part of the system then they should go into the (newly created)
- directory /usr/src/sbin/ipfw.
-
- 6) Build yourself a kernel, make a backup of the current kernel and
- and install the new one. It should behave in a completely normal
- fashion since you won't have defined any firewalls yet.
-
- 7) Explore the ipfw program. The smartest way to do this is to
- compile the program and then run it.To do it you SHOULD be root
- as the programm uses setsockopt on RAW sockets to define firewalls,
- and also reads kernel symbols.If any other user will run ipw
- it will detect that it isn't being run by root and will just
- complain and exit.
- The ipfw program takes command line parameters
- and (assuming they are valid) issues a single appropriate setsockopt
- call. If you're defining 5 firewalls then you'll have to run the
- program 5 times. See below for a description of the command syntax
- of ipfirewall.
-
- ====================================================================
- WARNING!!! WARNING!!! WARNING!!! WARNING!!! WARNING!!! WARNING!!!
- The ipfw program can be used to put your machine into very
- disfunctional state.So if you want to test it make sure you
- a) Have read carifully this README till it's end.
- b) First time run it from machine console,as else you can
- simply shut down your own access to it.
- ====================================================================
- Make sure that you never setup the program as setuid root!!! Instead,
- always run it from the root command line or from "/etc/rc.local"
- as part of the boot process.
-
- 8) Use the "ipfirewall" checkb or checkf command (see below) to pass some
- test packets through the firewalls that you've defined.
-
- 9) You may find it useful to create a file in which the first line is
- "ipfirewall flush" to flush any existing firewalls and the remaining
- lines are the ipfirewall commands needed to define the firewalls that
- you want to use. This will ensure that you're always working from a
- known state.
-
- 10) If you've gotten this far then you're probably ready to let the critter
- see prime time. Copy your file of ipfirewall commands into the
- /etc/rc.local file and reboot the system. Once you're up, use the
- ipfirewall list command to see that you've got the firewalls that you
- wanted and try to test the firewall with real packets from trusted
- and untrusted hosts.
-
-Enough of that. Here's the syntax for the ipfirewall command. It is rather
-complex and yet simple at the same time (if you know what I mean). There
-are seven sub-commands. Probably the easiest way to get into this is to give
-you a roughly BNF style grammar for the command (curly brackets are used for
-precedence, alternatives are separated by |, optional things are enclosed
-in square brackets, white space is required if it appears below and must
-not appear if there isn't any between the tokens below (i.e. no white space
-around periods, colons or slashes, whitespace required between all other
-tokens)):
-
- command ::= ipfirewall <list> | <flush> | <check> | <add> | <del>
-
- <list> ::= list
-
- <flush> ::= flush
-
- <check> ::= { checkb[locking] | checkf[orwarding] } <chkparms>
-
- <add> ::= { addb[locking] | addf[orwarding] } <add-del-parms>
-
- <del> ::= { delb[locking] | delf[orwarding] } <add-del-parms>
-
- <chkparms> ::= <protocol> from <ipaddr> <port> to <ipaddr> <port>
-
- <protocol> ::= tcp | udp
-
- <ipaddr> ::= <int>.<int>.<int>.<int> | <hostname>
-
- <hostname> ::= a host name from /etc/hosts
-
- <port> ::= <int> | <service>
-
- <service> ::= a service from /etc/services
-
- <int> ::= a non-negative integer
-
- <add-del-parms> ::= { accept | deny } { <universal_firewall> | <protocol_firewall> }
-
- <universal_firewall> ::= all from <masked_ipaddr> to <masked_ipaddr>
-
- <masked_ipaddr> ::= { <ipaddr>/<bits> } | { <ipaddr>:<ipaddr> } | <ipaddr>
-
- <bits> ::= integer in the range 0 to 32 inclusive
-
- <protocol_firewall> ::= <protocol> from <end_firewall> to <end_firewall>
-
- <end_firewall> ::= <masked_ipaddr> <port_list>
-
- <port_list> ::= [ <port>:<port> ] <sub_port_list>
-
- <sub_port_list> ::= <port> [ <sub_port_list> ]
-
-Although I think that the above grammar is complete, it isn't exactly what
-one would call easy to comprehend! Here's the basic idea along with what
-each of the forms mean:
-
- The "ipfirewall list" command prints a list of the firewalls on both the
- forwarding and blocking chain in some more or less understudable format.
-
- The "ipfirewall flush" command empties the two firewall chains.
-
- The "ipfirewall addblocking" and "ipfirewall addforwarding" commands take
- a firewall description and add the firewall to the appropriate firewall
- chain.Take notice,that if you will add some description more then once,
- it will take more then one entry in memory.It does not lead to significant
- slow down of computer operation though.
-
- The "ipfirewall delblocking" and "ipfirewall delforwarding" commands take
- a firewall description and deletes the firewall from the appropriate
- firewall chain.The description must be exactly the same as it was defined
- by add command.One delete command removes ALL same entries from firewall
- chains.
-
- There are two basic kinds of firewall descriptions. Universal firewall
- descriptions match all IP packets between specified pairs of hosts.
- Universal firewalls only check IP addresses (i.e. they match any combination
- of protocol and port numbers). Protocol-specific firewalls match either
- TCP/IP or UDP/IP packets between specified pairs of hosts. In addition
- to host descriptions, protocol-specific firewalls optionally take a
- description of which port numbers to match.
-
- A host description consists of an IP address and a mask. The IP address
- is specified as either a domain name or in the familiar
- nn.nn.nn.nn format. The mask indicates how much of the IP address
- should be looked at when vetting packets. There are two ways to
- specify the mask. The first way is to suffix the IP address in the
- firewall with a slash and an integer in the range 0 through 32 inclusive.
- This integer is taken to be the number of high order bits of the IP
- address which are to be checked (for example, 192.153.211.0/24 checks
- the top 24 bits of the IP address, 192.153.211.17/32 checks all the
- bits and 0.0.0.0/0 checks none of the bits (i.e. all IP addresses are
- matched by this example)). The second way to specify a mask is to
- suffix the IP address with a colon followed by another IP address.
- This second address is the mask. Specifications equivalent to the
- above three examples using this syntax would be
-
- 192.153.211.0:255.255.255.0
- 192.153.211.17:255.255.255.255
- 0.0.0.0:0.0.0.0
-
- The first form is taken from the syntax accepted by a Telebit NetBlazer.
- The second form is more along the lines of how a netmask is specified
- in /etc/netmasks. Finally, if no mask is specified then a mask of all
- 1's is supplied (i.e. no mask is equivalent to /32 or :255.255.255.255).
-
- The optional description of port numbers to mask can take three forms.
- The simplest form is to omit the list in which case all port numbers
- match. The next form is to specify a list of port numbers (either as
- positive integers or service names from /etc/services). The final form
- is actually a special case of the second form in which the first pair
- of port numbers is separated by a colon instead of white space. This
- pair specifies a range of port numbers (i.e. x:y specifies that all
- ports between x and y inclusive should match). A port description
- matches a particular port number if any of the following is true:
-
- - the port description is null
- - the first pair of port numbers is a range and the port number
- is in the range (inclusive)
- - the port number is equal to any of the port numbers in the list
-
- There is a limit of a total of 10 port numbers in the source and
- destination port lists. This limit is arbitrary and easy to increase.
- It is determined by the value of the IP_FIREWALL_MAX_PORTS #define
- variable in ip_firewall.h. Each increase of 1 for this value adds two
- bytes to the size of each firewall. Since the size of a firewall is only
- slightly over 30 bytes right now, this limit of 10 could probably
- be increased by quite a bit before it became a concern. I've been
- thinking of increasing it to 20 which would be longer than any
- reasonable firewall would need and would only consume 20 more bytes
- per firewall. The counter argument to any increase is that it is
- always possible to construct an equivalent set of two or more firewalls
- that behaves like a single firewall with a really long port list.
-
- This probably all sounds hopelessly complicated. It is actually not
- all that tricky (I'm just not very good at explaining it yet). A few
- examples will probably help a lot now:
-
- Block all IP packets originating from the host hackers-den:
-
- ipfirewall addb deny all from hackers-den to 0.0.0.0/0
-
- Block all telnet packets to our telnet server from anywhere:
-
- ipfirewall addb deny tcp from 0.0.0.0/0 to mymachine/32 telnet
-
- Don't forward telnet, rlogin and rsh packets onto our local
- class C network:
-
- ipfirewall addf deny tcp from 0.0.0.0/0 to ournetwork/24 telnet login shell
-
- Don't let anyone on the local machine or any machine inside
- our local network ftp access to games.com:
-
- ipfirewall addb deny tcp from games.com ftp to 0.0.0.0/0
-
- This last one might look a little strange. It doesn't prevent
- anyone from sending packets to the games.com ftp server. What it
- does do is block any packets that the games.com ftp server sends
- back!
-
- The "ipfirewall checkblocking" and "ipfirewall checkforwarding" commands
- take a description of an IP packet and check to see if the blocking
- or forwarding chain of firewalls respectively accept or reject the packet.
- It is used to make sure that the firewalls that you've defined work as
- expected. The basic syntax is probably best understood by looking at
- a couple of examples:
-
- ipfirewall checkb from bsdi.com 3001 to mymachine telnet
-
- checks to see if the blocking firewall will block a telnet packet from
- a telnet session originating on bsdi.com to the host mymachine will be
- blocked or not. Note that someone connecting to our telnet server
- could be using practically any port number. To be really sure, the
- firewall used to prevent access should be as simple as possible and/or
- you should try a variety of port numbers in addition to the rather
- arbitrarily chosen port of 3001.
-
- One final note on the check* ,add* and del* command syntax. The noise word
- "to" exists in the syntax so that I can detect the end of a list of
- port numbers in the from description. Since I needed a noise word to
- detect this case, I added the noise word "from" in front of the from
- case for consistency.
-
- Finally, have a look at the file "filters". It is the set of filters
- that I run at home.<Danny>
- Also check "scripts",where individual access restrictions written.
- We use those for our dial-in PPP/SLIP users,to allow some of them
- to access our internal networks,while disallowing other.This way we
- open access to user's IP,when he enters the system ,and shut it
- down when he leaves.All those changes may be applyed at any time,
- and so entries added and deleted from firewall while system is
- is working.No any side effects will arise.<Ugen>
-
-Now for a bit of a description of how the firewalls are applied (i.e. what
-happens in the kernel):
-
- When an IP packet is received, the ipintr() routine in ip_input.c is
- called. This routine does a bit of basic error checking. If it
- detects any errors in the packet it generally drops the packet on
- the floor. The idea behind the ipfirewall facility is to treat packets
- that we don't want to accept as bad packets (i.e. drop them on the
- floor). The ipfirewall facility intercedes in the normal processing
- at two points. Just after the basic sanity checks are done, we pass
- any packets not targeted at the loopback network (127.0.0.0/8) to the
- firewall checker along with the chain of blocking firewalls.If the firewall
- checker tells us to block the packet then we branch to the "bad:" label
- in ipintr() which is where all bad packets are dropped on the floor.
- Otherwise, we allow normal processing of the packet to continue. The
- exact point at which we intercede was chosen to be after the basic
- sanity checking and before the option processing is done. We want to
- be after the basic sanity checking so that we don't have to be able
- to handle complete garbage. We want to be before the option processing
- because option processing is done in separate rather complex routine.
- Why bother doing this special processing if we might be dropping the
- packet?
-
- The second point at which we intercede is when a packet is about to be
- forwarded to another host. All such packets are passed to the ip_forward
- routine. The ipfirewall code is at the very top of this routine. If
- the packet isn't targetted at the loopback interface (is it possible
- that it could be when we reach this point? I doubt it but safety first)
- then pass the packet to the firewall checker along with the forwarding
- firewall chain. If the firewall checker indicates that the packet should
- not be forwarded then we drop in (using code copied from a few lines
- further into the routine which drops broadcast packets which are not
- to be forwarded).
-
-There are a couple of consequences of this approach:
-
- 1) Packets which are blocked are never forwarded (something to keep
- in mind when designing firewalls).
- 2) Packets targeted at the loopback interface (127.0.0.0/8) are never
- blocked. Blocking packets to the loopback interface seems pointless
- and potentially quite confusing. It also makes a possibly common
- case very cheap.
- 3) The sender of a packet which is blocked receives no indication that
- the packet was dropped. The Telebit NetBlazer can be configured to
- silently drop a blocked packet or to send back a "you can't get there
- from here" packet to the sender. Implementing the later would have
- been more work (possibly quite a bit more, I don't really know). Also,
- I don't see any reason to give a potential hacker any more information
- than necessary. Dropping the packet into the bit bucket seems like
- the best way to keep a hacker guessing.<Danny>
- Well,anyway i working on this feature.It would be made optional and
- configurable by some ICMP_UNREACH_ON_DROP or like this.<Ugen>
-
-Now for some details on how the firewall checker works:
-
- The firewall checker takes two parameters. The first parameter is a pointer
- to the packet in question. The second parameter is a pointer to the
- appropriate firewall chain. At the present time, the firewall checker passes
- these parameters to a second routine which is the real firewall checker.
- If the real checker says NO then an appropriate message is printed
- onto the console. This is useful for debugging purposes. Whether or
- not it remains in the long term depends on whether it is considered useful
- for logging purposes (I'm a little reluctant to leave it in since it
- provides a hacker with a way to commit a "denial of service" offense
- against you by filling up your /var/log/messages file's file system
- with error messages. There are ways of preventing this but ...<Danny>).
- In default configuration now no information about dropped packets
- printed.You may,however,define it,as i do by adding
- option IPFIREWALL_VERBOSE
- to your kernel configuration file.Very useful thingy!<Ugen>
-
- A return value of 0 from this routine (or the real firewall checker)
- indicates that the packet is to be dropped. A value of 1 indicates
- that the packet is to be accepted. In the early testing stages you
- might want to make the top level firewall checker always return 1 even
- if the real checker returns 0 just in case the real firewall checker
- screws up (or your firewalls aren't as well designed as they should be).
- In fact, this might be a useful optional feature (providing a way to
- leave a door unlocked doesn't seem all that wise but it has to be
- balanced against the inconvenience to legitimate users who might get
- screwed up by poorly designed firewalls).
-
- The real firewall returns 1 (accept the packet) if the chain is empty. If
- efficiency is a concern (which it is in this code), this check should
- be done in ip_input.c before calling the firewall checker.
-
- Assuming that there is a firewall chain to scan through, the real firewall
- checker picks up the src and dst IP addresses from the IP packet. It
- then goes through the firewall chain looking for the first firewall that
- matches the packet. Once a matching firewall has been found, a value of
- 1 is returned if the firewall is an accept firewall and a value of 0 is
- returned otherwise.
-
- The following processing is done for each firewall on the chain:
-
- 1) check the src and dst IP addresses. If they don't match then
- there isn't any point in looking any further at this firewall.
- This check is done by anding the packet's IP addresses the
- with appropriate masks and comparing the results to the
- appropriate addresses in the firewall. Note that the mask is
- NOT applied to the address in the firewall. If it has any 1
- bits that are 0 bits in the mask then the firewall will never
- match (this will be checked in ipfirewall soon). If the addresses
- match then we continue with the next step.
-
- 2) If the firewall is a universal firewall then we've got a match.
- Return either 0 or 1 as appropriate. Otherwise, continue with
- the next step.
-
- 3) Examine the IP protocol from the packet. If we havn't had to
- look at it before then we get it and set a local variable to
- IP_FIREWALL_TCP for TCP/IP packets, IP_FIREWALL_UDP for UDP/IP
- packets, IP_FIREWALL_ICMP for ICMP packets, and IP_FIREWALL_UNIVERSAL
- for all other packet types. Also, if the packet is a TCP/IP or
- a UDP/IP packet, save the source and destination port numbers
- at this point (taking advantage of the fact that the port numbers
- are stored in the same place in either a TCP/IP or a UDP/IP
- packet header). If the packet is neither a TCP/IP or a UDP/IP
- packet then this firewall won't match it (on to the next firewall).
- If this packet's protocol doesn't match this firewall's protocol
- (which can't be universal or we wouldn't be here) then on to
- the next firewall. Otherwise, continue with the next step.
-
- 4) We're checking either a TCP/IP or a UDP/IP packet. If the
- firewall's source port list is empty or the packet's source
- port matches something in the source port list AND if the firewall's
- destination port list is empty or the packet's destination
- port matches something in the destination port list then
- we've got a match (return 0 or 1 as appropriate). Otherwise,
- on to the next firewall.
-
- As indicated above, if no packet on the chain matches the packet then
- it is accepted if the first firewall was a deny firewall and it is rejected
- if the first firewall was an accept packet. This is equivalent to the
- default behaviour of a Telebit NetBlazer. They provide a way to override
- this behaviour. I'm not convinced that it is necessary (I'm open to
- suggestions).
-
-That's about it for the firewall checker. The ipfirewall program communicates
-with the kernel part of the firewall facility by making setsockopt calls
-on RAW IP sockets. Only root is allowed to open a RAW IP socket. This
-ensures that only root uses ipfirewall to manipulate the firewall facility.
-Also, somewhere in the kernel source or on a man page, I read that the
-RAW IP setsockopt calls are intended for manipulating the IP protocol layer
-as opposed to manipulating any particular instance of a socket. This seems
-like a reasonable description of what the firewall setsockopt command
-codes do.
-
-There are seven setsockopt command codes defined by the firewall facility
-(in netinet/in.h). They are:
-
- IP_FLUSH_FIREWALLS flush (i.e. free) both firewall chains.
-
- IP_ADD_FORWARDING_FIREWALL add firewall pointed at by optval parm to
- the end of the forwarding firewall chain.
-
- IP_ADD_BLOCKING_FIREWALL add firewall pointed at by optval parm to
- the end of the blocking firewall chain.
-
- IP_DEL_FORWARDING_FIREWALL delete firewall pointed at by optval parm
- from the forwarding firewall chain.
-
- IP_DEL_BLOCKING_FIREWALL delete firewall pointed at by optval parm
- from the blocking firewall chain.
-
- IP_CHECK_FORWARDING_FIREWALL pass the IP packet do the firewall checker
- along with the forwarding firewall chain.
- Return 0 if packet was accepted, -1 (with
- errno set to EACCES) if it wasn't.
-
- IP_CHECK_BLOCKING_FIREWALL pass the IP packet do the firewall checker
- along with the blocking firewall chain.
- Return 0 if packet was accepted, -1 (with
- errno set to EACCES) if it wasn't.
-
- The IP_ADD_* and IP_DEL_* command codes do a fair bit of validity checking.
- It is quite unlikely that a garbage firewall could get past them that
- would cause major problems in the firewall checker. It IS possible for
- a garbage packet to get past the checks which causes major grief because
- it either blocks or accepts packets according to unusual rules (the rules
- will conform to the ones described above but will probably come as quite
- a surprise).
-
- The IP_CHECK_* command codes expect the optval parameter to point
- to a struct ip immediately followed by a header appropriate to the protocol
- value described in the ip_p field of the ip header. The exact requirements
- are as follows:
-
- - The length of the optval parameter must be at least
-
- sizeof(struct ip) + 2 * sizeof(u_short)
-
- since this is the amount of memory that might be referenced by
- the firewall checker.
-
- - The ip_hl field of the ip structure must be equal to
-
- sizeof(struct ip) / sizeof(int)
-
- since this value indicates that the tcp/udp/??? header immediately
- follows the ip header (appropriate for the purposes that this
- interface is intended for).
-
- Failure to follow these rules (for either the IP_ADD_*,IP_DEL_* or the
- IP_CHECK_*_FIREWALL commands) will result in a return value of -1 with
- errno set to EINVAL (for now, it will also result in an appropriate
- message on the console).
-
- To read current configuration of firewalls,the kvm_read() function used.
- Symbols,which you have to find are :
- struct ip_firewall * ip_firewall_blocking_chain ;
- struct ip_firewall * ip_firewall_forwarding_chain ;
- Both are pointers to the linked list of firewall entries.
- Of corse you have to be at least kmem group member,to read kernel symbols.
-
-That's about all that I can think of for now. There are a couple of details
-that are worth reading about in the ip_firewall.h file. Other than that, let
-me know how you do. If you have any problems, give me a call at home (403
-449-1835) or send me e-mail at "danny@BouletFermat.ab.ca". If you call, please
-keep in mind that I live in the Canadian Mountain timezone (GMT-0600).
-
--Danny
-
-So that's it..if you want to say something to me-call me or mail:
-Phone: 972-4-550-330
-E-mail ugen@NetVision.net.il
-If you call,remember that i live in Israel timezone which is GMT+02.
-
--Ugen
-
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