canohost.c 10.8 KB
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/* $OpenBSD: canohost.c,v 1.70 2014/01/19 04:17:29 dtucker Exp $ */
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/*
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 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Functions for returning the canonical host name of the remote site.
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 *
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 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
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 */
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#include "includes.h"
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#include <sys/types.h>
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#include <sys/socket.h>

#include <netinet/in.h>
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#include <arpa/inet.h>
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#include <errno.h>
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#include <netdb.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 <stdarg.h>
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#include <unistd.h>
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#include "xmalloc.h"
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#include "packet.h"
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#include "log.h"
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#include "canohost.h"
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#include "misc.h"
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static void check_ip_options(int, char *);
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static char *canonical_host_ip = NULL;
static int cached_port = -1;
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/*
 * Return the canonical name of the host at the other end of the socket. The
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 * caller should free the returned string.
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 */
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static char *
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get_remote_hostname(int sock, int use_dns)
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{
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	struct sockaddr_storage from;
	socklen_t fromlen;
	struct addrinfo hints, *ai, *aitop;
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	char name[NI_MAXHOST], ntop[NI_MAXHOST], ntop2[NI_MAXHOST];
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	/* Get IP address of client. */
	fromlen = sizeof(from);
	memset(&from, 0, sizeof(from));
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	if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
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		debug("getpeername failed: %.100s", strerror(errno));
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		cleanup_exit(255);
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	}
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	if (from.ss_family == AF_INET)
		check_ip_options(sock, ntop);

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	ipv64_normalise_mapped(&from, &fromlen);

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	if (from.ss_family == AF_INET6)
		fromlen = sizeof(struct sockaddr_in6);
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	if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
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	    NULL, 0, NI_NUMERICHOST) != 0)
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		fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");
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	if (!use_dns)
		return xstrdup(ntop);

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	debug3("Trying to reverse map address %.100s.", ntop);
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	/* Map the IP address to a host name. */
	if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
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	    NULL, 0, NI_NAMEREQD) != 0) {
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		/* Host name not found.  Use ip address. */
		return xstrdup(ntop);
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	}
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	/*
	 * if reverse lookup result looks like a numeric hostname,
	 * someone is trying to trick us by PTR record like following:
	 *	1.1.1.10.in-addr.arpa.	IN PTR	2.3.4.5
	 */
	memset(&hints, 0, sizeof(hints));
	hints.ai_socktype = SOCK_DGRAM;	/*dummy*/
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	hints.ai_flags = AI_NUMERICHOST;
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	if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
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		logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
		    name, ntop);
		freeaddrinfo(ai);
		return xstrdup(ntop);
	}

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	/* Names are stores in lowercase. */
	lowercase(name);

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	/*
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	 * Map it back to an IP address and check that the given
	 * address actually is an address of this host.  This is
	 * necessary because anyone with access to a name server can
	 * define arbitrary names for an IP address. Mapping from
	 * name to IP address can be trusted better (but can still be
	 * fooled if the intruder has access to the name server of
	 * the domain).
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	 */
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	memset(&hints, 0, sizeof(hints));
	hints.ai_family = from.ss_family;
	hints.ai_socktype = SOCK_STREAM;
	if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
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		logit("reverse mapping checking getaddrinfo for %.700s "
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		    "[%s] failed - POSSIBLE BREAK-IN ATTEMPT!", name, ntop);
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		return xstrdup(ntop);
	}
	/* Look for the address from the list of addresses. */
	for (ai = aitop; ai; ai = ai->ai_next) {
		if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
		    sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
		    (strcmp(ntop, ntop2) == 0))
				break;
	}
	freeaddrinfo(aitop);
	/* If we reached the end of the list, the address was not there. */
	if (!ai) {
		/* Address not found for the host name. */
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		logit("Address %.100s maps to %.600s, but this does not "
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		    "map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
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		    ntop, name);
		return xstrdup(ntop);
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	}
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	return xstrdup(name);
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}

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/*
 * If IP options are supported, make sure there are none (log and
 * disconnect them if any are found).  Basically we are worried about
 * source routing; it can be used to pretend you are somebody
 * (ip-address) you are not. That itself may be "almost acceptable"
 * under certain circumstances, but rhosts autentication is useless
 * if source routing is accepted. Notice also that if we just dropped
 * source routing here, the other side could use IP spoofing to do
 * rest of the interaction and could still bypass security.  So we
 * exit here if we detect any IP options.
 */
/* IPv4 only */
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static void
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check_ip_options(int sock, char *ipaddr)
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{
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#ifdef IP_OPTIONS
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	u_char options[200];
	char text[sizeof(options) * 3 + 1];
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	socklen_t option_size, i;
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	int ipproto;
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	struct protoent *ip;

	if ((ip = getprotobyname("ip")) != NULL)
		ipproto = ip->p_proto;
	else
		ipproto = IPPROTO_IP;
	option_size = sizeof(options);
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	if (getsockopt(sock, ipproto, IP_OPTIONS, options,
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	    &option_size) >= 0 && option_size != 0) {
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		text[0] = '\0';
		for (i = 0; i < option_size; i++)
			snprintf(text + i*3, sizeof(text) - i*3,
			    " %2.2x", options[i]);
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		fatal("Connection from %.100s with IP options:%.800s",
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		    ipaddr, text);
	}
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#endif /* IP_OPTIONS */
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}

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void
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ipv64_normalise_mapped(struct sockaddr_storage *addr, socklen_t *len)
{
	struct sockaddr_in6 *a6 = (struct sockaddr_in6 *)addr;
	struct sockaddr_in *a4 = (struct sockaddr_in *)addr;
	struct in_addr inaddr;
	u_int16_t port;

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	if (addr->ss_family != AF_INET6 ||
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	    !IN6_IS_ADDR_V4MAPPED(&a6->sin6_addr))
		return;

	debug3("Normalising mapped IPv4 in IPv6 address");

	memcpy(&inaddr, ((char *)&a6->sin6_addr) + 12, sizeof(inaddr));
	port = a6->sin6_port;

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	bzero(a4, sizeof(*a4));
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	a4->sin_family = AF_INET;
	*len = sizeof(*a4);
	memcpy(&a4->sin_addr, &inaddr, sizeof(inaddr));
	a4->sin_port = port;
}

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/*
 * Return the canonical name of the host in the other side of the current
 * connection.  The host name is cached, so it is efficient to call this
 * several times.
 */
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const char *
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get_canonical_hostname(int use_dns)
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{
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	char *host;
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	static char *canonical_host_name = NULL;
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	static char *remote_ip = NULL;
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	/* Check if we have previously retrieved name with same option. */
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	if (use_dns && canonical_host_name != NULL)
		return canonical_host_name;
	if (!use_dns && remote_ip != NULL)
		return remote_ip;
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	/* Get the real hostname if socket; otherwise return UNKNOWN. */
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	if (packet_connection_is_on_socket())
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		host = get_remote_hostname(packet_get_connection_in(), use_dns);
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	else
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		host = "UNKNOWN";
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	if (use_dns)
		canonical_host_name = host;
	else
		remote_ip = host;
	return host;
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}

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/*
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 * Returns the local/remote IP-address/hostname of socket as a string.
 * The returned string must be freed.
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 */
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static char *
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get_socket_address(int sock, int remote, int flags)
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{
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	struct sockaddr_storage addr;
	socklen_t addrlen;
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	char ntop[NI_MAXHOST];
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	int r;
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	/* Get IP address of client. */
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	addrlen = sizeof(addr);
	memset(&addr, 0, sizeof(addr));

	if (remote) {
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		if (getpeername(sock, (struct sockaddr *)&addr, &addrlen)
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		    < 0)
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			return NULL;
	} else {
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		if (getsockname(sock, (struct sockaddr *)&addr, &addrlen)
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		    < 0)
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			return NULL;
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	}
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	/* Work around Linux IPv6 weirdness */
	if (addr.ss_family == AF_INET6)
		addrlen = sizeof(struct sockaddr_in6);

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	ipv64_normalise_mapped(&addr, &addrlen);

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	/* Get the address in ascii. */
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	if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
	    sizeof(ntop), NULL, 0, flags)) != 0) {
		error("get_socket_address: getnameinfo %d failed: %s", flags,
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		    ssh_gai_strerror(r));
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		return NULL;
	}
	return xstrdup(ntop);
}
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char *
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get_peer_ipaddr(int sock)
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{
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	char *p;

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	if ((p = get_socket_address(sock, 1, NI_NUMERICHOST)) != NULL)
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		return p;
	return xstrdup("UNKNOWN");
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}

char *
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get_local_ipaddr(int sock)
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{
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	char *p;

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	if ((p = get_socket_address(sock, 0, NI_NUMERICHOST)) != NULL)
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		return p;
	return xstrdup("UNKNOWN");
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}

char *
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get_local_name(int fd)
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{
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	char *host, myname[NI_MAXHOST];

	/* Assume we were passed a socket */
	if ((host = get_socket_address(fd, 0, NI_NAMEREQD)) != NULL)
		return host;

	/* Handle the case where we were passed a pipe */
	if (gethostname(myname, sizeof(myname)) == -1) {
		verbose("get_local_name: gethostname: %s", strerror(errno));
	} else {
		host = xstrdup(myname);
	}

	return host;
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}

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void
clear_cached_addr(void)
{
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	free(canonical_host_ip);
	canonical_host_ip = NULL;
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	cached_port = -1;
}

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/*
 * Returns the IP-address of the remote host as a string.  The returned
 * string must not be freed.
 */
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const char *
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get_remote_ipaddr(void)
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{
	/* Check whether we have cached the ipaddr. */
	if (canonical_host_ip == NULL) {
		if (packet_connection_is_on_socket()) {
			canonical_host_ip =
			    get_peer_ipaddr(packet_get_connection_in());
			if (canonical_host_ip == NULL)
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				cleanup_exit(255);
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		} else {
			/* If not on socket, return UNKNOWN. */
			canonical_host_ip = xstrdup("UNKNOWN");
		}
	}
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	return canonical_host_ip;
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}

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const char *
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get_remote_name_or_ip(u_int utmp_len, int use_dns)
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{
	static const char *remote = "";
	if (utmp_len > 0)
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		remote = get_canonical_hostname(use_dns);
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	if (utmp_len == 0 || strlen(remote) > utmp_len)
		remote = get_remote_ipaddr();
	return remote;
}

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/* Returns the local/remote port for the socket. */
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int
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get_sock_port(int sock, int local)
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{
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	struct sockaddr_storage from;
	socklen_t fromlen;
	char strport[NI_MAXSERV];
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	int r;
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	/* Get IP address of client. */
	fromlen = sizeof(from);
	memset(&from, 0, sizeof(from));
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	if (local) {
		if (getsockname(sock, (struct sockaddr *)&from, &fromlen) < 0) {
			error("getsockname failed: %.100s", strerror(errno));
			return 0;
		}
	} else {
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		if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
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			debug("getpeername failed: %.100s", strerror(errno));
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			return -1;
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		}
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	}
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	/* Work around Linux IPv6 weirdness */
	if (from.ss_family == AF_INET6)
		fromlen = sizeof(struct sockaddr_in6);

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	/* Return port number. */
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	if ((r = getnameinfo((struct sockaddr *)&from, fromlen, NULL, 0,
	    strport, sizeof(strport), NI_NUMERICSERV)) != 0)
		fatal("get_sock_port: getnameinfo NI_NUMERICSERV failed: %s",
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		    ssh_gai_strerror(r));
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	return atoi(strport);
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}

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/* Returns remote/local port number for the current connection. */
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static int
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get_port(int local)
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{
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	/*
	 * If the connection is not a socket, return 65535.  This is
	 * intentionally chosen to be an unprivileged port number.
	 */
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	if (!packet_connection_is_on_socket())
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		return 65535;
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	/* Get socket and return the port number. */
	return get_sock_port(packet_get_connection_in(), local);
}

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int
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get_peer_port(int sock)
{
	return get_sock_port(sock, 0);
}
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int
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get_remote_port(void)
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{
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	/* Cache to avoid getpeername() on a dead connection */
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	if (cached_port == -1)
		cached_port = get_port(0);
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	return cached_port;
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}

int
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get_local_port(void)
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{
	return get_port(1);
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}