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clientname.c

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/* -*- c-file-style: "linux" -*-
   
   rsync -- fast file replication program
   
   Copyright (C) 1992-2001 by Andrew Tridgell <tridge@samba.org>
   Copyright (C) 2001, 2002 by Martin Pool <mbp@samba.org>
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/**
 * @file clientname.c
 * 
 * Functions for looking up the remote name or addr of a socket.
 *
 * This file is now converted to use the new-style getaddrinfo()
 * interface, which supports IPv6 but is also supported on recent
 * IPv4-only machines.  On systems that don't have that interface, we
 * emulate it using the KAME implementation.
 **/

#include "rsync.h"

static const char default_name[] = "UNKNOWN";


/**
 * Return the IP addr of the client as a string 
 **/
char *client_addr(int fd)
{
        struct sockaddr_storage ss;
        socklen_t length = sizeof ss;
        static char addr_buf[100];
        static int initialised;

        if (initialised) return addr_buf;

        initialised = 1;

        client_sockaddr(fd, &ss, &length);

        getnameinfo((struct sockaddr *)&ss, length,
                    addr_buf, sizeof(addr_buf), NULL, 0, NI_NUMERICHOST);
        
        return addr_buf;
}


static int get_sockaddr_family(const struct sockaddr_storage *ss)
{
        return ((struct sockaddr *) ss)->sa_family;
}


/**
 * Return the DNS name of the client.
 *
 * The name is statically cached so that repeated lookups are quick,
 * so there is a limit of one lookup per customer.
 *
 * If anything goes wrong, including the name->addr->name check, then
 * we just use "UNKNOWN", so you can use that value in hosts allow
 * lines.
 *
 * After translation from sockaddr to name we do a forward lookup to
 * make sure nobody is spoofing PTR records.
 **/
char *client_name(int fd)
{
        struct sockaddr_storage ss;
        socklen_t ss_len = sizeof ss;
        static char name_buf[100];
        static char port_buf[100];
        static int initialised;

        if (initialised) return name_buf;

        strcpy(name_buf, default_name);
        initialised = 1;

        client_sockaddr(fd, &ss, &ss_len);

        if (!lookup_name(fd, &ss, ss_len, name_buf, sizeof name_buf,
                         port_buf, sizeof port_buf))
                check_name(fd, &ss, name_buf);

        return name_buf;
}



/**
 * Get the sockaddr for the client.
 *
 * If it comes in as an ipv4 address mapped into IPv6 format then we
 * convert it back to a regular IPv4.
 **/
void client_sockaddr(int fd,
                     struct sockaddr_storage *ss,
                     socklen_t *ss_len)
{
        if (getpeername(fd, (struct sockaddr *) ss, ss_len)) {
                /* FIXME: Can we really not continue? */
                rprintf(FERROR, RSYNC_NAME ": getpeername on fd%d failed: %s\n",
                        fd, strerror(errno));
                exit_cleanup(RERR_SOCKETIO);
        }

#ifdef INET6
        if (get_sockaddr_family(ss) == AF_INET6 && 
            IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)ss)->sin6_addr)) {
                /* OK, so ss is in the IPv6 family, but it is really
                 * an IPv4 address: something like
                 * "::ffff:10.130.1.2".  If we use it as-is, then the
                 * reverse lookup might fail or perhaps something else
                 * bad might happen.  So instead we convert it to an
                 * equivalent address in the IPv4 address family.  */
                struct sockaddr_in6 sin6;
                struct sockaddr_in *sin;

                memcpy(&sin6, ss, sizeof(sin6));
                sin = (struct sockaddr_in *)ss;
                memset(sin, 0, sizeof(*sin));
                sin->sin_family = AF_INET;
                *ss_len = sizeof(struct sockaddr_in);
#ifdef HAVE_SOCKADDR_LEN
                sin->sin_len = *ss_len;
#endif
                sin->sin_port = sin6.sin6_port;

                /* There is a macro to extract the mapped part
                 * (IN6_V4MAPPED_TO_SINADDR ?), but it does not seem
                 * to be present in the Linux headers. */
                memcpy(&sin->sin_addr, &sin6.sin6_addr.s6_addr[12],
                        sizeof(sin->sin_addr));
        }
#endif
}


/**
 * Look up a name from @p ss into @p name_buf.
 *
 * @param fd file descriptor for client socket.
 **/
int lookup_name(int fd, const struct sockaddr_storage *ss,
                socklen_t ss_len,
                char *name_buf, size_t name_buf_len,
                char *port_buf, size_t port_buf_len)
{
        int name_err;
        
        /* reverse lookup */
        name_err = getnameinfo((struct sockaddr *) ss, ss_len,
                               name_buf, name_buf_len,
                               port_buf, port_buf_len,
                               NI_NAMEREQD | NI_NUMERICSERV);
        if (name_err != 0) {
                strcpy(name_buf, default_name);
                rprintf(FERROR, RSYNC_NAME ": name lookup failed for %s: %s\n",
                        client_addr(fd),
                        gai_strerror(name_err));
                return name_err;
        }

        return 0;
}



/**
 * Compare an addrinfo from the resolver to a sockinfo.
 *
 * Like strcmp, returns 0 for identical.
 **/
int compare_addrinfo_sockaddr(const struct addrinfo *ai,
                              const struct sockaddr_storage *ss)
{
        int ss_family = get_sockaddr_family(ss);
        const char fn[] = "compare_addrinfo_sockaddr";
                      
        if (ai->ai_family != ss_family) {
                rprintf(FERROR,
                        "%s: response family %d != %d\n",
                        fn, ai->ai_family, ss_family);
                return 1;
        }

        /* The comparison method depends on the particular AF. */
        if (ss_family == AF_INET) {
                const struct sockaddr_in *sin1, *sin2;

                sin1 = (const struct sockaddr_in *) ss;
                sin2 = (const struct sockaddr_in *) ai->ai_addr;
                
                return memcmp(&sin1->sin_addr, &sin2->sin_addr,
                              sizeof sin1->sin_addr);
        }
#ifdef INET6
        else if (ss_family == AF_INET6) {
                const struct sockaddr_in6 *sin1, *sin2;

                sin1 = (const struct sockaddr_in6 *) ss;
                sin2 = (const struct sockaddr_in6 *) ai->ai_addr;
                
                return memcmp(&sin1->sin6_addr, &sin2->sin6_addr,
                              sizeof sin1->sin6_addr);
        }
#endif /* INET6 */
        else {
                /* don't know */
                return 1;
        }
}


/**
 * Do a forward lookup on @p name_buf and make sure it corresponds to
 * @p ss -- otherwise we may be being spoofed.  If we suspect we are,
 * then we don't abort the connection but just emit a warning, and
 * change @p name_buf to be "UNKNOWN".
 *
 * We don't do anything with the service when checking the name,
 * because it doesn't seem that it could be spoofed in any way, and
 * getaddrinfo on random service names seems to cause problems on AIX.
 **/
int check_name(int fd,
               const struct sockaddr_storage *ss,
               char *name_buf)
{
        struct addrinfo hints, *res, *res0;
        int error;
        int ss_family = get_sockaddr_family(ss);

        memset(&hints, 0, sizeof(hints));
        hints.ai_family = ss_family;
        hints.ai_flags = AI_CANONNAME;
        hints.ai_socktype = SOCK_STREAM;
        error = getaddrinfo(name_buf, NULL, &hints, &res0);
        if (error) {
                rprintf(FERROR,
                        RSYNC_NAME ": forward name lookup for %s failed: %s\n",
                        name_buf, gai_strerror(error));
                strcpy(name_buf, default_name);
                return error;
        }


        /* Given all these results, we expect that one of them will be
         * the same as ss.  The comparison is a bit complicated. */
        for (res = res0; res; res = res->ai_next) {
                if (!compare_addrinfo_sockaddr(res, ss))
                        break;  /* OK, identical */
        }

        if (!res0) {
                /* We hit the end of the list without finding an
                 * address that was the same as ss. */
                rprintf(FERROR, RSYNC_NAME
                        ": no known address for \"%s\": "
                        "spoofed address?\n",
                        name_buf);
                strcpy(name_buf, default_name);
        } else if (res == NULL) {
                /* We hit the end of the list without finding an
                 * address that was the same as ss. */
                rprintf(FERROR, RSYNC_NAME
                        ": %s is not a known address for \"%s\": "
                        "spoofed address?\n",
                        client_addr(fd),
                        name_buf);
                strcpy(name_buf, default_name);
        }

        freeaddrinfo(res0);
        return 0;
}

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