837 lines
21 KiB
C
837 lines
21 KiB
C
/*-
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* Copyright (c) 2001 Charles Mott <cmott@scientech.com>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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/* file: alias_proxy.c
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This file encapsulates special operations related to transparent
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proxy redirection. This is where packets with a particular destination,
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usually tcp port 80, are redirected to a proxy server.
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When packets are proxied, the destination address and port are
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modified. In certain cases, it is necessary to somehow encode
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the original address/port info into the packet. Two methods are
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presently supported: addition of a [DEST addr port] string at the
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beginning a of tcp stream, or inclusion of an optional field
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in the IP header.
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There is one public API function:
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PacketAliasProxyRule() -- Adds and deletes proxy
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rules.
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Rules are stored in a linear linked list, so lookup efficiency
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won't be too good for large lists.
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Initial development: April, 1998 (cjm)
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*/
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/* System includes */
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#include <ctype.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <netdb.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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/* BSD IPV4 includes */
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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/tcp.h>
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#include <arpa/inet.h>
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#include "alias_local.h" /* Functions used by alias*.c */
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#include "alias.h" /* Public API functions for libalias */
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/*
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Data structures
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*/
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/*
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* A linked list of arbitrary length, based on struct proxy_entry is
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* used to store proxy rules.
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*/
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struct proxy_entry
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{
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#define PROXY_TYPE_ENCODE_NONE 1
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#define PROXY_TYPE_ENCODE_TCPSTREAM 2
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#define PROXY_TYPE_ENCODE_IPHDR 3
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int rule_index;
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int proxy_type;
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u_char proto;
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u_short proxy_port;
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u_short server_port;
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struct in_addr server_addr;
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struct in_addr src_addr;
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struct in_addr src_mask;
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struct in_addr dst_addr;
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struct in_addr dst_mask;
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struct proxy_entry *next;
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struct proxy_entry *last;
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};
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/*
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File scope variables
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*/
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static struct proxy_entry *proxyList;
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/* Local (static) functions:
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IpMask() -- Utility function for creating IP
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masks from integer (1-32) specification.
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IpAddr() -- Utility function for converting string
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to IP address
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IpPort() -- Utility function for converting string
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to port number
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RuleAdd() -- Adds an element to the rule list.
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RuleDelete() -- Removes an element from the rule list.
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RuleNumberDelete() -- Removes all elements from the rule list
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having a certain rule number.
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ProxyEncodeTcpStream() -- Adds [DEST x.x.x.x xxxx] to the beginning
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of a TCP stream.
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ProxyEncodeIpHeader() -- Adds an IP option indicating the true
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destination of a proxied IP packet
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*/
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static int IpMask(int, struct in_addr *);
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static int IpAddr(char *, struct in_addr *);
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static int IpPort(char *, int, int *);
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static void RuleAdd(struct proxy_entry *);
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static void RuleDelete(struct proxy_entry *);
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static int RuleNumberDelete(int);
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static void ProxyEncodeTcpStream(struct alias_link *, struct ip *, int);
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static void ProxyEncodeIpHeader(struct ip *, int);
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static int
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IpMask(int nbits, struct in_addr *mask)
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{
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int i;
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u_int imask;
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if (nbits < 0 || nbits > 32)
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return -1;
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imask = 0;
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for (i=0; i<nbits; i++)
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imask = (imask >> 1) + 0x80000000;
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mask->s_addr = htonl(imask);
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return 0;
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}
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static int
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IpAddr(char *s, struct in_addr *addr)
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{
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if (inet_aton(s, addr) == 0)
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return -1;
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else
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return 0;
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}
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static int
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IpPort(char *s, int proto, int *port)
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{
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int n;
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n = sscanf(s, "%d", port);
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if (n != 1)
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{
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struct servent *se;
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if (proto == IPPROTO_TCP)
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se = getservbyname(s, "tcp");
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else if (proto == IPPROTO_UDP)
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se = getservbyname(s, "udp");
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else
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return -1;
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if (se == NULL)
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return -1;
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*port = (u_int) ntohs(se->s_port);
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}
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return 0;
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}
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void
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RuleAdd(struct proxy_entry *entry)
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{
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int rule_index;
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struct proxy_entry *ptr;
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struct proxy_entry *ptr_last;
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if (proxyList == NULL)
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{
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proxyList = entry;
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entry->last = NULL;
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entry->next = NULL;
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return;
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}
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rule_index = entry->rule_index;
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ptr = proxyList;
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ptr_last = NULL;
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while (ptr != NULL)
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{
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if (ptr->rule_index >= rule_index)
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{
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if (ptr_last == NULL)
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{
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entry->next = proxyList;
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entry->last = NULL;
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proxyList->last = entry;
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proxyList = entry;
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return;
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}
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ptr_last->next = entry;
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ptr->last = entry;
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entry->last = ptr->last;
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entry->next = ptr;
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return;
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}
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ptr_last = ptr;
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ptr = ptr->next;
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}
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ptr_last->next = entry;
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entry->last = ptr_last;
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entry->next = NULL;
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}
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static void
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RuleDelete(struct proxy_entry *entry)
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{
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if (entry->last != NULL)
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entry->last->next = entry->next;
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else
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proxyList = entry->next;
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if (entry->next != NULL)
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entry->next->last = entry->last;
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free(entry);
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}
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static int
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RuleNumberDelete(int rule_index)
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{
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int err;
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struct proxy_entry *ptr;
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err = -1;
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ptr = proxyList;
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while (ptr != NULL)
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{
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struct proxy_entry *ptr_next;
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ptr_next = ptr->next;
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if (ptr->rule_index == rule_index)
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{
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err = 0;
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RuleDelete(ptr);
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}
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ptr = ptr_next;
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}
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return err;
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}
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static void
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ProxyEncodeTcpStream(struct alias_link *link,
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struct ip *pip,
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int maxpacketsize)
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{
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int slen;
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char buffer[40];
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struct tcphdr *tc;
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/* Compute pointer to tcp header */
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tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
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/* Don't modify if once already modified */
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if (GetAckModified (link))
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return;
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/* Translate destination address and port to string form */
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snprintf(buffer, sizeof(buffer) - 2, "[DEST %s %d]",
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inet_ntoa(GetProxyAddress (link)), (u_int) ntohs(GetProxyPort (link)));
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/* Pad string out to a multiple of two in length */
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slen = strlen(buffer);
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switch (slen % 2)
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{
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case 0:
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strcat(buffer, " \n");
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slen += 2;
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break;
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case 1:
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strcat(buffer, "\n");
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slen += 1;
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}
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/* Check for packet overflow */
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if ((ntohs(pip->ip_len) + strlen(buffer)) > maxpacketsize)
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return;
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/* Shift existing TCP data and insert destination string */
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{
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int dlen;
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int hlen;
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u_char *p;
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hlen = (pip->ip_hl + tc->th_off) << 2;
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dlen = ntohs (pip->ip_len) - hlen;
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/* Modify first packet that has data in it */
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if (dlen == 0)
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return;
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p = (char *) pip;
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p += hlen;
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memmove(p + slen, p, dlen);
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memcpy(p, buffer, slen);
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}
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/* Save information about modfied sequence number */
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{
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int delta;
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SetAckModified(link);
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delta = GetDeltaSeqOut(pip, link);
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AddSeq(pip, link, delta+slen);
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}
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/* Update IP header packet length and checksum */
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{
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int accumulate;
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accumulate = pip->ip_len;
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pip->ip_len = htons(ntohs(pip->ip_len) + slen);
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accumulate -= pip->ip_len;
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ADJUST_CHECKSUM(accumulate, pip->ip_sum);
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}
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/* Update TCP checksum, Use TcpChecksum since so many things have
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already changed. */
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tc->th_sum = 0;
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tc->th_sum = TcpChecksum (pip);
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}
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static void
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ProxyEncodeIpHeader(struct ip *pip,
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int maxpacketsize)
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{
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#define OPTION_LEN_BYTES 8
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#define OPTION_LEN_INT16 4
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#define OPTION_LEN_INT32 2
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u_char option[OPTION_LEN_BYTES];
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#ifdef DEBUG
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fprintf(stdout, " ip cksum 1 = %x\n", (u_int) IpChecksum(pip));
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fprintf(stdout, "tcp cksum 1 = %x\n", (u_int) TcpChecksum(pip));
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#endif
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/* Check to see that there is room to add an IP option */
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if (pip->ip_hl > (0x0f - OPTION_LEN_INT32))
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return;
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/* Build option and copy into packet */
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{
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u_char *ptr;
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struct tcphdr *tc;
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ptr = (u_char *) pip;
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ptr += 20;
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memcpy(ptr + OPTION_LEN_BYTES, ptr, ntohs(pip->ip_len) - 20);
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option[0] = 0x64; /* class: 3 (reserved), option 4 */
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option[1] = OPTION_LEN_BYTES;
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memcpy(&option[2], (u_char *) &pip->ip_dst, 4);
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tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
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memcpy(&option[6], (u_char *) &tc->th_sport, 2);
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memcpy(ptr, option, 8);
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}
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/* Update checksum, header length and packet length */
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{
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int i;
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int accumulate;
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u_short *sptr;
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sptr = (u_short *) option;
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accumulate = 0;
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for (i=0; i<OPTION_LEN_INT16; i++)
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accumulate -= *(sptr++);
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sptr = (u_short *) pip;
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accumulate += *sptr;
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pip->ip_hl += OPTION_LEN_INT32;
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accumulate -= *sptr;
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accumulate += pip->ip_len;
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pip->ip_len = htons(ntohs(pip->ip_len) + OPTION_LEN_BYTES);
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accumulate -= pip->ip_len;
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ADJUST_CHECKSUM(accumulate, pip->ip_sum);
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}
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#undef OPTION_LEN_BYTES
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#undef OPTION_LEN_INT16
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#undef OPTION_LEN_INT32
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#ifdef DEBUG
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fprintf(stdout, " ip cksum 2 = %x\n", (u_int) IpChecksum(pip));
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fprintf(stdout, "tcp cksum 2 = %x\n", (u_int) TcpChecksum(pip));
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#endif
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}
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/* Functions by other packet alias source files
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ProxyCheck() -- Checks whether an outgoing packet should
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be proxied.
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ProxyModify() -- Encodes the original destination address/port
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for a packet which is to be redirected to
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a proxy server.
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*/
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int
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ProxyCheck(struct ip *pip,
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struct in_addr *proxy_server_addr,
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u_short *proxy_server_port)
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{
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u_short dst_port;
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struct in_addr src_addr;
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struct in_addr dst_addr;
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struct proxy_entry *ptr;
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src_addr = pip->ip_src;
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dst_addr = pip->ip_dst;
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dst_port = ((struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)))
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->th_dport;
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ptr = proxyList;
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while (ptr != NULL)
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{
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u_short proxy_port;
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proxy_port = ptr->proxy_port;
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if ((dst_port == proxy_port || proxy_port == 0)
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&& pip->ip_p == ptr->proto
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&& src_addr.s_addr != ptr->server_addr.s_addr)
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{
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struct in_addr src_addr_masked;
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struct in_addr dst_addr_masked;
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src_addr_masked.s_addr = src_addr.s_addr & ptr->src_mask.s_addr;
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dst_addr_masked.s_addr = dst_addr.s_addr & ptr->dst_mask.s_addr;
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if ((src_addr_masked.s_addr == ptr->src_addr.s_addr)
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&& (dst_addr_masked.s_addr == ptr->dst_addr.s_addr))
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{
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if ((*proxy_server_port = ptr->server_port) == 0)
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*proxy_server_port = dst_port;
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*proxy_server_addr = ptr->server_addr;
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return ptr->proxy_type;
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}
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}
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ptr = ptr->next;
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}
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return 0;
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}
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void
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ProxyModify(struct alias_link *link,
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struct ip *pip,
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int maxpacketsize,
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int proxy_type)
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{
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switch (proxy_type)
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{
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case PROXY_TYPE_ENCODE_IPHDR:
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ProxyEncodeIpHeader(pip, maxpacketsize);
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break;
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case PROXY_TYPE_ENCODE_TCPSTREAM:
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ProxyEncodeTcpStream(link, pip, maxpacketsize);
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break;
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}
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}
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/*
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Public API functions
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*/
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int
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PacketAliasProxyRule(const char *cmd)
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{
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/*
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* This function takes command strings of the form:
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*
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* server <addr>[:<port>]
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* [port <port>]
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* [rule n]
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* [proto tcp|udp]
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* [src <addr>[/n]]
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* [dst <addr>[/n]]
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* [type encode_tcp_stream|encode_ip_hdr|no_encode]
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*
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* delete <rule number>
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*
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* Subfields can be in arbitrary order. Port numbers and addresses
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* must be in either numeric or symbolic form. An optional rule number
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* is used to control the order in which rules are searched. If two
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* rules have the same number, then search order cannot be guaranteed,
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* and the rules should be disjoint. If no rule number is specified,
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* then 0 is used, and group 0 rules are always checked before any
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* others.
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*/
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int i, n, len;
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int cmd_len;
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int token_count;
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int state;
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char *token;
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char buffer[256];
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char str_port[sizeof(buffer)];
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char str_server_port[sizeof(buffer)];
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char *res = buffer;
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int rule_index;
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int proto;
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int proxy_type;
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int proxy_port;
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int server_port;
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struct in_addr server_addr;
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struct in_addr src_addr, src_mask;
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struct in_addr dst_addr, dst_mask;
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struct proxy_entry *proxy_entry;
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/* Copy command line into a buffer */
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cmd += strspn(cmd, " \t");
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cmd_len = strlen(cmd);
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if (cmd_len > (sizeof(buffer) - 1))
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return -1;
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strcpy(buffer, cmd);
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|
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/* Convert to lower case */
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len = strlen(buffer);
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for (i=0; i<len; i++)
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buffer[i] = tolower((unsigned char)buffer[i]);
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|
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/* Set default proxy type */
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/* Set up default values */
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rule_index = 0;
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proxy_type = PROXY_TYPE_ENCODE_NONE;
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proto = IPPROTO_TCP;
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proxy_port = 0;
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server_addr.s_addr = 0;
|
|
server_port = 0;
|
|
src_addr.s_addr = 0;
|
|
IpMask(0, &src_mask);
|
|
dst_addr.s_addr = 0;
|
|
IpMask(0, &dst_mask);
|
|
|
|
str_port[0] = 0;
|
|
str_server_port[0] = 0;
|
|
|
|
/* Parse command string with state machine */
|
|
#define STATE_READ_KEYWORD 0
|
|
#define STATE_READ_TYPE 1
|
|
#define STATE_READ_PORT 2
|
|
#define STATE_READ_SERVER 3
|
|
#define STATE_READ_RULE 4
|
|
#define STATE_READ_DELETE 5
|
|
#define STATE_READ_PROTO 6
|
|
#define STATE_READ_SRC 7
|
|
#define STATE_READ_DST 8
|
|
state = STATE_READ_KEYWORD;
|
|
token = strsep(&res, " \t");
|
|
token_count = 0;
|
|
while (token != NULL)
|
|
{
|
|
token_count++;
|
|
switch (state)
|
|
{
|
|
case STATE_READ_KEYWORD:
|
|
if (strcmp(token, "type") == 0)
|
|
state = STATE_READ_TYPE;
|
|
else if (strcmp(token, "port") == 0)
|
|
state = STATE_READ_PORT;
|
|
else if (strcmp(token, "server") == 0)
|
|
state = STATE_READ_SERVER;
|
|
else if (strcmp(token, "rule") == 0)
|
|
state = STATE_READ_RULE;
|
|
else if (strcmp(token, "delete") == 0)
|
|
state = STATE_READ_DELETE;
|
|
else if (strcmp(token, "proto") == 0)
|
|
state = STATE_READ_PROTO;
|
|
else if (strcmp(token, "src") == 0)
|
|
state = STATE_READ_SRC;
|
|
else if (strcmp(token, "dst") == 0)
|
|
state = STATE_READ_DST;
|
|
else
|
|
return -1;
|
|
break;
|
|
|
|
case STATE_READ_TYPE:
|
|
if (strcmp(token, "encode_ip_hdr") == 0)
|
|
proxy_type = PROXY_TYPE_ENCODE_IPHDR;
|
|
else if (strcmp(token, "encode_tcp_stream") == 0)
|
|
proxy_type = PROXY_TYPE_ENCODE_TCPSTREAM;
|
|
else if (strcmp(token, "no_encode") == 0)
|
|
proxy_type = PROXY_TYPE_ENCODE_NONE;
|
|
else
|
|
return -1;
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
case STATE_READ_PORT:
|
|
strcpy(str_port, token);
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
case STATE_READ_SERVER:
|
|
{
|
|
int err;
|
|
char *p;
|
|
char s[sizeof(buffer)];
|
|
|
|
p = token;
|
|
while (*p != ':' && *p != 0)
|
|
p++;
|
|
|
|
if (*p != ':')
|
|
{
|
|
err = IpAddr(token, &server_addr);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
else
|
|
{
|
|
*p = ' ';
|
|
|
|
n = sscanf(token, "%s %s", s, str_server_port);
|
|
if (n != 2)
|
|
return -1;
|
|
|
|
err = IpAddr(s, &server_addr);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
}
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
case STATE_READ_RULE:
|
|
n = sscanf(token, "%d", &rule_index);
|
|
if (n != 1 || rule_index < 0)
|
|
return -1;
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
case STATE_READ_DELETE:
|
|
{
|
|
int err;
|
|
int rule_to_delete;
|
|
|
|
if (token_count != 2)
|
|
return -1;
|
|
|
|
n = sscanf(token, "%d", &rule_to_delete);
|
|
if (n != 1)
|
|
return -1;
|
|
err = RuleNumberDelete(rule_to_delete);
|
|
if (err)
|
|
return -1;
|
|
return 0;
|
|
}
|
|
|
|
case STATE_READ_PROTO:
|
|
if (strcmp(token, "tcp") == 0)
|
|
proto = IPPROTO_TCP;
|
|
else if (strcmp(token, "udp") == 0)
|
|
proto = IPPROTO_UDP;
|
|
else
|
|
return -1;
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
case STATE_READ_SRC:
|
|
case STATE_READ_DST:
|
|
{
|
|
int err;
|
|
char *p;
|
|
struct in_addr mask;
|
|
struct in_addr addr;
|
|
|
|
p = token;
|
|
while (*p != '/' && *p != 0)
|
|
p++;
|
|
|
|
if (*p != '/')
|
|
{
|
|
IpMask(32, &mask);
|
|
err = IpAddr(token, &addr);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
else
|
|
{
|
|
int nbits;
|
|
char s[sizeof(buffer)];
|
|
|
|
*p = ' ';
|
|
n = sscanf(token, "%s %d", s, &nbits);
|
|
if (n != 2)
|
|
return -1;
|
|
|
|
err = IpAddr(s, &addr);
|
|
if (err)
|
|
return -1;
|
|
|
|
err = IpMask(nbits, &mask);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
|
|
if (state == STATE_READ_SRC)
|
|
{
|
|
src_addr = addr;
|
|
src_mask = mask;
|
|
}
|
|
else
|
|
{
|
|
dst_addr = addr;
|
|
dst_mask = mask;
|
|
}
|
|
}
|
|
state = STATE_READ_KEYWORD;
|
|
break;
|
|
|
|
default:
|
|
return -1;
|
|
break;
|
|
}
|
|
|
|
do {
|
|
token = strsep(&res, " \t");
|
|
} while (token != NULL && !*token);
|
|
}
|
|
#undef STATE_READ_KEYWORD
|
|
#undef STATE_READ_TYPE
|
|
#undef STATE_READ_PORT
|
|
#undef STATE_READ_SERVER
|
|
#undef STATE_READ_RULE
|
|
#undef STATE_READ_DELETE
|
|
#undef STATE_READ_PROTO
|
|
#undef STATE_READ_SRC
|
|
#undef STATE_READ_DST
|
|
|
|
/* Convert port strings to numbers. This needs to be done after
|
|
the string is parsed, because the prototype might not be designated
|
|
before the ports (which might be symbolic entries in /etc/services) */
|
|
|
|
if (strlen(str_port) != 0)
|
|
{
|
|
int err;
|
|
|
|
err = IpPort(str_port, proto, &proxy_port);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
else
|
|
{
|
|
proxy_port = 0;
|
|
}
|
|
|
|
if (strlen(str_server_port) != 0)
|
|
{
|
|
int err;
|
|
|
|
err = IpPort(str_server_port, proto, &server_port);
|
|
if (err)
|
|
return -1;
|
|
}
|
|
else
|
|
{
|
|
server_port = 0;
|
|
}
|
|
|
|
/* Check that at least the server address has been defined */
|
|
if (server_addr.s_addr == 0)
|
|
return -1;
|
|
|
|
/* Add to linked list */
|
|
proxy_entry = malloc(sizeof(struct proxy_entry));
|
|
if (proxy_entry == NULL)
|
|
return -1;
|
|
|
|
proxy_entry->proxy_type = proxy_type;
|
|
proxy_entry->rule_index = rule_index;
|
|
proxy_entry->proto = proto;
|
|
proxy_entry->proxy_port = htons(proxy_port);
|
|
proxy_entry->server_port = htons(server_port);
|
|
proxy_entry->server_addr = server_addr;
|
|
proxy_entry->src_addr.s_addr = src_addr.s_addr & src_mask.s_addr;
|
|
proxy_entry->dst_addr.s_addr = dst_addr.s_addr & dst_mask.s_addr;
|
|
proxy_entry->src_mask = src_mask;
|
|
proxy_entry->dst_mask = dst_mask;
|
|
|
|
RuleAdd(proxy_entry);
|
|
|
|
return 0;
|
|
}
|