1155 lines
32 KiB
C
1155 lines
32 KiB
C
/* -*- mode: c; tab-width: 8; c-basic-indent: 4; -*- */
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/*
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Alias.c provides supervisory control for the functions of the
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packet aliasing software. It consists of routines to monitor
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TCP connection state, protocol-specific aliasing routines,
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fragment handling and the following outside world functional
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interfaces: SaveFragmentPtr, GetFragmentPtr, FragmentAliasIn,
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PacketAliasIn and PacketAliasOut.
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The other C program files are briefly described. The data
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structure framework which holds information needed to translate
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packets is encapsulated in alias_db.c. Data is accessed by
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function calls, so other segments of the program need not know
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about the underlying data structures. Alias_ftp.c contains
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special code for modifying the ftp PORT command used to establish
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data connections, while alias_irc.c do the same for IRC
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DCC. Alias_util.c contains a few utility routines.
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This software is placed into the public domain with no restrictions
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on its distribution.
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Version 1.0 August, 1996 (cjm)
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Version 1.1 August 20, 1996 (cjm)
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PPP host accepts incoming connections for ports 0 to 1023.
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(Gary Roberts pointed out the need to handle incoming
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connections.)
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Version 1.2 September 7, 1996 (cjm)
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Fragment handling error in alias_db.c corrected.
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(Tom Torrance helped fix this problem.)
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Version 1.4 September 16, 1996 (cjm)
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- A more generalized method for handling incoming
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connections, without the 0-1023 restriction, is
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implemented in alias_db.c
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- Improved ICMP support in alias.c. Traceroute
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packet streams can now be correctly aliased.
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- TCP connection closing logic simplified in
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alias.c and now allows for additional 1 minute
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"grace period" after FIN or RST is observed.
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Version 1.5 September 17, 1996 (cjm)
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Corrected error in handling incoming UDP packets with 0 checksum.
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(Tom Torrance helped fix this problem.)
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Version 1.6 September 18, 1996 (cjm)
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Simplified ICMP aliasing scheme. Should now support
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traceroute from Win95 as well as FreeBSD.
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Version 1.7 January 9, 1997 (cjm)
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- Out-of-order fragment handling.
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- IP checksum error fixed for ftp transfers
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from aliasing host.
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- Integer return codes added to all
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aliasing/de-aliasing functions.
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- Some obsolete comments cleaned up.
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- Differential checksum computations for
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IP header (TCP, UDP and ICMP were already
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differential).
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Version 2.1 May 1997 (cjm)
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- Added support for outgoing ICMP error
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messages.
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- Added two functions PacketAliasIn2()
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and PacketAliasOut2() for dynamic address
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control (e.g. round-robin allocation of
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incoming packets).
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Version 2.2 July 1997 (cjm)
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- Rationalized API function names to begin
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with "PacketAlias..."
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- Eliminated PacketAliasIn2() and
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PacketAliasOut2() as poorly conceived.
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See HISTORY file for additional revisions.
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*/
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#include <stdio.h>
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#include <unistd.h>
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#include <sys/param.h>
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#include <sys/types.h>
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#include <netinet/in_systm.h>
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#include <netinet/in.h>
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#include <netinet/ip.h>
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#include <netinet/ip_icmp.h>
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#include <netinet/tcp.h>
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#include <netinet/udp.h>
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#include "alias_local.h"
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#include "alias.h"
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#define NETBIOS_NS_PORT_NUMBER 137
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#define NETBIOS_DGM_PORT_NUMBER 138
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#define FTP_CONTROL_PORT_NUMBER 21
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#define FTP_CONTROL_PORT_NUMBER 21
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#define IRC_CONTROL_PORT_NUMBER_1 6667
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#define IRC_CONTROL_PORT_NUMBER_2 6668
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#define CUSEEME_PORT_NUMBER 7648
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/*
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The following macro is used to update an
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internet checksum. "delta" is a 32-bit
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accumulation of all the changes to the
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checksum (adding in new 16-bit words and
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subtracting out old words), and "cksum"
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is the checksum value to be updated.
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*/
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#define ADJUST_CHECKSUM(acc, cksum) { \
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acc += cksum; \
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if (acc < 0) \
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{ \
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acc = -acc; \
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acc = (acc >> 16) + (acc & 0xffff); \
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acc += acc >> 16; \
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cksum = (u_short) ~acc; \
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} \
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else \
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{ \
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acc = (acc >> 16) + (acc & 0xffff); \
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acc += acc >> 16; \
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cksum = (u_short) acc; \
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} \
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}
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/* TCP Handling Routines
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TcpMonitorIn() -- These routines monitor TCP connections, and
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TcpMonitorOut() -- delete a link node when a connection is closed.
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These routines look for SYN, ACK and RST flags to determine when TCP
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connections open and close. When a TCP connection closes, the data
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structure containing packet aliasing information is deleted after
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a timeout period.
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*/
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/* Local prototypes */
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static void TcpMonitorIn(struct ip *, struct alias_link *);
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static void TcpMonitorOut(struct ip *, struct alias_link *);
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static void
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TcpMonitorIn(struct ip *pip, struct alias_link *link)
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{
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struct tcphdr *tc;
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tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
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switch (GetStateIn(link))
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{
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case ALIAS_TCP_STATE_NOT_CONNECTED:
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if (tc->th_flags & TH_SYN)
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SetStateIn(link, ALIAS_TCP_STATE_CONNECTED);
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break;
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case ALIAS_TCP_STATE_CONNECTED:
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if (tc->th_flags & TH_FIN
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|| tc->th_flags & TH_RST)
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SetStateIn(link, ALIAS_TCP_STATE_DISCONNECTED);
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break;
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}
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}
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static void
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TcpMonitorOut(struct ip *pip, struct alias_link *link)
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{
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struct tcphdr *tc;
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tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
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switch (GetStateOut(link))
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{
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case ALIAS_TCP_STATE_NOT_CONNECTED:
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if (tc->th_flags & TH_SYN)
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SetStateOut(link, ALIAS_TCP_STATE_CONNECTED);
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break;
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case ALIAS_TCP_STATE_CONNECTED:
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if (tc->th_flags & TH_FIN
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|| tc->th_flags & TH_RST)
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SetStateOut(link, ALIAS_TCP_STATE_DISCONNECTED);
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break;
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}
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}
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/* Protocol Specific Packet Aliasing Routines
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IcmpAliasIn(), IcmpAliasIn1(), IcmpAliasIn2(), IcmpAliasIn3()
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IcmpAliasOut(), IcmpAliasOut1(), IcmpAliasOut2(), IcmpAliasOut3()
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UdpAliasIn(), UdpAliasOut()
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TcpAliasIn(), TcpAliasOut()
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These routines handle protocol specific details of packet aliasing.
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One may observe a certain amount of repetitive arithmetic in these
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functions, the purpose of which is to compute a revised checksum
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without actually summing over the entire data packet, which could be
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unnecessarily time consuming.
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The purpose of the packet aliasing routines is to replace the source
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address of the outgoing packet and then correctly put it back for
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any incoming packets. For TCP and UDP, ports are also re-mapped.
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For ICMP echo/timestamp requests and replies, the following scheme
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is used: the id number is replaced by an alias for the outgoing
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packet.
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ICMP error messages are handled by looking at the IP fragment
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in the data section of the message.
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For TCP and UDP protocols, a port number is chosen for an outgoing
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packet, and then incoming packets are identified by IP address and
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port numbers. For TCP packets, there is additional logic in the event
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that sequence and ack numbers have been altered (as is the case for
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FTP data port commands).
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The port numbers used by the packet aliasing module are not true
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ports in the Unix sense. No sockets are actually bound to ports.
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They are more correctly thought of as placeholders.
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All packets go through the aliasing mechanism, whether they come from
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the gateway machine or other machines on a local area network.
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*/
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/* Local prototypes */
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static int IcmpAliasIn1(struct ip *);
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static int IcmpAliasIn2(struct ip *);
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static int IcmpAliasIn3(struct ip *);
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static int IcmpAliasIn (struct ip *);
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static int IcmpAliasOut1(struct ip *);
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static int IcmpAliasOut2(struct ip *);
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static int IcmpAliasOut3(struct ip *);
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static int IcmpAliasOut (struct ip *);
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static int UdpAliasOut(struct ip *);
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static int UdpAliasIn (struct ip *);
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static int TcpAliasOut(struct ip *, int);
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static int TcpAliasIn (struct ip *);
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static int
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IcmpAliasIn1(struct ip *pip)
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{
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/*
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De-alias incoming echo and timestamp replies
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*/
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struct alias_link *link;
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struct icmp *ic;
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ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
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/* Get source address from ICMP data field and restore original data */
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link = FindIcmpIn(pip->ip_src, pip->ip_dst, ic->icmp_id);
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if (link != NULL)
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{
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u_short original_id;
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int accumulate;
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original_id = GetOriginalPort(link);
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/* Adjust ICMP checksum */
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accumulate = ic->icmp_id;
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accumulate -= original_id;
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ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
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/* Put original sequence number back in */
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ic->icmp_id = original_id;
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/* Put original address back into IP header */
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{
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struct in_addr original_address;
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original_address = GetOriginalAddress(link);
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &original_address,
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(u_short *) &pip->ip_dst,
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2);
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pip->ip_dst = original_address;
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}
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return(PKT_ALIAS_OK);
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}
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return(PKT_ALIAS_IGNORED);
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}
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static int
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IcmpAliasIn2(struct ip *pip)
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{
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/*
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Alias incoming ICMP error messages containing
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IP header and first 64 bits of datagram.
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*/
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struct ip *ip;
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struct icmp *ic, *ic2;
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struct udphdr *ud;
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struct tcphdr *tc;
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struct alias_link *link;
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ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
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ip = (struct ip *) ic->icmp_data;
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ud = (struct udphdr *) ((char *) ip + (ip->ip_hl <<2));
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tc = (struct tcphdr *) ud;
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ic2 = (struct icmp *) ud;
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if (ip->ip_p == IPPROTO_UDP)
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link = FindUdpTcpIn(ip->ip_dst, ip->ip_src,
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ud->uh_dport, ud->uh_sport,
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IPPROTO_UDP);
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else if (ip->ip_p == IPPROTO_TCP)
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link = FindUdpTcpIn(ip->ip_dst, ip->ip_src,
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tc->th_dport, tc->th_sport,
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IPPROTO_TCP);
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else if (ip->ip_p == IPPROTO_ICMP) {
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if (ic2->icmp_type == ICMP_ECHO || ic2->icmp_type == ICMP_TSTAMP)
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link = FindIcmpIn(ip->ip_dst, ip->ip_src, ic2->icmp_id);
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else
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link = NULL;
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} else
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link = NULL;
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if (link != NULL)
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{
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if (ip->ip_p == IPPROTO_UDP || ip->ip_p == IPPROTO_TCP)
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{
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u_short *sptr;
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int accumulate;
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struct in_addr original_address;
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u_short original_port;
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original_address = GetOriginalAddress(link);
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original_port = GetOriginalPort(link);
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/* Adjust ICMP checksum */
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sptr = (u_short *) &(ip->ip_src);
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accumulate = *sptr++;
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accumulate += *sptr;
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sptr = (u_short *) &original_address;
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accumulate -= *sptr++;
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accumulate -= *sptr;
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accumulate += ud->uh_sport;
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accumulate -= original_port;
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ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
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/* Un-alias address in IP header */
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &original_address,
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(u_short *) &pip->ip_dst,
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2);
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pip->ip_dst = original_address;
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/* Un-alias address and port number of original IP packet
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fragment contained in ICMP data section */
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ip->ip_src = original_address;
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ud->uh_sport = original_port;
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}
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else if (pip->ip_p == IPPROTO_ICMP)
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{
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u_short *sptr;
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int accumulate;
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struct in_addr original_address;
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u_short original_id;
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original_address = GetOriginalAddress(link);
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original_id = GetOriginalPort(link);
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/* Adjust ICMP checksum */
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sptr = (u_short *) &(ip->ip_src);
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accumulate = *sptr++;
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accumulate += *sptr;
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sptr = (u_short *) &original_address;
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accumulate -= *sptr++;
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accumulate -= *sptr;
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accumulate += ic2->icmp_id;
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accumulate -= original_id;
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ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
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/* Un-alias address in IP header */
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &original_address,
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(u_short *) &pip->ip_dst,
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2);
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pip->ip_dst = original_address;
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/* Un-alias address of original IP packet and seqence number of
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embedded icmp datagram */
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ip->ip_src = original_address;
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ic2->icmp_id = original_id;
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}
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return(PKT_ALIAS_OK);
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}
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return(PKT_ALIAS_IGNORED);
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}
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static int
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IcmpAliasIn3(struct ip *pip)
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{
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struct in_addr original_address;
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original_address = FindOriginalAddress(pip->ip_dst);
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &original_address,
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(u_short *) &pip->ip_dst,
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2);
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pip->ip_dst = original_address;
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return PKT_ALIAS_OK;
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}
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static int
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IcmpAliasIn(struct ip *pip)
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{
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int iresult;
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struct icmp *ic;
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ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
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iresult = PKT_ALIAS_IGNORED;
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switch (ic->icmp_type)
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{
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case ICMP_ECHOREPLY:
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case ICMP_TSTAMPREPLY:
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if (ic->icmp_code == 0)
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{
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iresult = IcmpAliasIn1(pip);
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}
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break;
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case ICMP_UNREACH:
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case ICMP_SOURCEQUENCH:
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case ICMP_TIMXCEED:
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case ICMP_PARAMPROB:
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iresult = IcmpAliasIn2(pip);
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break;
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case ICMP_ECHO:
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case ICMP_TSTAMP:
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iresult = IcmpAliasIn3(pip);
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break;
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}
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return(iresult);
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}
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static int
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IcmpAliasOut1(struct ip *pip)
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{
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/*
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Alias ICMP echo and timestamp packets
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*/
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struct alias_link *link;
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struct icmp *ic;
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ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
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/* Save overwritten data for when echo packet returns */
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link = FindIcmpOut(pip->ip_src, pip->ip_dst, ic->icmp_id);
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if (link != NULL)
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{
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u_short alias_id;
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int accumulate;
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alias_id = GetAliasPort(link);
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/* Since data field is being modified, adjust ICMP checksum */
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accumulate = ic->icmp_id;
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accumulate -= alias_id;
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ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
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/* Alias sequence number */
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ic->icmp_id = alias_id;
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/* Change source address */
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{
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struct in_addr alias_address;
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alias_address = GetAliasAddress(link);
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &alias_address,
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(u_short *) &pip->ip_src,
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2);
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pip->ip_src = alias_address;
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}
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return(PKT_ALIAS_OK);
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}
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return(PKT_ALIAS_IGNORED);
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}
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|
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|
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static int
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IcmpAliasOut2(struct ip *pip)
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{
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/*
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Alias outgoing ICMP error messages containing
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IP header and first 64 bits of datagram.
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*/
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struct in_addr alias_addr;
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struct ip *ip;
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struct icmp *ic;
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ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
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ip = (struct ip *) ic->icmp_data;
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alias_addr = FindAliasAddress(ip->ip_src);
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/* Alias destination address in IP fragment */
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DifferentialChecksum(&ic->icmp_cksum,
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(u_short *) &alias_addr,
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(u_short *) &ip->ip_dst,
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2);
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ip->ip_dst = alias_addr;
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/* alias source address in IP header */
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DifferentialChecksum(&pip->ip_sum,
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(u_short *) &alias_addr,
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(u_short *) &pip->ip_src,
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2);
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pip->ip_src = alias_addr;
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return PKT_ALIAS_OK;
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}
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|
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|
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static int
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IcmpAliasOut3(struct ip *pip)
|
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{
|
|
/*
|
|
Handle outgoing echo and timestamp replies. The
|
|
only thing which is done in this case is to alias
|
|
the source IP address of the packet.
|
|
*/
|
|
struct in_addr alias_addr;
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|
|
alias_addr = FindAliasAddress(pip->ip_src);
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &alias_addr,
|
|
(u_short *) &pip->ip_src,
|
|
2);
|
|
pip->ip_src = alias_addr;
|
|
|
|
return PKT_ALIAS_OK;
|
|
}
|
|
|
|
|
|
static int
|
|
IcmpAliasOut(struct ip *pip)
|
|
{
|
|
int iresult;
|
|
struct icmp *ic;
|
|
|
|
ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
|
|
|
|
iresult = PKT_ALIAS_IGNORED;
|
|
switch (ic->icmp_type)
|
|
{
|
|
case ICMP_ECHO:
|
|
case ICMP_TSTAMP:
|
|
if (ic->icmp_code == 0)
|
|
{
|
|
iresult = IcmpAliasOut1(pip);
|
|
}
|
|
break;
|
|
case ICMP_UNREACH:
|
|
case ICMP_SOURCEQUENCH:
|
|
case ICMP_TIMXCEED:
|
|
case ICMP_PARAMPROB:
|
|
iresult = IcmpAliasOut2(pip);
|
|
break;
|
|
case ICMP_ECHOREPLY:
|
|
case ICMP_TSTAMPREPLY:
|
|
iresult = IcmpAliasOut3(pip);
|
|
}
|
|
return(iresult);
|
|
}
|
|
|
|
static int
|
|
UdpAliasIn(struct ip *pip)
|
|
{
|
|
struct udphdr *ud;
|
|
struct alias_link *link;
|
|
|
|
ud = (struct udphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
|
|
link = FindUdpTcpIn(pip->ip_src, pip->ip_dst,
|
|
ud->uh_sport, ud->uh_dport,
|
|
IPPROTO_UDP);
|
|
if (link != NULL)
|
|
{
|
|
struct in_addr alias_address;
|
|
struct in_addr original_address;
|
|
u_short alias_port;
|
|
int accumulate;
|
|
u_short *sptr;
|
|
|
|
alias_address = GetAliasAddress(link);
|
|
original_address = GetOriginalAddress(link);
|
|
alias_port = ud->uh_dport;
|
|
ud->uh_dport = GetOriginalPort(link);
|
|
|
|
/* If NETBIOS Datagram, It should be alias address in UDP Data, too */
|
|
if (ntohs(ud->uh_dport) == NETBIOS_DGM_PORT_NUMBER
|
|
|| ntohs(ud->uh_sport) == NETBIOS_DGM_PORT_NUMBER )
|
|
{
|
|
AliasHandleUdpNbt(pip, link, &original_address, ud->uh_dport);
|
|
} else if (ntohs(ud->uh_dport) == NETBIOS_NS_PORT_NUMBER
|
|
|| ntohs(ud->uh_sport) == NETBIOS_NS_PORT_NUMBER )
|
|
{
|
|
AliasHandleUdpNbtNS(pip, link,
|
|
&alias_address,
|
|
&alias_port,
|
|
&original_address,
|
|
&ud->uh_dport );
|
|
}
|
|
|
|
if (ntohs(ud->uh_dport) == CUSEEME_PORT_NUMBER)
|
|
AliasHandleCUSeeMeIn(pip, original_address);
|
|
|
|
/* If UDP checksum is not zero, then adjust since destination port */
|
|
/* is being unaliased and destination port is being altered. */
|
|
if (ud->uh_sum != 0)
|
|
{
|
|
accumulate = alias_port;
|
|
accumulate -= ud->uh_dport;
|
|
sptr = (u_short *) &alias_address;
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
sptr = (u_short *) &original_address;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
ADJUST_CHECKSUM(accumulate, ud->uh_sum)
|
|
}
|
|
|
|
/* Restore original IP address */
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &original_address,
|
|
(u_short *) &pip->ip_dst,
|
|
2);
|
|
pip->ip_dst = original_address;
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
return(PKT_ALIAS_IGNORED);
|
|
}
|
|
|
|
static int
|
|
UdpAliasOut(struct ip *pip)
|
|
{
|
|
struct udphdr *ud;
|
|
struct alias_link *link;
|
|
|
|
ud = (struct udphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
|
|
link = FindUdpTcpOut(pip->ip_src, pip->ip_dst,
|
|
ud->uh_sport, ud->uh_dport,
|
|
IPPROTO_UDP);
|
|
if (link != NULL)
|
|
{
|
|
u_short alias_port;
|
|
struct in_addr alias_address;
|
|
|
|
alias_address = GetAliasAddress(link);
|
|
alias_port = GetAliasPort(link);
|
|
|
|
if (ntohs(ud->uh_dport) == CUSEEME_PORT_NUMBER)
|
|
AliasHandleCUSeeMeOut(pip, link);
|
|
|
|
/* If NETBIOS Datagram, It should be alias address in UDP Data, too */
|
|
if (ntohs(ud->uh_dport) == NETBIOS_DGM_PORT_NUMBER
|
|
|| ntohs(ud->uh_sport) == NETBIOS_DGM_PORT_NUMBER )
|
|
{
|
|
AliasHandleUdpNbt(pip, link, &alias_address, alias_port);
|
|
} else if (ntohs(ud->uh_dport) == NETBIOS_NS_PORT_NUMBER
|
|
|| ntohs(ud->uh_sport) == NETBIOS_NS_PORT_NUMBER )
|
|
{
|
|
AliasHandleUdpNbtNS(pip, link,
|
|
&pip->ip_src,
|
|
&ud->uh_sport,
|
|
&alias_address,
|
|
&alias_port);
|
|
}
|
|
|
|
/* If UDP checksum is not zero, adjust since source port is */
|
|
/* being aliased and source address is being altered */
|
|
if (ud->uh_sum != 0)
|
|
{
|
|
int accumulate;
|
|
u_short *sptr;
|
|
|
|
accumulate = ud->uh_sport;
|
|
accumulate -= alias_port;
|
|
sptr = (u_short *) &(pip->ip_src);
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
sptr = (u_short *) &alias_address;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
ADJUST_CHECKSUM(accumulate, ud->uh_sum)
|
|
}
|
|
|
|
/* Put alias port in UDP header */
|
|
ud->uh_sport = alias_port;
|
|
|
|
/* Change source address */
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &alias_address,
|
|
(u_short *) &pip->ip_src,
|
|
2);
|
|
pip->ip_src = alias_address;
|
|
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
return(PKT_ALIAS_IGNORED);
|
|
}
|
|
|
|
|
|
|
|
static int
|
|
TcpAliasIn(struct ip *pip)
|
|
{
|
|
struct tcphdr *tc;
|
|
struct alias_link *link;
|
|
|
|
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
|
|
link = FindUdpTcpIn(pip->ip_src, pip->ip_dst,
|
|
tc->th_sport, tc->th_dport,
|
|
IPPROTO_TCP);
|
|
if (link != NULL)
|
|
{
|
|
struct in_addr alias_address;
|
|
struct in_addr original_address;
|
|
u_short alias_port;
|
|
int accumulate;
|
|
u_short *sptr;
|
|
|
|
alias_address = GetAliasAddress(link);
|
|
original_address = GetOriginalAddress(link);
|
|
alias_port = tc->th_dport;
|
|
tc->th_dport = GetOriginalPort(link);
|
|
|
|
/* Adjust TCP checksum since destination port is being unaliased */
|
|
/* and destination port is being altered. */
|
|
accumulate = alias_port;
|
|
accumulate -= tc->th_dport;
|
|
sptr = (u_short *) &alias_address;
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
sptr = (u_short *) &original_address;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
|
|
/* See if ack number needs to be modified */
|
|
if (GetAckModified(link) == 1)
|
|
{
|
|
int delta;
|
|
|
|
delta = GetDeltaAckIn(pip, link);
|
|
if (delta != 0)
|
|
{
|
|
sptr = (u_short *) &tc->th_ack;
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
tc->th_ack = htonl(ntohl(tc->th_ack) - delta);
|
|
sptr = (u_short *) &tc->th_ack;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
}
|
|
}
|
|
|
|
ADJUST_CHECKSUM(accumulate, tc->th_sum);
|
|
|
|
/* Restore original IP address */
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &original_address,
|
|
(u_short *) &pip->ip_dst,
|
|
2);
|
|
pip->ip_dst = original_address;
|
|
|
|
/* Monitor TCP connection state */
|
|
TcpMonitorIn(pip, link);
|
|
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
return(PKT_ALIAS_IGNORED);
|
|
}
|
|
|
|
static int
|
|
TcpAliasOut(struct ip *pip, int maxpacketsize)
|
|
{
|
|
struct tcphdr *tc;
|
|
struct alias_link *link;
|
|
|
|
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
|
|
link = FindUdpTcpOut(pip->ip_src, pip->ip_dst,
|
|
tc->th_sport, tc->th_dport,
|
|
IPPROTO_TCP);
|
|
if (link !=NULL)
|
|
{
|
|
struct in_addr alias_address;
|
|
u_short alias_port;
|
|
int accumulate;
|
|
u_short *sptr;
|
|
|
|
alias_port = GetAliasPort(link);
|
|
alias_address = GetAliasAddress(link);
|
|
|
|
/* Monitor tcp connection state */
|
|
TcpMonitorOut(pip, link);
|
|
|
|
/* Special processing for ftp connection */
|
|
if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER
|
|
|| ntohs(tc->th_sport) == FTP_CONTROL_PORT_NUMBER)
|
|
AliasHandleFtpOut(pip, link, maxpacketsize);
|
|
if (ntohs(tc->th_dport) == IRC_CONTROL_PORT_NUMBER_1
|
|
|| ntohs(tc->th_dport) == IRC_CONTROL_PORT_NUMBER_2)
|
|
AliasHandleIrcOut(pip, link, maxpacketsize);
|
|
|
|
/* Adjust TCP checksum since source port is being aliased */
|
|
/* and source address is being altered */
|
|
accumulate = tc->th_sport;
|
|
accumulate -= alias_port;
|
|
sptr = (u_short *) &(pip->ip_src);
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
sptr = (u_short *) &alias_address;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
|
|
/* Modify sequence number if necessary */
|
|
if (GetAckModified(link) == 1)
|
|
{
|
|
int delta;
|
|
|
|
delta = GetDeltaSeqOut(pip, link);
|
|
if (delta != 0)
|
|
{
|
|
sptr = (u_short *) &tc->th_seq;
|
|
accumulate += *sptr++;
|
|
accumulate += *sptr;
|
|
tc->th_seq = htonl(ntohl(tc->th_seq) + delta);
|
|
sptr = (u_short *) &tc->th_seq;
|
|
accumulate -= *sptr++;
|
|
accumulate -= *sptr;
|
|
}
|
|
}
|
|
|
|
ADJUST_CHECKSUM(accumulate, tc->th_sum)
|
|
|
|
/* Put alias address in TCP header */
|
|
tc->th_sport = alias_port;
|
|
|
|
/* Change source address */
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &alias_address,
|
|
(u_short *) &pip->ip_src,
|
|
2);
|
|
pip->ip_src = alias_address;
|
|
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
return(PKT_ALIAS_IGNORED);
|
|
}
|
|
|
|
|
|
|
|
|
|
/* Fragment Handling
|
|
|
|
FragmentIn()
|
|
FragmentOut()
|
|
|
|
The packet aliasing module has a limited ability for handling IP
|
|
fragments. If the ICMP, TCP or UDP header is in the first fragment
|
|
received, then the id number of the IP packet is saved, and other
|
|
fragments are identified according to their ID number and IP address
|
|
they were sent from. Pointers to unresolved fragments can also be
|
|
saved and recalled when a header fragment is seen.
|
|
*/
|
|
|
|
/* Local prototypes */
|
|
static int FragmentIn(struct ip *);
|
|
static int FragmentOut(struct ip *);
|
|
|
|
|
|
static int
|
|
FragmentIn(struct ip *pip)
|
|
{
|
|
struct alias_link *link;
|
|
|
|
link = FindFragmentIn2(pip->ip_src, pip->ip_dst, pip->ip_id);
|
|
if (link != NULL)
|
|
{
|
|
struct in_addr original_address;
|
|
|
|
GetFragmentAddr(link, &original_address);
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &original_address,
|
|
(u_short *) &pip->ip_dst,
|
|
2);
|
|
pip->ip_dst = original_address;
|
|
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
return(PKT_ALIAS_UNRESOLVED_FRAGMENT);
|
|
}
|
|
|
|
|
|
static int
|
|
FragmentOut(struct ip *pip)
|
|
{
|
|
struct in_addr alias_address;
|
|
|
|
alias_address = FindAliasAddress(pip->ip_src);
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
(u_short *) &alias_address,
|
|
(u_short *) &pip->ip_src,
|
|
2);
|
|
pip->ip_src = alias_address;
|
|
|
|
return(PKT_ALIAS_OK);
|
|
}
|
|
|
|
|
|
|
|
|
|
|
|
|
|
/* Outside World Access
|
|
|
|
PacketAliasSaveFragment()
|
|
PacketAliasGetFragment()
|
|
PacketAliasFragmentIn()
|
|
PacketAliasIn()
|
|
PacketAliasOut()
|
|
|
|
(prototypes in alias.h)
|
|
*/
|
|
|
|
|
|
int
|
|
PacketAliasSaveFragment(char *ptr)
|
|
{
|
|
int iresult;
|
|
struct alias_link *link;
|
|
struct ip *pip;
|
|
|
|
pip = (struct ip *) ptr;
|
|
link = AddFragmentPtrLink(pip->ip_src, pip->ip_id);
|
|
iresult = PKT_ALIAS_ERROR;
|
|
if (link != NULL)
|
|
{
|
|
SetFragmentPtr(link, ptr);
|
|
iresult = PKT_ALIAS_OK;
|
|
}
|
|
return(iresult);
|
|
}
|
|
|
|
|
|
char *
|
|
PacketAliasGetFragment(char *ptr)
|
|
{
|
|
struct alias_link *link;
|
|
char *fptr;
|
|
struct ip *pip;
|
|
|
|
pip = (struct ip *) ptr;
|
|
link = FindFragmentPtr(pip->ip_src, pip->ip_id);
|
|
if (link != NULL)
|
|
{
|
|
GetFragmentPtr(link, &fptr);
|
|
SetFragmentPtr(link, NULL);
|
|
SetExpire(link, 0); /* Deletes link */
|
|
|
|
return(fptr);
|
|
}
|
|
else
|
|
{
|
|
return(NULL);
|
|
}
|
|
}
|
|
|
|
|
|
void
|
|
PacketAliasFragmentIn(char *ptr, /* Points to correctly de-aliased
|
|
header fragment */
|
|
char *ptr_fragment /* Points to fragment which must
|
|
be de-aliased */
|
|
)
|
|
{
|
|
struct ip *pip;
|
|
struct ip *fpip;
|
|
|
|
pip = (struct ip *) ptr;
|
|
fpip = (struct ip *) ptr_fragment;
|
|
|
|
DifferentialChecksum(&fpip->ip_sum,
|
|
(u_short *) &pip->ip_dst,
|
|
(u_short *) &fpip->ip_dst,
|
|
2);
|
|
fpip->ip_dst = pip->ip_dst;
|
|
}
|
|
|
|
|
|
int
|
|
PacketAliasIn(char *ptr, int maxpacketsize)
|
|
{
|
|
struct in_addr alias_addr;
|
|
struct ip *pip;
|
|
int iresult;
|
|
|
|
HouseKeeping();
|
|
ClearCheckNewLink();
|
|
pip = (struct ip *) ptr;
|
|
alias_addr = pip->ip_dst;
|
|
|
|
/* Defense against mangled packets */
|
|
if (ntohs(pip->ip_len) > maxpacketsize
|
|
|| (pip->ip_hl<<2) > maxpacketsize)
|
|
return PKT_ALIAS_IGNORED;
|
|
|
|
iresult = PKT_ALIAS_IGNORED;
|
|
if ( (ntohs(pip->ip_off) & IP_OFFMASK) == 0 )
|
|
{
|
|
switch (pip->ip_p)
|
|
{
|
|
case IPPROTO_ICMP:
|
|
iresult = IcmpAliasIn(pip);
|
|
break;
|
|
case IPPROTO_UDP:
|
|
iresult = UdpAliasIn(pip);
|
|
break;
|
|
case IPPROTO_TCP:
|
|
iresult = TcpAliasIn(pip);
|
|
break;
|
|
}
|
|
|
|
if (ntohs(pip->ip_off) & IP_MF)
|
|
{
|
|
struct alias_link *link;
|
|
|
|
link = FindFragmentIn1(pip->ip_src, alias_addr, pip->ip_id);
|
|
if (link != NULL)
|
|
{
|
|
iresult = PKT_ALIAS_FOUND_HEADER_FRAGMENT;
|
|
SetFragmentAddr(link, pip->ip_dst);
|
|
}
|
|
else
|
|
{
|
|
iresult = PKT_ALIAS_ERROR;
|
|
}
|
|
}
|
|
}
|
|
else
|
|
{
|
|
iresult = FragmentIn(pip);
|
|
}
|
|
|
|
return(iresult);
|
|
}
|
|
|
|
|
|
|
|
/* Unregistered address ranges */
|
|
|
|
/* 10.0.0.0 -> 10.255.255.255 */
|
|
#define UNREG_ADDR_A_LOWER 0x0a000000
|
|
#define UNREG_ADDR_A_UPPER 0x0affffff
|
|
|
|
/* 172.16.0.0 -> 172.31.255.255 */
|
|
#define UNREG_ADDR_B_LOWER 0xac100000
|
|
#define UNREG_ADDR_B_UPPER 0xac1fffff
|
|
|
|
/* 192.168.0.0 -> 192.168.255.255 */
|
|
#define UNREG_ADDR_C_LOWER 0xc0a80000
|
|
#define UNREG_ADDR_C_UPPER 0xc0a8ffff
|
|
|
|
|
|
|
|
int
|
|
PacketAliasOut(char *ptr, /* valid IP packet */
|
|
int maxpacketsize /* How much the packet data may grow
|
|
(FTP and IRC inline changes) */
|
|
)
|
|
{
|
|
int iresult;
|
|
struct in_addr addr_save;
|
|
struct ip *pip;
|
|
|
|
HouseKeeping();
|
|
ClearCheckNewLink();
|
|
pip = (struct ip *) ptr;
|
|
|
|
/* Defense against mangled packets */
|
|
if (ntohs(pip->ip_len) > maxpacketsize
|
|
|| (pip->ip_hl<<2) > maxpacketsize)
|
|
return PKT_ALIAS_IGNORED;
|
|
|
|
addr_save = GetDefaultAliasAddress();
|
|
if (packetAliasMode & PKT_ALIAS_UNREGISTERED_ONLY)
|
|
{
|
|
unsigned int addr;
|
|
int iclass;
|
|
|
|
iclass = 0;
|
|
addr = ntohl(pip->ip_src.s_addr);
|
|
if (addr >= UNREG_ADDR_C_LOWER && addr <= UNREG_ADDR_C_UPPER)
|
|
iclass = 3;
|
|
else if (addr >= UNREG_ADDR_B_LOWER && addr <= UNREG_ADDR_B_UPPER)
|
|
iclass = 2;
|
|
else if (addr >= UNREG_ADDR_A_LOWER && addr <= UNREG_ADDR_A_UPPER)
|
|
iclass = 1;
|
|
|
|
if (iclass == 0)
|
|
{
|
|
SetDefaultAliasAddress(pip->ip_src);
|
|
}
|
|
}
|
|
|
|
iresult = PKT_ALIAS_IGNORED;
|
|
if ((ntohs(pip->ip_off) & IP_OFFMASK) == 0)
|
|
{
|
|
switch (pip->ip_p)
|
|
{
|
|
case IPPROTO_ICMP:
|
|
iresult = IcmpAliasOut(pip);
|
|
break;
|
|
case IPPROTO_UDP:
|
|
iresult = UdpAliasOut(pip);
|
|
break;
|
|
case IPPROTO_TCP:
|
|
iresult = TcpAliasOut(pip, maxpacketsize);
|
|
break;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
iresult = FragmentOut(pip);
|
|
}
|
|
|
|
SetDefaultAliasAddress(addr_save);
|
|
return(iresult);
|
|
}
|