diff options
Diffstat (limited to 'sbin/ipfw')
| -rw-r--r-- | sbin/ipfw/ipfirewall.4 | 206 | ||||
| -rw-r--r-- | sbin/ipfw/ipfw.1 | 527 |
2 files changed, 0 insertions, 733 deletions
diff --git a/sbin/ipfw/ipfirewall.4 b/sbin/ipfw/ipfirewall.4 deleted file mode 100644 index f11cbd54..0000000 --- a/sbin/ipfw/ipfirewall.4 +++ /dev/null @@ -1,206 +0,0 @@ -.Dd November 16, 1994 -.Dt IPFW(4)/IPACCT 4 -.Os -.Sh NAME - - ipfirewall,ipfw - IP packets filter. - ipaccounting,ipacct - IP packets/traffic accounting. - -.Sh SYNOPSIS -#include <netinet/ip_fw.h> - -setsockopt(raw_socket,IPPROTO_IP,<ipfw/ipacct option>, - <struct ip|struct ipfw>,<size>) - -Ipfw options: - IP_FW_ADD_BLK - add entry to blocking chain. - IP_FW_ADD_FWD - add entry to forwarding chain. - IP_FW_CHK_BLK - check ip packet against blocking chain. - IP_FW_CHK_FWD - check ip packet against forwarding chain. - IP_FW_DEL_BLK - delete entry from blocking chain. - IP_FW_DEL_FWD - delete entry from forwarding chain. - IP_FW_FLUSH - flush all blocking & forwarding chain entries. - IP_FW_POLICY - define default ipfw policy. - -Ipacct options: - IP_ACCT_ADD - add entry to accounting chain. - IP_ACCT_DEL - delete entry from accounting chain. - IP_ACCT_FLUSH - flush all accounting chain entries. - IP_ACCT_ZERO - zero all accounting chain entries. - -Ipfw/ipacct entry structure: - #define IP_FW_MAX_PORTS 10 - -struct ip_fw { - struct ip_fw *next; - struct in_addr src, dst; - struct in_addr src_mask, dst_mask; - u_short flags; - u_short n_src_p, n_dst_p; - u_short ports[IP_FW_MAX_PORTS]; - u_long p_cnt,b_cnt; -} - -Flags values for "flags" field: - IP_FW_F_ALL - The entry should match all IP packets. - IP_FW_F_TCP - The entry should match TCP packets. - IP_FW_F_UDP - The entry should match UDP packets. - IP_FW_F_ICMP - The entry should match ICMP packets. - IP_FW_F_KIND - Mask value to separate protocol kind. - IP_FW_F_ACCEPT - This entry is accepting ( see below ) - IP_FW_F_SRNG - Source ports are range ( see below ) - IP_FW_F_DRNG - Destination ports are range ( see below ) - IP_FW_F_PRN - Print this entry ( see below ) - IP_FW_F_BIDIR - This acct entry is bidirectional ( see below ) - IP_FW_F_MASK - Mask to match all valid flag bits. - -Kernel symbols to kvm_nlist(): - struct ip_fw *ip_fw_blk_chain - chain of forwarding entries. - struct ip_fw *ip_fw_fwd_chain - chain of blocking entries. - int ip_fw_policy - default policy. - struct ip_fw *ip_acct_chain - chain of accounting entries. - -Options in the kernel configuration file: - IPFIREWALL - enable ipfirewall. - IPFIREWALL_VERBOSE - enable firewall output ( see below ) - DEBUG_IPFIREWALL - enable extensive debugging output. - IPACCT - enable ipaccounting. - -.Sh DESCRIPTION -Ipfirewall (later ipfw) is a system facility,which allows filtering -of incoming and/or forwarding packets on the protocol+source/destination -adress/ports base. -Ipaccounting (later ipacct) is a system facility,which allows counting -of incoming,outgoing and forwarding traffic by packet/byte count. - -Basic idea is that every packet checked against number of entries -in several chains.There are 3 chains: - Blocking - this chain defines whenever packet should be accepted - ever for local delivery or for forwarding. - Forwarding - this chain defines whenever packet should be accepted - for forwarding only. - Accounting - this chain defines types of packets , which should be - counted. - -Entries added to chains by means of setsockopt() call on RAW IP socket. -Options to add/remove specific entries or to flush all entries described -above. Value passed to setsockopt() is a value of struct ip_fw for -entry. If entry added , it checked by such rules that when we start -searching chain for matching entry the first matching is the best match, -[ or at least one of them :^) ]. - That means: - * First in chain entries with specific protocol and small ranges - of src/dst adresses and ports. - * Later going entries with wider ranges of ports and adresses. - * Later entries matching every port for some adress range. - * Later universal entries matching any protocol. - -While deleting entry , every entry which equal to that passed to -setsockopt() will be removed. -Flush removes all entries. - -Every entry have several fields,by which packets matched: - struct ip_fw *next - next entry in chain.(Set internally) - - struct in_addr src - source adress to be matched. - struct in_addr src_mask - source adress mask. - To match whole networks/subnets or adress groups - mask bits should be zeroed here and also - in src_mask field. Valuable bits should be set - in src_mask field. - struct in_addr dst - destination adress to be matched. - struct in_addr dst_mask - destination adress mask. - - u_short flags - flags field.See exact description of flags meaning - in description later. - - u_short n_src_p - number of source ports in "ports" array. - u_short n_dst_p - number of destination ports in "ports" array. - u_short ports[] - ports array.Overall length currently defined - to reasonable maximum - 10,and could be changed. - The packet's src port can ever match one of - ports[0] ... ports[--n_src_p] numbers,or if - flag IP_FW_F_SRNG set take port[0] as bottom - range value and ports[1] as top one.n_src_p should - be set to 2 then.If n_src_p equal to 0 , every port - match. The same rules apply to packet's dst port, - except that it matched against ports[n_src_p] ... - ... ports[n_src_p+n_dst_p--],or if IP_FW_F_DRNG set, - range is ports[n_src_p] to ports[n_srcp++]. - - u_long p_cnt - packets count for ipacct entries. - u_long b_cnt - bytes count for ipacct entries. - -Packet matching proceeds in following way: - -a) If packet entry protocol set to ALL, see c). - -b) If entry protocol set to TCP/UDP/ICMP and packet protocol - different - no match,if packet protocol and entry protocol - same - continue. - -c) If source addres pattern does not equal to packets sources adress - masked with src_mask , or destination pattern not equal to packets - destination adress masked with dst_mask - no match. - If they does and protocol set to ALL/ICMP - got match. - If they does and protocol set to TCP/UDP - continue. - -d) If src port doesn't match or dst port doesn't match - all - packet don't match. If they does - got match. - -In ipfw packet matched consequently against every chain entry. -Search continues untill first matching entry found.If IP_FW_F_ACCEPT -flag set - packet accepted.If it is not set - packet denied. -If no matching entry found , all unmatched packets ever accepted or -denied depending on global polici value. It can be set with -IP_FW_POLICY raw socket option. Deny value is 0, other values -(default 1) is accept. - -Entries can be added with IP_FW_F_PRN flag set.If kernel compiled -with IPFIREWALL_VERBOSE option,packets matching this entries will -be printed by kernel printf's. - -If some chain is empty,every packet accepted by this chain no -matter what default policy is. - -To check whenever or not packet denied by some chain , checking -options to setsockopt() can be issued. Then the argument is -a buffer representing ip packet,thus it has to be -struct ip + struct tcphdr . -Then setsockopt() return value 0 on accept or another on deny. - -Ipaccounting entries added the same way as ipfw ones.Packet checked -against all entries in chain and values of p_cnt and b_cnt in matching -entries rised.p_cnt rises by 1 and b_cnt by ip_len value of ip packet. -Thus all traffic size counted including IP headers. - -If IP_FW_F_BIDIR flag is set in accounting entry,packets counted are -those which match entry in standart way along with packets which match -entry while their source and destination addr/port pairs swapped. - -Zero option allows all accounting to be cleared. - -.Sh DIAGNOSTICS - -[EINVAL] The IP option field was improperly formed; an option - field was shorter than the minimum value or longer than - the option buffer provided.An structural error in - ip_fw structure occured (n_src_p+n_dst_p too big, - ports set for ALL/ICMP protocols etc.) - -.Sh SEE ALSO - -ip(4), setsockopt(2), kvm_nlist(3), kvm_read(3) - -.Sh BUGS - Ipfw/ipacct facilities are new and , although serious bugs has -been tracked,some less important ones expected. - This man page also uncomplete bad styled. - -.Sh HISTORY - Ipfw facility has been intitially written as package to BSDI -by Daniel Boulet <danny@BouletFermat.ab.ca>. - It has been havily modified and ported to FreeBSD 2.0 -by Ugen J.S.Antsilevich <ugen@NetVision.net.il> - Ipacct facility written for FreeBSD 2.0 -by Ugen J.S.Antsilevich <ugen@NetVision.net.il> diff --git a/sbin/ipfw/ipfw.1 b/sbin/ipfw/ipfw.1 deleted file mode 100644 index 720b259..0000000 --- a/sbin/ipfw/ipfw.1 +++ /dev/null @@ -1,527 +0,0 @@ -.\" -.\" ipfw - a utility for manipulating the configuration of an IP firewall. -.\" -.\" Redistribution and use in source and binary forms, with or without -.\" modification, are permitted provided that the following conditions -.\" are met: -.\" 1. Redistributions of source code must retain the above copyright -.\" notice, this list of conditions and the following disclaimer. -.\" 2. Redistributions in binary form must reproduce the above copyright -.\" notice, this list of conditions and the following disclaimer in the -.\" documentation and/or other materials provided with the distribution. -.\" -.\" @(#)ipfw.1 -.\" -.TH ipfw 1 "October 27, 1994" "" "FreeBSD" - -.SH NAME -ipfw - a utility for manipulating the configuration of an IP firewall. -.SH SYNOPSIS -.na -.B ipfw -.RB [options] -.SH DESCRIPTION -The -.B ipfw -command is used to configure an active IP firewall, setting masks on just -what sites are allowed to connect through it, which packets are rejected, -etc. -.SH OPTIONS -The command-line syntax of this command is rather involved, and rather than -spend a lot of time that I just don't have at the moment creating a -.B real -man page, with properly formatted sections and all, I'm just going to loosely -format the README I got. This really needs an nroff expert to go through -it with a chainsaw and do a -.N REAL -job of formatting it! This all looks rather horrible at present, and -I would actually almost recommend that you simply read the man page text -directly, rather than trying to format it. Sorry, but I do NOT speak -nroff, nor do I ever wish to learn how! :-) [-jkh]. -.PP -For a sample kernel configuration file that will enable the right kernel -features necessary for firewalling, see -.I /sys/i386/conf/IPFIREWALL -. -.PP -.B WARNING!!! WARNING!!! WARNING!!! WARNING!!! WARNING!!! WARNING!!! -.PP -This utility can be used to put your machine into very dysfunctional state, -so if you want to test it then you should first make sure to read this man page -all the way through, and don't run it anywhere from the system console! -Using -.I ipfw -incorrectly is a really good way to kick yourself off your own machine -if you're logged in over a network! Also make sure to never set this -utility to be setuid root! It's a blatant security hole that way. -Instead, run it as root or from "/etc/rc.local" as part of the boot process. -It's also a good idea to use the checkb or checkf command options (see below) -to pass some test packets through the firewalls that you've defined before -going "live". -.PP -You may find it useful to create a file in which the first line is -.I firewall flush -to flush any existing firewalls before defining the explicit firewalls -that you wish to use. This will ensure that you're always working from a -known state. -.PP -The syntax for the -.BI ipfirewall -command option is rather complex and yet simple at the same time (if you know -what I mean). There are seven sub-commands, and 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)): -.PP -.nf - 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> ] -.fi -.PP -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: -.PP -The -.I ipfirewall list -command prints a list of the firewalls on both the -forwarding and blocking chain in some more or less comprehensible format. -.PP -The -.I ipfirewall flush -command empties the two firewall chains. -.PP -The -.I ipfirewall addblocking -and -.I ipfirewall addforwarding -commands take a firewall description and add the firewall to the appropriate -firewall chain. Note that you'll probably need to add some descriptions more -then once, which will naturally take more then one entry in memory. It does -not lead to significant degradation of performance, so don't worry about it. -.PP -The -.I ipfirewall delblocking -and -.I ipfirewall delforwarding -commands take a firewall description and delete the firewall from the -appropriate firewall chain. The description must exactly match that given -to an earlier add command. One delete command removes ALL matching entries -from firewall chains. -.PP -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 (e.g. 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. -.PP -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 -.PP -.nf -192.153.211.0:255.255.255.0 -192.153.211.17:255.255.255.255 -0.0.0.0:0.0.0.0 -.fi -.PP -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). -.PP -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: -.nf - - 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 -.fi -.PP -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. -.PP -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: -.PP -Block all IP packets originating from the host hackers-den: -.PP -.nf - ipfirewall addb deny all from hackers-den to 0.0.0.0/0 -.fi -.PP -Block all telnet packets to our telnet server from anywhere: -.PP -.nf - ipfirewall addb deny tcp from 0.0.0.0/0 to mymachine/32 telnet -.fi -.PP -Don't forward telnet, rlogin and rsh packets onto our local -class C network: -.PP -.nf - ipfirewall addf deny tcp from 0.0.0.0/0 to ournetwork/24 telnet login shell -.fi -.PP -Don't let anyone on the local machine or any machine inside -our local network ftp access to games.com: -.PP -.nf - ipfirewall addb deny tcp from games.com ftp to 0.0.0.0/0 -.fi -.PP -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! -.PP -The -.I ipfirewall checkblocking -and -.I 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: -.PP -.nf - ipfirewall checkb from bsdi.com 3001 to mymachine telnet -.fi -.PP -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. -.PP -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. -.PP -Finally, have a look at the file -.I "/usr/share/misc/ipfw.samp.filters" -. It is the set of filters that I run at home [Danny]. -.PP -Also check -.I "/usr/share/misc/ipfw.samp.scripts" -For examples of individual access restrictions. -We [NetVision] use those for our dial-in PPP/SLIP users to allow some of them -to access our internal networks, while disallowing others. -This way we open access for the user's IP when he enters the system and shut it -down when he leaves. All such changes may be applyed at any time, -and so entries added and deleted from firewall while the system is -is working have no other side effects [Ugen]. - -.SH "TECHNICAL DETAILS" -A bit of a description of how the firewalls are applied (i.e. what happens in -the kernel) may be instructive to the advanced firewall-builder: -.PP -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? -.PP -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). -.PP -There are a couple of consequences of this approach: -.PP -1) Packets which are blocked are never forwarded (something to keep -in mind when designing firewalls). -.PP -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. -.PP -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] -.PP -(I am working on this feature, it would be made optional and -configurable by some ICMP_UNREACH_ON_DROP option, or such [Ugen]). -.PP -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 -.I options IPFIREWALL_VERBOSE -to your kernel configuration file. Very useful thingy! [Ugen] - -.PP -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). - -.PP -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. - -.PP -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. -.PP -The following processing is done for each firewall on the chain: -.PP -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. -.PP -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. -.PP -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. -.PP -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. -.PP -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). -.PP -That's about it for the firewall checker. The -.I ipfw -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 -.I ipfw 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. -.PP -There are seven setsockopt command codes defined by the firewall facility -(in netinet/in.h). They are: -.PP -.nf - 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 course, you must at least be a member of group kmem to read kernel - symbols. -.fi -.PP -There are a couple of additional details that are worth reading about in -the ip_firewall.h file. Other than that, let the authors know how you do! -If you have any problems, you may call Danny Boulet at home (403 449-1835) -or send e-mail to <danny@BouletFermat.ab.ca>. If you call, please keep in -mind that Danny lives in the Canadian Mountain timezone (GMT-0600). -.PP -You may also reach some commercial users of this package (and also those -responsible for porting it to FreeBSD and adding several additional -commands), at 972-4-550-330, or via email at <ugen@NetVision.net.il>. -If you call, remember that Ugen lives in the Israel timezone, which is GMT+02. - -.SH FILES -/usr/share/misc/ipfw.samp.filters -/usr/share/misc/ipfw.samp.scripts -.SH "BUGS" -You can very easily hose your machine utterly if you don't know what you're -doing. Dieses Befehl ist nur fuer Experten! -.SH "SEE ALSO" -.BR reboot (1) , -.PP -.BR /sys/i386/conf/IPFIREWALL -.SH AUTHORS -Daniel Boulet <danny@BouletFermat.ab.ca> -.PP -Ugen J.S.Antsilevich <ugen@NetVision.net.il> -.PP -Jordan K. Hubbard <jkh@FreeBSD.org> [Crimes committed in this manpage] |
