network.c   [plain text]

/*
 * kdc/network.c
 *
 * Copyright 1990,2000 by the Massachusetts Institute of Technology.
 *
 * Export of this software from the United States of America may
 *   require a specific license from the United States Government.
 *   It is the responsibility of any person or organization contemplating
 *   export to obtain such a license before exporting.
 * 
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of M.I.T. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  Furthermore if you modify this software you must label
 * your software as modified software and not distribute it in such a
 * fashion that it might be confused with the original M.I.T. software.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 * 
 *
 * Network code for Kerberos v5 KDC.
 */

#include "k5-int.h"
#include "com_err.h"
#include "kdc_util.h"
#include "extern.h"
#include "kdc5_err.h"
#include "adm_proto.h"
#include <sys/ioctl.h>
#include <syslog.h>

#include <stddef.h>
#include <ctype.h>
#include "port-sockets.h"
#include "socket-utils.h"

#ifdef HAVE_NETINET_IN_H
#include <sys/types.h>
#include <netinet/in.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_SOCKIO_H
/* for SIOCGIFCONF, etc. */
#include <sys/sockio.h>
#endif
#include <sys/time.h>
#if HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#include <arpa/inet.h>

#ifndef ARPHRD_ETHER /* OpenBSD breaks on multiple inclusions */
#include <net/if.h>
#endif

#ifdef HAVE_SYS_FILIO_H
#include <sys/filio.h>		/* FIONBIO */
#endif

#include "fake-addrinfo.h"

/* Misc utility routines.  */
static void
set_sa_port(struct sockaddr *addr, int port)
{
    switch (addr->sa_family) {
    case AF_INET:
	sa2sin(addr)->sin_port = port;
	break;
#ifdef KRB5_USE_INET6
    case AF_INET6:
	sa2sin6(addr)->sin6_port = port;
	break;
#endif
    default:
	break;
    }
}

static int ipv6_enabled()
{
#ifdef KRB5_USE_INET6
    static int result = -1;
    if (result == -1) {
	int s;
	s = socket(AF_INET6, SOCK_STREAM, 0);
	if (s >= 0) {
	    result = 1;
	    close(s);
	} else
	    result = 0;
    }
    return result;
#else
    return 0;
#endif
}

static int
setreuseaddr(int sock, int value)
{
    return setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &value, sizeof(value));
}

#if defined(KRB5_USE_INET6) && defined(IPV6_V6ONLY)
static int
setv6only(int sock, int value)
{
    return setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, &value, sizeof(value));
}
#endif


static const char *paddr (struct sockaddr *sa)
{
    static char buf[100];
    char portbuf[10];
    if (getnameinfo(sa, socklen(sa),
		    buf, sizeof(buf), portbuf, sizeof(portbuf),
		    NI_NUMERICHOST|NI_NUMERICSERV))
	strcpy(buf, "<unprintable>");
    else {
	unsigned int len = sizeof(buf) - strlen(buf);
	char *p = buf + strlen(buf);
	if (len > 2+strlen(portbuf)) {
	    *p++ = '.';
	    len--;
	    strncpy(p, portbuf, len);
	}
    }
    return buf;
}

/* KDC data.  */

enum kdc_conn_type { CONN_UDP, CONN_TCP_LISTENER, CONN_TCP };

/* Per-connection info.  */
struct connection {
    int fd;
    enum kdc_conn_type type;
    void (*service)(struct connection *, const char *, int);
    union {
	/* Type-specific information.  */
	struct {
	    int x;
	} udp;
	struct {
	    int x;
	} tcp_listener;
	struct {
	    /* connection */
	    struct sockaddr_storage addr_s;
	    socklen_t addrlen;
	    char addrbuf[56];
	    krb5_fulladdr faddr;
	    krb5_address kaddr;
	    /* incoming */
	    size_t bufsiz;
	    size_t offset;
	    char *buffer;
	    size_t msglen;
	    /* outgoing */
	    krb5_data *response;
	    unsigned char lenbuf[4];
	    sg_buf sgbuf[2];
	    sg_buf *sgp;
	    int sgnum;
	    /* crude denial-of-service avoidance support */
	    time_t start_time;
	} tcp;
    } u;
};


#define SET(TYPE) struct { TYPE *data; int n, max; }

/* Start at the top and work down -- this should allow for deletions
   without disrupting the iteration, since we delete by overwriting
   the element to be removed with the last element.  */
#define FOREACH_ELT(set,idx,vvar) \
  for (idx = set.n-1; idx >= 0 && (vvar = set.data[idx], 1); idx--)

#define GROW_SET(set, incr, tmpptr) \
  (((int)(set.max + incr) < set.max					\
    || (((size_t)((int)(set.max + incr) * sizeof(set.data[0]))		\
	 / sizeof(set.data[0]))						\
	!= (set.max + incr)))						\
   ? 0				/* overflow */				\
   : ((tmpptr = realloc(set.data,					\
			(int)(set.max + incr) * sizeof(set.data[0])))	\
      ? (set.data = tmpptr, set.max += incr, 1)				\
      : 0))

/* 1 = success, 0 = failure */
#define ADD(set, val, tmpptr) \
  ((set.n < set.max || GROW_SET(set, 10, tmpptr))			\
   ? (set.data[set.n++] = val, 1)					\
   : 0)

#define DEL(set, idx) \
  (set.data[idx] = set.data[--set.n], 0)

#define FREE_SET_DATA(set) if(set.data) free(set.data);                 \
   (set.data = 0, set.max = 0, set.n = 0)


/* Set<struct connection *> connections; */
static SET(struct connection *) connections;
#define n_sockets	connections.n
#define conns		connections.data

/* Set<u_short> udp_port_data, tcp_port_data; */
static SET(u_short) udp_port_data, tcp_port_data;

#include "cm.h"

static struct select_state sstate;

static int getcurtime (struct timeval *tvp);

static krb5_error_code add_udp_port(int port)
{
    int	i;
    void *tmp;
    u_short val;
    u_short s_port = port;

    if (s_port != port)
	return EINVAL;

    FOREACH_ELT (udp_port_data, i, val)
	if (s_port == val)
	    return 0;
    if (!ADD(udp_port_data, s_port, tmp))
	return ENOMEM;
    return 0;
}

static krb5_error_code add_tcp_port(int port)
{
    int	i;
    void *tmp;
    u_short val;
    u_short s_port = port;

    if (s_port != port)
	return EINVAL;

    FOREACH_ELT (tcp_port_data, i, val)
	if (s_port == val)
	    return 0;
    if (!ADD(tcp_port_data, s_port, tmp))
	return ENOMEM;
    return 0;
}


#define USE_AF AF_INET
#define USE_TYPE SOCK_DGRAM
#define USE_PROTO 0
#define SOCKET_ERRNO errno
#include "foreachaddr.h"

struct socksetup {
    const char *prog;
    krb5_error_code retval;
};

static struct connection *
add_fd (struct socksetup *data, int sock, enum kdc_conn_type conntype,
	void (*service)(struct connection *, const char *, int))
{
    struct connection *newconn;
    void *tmp;

    newconn = malloc(sizeof(*newconn));
    if (newconn == 0) {
	data->retval = errno;
	com_err(data->prog, errno,
		"cannot allocate storage for connection info");
	return 0;
    }
    if (!ADD(connections, newconn, tmp)) {
	data->retval = errno;
	com_err(data->prog, data->retval, "cannot save socket info");
	free(newconn);
	return 0;
    }

    memset(newconn, 0, sizeof(*newconn));
    newconn->type = conntype;
    newconn->fd = sock;
    newconn->service = service;
    return newconn;
}

static void process_packet(struct connection *, const char *, int);
static void accept_tcp_connection(struct connection *, const char *, int);
static void process_tcp_connection(struct connection *, const char *, int);

static struct connection *
add_udp_fd (struct socksetup *data, int sock)
{
    return add_fd(data, sock, CONN_UDP, process_packet);
}

static struct connection *
add_tcp_listener_fd (struct socksetup *data, int sock)
{
    return add_fd(data, sock, CONN_TCP_LISTENER, accept_tcp_connection);
}

static struct connection *
add_tcp_data_fd (struct socksetup *data, int sock)
{
    return add_fd(data, sock, CONN_TCP, process_tcp_connection);
}

static void
delete_fd (struct connection *xconn)
{
    struct connection *conn;
    int i;

    FOREACH_ELT(connections, i, conn)
	if (conn == xconn) {
	    DEL(connections, i);
	    break;
	}
    free(xconn);
}

static int
setnbio(int sock)
{
    static const int one = 1;
    return ioctlsocket(sock, FIONBIO, (const void *)&one);
}

static int
setnolinger(int s)
{
    static const struct linger ling = { 0, 0 };
    return setsockopt(s, SOL_SOCKET, SO_LINGER, &ling, sizeof(ling));
}

/* Returns -1 or socket fd.  */
static int
setup_a_tcp_listener(struct socksetup *data, struct sockaddr *addr)
{
    int sock;

    sock = socket(addr->sa_family, SOCK_STREAM, 0);
    if (sock == -1) {
	com_err(data->prog, errno, "Cannot create TCP server socket on %s",
		paddr(addr));
	return -1;
    }
    if (setreuseaddr(sock, 1) < 0)
	com_err(data->prog, errno,
		"Cannot enable SO_REUSEADDR on fd %d", sock);
#ifdef KRB5_USE_INET6
    if (addr->sa_family == AF_INET6) {
#ifdef IPV6_V6ONLY
	if (setv6only(sock, 1))
	    com_err(data->prog, errno, "setsockopt(IPV6_V6ONLY,1) failed");
	else
	    com_err(data->prog, 0, "setsockopt(IPV6_V6ONLY,1) worked");
#else
	krb5_klog_syslog(LOG_INFO, "no IPV6_V6ONLY socket option support");
#endif /* IPV6_V6ONLY */
    }
#endif /* KRB5_USE_INET6 */
    if (bind(sock, addr, socklen(addr)) == -1) {
	com_err(data->prog, errno,
		"Cannot bind TCP server socket on %s", paddr(addr));
	close(sock);
	return -1;
    }
    if (listen(sock, 5) < 0) {
	com_err(data->prog, errno, "Cannot listen on TCP server socket on %s",
		paddr(addr));
	close(sock);
	return -1;
    }
    if (setnbio(sock)) {
	com_err(data->prog, errno,
		"cannot set listening tcp socket on %s non-blocking",
		paddr(addr));
	close(sock);
	return -1;
    }
    if (setnolinger(sock)) {
	com_err(data->prog, errno, "disabling SO_LINGER on TCP socket on %s",
		paddr(addr));
	close(sock);
	return -1;
    }
    return sock;
}

static int
setup_tcp_listener_ports(struct socksetup *data)
{
    struct sockaddr_in sin4;
#ifdef KRB5_USE_INET6
    struct sockaddr_in6 sin6;
#endif
    int i, port;

    memset(&sin4, 0, sizeof(sin4));
    sin4.sin_family = AF_INET;
#ifdef HAVE_SA_LEN
    sin4.sin_len = sizeof(sin4);
#endif
    sin4.sin_addr.s_addr = INADDR_ANY;

#ifdef KRB5_USE_INET6
    memset(&sin6, 0, sizeof(sin6));
    sin6.sin6_family = AF_INET6;
#ifdef SIN6_LEN
    sin6.sin6_len = sizeof(sin6);
#endif
    sin6.sin6_addr = in6addr_any;
#endif

    FOREACH_ELT (tcp_port_data, i, port) {
	int s4, s6;

	set_sa_port((struct sockaddr *)&sin4, htons(port));
	if (!ipv6_enabled()) {
	    s4 = setup_a_tcp_listener(data, (struct sockaddr *)&sin4);
	    if (s4 < 0)
		return -1;
	    s6 = -1;
	} else {
#ifndef KRB5_USE_INET6
	    abort();
#else
	    s4 = s6 = -1;

	    set_sa_port((struct sockaddr *)&sin6, htons(port));

	    s6 = setup_a_tcp_listener(data, (struct sockaddr *)&sin6);
	    if (s6 < 0)
		return -1;

	    s4 = setup_a_tcp_listener(data, (struct sockaddr *)&sin4);
#endif /* KRB5_USE_INET6 */
	}

	/* Sockets are created, prepare to listen on them.  */
	if (s4 >= 0) {
	    FD_SET(s4, &sstate.rfds);
	    if (s4 >= sstate.max)
		sstate.max = s4 + 1;
	    if (add_tcp_listener_fd(data, s4) == 0)
		close(s4);
	    else
		krb5_klog_syslog(LOG_INFO, "listening on fd %d: tcp %s",
				 s4, paddr((struct sockaddr *)&sin4));
	}
#ifdef KRB5_USE_INET6
	if (s6 >= 0) {
	    FD_SET(s6, &sstate.rfds);
	    if (s6 >= sstate.max)
		sstate.max = s6 + 1;
	    if (add_tcp_listener_fd(data, s6) == 0) {
		close(s6);
		s6 = -1;
	    } else
		krb5_klog_syslog(LOG_INFO, "listening on fd %d: tcp %s",
				 s6, paddr((struct sockaddr *)&sin6));
	    if (s4 < 0)
		krb5_klog_syslog(LOG_INFO,
				 "assuming IPv6 socket accepts IPv4");
	}
#endif
    }
    return 0;
}

static int
setup_udp_port(void *P_data, struct sockaddr *addr)
{
    struct socksetup *data = P_data;
    int sock = -1, i;
    char haddrbuf[NI_MAXHOST];
    int err;
    u_short port;

    err = getnameinfo(addr, socklen(addr), haddrbuf, sizeof(haddrbuf),
		      0, 0, NI_NUMERICHOST);
    if (err)
	strcpy(haddrbuf, "<unprintable>");

    switch (addr->sa_family) {
    case AF_INET:
	break;
#ifdef AF_INET6
    case AF_INET6:
#ifdef KRB5_USE_INET6
	break;
#else
	{
	    static int first = 1;
	    if (first) {
		krb5_klog_syslog (LOG_INFO, "skipping local ipv6 addresses");
		first = 0;
	    }
	    return 0;
	}
#endif
#endif
#ifdef AF_LINK /* some BSD systems, AIX */
    case AF_LINK:
	return 0;
#endif
#ifdef AF_DLI /* Direct Link Interface - DEC Ultrix/OSF1 link layer? */
    case AF_DLI:
	return 0;
#endif
    default:
	krb5_klog_syslog (LOG_INFO,
			  "skipping unrecognized local address family %d",
			  addr->sa_family);
	return 0;
    }

    FOREACH_ELT (udp_port_data, i, port) {
	sock = socket (addr->sa_family, SOCK_DGRAM, 0);
	if (sock == -1) {
	    data->retval = errno;
	    com_err(data->prog, data->retval,
		    "Cannot create server socket for port %d address %s",
		    port, haddrbuf);
	    return 1;
	}
	set_sa_port(addr, htons(port));
	if (bind (sock, (struct sockaddr *)addr, socklen (addr)) == -1) {
	    data->retval = errno;
	    com_err(data->prog, data->retval,
		    "Cannot bind server socket to port %d address %s",
		    port, haddrbuf);
	    return 1;
	}
	FD_SET (sock, &sstate.rfds);
	if (sock >= sstate.max)
	    sstate.max = sock + 1;
	krb5_klog_syslog (LOG_INFO, "listening on fd %d: udp %s", sock,
			  paddr((struct sockaddr *)addr));
	if (add_udp_fd (data, sock) == 0)
	    return 1;
    }
    return 0;
}

#if 1
static void klog_handler(const void *data, size_t len)
{
    static char buf[BUFSIZ];
    static int bufoffset;
    void *p;

#define flush_buf() \
  (bufoffset						\
   ? (((buf[0] == 0 || buf[0] == '\n')			\
       ? (fork()==0?abort():(void)0)			\
       : (void)0),					\
      krb5_klog_syslog(LOG_INFO, "%s", buf),		\
      memset(buf, 0, sizeof(buf)),			\
      bufoffset = 0)					\
   : 0)

    p = memchr(data, 0, len);
    if (p)
	len = (const char *)p - (const char *)data;
scan_for_newlines:
    if (len == 0)
	return;
    p = memchr(data, '\n', len);
    if (p) {
	if (p != data)
	    klog_handler(data, (size_t)((const char *)p - (const char *)data));
	flush_buf();
	len -= ((const char *)p - (const char *)data) + 1;
	data = 1 + (const char *)p;
	goto scan_for_newlines;
    } else if (len > sizeof(buf) - 1 || len + bufoffset > sizeof(buf) - 1) {
	size_t x = sizeof(buf) - len - 1;
	klog_handler(data, x);
	flush_buf();
	len -= x;
	data = (const char *)data + x;
	goto scan_for_newlines;
    } else {
	memcpy(buf + bufoffset, data, len);
	bufoffset += len;
    }
}
#endif

/* XXX */
extern int krb5int_debug_sendto_kdc;
extern void (*krb5int_sendtokdc_debug_handler)(const void*, size_t);

krb5_error_code
setup_network(const char *prog)
{
    struct socksetup setup_data;
    krb5_error_code retval;
    char *cp;
    int i, port;

    FD_ZERO(&sstate.rfds);
    FD_ZERO(&sstate.wfds);
    FD_ZERO(&sstate.xfds);
    sstate.max = 0;

/*    krb5int_debug_sendto_kdc = 1; */
    krb5int_sendtokdc_debug_handler = klog_handler;

    /* Handle each realm's ports */
    for (i=0; i<kdc_numrealms; i++) {
	cp = kdc_realmlist[i]->realm_ports;
	while (cp && *cp) {
	    if (*cp == ',' || isspace((int) *cp)) {
		cp++;
		continue;
	    }
	    port = strtol(cp, &cp, 10);
	    if (cp == 0)
		break;
	    retval = add_udp_port(port);
	    if (retval)
		return retval;
	}

	cp = kdc_realmlist[i]->realm_tcp_ports;
	while (cp && *cp) {
	    if (*cp == ',' || isspace((int) *cp)) {
		cp++;
		continue;
	    }
	    port = strtol(cp, &cp, 10);
	    if (cp == 0)
		break;
	    retval = add_tcp_port(port);
	    if (retval)
		return retval;
	}
    }

    setup_data.prog = prog;
    setup_data.retval = 0;
    krb5_klog_syslog (LOG_INFO, "setting up network...");
    /* To do: Use RFC 2292 interface (or follow-on) and IPV6_PKTINFO,
       so we might need only one UDP socket; fall back to binding
       sockets on each address only if IPV6_PKTINFO isn't
       supported.  */
    if (foreach_localaddr (&setup_data, setup_udp_port, 0, 0)) {
	return setup_data.retval;
    }
    setup_tcp_listener_ports(&setup_data);
    krb5_klog_syslog (LOG_INFO, "set up %d sockets", n_sockets);
    if (n_sockets == 0) {
	com_err(prog, 0, "no sockets set up?");
	exit (1);
    }

    return 0;
}

static void init_addr(krb5_fulladdr *faddr, struct sockaddr *sa)
{
    switch (sa->sa_family) {
    case AF_INET:
	faddr->address->addrtype = ADDRTYPE_INET;
	faddr->address->length = 4;
	faddr->address->contents = (krb5_octet *) &sa2sin(sa)->sin_addr;
	faddr->port = ntohs(sa2sin(sa)->sin_port);
	break;
#ifdef KRB5_USE_INET6
    case AF_INET6:
	if (IN6_IS_ADDR_V4MAPPED(&sa2sin6(sa)->sin6_addr)) {
	    faddr->address->addrtype = ADDRTYPE_INET;
	    faddr->address->length = 4;
	    faddr->address->contents = 12 + (krb5_octet *) &sa2sin6(sa)->sin6_addr;
	} else {
	    faddr->address->addrtype = ADDRTYPE_INET6;
	    faddr->address->length = 16;
	    faddr->address->contents = (krb5_octet *) &sa2sin6(sa)->sin6_addr;
	}
	faddr->port = ntohs(sa2sin6(sa)->sin6_port);
	break;
#endif
    default:
	faddr->address->addrtype = -1;
	faddr->address->length = 0;
	faddr->address->contents = 0;
	faddr->port = 0;
	break;
    }
}

static void process_packet(struct connection *conn, const char *prog,
			   int selflags)
{
    int cc;
    socklen_t saddr_len;
    krb5_fulladdr faddr;
    krb5_error_code retval;
    struct sockaddr_storage saddr;
    krb5_address addr;
    krb5_data request;
    krb5_data *response;
    char pktbuf[MAX_DGRAM_SIZE];
    int port_fd = conn->fd;

    response = NULL;
    saddr_len = sizeof(saddr);
    cc = recvfrom(port_fd, pktbuf, sizeof(pktbuf), 0,
		  (struct sockaddr *)&saddr, &saddr_len);
    if (cc == -1) {
	if (errno != EINTR
	    /* This is how Linux indicates that a previous
	       transmission was refused, e.g., if the client timed out
	       before getting the response packet.  */
	    && errno != ECONNREFUSED
	    )
	    com_err(prog, errno, "while receiving from network");
	return;
    }
    if (!cc)
	return;		/* zero-length packet? */

    request.length = cc;
    request.data = pktbuf;
    faddr.address = &addr;
    init_addr(&faddr, ss2sa(&saddr));
    /* this address is in net order */
    if ((retval = dispatch(&request, &faddr, &response))) {
	com_err(prog, retval, "while dispatching (udp)");
	return;
    }
    cc = sendto(port_fd, response->data, (socklen_t) response->length, 0,
		(struct sockaddr *)&saddr, saddr_len);
    if (cc == -1) {
	char addrbuf[46];
        krb5_free_data(kdc_context, response);
	if (inet_ntop(((struct sockaddr *)&saddr)->sa_family,
		      addr.contents, addrbuf, sizeof(addrbuf)) == 0) {
	    strcpy(addrbuf, "?");
	}
	com_err(prog, errno, "while sending reply to %s/%d",
		addrbuf, faddr.port);
	return;
    }
    if (cc != response->length) {
	krb5_free_data(kdc_context, response);
	com_err(prog, 0, "short reply write %d vs %d\n",
		response->length, cc);
	return;
    }
    krb5_free_data(kdc_context, response);
    return;
}

static int tcp_data_counter;
static int max_tcp_data_connections = 30;

static void kill_tcp_connection(struct connection *);

static void accept_tcp_connection(struct connection *conn, const char *prog,
				  int selflags)
{
    int s;
    struct sockaddr_storage addr_s;
    struct sockaddr *addr = (struct sockaddr *)&addr_s;
    socklen_t addrlen = sizeof(addr_s);
    struct socksetup sockdata;
    struct connection *newconn;
    char tmpbuf[10];

    s = accept(conn->fd, addr, &addrlen);
    if (s < 0)
	return;
    setnbio(s), setnolinger(s);

    sockdata.prog = prog;
    sockdata.retval = 0;

    newconn = add_tcp_data_fd(&sockdata, s);
    if (newconn == 0)
	return;

    if (getnameinfo((struct sockaddr *)&addr_s, addrlen,
		    newconn->u.tcp.addrbuf, sizeof(newconn->u.tcp.addrbuf),
		    tmpbuf, sizeof(tmpbuf),
		    NI_NUMERICHOST | NI_NUMERICSERV))
	strcpy(newconn->u.tcp.addrbuf, "???");
    else {
	char *p, *end;
	p = newconn->u.tcp.addrbuf;
	end = p + sizeof(newconn->u.tcp.addrbuf);
	p += strlen(p);
	if (end - p > 2 + strlen(tmpbuf)) {
	    *p++ = '.';
	    strcpy(p, tmpbuf);
	}
    }
#if 0
    krb5_klog_syslog(LOG_INFO, "accepted TCP connection on socket %d from %s",
		     s, newconn->u.tcp.addrbuf);
#endif

    newconn->u.tcp.addr_s = addr_s;
    newconn->u.tcp.addrlen = addrlen;
    newconn->u.tcp.bufsiz = 1024 * 1024;
    newconn->u.tcp.buffer = malloc(newconn->u.tcp.bufsiz);
    newconn->u.tcp.start_time = time(0);

    if (++tcp_data_counter > max_tcp_data_connections) {
	struct connection *oldest_tcp = NULL;
	struct connection *c;
	int i;

	krb5_klog_syslog(LOG_INFO, "too many connections");

	FOREACH_ELT (connections, i, c) {
	    if (c->type != CONN_TCP)
		continue;
	    if (c == newconn)
		continue;
#if 0
	    krb5_klog_syslog(LOG_INFO, "fd %d started at %ld", c->fd,
			     c->u.tcp.start_time);
#endif
	    if (oldest_tcp == NULL
		|| oldest_tcp->u.tcp.start_time > c->u.tcp.start_time)
		oldest_tcp = c;
	}
	if (oldest_tcp != NULL) {
	    krb5_klog_syslog(LOG_INFO, "dropping tcp fd %d from %s",
			     oldest_tcp->fd, oldest_tcp->u.tcp.addrbuf);
	    kill_tcp_connection(oldest_tcp);
	}
    }
    if (newconn->u.tcp.buffer == 0) {
	com_err(prog, errno, "allocating buffer for new TCP session from %s",
		newconn->u.tcp.addrbuf);
	delete_fd(newconn);
	close(s);
	tcp_data_counter--;
	return;
    }
    newconn->u.tcp.offset = 0;
    newconn->u.tcp.faddr.address = &newconn->u.tcp.kaddr;
    init_addr(&newconn->u.tcp.faddr, ss2sa(&newconn->u.tcp.addr_s));
    SG_SET(&newconn->u.tcp.sgbuf[0], newconn->u.tcp.lenbuf, 4);
    SG_SET(&newconn->u.tcp.sgbuf[1], 0, 0);

    FD_SET(s, &sstate.rfds);
    if (sstate.max <= s)
	sstate.max = s + 1;
}

static void
kill_tcp_connection(struct connection *conn)
{
    if (conn->u.tcp.response)
	krb5_free_data(kdc_context, conn->u.tcp.response);
    if (conn->u.tcp.buffer)
	free(conn->u.tcp.buffer);
    FD_CLR(conn->fd, &sstate.rfds);
    FD_CLR(conn->fd, &sstate.wfds);
    if (sstate.max == conn->fd + 1)
	while (sstate.max > 0
	       && ! FD_ISSET(sstate.max-1, &sstate.rfds)
	       && ! FD_ISSET(sstate.max-1, &sstate.wfds)
	       /* && ! FD_ISSET(sstate.max-1, &sstate.xfds) */
	    )
	    sstate.max--;
    close(conn->fd);
    conn->fd = -1;
    delete_fd(conn);
    tcp_data_counter--;
}

static krb5_error_code
make_toolong_error (krb5_data **out)
{
    krb5_error errpkt;
    krb5_error_code retval;
    krb5_data *scratch;

    retval = krb5_us_timeofday(kdc_context, &errpkt.stime, &errpkt.susec);
    if (retval)
	return retval;
    errpkt.error = KRB_ERR_FIELD_TOOLONG;
    errpkt.server = tgs_server;
    errpkt.client = NULL;
    errpkt.cusec = 0;
    errpkt.ctime = 0;
    errpkt.text.length = 0;
    errpkt.text.data = 0;
    errpkt.e_data.length = 0;
    errpkt.e_data.data = 0;
    scratch = malloc(sizeof(*scratch));
    if (scratch == NULL)
	return ENOMEM;
    retval = krb5_mk_error(kdc_context, &errpkt, scratch);
    if (retval) {
	free(scratch);
	return retval;
    }

    *out = scratch;
    return 0;
}

static void
process_tcp_connection(struct connection *conn, const char *prog, int selflags)
{
    if (selflags & SSF_WRITE) {
	ssize_t nwrote;
	SOCKET_WRITEV_TEMP tmp;

	nwrote = SOCKET_WRITEV(conn->fd, conn->u.tcp.sgp, conn->u.tcp.sgnum,
			       tmp);
	if (nwrote < 0) {
	    goto kill_tcp_connection;
	}
	if (nwrote == 0)
	    /* eof */
	    goto kill_tcp_connection;
	while (nwrote) {
	    sg_buf *sgp = conn->u.tcp.sgp;
	    if (nwrote < SG_LEN(sgp)) {
		SG_ADVANCE(sgp, nwrote);
		nwrote = 0;
	    } else {
		nwrote -= SG_LEN(sgp);
		conn->u.tcp.sgp++;
		conn->u.tcp.sgnum--;
		if (conn->u.tcp.sgnum == 0 && nwrote != 0)
		    abort();
	    }
	}
	if (conn->u.tcp.sgnum == 0) {
	    /* finished sending */
	    /* We should go back to reading, though if we sent a
	       FIELD_TOOLONG error in reply to a length with the high
	       bit set, RFC 4120 says we have to close the TCP
	       stream.  */
	    goto kill_tcp_connection;
	}
    } else if (selflags & SSF_READ) {
	/* Read message length and data into one big buffer, already
	   allocated at connect time.  If we have a complete message,
	   we stop reading, so we should only be here if there is no
	   data in the buffer, or only an incomplete message.  */
	size_t len;
	ssize_t nread;
	if (conn->u.tcp.offset < 4) {
	    /* msglen has not been computed */
	    /* XXX Doing at least two reads here, letting the kernel
	       worry about buffering.  It'll be faster when we add
	       code to manage the buffer here.  */
	    len = 4 - conn->u.tcp.offset;
	    nread = SOCKET_READ(conn->fd,
				conn->u.tcp.buffer + conn->u.tcp.offset, len);
	    if (nread < 0)
		/* error */
		goto kill_tcp_connection;
	    if (nread == 0)
		/* eof */
		goto kill_tcp_connection;
	    conn->u.tcp.offset += nread;
	    if (conn->u.tcp.offset == 4) {
		unsigned char *p = (unsigned char *)conn->u.tcp.buffer;
		conn->u.tcp.msglen = ((p[0] << 24)
				      | (p[1] << 16)
				      | (p[2] <<  8)
				      | p[3]);
		if (conn->u.tcp.msglen > conn->u.tcp.bufsiz - 4) {
		    krb5_error_code err;
		    /* message too big */
		    krb5_klog_syslog(LOG_ERR, "TCP client %s wants %lu bytes, cap is %lu",
				     conn->u.tcp.addrbuf, (unsigned long) conn->u.tcp.msglen,
				     (unsigned long) conn->u.tcp.bufsiz - 4);
		    /* XXX Should return an error.  */
		    err = make_toolong_error (&conn->u.tcp.response);
		    if (err) {
			krb5_klog_syslog(LOG_ERR,
					 "error constructing KRB_ERR_FIELD_TOOLONG error! %s",
					 error_message(err));
			goto kill_tcp_connection;
		    }
		    goto have_response;
		}
	    }
	} else {
	    /* msglen known */
	    krb5_data request;
	    krb5_error_code err;

	    len = conn->u.tcp.msglen - (conn->u.tcp.offset - 4);
	    nread = SOCKET_READ(conn->fd,
				conn->u.tcp.buffer + conn->u.tcp.offset, len);
	    if (nread < 0)
		/* error */
		goto kill_tcp_connection;
	    if (nread == 0)
		/* eof */
		goto kill_tcp_connection;
	    conn->u.tcp.offset += nread;
	    if (conn->u.tcp.offset < conn->u.tcp.msglen + 4)
		return;
	    /* have a complete message, and exactly one message */
	    request.length = conn->u.tcp.msglen;
	    request.data = conn->u.tcp.buffer + 4;
	    err = dispatch(&request, &conn->u.tcp.faddr,
			   &conn->u.tcp.response);
	    if (err) {
		com_err(prog, err, "while dispatching (tcp)");
		goto kill_tcp_connection;
	    }
	have_response:
	    conn->u.tcp.lenbuf[0] = 0xff & (conn->u.tcp.response->length >> 24);
	    conn->u.tcp.lenbuf[1] = 0xff & (conn->u.tcp.response->length >> 16);
	    conn->u.tcp.lenbuf[2] = 0xff & (conn->u.tcp.response->length >> 8);
	    conn->u.tcp.lenbuf[3] = 0xff & (conn->u.tcp.response->length >> 0);
	    SG_SET(&conn->u.tcp.sgbuf[1], conn->u.tcp.response->data,
		   conn->u.tcp.response->length);
	    conn->u.tcp.sgp = conn->u.tcp.sgbuf;
	    conn->u.tcp.sgnum = 2;
	    FD_CLR(conn->fd, &sstate.rfds);
	    FD_SET(conn->fd, &sstate.wfds);
	}
    } else
	abort();

    return;

kill_tcp_connection:
    kill_tcp_connection(conn);
}

static void service_conn(struct connection *conn, const char *prog,
			 int selflags)
{
    conn->service(conn, prog, selflags);
}

krb5_error_code
listen_and_process(const char *prog)
{
    int			nfound;
    /* This struct contains 3 fd_set objects; on some platforms, they
       can be rather large.  Making this static avoids putting all
       that junk on the stack.  */
    static struct select_state sout;
    int			i, sret;
    int			netchanged; 
    krb5_error_code	err;

    netchanged = 0;
    if (conns == (struct connection **) NULL){
       sleep(30);
       err = setup_network(prog);
       if (conns == (struct connection **) NULL)
                       return KDC5_NONET;
               if (err){
                       com_err(prog, err,"while initalizing the network");
                       return err;
               }
     }   
 
    while (!signal_requests_exit) {
	if (signal_requests_hup) {
	    krb5_klog_reopen(kdc_context);
	    signal_requests_hup = 0;
	}


       if (signal_requests_network) {
               com_err(prog, EINTR, "signal_requests_network recieved");
               err = getcurtime(&(sstate.end_time));
               if(err) {
                       com_err(prog, err, "while getting the time");
                       continue;
               }
               sstate.end_time.tv_sec += 3;
               netchanged = 1;
       } else {
               sstate.end_time.tv_sec = sstate.end_time.tv_usec = 0;
       }


	err = krb5int_cm_call_select(&sstate, &sout, &sret);
	if (err) {
	    com_err(prog, err, "while selecting for network input(1)");
	    continue;
	}
	if (sret == -1) {
	    if (errno != EINTR)
		com_err(prog, errno, "while selecting for network input(2)");
	    continue;
	}
	if(netchanged && (sret == 0)) {
               signal_requests_network = 0;
               (void)closedown_network(prog);
               err = setup_network(prog);
               if(err) {
                       com_err(prog, err, "while re-initializing network");
                       return err;
               }
               netchanged = 0;
       }

	nfound = sret;
	for (i=0; i<n_sockets && nfound > 0; i++) {
	    int sflags = 0;
	    if (conns[i]->fd < 0)
		abort();
	    if (FD_ISSET(conns[i]->fd, &sout.rfds))
		sflags |= SSF_READ, nfound--;
	    if (FD_ISSET(conns[i]->fd, &sout.wfds))
		sflags |= SSF_WRITE, nfound--;
	    if (sflags)
		service_conn(conns[i], prog, sflags);
	}
    }
    return 0;
}

krb5_error_code
closedown_network(const char *prog)
{
    int i;
    struct connection *conn;

    if (conns == (struct connection **) NULL)
	return KDC5_NONET;

    FOREACH_ELT (connections, i, conn) {
	if (conn->fd >= 0)
	    (void) close(conn->fd);
	DEL (connections, i);
	/* There may also be per-connection data in the tcp structure
	   (tcp.buffer, tcp.response) that we're not freeing here.
	   That should only happen if we quit with a connection in
	   progress.  */
	free(conn);
    }
    FREE_SET_DATA(connections);
    FREE_SET_DATA(udp_port_data);
    FREE_SET_DATA(tcp_port_data);

    return 0;
}

// stolen from sendto_kdc.c
static int getcurtime (struct timeval *tvp)
{
#ifdef _WIN32
    struct _timeb tb;
    _ftime(&tb);
    tvp->tv_sec = tb.time;
    tvp->tv_usec = tb.millitm * 1000;
    /* Can _ftime fail?  */
    return 0;
#else
    if (gettimeofday(tvp, 0)) {
      //dperror("gettimeofday");
      return errno;
    }
    return 0;
#endif
}


#endif /* INET */