Create the alias library. This is currently only used by

ppp (or will be shortly).  Natd can now be updated to use
this library rather than carrying its own version of the code.

Submitted by:	Charles Mott <cmott@srv.net>

1 files changed, 1142 insertions, 0 deletions

diff --git a/lib/libalias/alias.c b/lib/libalias/alias.c
new file mode 100644
index 0000000..1a9eb36
--- /dev/null
+++ b/lib/libalias/alias.c
@@ -0,0 +1,1142 @@
+/* -*- mode: c; tab-width: 8; c-basic-indent: 4; -*- */
+/*
+    Alias.c provides supervisory control for the functions of the
+    packet aliasing software.  It consists of routines to monitor
+    TCP connection state, protocol-specific aliasing routines,
+    fragment handling and the following outside world functional
+    interfaces: SaveFragmentPtr, GetFragmentPtr, FragmentAliasIn,
+    PacketAliasIn and PacketAliasOut.
+
+    The other C program files are briefly described. The data
+    structure framework which holds information needed to translate
+    packets is encapsulated in alias_db.c.  Data is accessed by
+    function calls, so other segments of the program need not know
+    about the underlying data structures.  Alias_ftp.c contains
+    special code for modifying the ftp PORT command used to establish
+    data connections, while alias_irc.c do the same for IRC
+    DCC. Alias_util.c contains a few utility routines.
+
+    This software is placed into the public domain with no restrictions
+    on its distribution.
+
+    Version 1.0 August, 1996  (cjm)
+
+    Version 1.1 August 20, 1996  (cjm)
+        PPP host accepts incoming connections for ports 0 to 1023.
+        (Gary Roberts pointed out the need to handle incoming
+         connections.)
+
+    Version 1.2 September 7, 1996 (cjm)
+        Fragment handling error in alias_db.c corrected.
+        (Tom Torrance helped fix this problem.)
+
+    Version 1.4 September 16, 1996 (cjm)
+        - A more generalized method for handling incoming
+          connections, without the 0-1023 restriction, is
+          implemented in alias_db.c
+        - Improved ICMP support in alias.c.  Traceroute
+          packet streams can now be correctly aliased.
+        - TCP connection closing logic simplified in
+          alias.c and now allows for additional 1 minute
+          "grace period" after FIN or RST is observed.
+
+    Version 1.5 September 17, 1996 (cjm)
+        Corrected error in handling incoming UDP packets with 0 checksum.
+        (Tom Torrance helped fix this problem.)
+
+    Version 1.6 September 18, 1996 (cjm)
+        Simplified ICMP aliasing scheme.  Should now support
+        traceroute from Win95 as well as FreeBSD.
+
+    Version 1.7 January 9, 1997 (cjm)
+        - Out-of-order fragment handling.
+        - IP checksum error fixed for ftp transfers
+          from aliasing host.
+        - Integer return codes added to all
+          aliasing/de-aliasing functions.
+        - Some obsolete comments cleaned up.
+        - Differential checksum computations for
+          IP header (TCP, UDP and ICMP were already
+          differential).
+
+    Version 2.1 May 1997 (cjm)
+        - Added support for outgoing ICMP error
+          messages.
+        - Added two functions PacketAliasIn2()
+          and PacketAliasOut2() for dynamic address
+          control (e.g. round-robin allocation of
+          incoming packets).
+*/
+
+#include <stdio.h>
+#include <unistd.h>
+
+#include <sys/param.h>
+#include <sys/types.h>
+
+#include <netinet/in_systm.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip_icmp.h>
+#include <netinet/tcp.h>
+#include <netinet/udp.h>
+
+#include "alias_local.h"
+#include "alias.h"
+
+#define FTP_CONTROL_PORT_NUMBER 21
+#define IRC_CONTROL_PORT_NUMBER_1 6667
+#define IRC_CONTROL_PORT_NUMBER_2 6668
+
+/*
+   The following macro is used to update an
+   internet checksum.  "delta" is a 32-bit
+   accumulation of all the changes to the
+   checksum (adding in new 16-bit words and
+   subtracting out old words), and "cksum"
+   is the checksum value to be updated.
+*/
+#define ADJUST_CHECKSUM(acc, cksum) { \
+    acc += cksum; \
+    if (acc < 0) \
+    { \
+        acc = -acc; \
+        acc = (acc >> 16) + (acc & 0xffff); \
+        acc += acc >> 16; \
+        cksum = (u_short) ~acc; \
+    } \
+    else \
+    { \
+        acc = (acc >> 16) + (acc & 0xffff); \
+        acc += acc >> 16; \
+        cksum = (u_short) acc; \
+    } \
+}
+
+
+
+
+/* TCP Handling Routines
+
+    TcpMonitorIn()  -- These routines monitor TCP connections, and
+    TcpMonitorOut() -- delete a link node when a connection is closed.
+
+These routines look for SYN, ACK and RST flags to determine when TCP
+connections open and close.  When a TCP connection closes, the data
+structure containing packet aliasing information is deleted after
+a timeout period.
+*/
+
+/* Local prototypes */
+static void TcpMonitorIn(struct ip *, struct alias_link *);
+
+static void TcpMonitorOut(struct ip *, struct alias_link *);
+
+
+static void
+TcpMonitorIn(struct ip *pip, struct alias_link *link)
+{
+    struct tcphdr *tc;
+
+    tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
+
+    switch (GetStateIn(link))
+    {
+        case 0:
+            if (tc->th_flags & TH_SYN) SetStateIn(link, 1);
+            break;
+        case 1:
+            if (tc->th_flags & TH_FIN
+             || tc->th_flags & TH_RST) SetStateIn(link, 2);
+    }
+}
+
+static void
+TcpMonitorOut(struct ip *pip, struct alias_link *link)
+{
+    struct tcphdr *tc;
+
+    tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
+     
+    switch (GetStateOut(link))
+    {
+        case 0:
+            if (tc->th_flags & TH_SYN) SetStateOut(link, 1);
+            break;
+        case 1:
+            if (tc->th_flags & TH_FIN
+             || tc->th_flags & TH_RST) SetStateOut(link, 2);
+    }
+}
+
+
+
+
+
+/* Protocol Specific Packet Aliasing Routines 
+
+    IcmpAliasIn(), IcmpAliasIn1(), IcmpAliasIn2(), IcmpAliasIn3()
+    IcmpAliasOut(), IcmpAliasOut1(), IcmpAliasOut2(), IcmpAliasOut3()
+    UdpAliasIn(), UdpAliasOut()
+    TcpAliasIn(), TcpAliasOut()
+
+These routines handle protocol specific details of packet aliasing.
+One may observe a certain amount of repetitive arithmetic in these
+functions, the purpose of which is to compute a revised checksum
+without actually summing over the entire data packet, which could be
+unnecessarily time consuming.
+
+The purpose of the packet aliasing routines is to replace the source
+address of the outgoing packet and then correctly put it back for
+any incoming packets.  For TCP and UDP, ports are also re-mapped.
+
+For ICMP echo/timestamp requests and replies, the following scheme
+is used: the id number is replaced by an alias for the outgoing
+packet.
+
+ICMP error messages are handled by looking at the IP fragment
+in the data section of the message.
+
+For TCP and UDP protocols, a port number is chosen for an outgoing
+packet, and then incoming packets are identified by IP address and
+port numbers.  For TCP packets, there is additional logic in the event
+that sequence and ack numbers have been altered (as is the case for
+FTP data port commands).
+
+The port numbers used by the packet aliasing module are not true
+ports in the Unix sense.  No sockets are actually bound to ports.
+They are more correctly thought of as placeholders.
+
+All packets go through the aliasing mechanism, whether they come from
+the gateway machine or other machines on a local area network.
+*/
+
+
+/* Local prototypes */
+static int IcmpAliasIn1(struct ip *);
+static int IcmpAliasIn2(struct ip *);
+static int IcmpAliasIn3(struct ip *);
+static int IcmpAliasIn (struct ip *);
+
+static int IcmpAliasOut1(struct ip *);
+static int IcmpAliasOut2(struct ip *);
+static int IcmpAliasOut3(struct ip *);
+static int IcmpAliasOut (struct ip *);
+
+static int UdpAliasOut(struct ip *);
+static int UdpAliasIn (struct ip *);
+
+static int TcpAliasOut(struct ip *, int);
+static int TcpAliasIn (struct ip *);
+
+
+static int
+IcmpAliasIn1(struct ip *pip)
+{
+/*
+    De-alias incoming echo and timestamp replies
+*/
+    struct alias_link *link;
+    struct icmp *ic;
+
+    ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
+
+/* Get source address from ICMP data field and restore original data */
+    link = FindIcmpIn(pip->ip_src, pip->ip_dst, ic->icmp_id);
+    if (link != NULL)
+    {
+        u_short original_id;
+        int accumulate;
+
+        original_id = GetOriginalPort(link);
+
+/* Adjust ICMP checksum */
+        accumulate  = ic->icmp_id;
+        accumulate -= original_id;
+        ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
+
+/* Put original sequence number back in */
+        ic->icmp_id = original_id;
+
+/* Put original address back into IP header */
+        {
+            struct in_addr original_address;
+
+            original_address = GetOriginalAddress(link);
+            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
+IcmpAliasIn2(struct ip *pip)
+{
+/*
+    Alias incoming ICMP error messages containing
+    IP header and first 64 bits of datagram.
+*/
+    struct ip *ip;
+    struct icmp *ic, *ic2;
+    struct udphdr *ud;
+    struct tcphdr *tc;
+    struct alias_link *link;
+
+    ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
+    ip = (struct ip *) ic->icmp_data;
+
+    ud = (struct udphdr *) ((char *) ip + (ip->ip_hl <<2));
+    tc = (struct tcphdr *) ud;
+    ic2 = (struct icmp *) ud;
+
+    if (ip->ip_p == IPPROTO_UDP)
+        link = FindUdpTcpIn(ip->ip_dst, ip->ip_src,
+                            ud->uh_dport, ud->uh_sport,
+                            IPPROTO_UDP);
+    else if (ip->ip_p == IPPROTO_TCP)
+        link = FindUdpTcpIn(ip->ip_dst, ip->ip_src,
+                            tc->th_dport, tc->th_sport,
+                            IPPROTO_TCP);
+    else if (ip->ip_p == IPPROTO_ICMP)
+        if (ic2->icmp_type == ICMP_ECHO || ic2->icmp_type == ICMP_TSTAMP)
+            link = FindIcmpIn(ip->ip_dst, ip->ip_src, ic2->icmp_id);
+         else
+            link = NULL;
+    else
+        link = NULL;
+
+    if (link != NULL)
+    {
+        if (ip->ip_p == IPPROTO_UDP || ip->ip_p == IPPROTO_TCP)
+        {
+            u_short *sptr;
+            int accumulate;
+            struct in_addr original_address;
+            u_short original_port;
+
+            original_address = GetOriginalAddress(link);
+            original_port = GetOriginalPort(link);
+    
+/* Adjust ICMP checksum */
+            sptr = (u_short *) &(ip->ip_src);
+            accumulate  = *sptr++;
+            accumulate += *sptr;
+            sptr = (u_short *) &original_address;
+            accumulate -= *sptr++;
+            accumulate -= *sptr;
+            accumulate += ud->uh_sport;
+            accumulate -= original_port;
+            ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
+
+/* Un-alias address in IP header */
+            DifferentialChecksum(&pip->ip_sum,
+                                 (u_short *) &original_address,
+                                 (u_short *) &pip->ip_dst,
+                                 2);
+            pip->ip_dst = original_address;
+
+/* Un-alias address and port number of original IP packet
+fragment contained in ICMP data section */
+            ip->ip_src = original_address;
+            ud->uh_sport = original_port; 
+        }
+        else if (pip->ip_p == IPPROTO_ICMP)
+        {
+            u_short *sptr;
+            int accumulate;
+            struct in_addr original_address;
+            u_short original_id;
+
+            original_address = GetOriginalAddress(link);
+            original_id = GetOriginalPort(link);
+
+/* Adjust ICMP checksum */
+            sptr = (u_short *) &(ip->ip_src);
+            accumulate  = *sptr++;
+            accumulate += *sptr;
+            sptr = (u_short *) &original_address;
+            accumulate -= *sptr++;
+            accumulate -= *sptr;
+            accumulate += ic2->icmp_id;
+            accumulate -= original_id;
+            ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
+
+/* Un-alias address in IP header */
+            DifferentialChecksum(&pip->ip_sum,
+                                 (u_short *) &original_address,
+                                 (u_short *) &pip->ip_dst,
+                                 2);
+            pip->ip_dst = original_address;
+
+/* Un-alias address of original IP packet and seqence number of 
+   embedded icmp datagram */
+            ip->ip_src = original_address;
+            ic2->icmp_id = original_id;
+        }
+        return(PKT_ALIAS_OK);
+    }
+    return(PKT_ALIAS_IGNORED);
+}
+
+
+static int
+IcmpAliasIn3(struct ip *pip)
+{
+    struct in_addr original_address;
+
+    original_address = FindOriginalAddress(pip->ip_dst);
+    DifferentialChecksum(&pip->ip_sum,
+                         (u_short *) &original_address,
+                         (u_short *) &pip->ip_dst,
+                         2);
+    pip->ip_dst = original_address;
+
+    return PKT_ALIAS_OK;
+}
+
+
+static int
+IcmpAliasIn(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_ECHOREPLY:
+        case ICMP_TSTAMPREPLY:
+            if (ic->icmp_code == 0)
+            {
+                iresult = IcmpAliasIn1(pip);
+            }
+            break;
+        case ICMP_UNREACH:
+        case ICMP_SOURCEQUENCH:
+        case ICMP_TIMXCEED:
+        case ICMP_PARAMPROB:
+            iresult = IcmpAliasIn2(pip);
+            break;
+        case ICMP_ECHO:
+        case ICMP_TSTAMP:
+            iresult = IcmpAliasIn3(pip);
+            break;
+    }
+    return(iresult);
+}
+
+
+static int
+IcmpAliasOut1(struct ip *pip)
+{
+/*
+    Alias ICMP echo and timestamp packets
+*/
+    struct alias_link *link;
+    struct icmp *ic;
+
+    ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
+
+/* Save overwritten data for when echo packet returns */
+    link = FindIcmpOut(pip->ip_src, pip->ip_dst, ic->icmp_id);
+    if (link != NULL)
+    {
+        u_short alias_id;
+        int accumulate;
+
+        alias_id = GetAliasPort(link);
+
+/* Since data field is being modified, adjust ICMP checksum */
+        accumulate  = ic->icmp_id;
+        accumulate -= alias_id;
+        ADJUST_CHECKSUM(accumulate, ic->icmp_cksum)
+
+/* Alias sequence number */
+        ic->icmp_id = alias_id;
+
+/* Change source address */
+        {
+            struct in_addr alias_address;
+
+            alias_address = GetAliasAddress(link);
+            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
+IcmpAliasOut2(struct ip *pip)
+{
+/*
+    Alias outgoing ICMP error messages containing
+    IP header and first 64 bits of datagram.
+*/
+    struct in_addr alias_addr;
+    struct ip *ip;
+    struct icmp *ic;
+
+    ic = (struct icmp *) ((char *) pip + (pip->ip_hl << 2));
+    ip = (struct ip *) ic->icmp_data;
+
+    alias_addr = FindAliasAddress(ip->ip_src);
+
+/* Alias destination address in IP fragment */
+    DifferentialChecksum(&ic->icmp_cksum,
+                         (u_short *) &alias_addr,
+                         (u_short *) &ip->ip_dst,
+                         2);
+    ip->ip_dst = alias_addr;
+
+/* alias source address in IP header */
+    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
+IcmpAliasOut3(struct ip *pip)
+{
+/*
+  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;
+
+    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 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 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 TCP 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
+
+        SaveFragmentPtr()
+        GetNextFragmentPtr()
+        FragmentAliasIn()
+        PacketAliasIn()
+        PacketAliasOut()
+        PacketAliasIn2()
+        PacketAliasOut2()
+
+(prototypes in alias.h)
+*/
+
+
+int
+SaveFragmentPtr(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 *
+GetNextFragmentPtr(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);
+        SetExpire(link, 0); /* Deletes link */
+
+        return(fptr);
+    }
+    else
+    {
+        return(NULL);
+    }
+}
+
+
+void
+FragmentAliasIn(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();
+    pip = (struct ip *) ptr;
+    alias_addr = pip->ip_dst;
+        
+    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();
+    pip = (struct ip *) ptr;
+
+    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);
+}
+
+
+int
+PacketAliasIn2(char *ptr,           /* valid IP packet */
+               struct in_addr addr, /* Default aliasing address */
+               int  maxpacketsize   /* How much the packet data may grow
+                                       (FTP and IRC inline changes) */
+              )
+{
+    int result_code;
+    struct in_addr addr_save;
+
+    ClearNewDefaultLink();
+    addr_save = GetDefaultAliasAddress();
+
+    SetDefaultTargetAddress(addr);
+    result_code = PacketAliasIn(ptr, maxpacketsize);
+    ClearDefaultTargetAddress();
+
+    if (result_code == PKT_ALIAS_OK)
+    {
+        if (CheckNewDefaultLink())
+            return PKT_ALIAS_NEW_LINK;
+    }
+
+    return result_code;
+}
+
+
+int
+PacketAliasOut2(char *ptr,          /* valid IP packet */
+               struct in_addr addr, /* Default aliasing address */
+               int  maxpacketsize   /* How much the packet data may grow
+                                       (FTP and IRC inline changes) */
+              )
+{
+    int result_code;
+    struct in_addr addr_save;
+
+    ClearNewDefaultLink();
+    addr_save = GetDefaultAliasAddress();
+
+    SetDefaultAliasAddress(addr);
+    result_code = PacketAliasOut(ptr, maxpacketsize);
+    SetDefaultAliasAddress(addr_save);
+
+    if (result_code == PKT_ALIAS_OK)
+    {
+        if (CheckNewDefaultLink())
+            return PKT_ALIAS_NEW_LINK;
+    }
+
+    return result_code;
+}