canohost.c

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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.
 *
 * 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".
 */

#include "includes.h"
RCSID("$OpenBSD: canohost.c,v 1.48 2005/12/28 22:46:06 stevesk Exp $");

#include "packet.h"
#include "xmalloc.h"
#include "log.h"
#include "canohost.h"

static void check_ip_options(int, char *);

/*
 * Return the canonical name of the host at the other end of the socket. The
 * caller should free the returned string with xfree.
 */

static char *
get_remote_hostname(int sock, int use_dns)
{
        struct sockaddr_storage from;
        int i;
        socklen_t fromlen;
        struct addrinfo hints, *ai, *aitop;
        char name[NI_MAXHOST], ntop[NI_MAXHOST], ntop2[NI_MAXHOST];

        /* Get IP address of client. */
        fromlen = sizeof(from);
        memset(&from, 0, sizeof(from));
        if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
                debug("getpeername failed: %.100s", strerror(errno));
                cleanup_exit(255);
        }

        ipv64_normalise_mapped(&from, &fromlen);

        if (from.ss_family == AF_INET6)
                fromlen = sizeof(struct sockaddr_in6);

        if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
            NULL, 0, NI_NUMERICHOST) != 0)
                fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");

        if (from.ss_family == AF_INET)
                check_ip_options(sock, ntop);

        if (!use_dns)
                return xstrdup(ntop);

        debug3("Trying to reverse map address %.100s.", ntop);
        /* Map the IP address to a host name. */
        if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
            NULL, 0, NI_NAMEREQD) != 0) {
                /* Host name not found.  Use ip address. */
                return xstrdup(ntop);
        }

        /*
         * 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*/
        hints.ai_flags = AI_NUMERICHOST;
        if (getaddrinfo(name, "0", &hints, &ai) == 0) {
                logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
                    name, ntop);
                freeaddrinfo(ai);
                return xstrdup(ntop);
        }

        /*
         * Convert it to all lowercase (which is expected by the rest
         * of this software).
         */
        for (i = 0; name[i]; i++)
                if (isupper(name[i]))
                        name[i] = tolower(name[i]);
        /*
         * 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).
         */
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = from.ss_family;
        hints.ai_socktype = SOCK_STREAM;
        if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
                logit("reverse mapping checking getaddrinfo for %.700s "
                    "failed - POSSIBLE BREAK-IN ATTEMPT!", name);
                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. */
                logit("Address %.100s maps to %.600s, but this does not "
                    "map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
                    ntop, name);
                return xstrdup(ntop);
        }
        return xstrdup(name);
}

/*
 * 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 */
static void
check_ip_options(int sock, char *ipaddr)
{
#ifdef IP_OPTIONS
        u_char options[200];
        char text[sizeof(options) * 3 + 1];
        socklen_t option_size;
        u_int i;
        int ipproto;
        struct protoent *ip;

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

void
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;

        if (addr->ss_family != AF_INET6 ||
            !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;

        memset(addr, 0, sizeof(*a4));

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

/*
 * 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.
 */

const char *
get_canonical_hostname(int use_dns)
{
        char *host;
        static char *canonical_host_name = NULL;
        static char *remote_ip = NULL;

        /* Check if we have previously retrieved name with same option. */
        if (use_dns && canonical_host_name != NULL)
                return canonical_host_name;
        if (!use_dns && remote_ip != NULL)
                return remote_ip;

        /* Get the real hostname if socket; otherwise return UNKNOWN. */
        if (packet_connection_is_on_socket())
                host = get_remote_hostname(packet_get_connection_in(), use_dns);
        else
                host = "UNKNOWN";

        if (use_dns)
                canonical_host_name = host;
        else
                remote_ip = host;
        return host;
}

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

        /* Get IP address of client. */
        addrlen = sizeof(addr);
        memset(&addr, 0, sizeof(addr));

        if (remote) {
                if (getpeername(sock, (struct sockaddr *)&addr, &addrlen)
                    < 0)
                        return NULL;
        } else {
                if (getsockname(sock, (struct sockaddr *)&addr, &addrlen)
                    < 0)
                        return NULL;
        }

        /* Work around Linux IPv6 weirdness */
        if (addr.ss_family == AF_INET6)
                addrlen = sizeof(struct sockaddr_in6);

        ipv64_normalise_mapped(&addr, &addrlen);

        /* Get the address in ascii. */
        if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
            sizeof(ntop), NULL, 0, flags)) != 0) {
                error("get_socket_address: getnameinfo %d failed: %s", flags,
                    r == EAI_SYSTEM ? strerror(errno) : gai_strerror(r));
                return NULL;
        }
        return xstrdup(ntop);
}

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

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

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

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

char *
get_local_name(int sock)
{
        return get_socket_address(sock, 0, NI_NAMEREQD);
}

/*
 * Returns the IP-address of the remote host as a string.  The returned
 * string must not be freed.
 */

const char *
get_remote_ipaddr(void)
{
        static char *canonical_host_ip = NULL;

        /* 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)
                                cleanup_exit(255);
                } else {
                        /* If not on socket, return UNKNOWN. */
                        canonical_host_ip = xstrdup("UNKNOWN");
                }
        }
        return canonical_host_ip;
}

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

/* Returns the local/remote port for the socket. */

static int
get_sock_port(int sock, int local)
{
        struct sockaddr_storage from;
        socklen_t fromlen;
        char strport[NI_MAXSERV];
        int r;

        /* Get IP address of client. */
        fromlen = sizeof(from);
        memset(&from, 0, sizeof(from));
        if (local) {
                if (getsockname(sock, (struct sockaddr *)&from, &fromlen) < 0) {
                        error("getsockname failed: %.100s", strerror(errno));
                        return 0;
                }
        } else {
                if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
                        debug("getpeername failed: %.100s", strerror(errno));
                        return -1;
                }
        }

        /* Work around Linux IPv6 weirdness */
        if (from.ss_family == AF_INET6)
                fromlen = sizeof(struct sockaddr_in6);

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

/* Returns remote/local port number for the current connection. */

static int
get_port(int local)
{
        /*
         * If the connection is not a socket, return 65535.  This is
         * intentionally chosen to be an unprivileged port number.
         */
        if (!packet_connection_is_on_socket())
                return 65535;

        /* Get socket and return the port number. */
        return get_sock_port(packet_get_connection_in(), local);
}

int
get_peer_port(int sock)
{
        return get_sock_port(sock, 0);
}

int
get_remote_port(void)
{
        static int port = -1;

        /* Cache to avoid getpeername() on a dead connection */
        if (port == -1)
                port = get_port(0);

        return port;
}

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

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