/*
  * rfc931() speaks a common subset of the RFC 931, AUTH, TAP and IDENT
  * protocols. The code queries an RFC 931 etc. compatible daemon on a remote
  * host to look up the owner of a connection. The information should not be
  * used for authentication purposes. This routine intercepts alarm signals.
  * 
  * Diagnostics are reported through syslog(3).
  * 
  * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  */

#ifndef lint
static char sccsid[] = "@(#) rfc931.c 1.7 93/09/11 20:45:30";
#endif

/* System libraries. */

#include <stdio.h>
#include <syslog.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <setjmp.h>
#include <signal.h>

extern char *strchr();
extern char *inet_ntoa();

/* Local stuff. */

#include "log_tcp.h"

#define	RFC931_PORT	113		/* Semi-well-known port */
#define	ANY_PORT	0		/* Any old port will do */

static jmp_buf timebuf;

typedef struct {
    FILE   *ifp;
    FILE   *ofp;
} FILE_PAIR;

/* fdup - duplicate a stdio stream */

static FILE *fdup(stream, mode)
FILE   *stream;
char   *mode;
{
    int     fd;
    FILE   *fp = 0;

    if ((fd = dup(fileno(stream))) < 0) {
	syslog(LOG_ERR, "dup: %m");
    } else if ((fp = fdopen(fd, mode)) == 0) {
	syslog(LOG_ERR, "fdopen: %m");
	close(fd);
    }
    return (fp);
}

/* fsocket - open stdio stream on top of socket */

static FILE *fsocket(domain, type, protocol, mode)
int     domain;
int     type;
int     protocol;
char   *mode;
{
    int     s;
    FILE   *fp = 0;

    if ((s = socket(domain, type, protocol)) < 0) {
	syslog(LOG_ERR, "socket: %m");
    } else if ((fp = fdopen(s, mode)) == 0) {
	syslog(LOG_ERR, "fdopen: %m");
	close(s);
    }
    return (fp);
}

/* ffsocket - open stdio stream pair on top of socket */

static FILE_PAIR *ffsocket(domain, type, protocol)
int     domain;
int     type;
int     protocol;
{
    static FILE_PAIR ffp;

    if ((ffp.ifp = fsocket(domain, type, protocol, "r")) != 0) {
	if ((ffp.ofp = fdup(ffp.ifp, "w")) != 0)
	    return (&ffp);
	fclose(ffp.ifp);
    }
    return (0);
}

/* ffclose - close stdio stream pair */

static int ffclose(ffp)
FILE_PAIR *ffp;
{
    int     ret;

    ret = fclose(ffp->ifp);
    return (fclose(ffp->ofp) || ret);
}

/* bind_connect - bind both ends of a socket */

int     bind_connect(s, local, remote, length)
int     s;
struct sockaddr *local;
struct sockaddr *remote;
int     length;
{
    if (bind(s, local, length) < 0) {
	syslog(LOG_ERR, "bind: %m");
	return (-1);
    } else {
	return (connect(s, remote, length));
    }
}

/* timeout - handle timeouts */

static void timeout(sig)
int     sig;
{
    longjmp(timebuf, sig);
}

/* rfc931 - return remote user name, given socket structures */

char   *rfc931(rmt_sin, our_sin)
struct sockaddr_in *rmt_sin;
struct sockaddr_in *our_sin;
{
    unsigned rmt_port;
    unsigned our_port;
    struct sockaddr_in rmt_query_sin;
    struct sockaddr_in our_query_sin;
    static char user[256];		/* XXX */
    char    buffer[512];		/* XXX */
    char   *cp;
    char   *result = FROM_UNKNOWN;	/* XXX */
    FILE_PAIR *ffp;

    /*
     * Use separate stdio streams for writing to and for reading from the
     * RFC931 etc. server. This is done because of a bug in the SunOS 4.1.x
     * stdio library. The bug may live in other stdio implementations, too.
     * When we use a single bidirectional stdio stream ("r+" or "w+" mode) we
     * read our own output. Such behaviour would make sense with resources
     * that support random-access operations, but not with sockets.
     */

    if ((ffp = ffsocket(AF_INET, SOCK_STREAM, 0)) != 0) {

	/*
	 * Set up a timer so we won't get stuck while waiting for the server.
	 */

	if (setjmp(timebuf) == 0) {
	    signal(SIGALRM, timeout);
	    alarm(RFC931_TIMEOUT);

	    /*
	     * Bind the local and remote ends of the query socket to the same
	     * IP addresses as the connection under investigation. We go
	     * through all this trouble because the local or remote system
	     * might have more than one network address. The RFC931 etc.
	     * client sends only port numbers; the server takes the IP
	     * addresses from the query socket.
	     */

	    our_query_sin = *our_sin;
	    our_query_sin.sin_port = htons(ANY_PORT);
	    rmt_query_sin = *rmt_sin;
	    rmt_query_sin.sin_port = htons(RFC931_PORT);

	    if (bind_connect(fileno(ffp->ifp),
			     (struct sockaddr *) & our_query_sin,
			     (struct sockaddr *) & rmt_query_sin,
			     sizeof(our_query_sin)) >= 0) {

		/*
		 * Send query to server. Neglect the risk that a 13-byte
		 * write would have to be fragmented by the local system and
		 * cause trouble with buggy System V stdio libraries.
		 */

		fprintf(ffp->ofp, "%u,%u\r\n",
			ntohs(rmt_sin->sin_port),
			ntohs(our_sin->sin_port));
		fflush(ffp->ofp);

		/*
		 * Read response from server. Use fgets()/sscanf() so we can
		 * work around System V stdio libraries that incorrectly
		 * assume EOF when a read from a socket returns less than
		 * requested.
		 */

		if (fgets(buffer, sizeof(buffer), ffp->ifp) != 0
		    && ferror(ffp->ifp) == 0 && feof(ffp->ifp) == 0
		    && sscanf(buffer, "%u , %u : USERID :%*[^:]:%255s",
			      &rmt_port, &our_port, user) == 3
		    && ntohs(rmt_sin->sin_port) == rmt_port
		    && ntohs(our_sin->sin_port) == our_port) {

		    /*
		     * Strip trailing carriage return. It is part of the
		     * protocol, not part of the data.
		     */

		    if (cp = strchr(user, '\r'))
			*cp = 0;
		    result = user;
		}
	    }
	    alarm(0);
	}
	ffclose(ffp);
    }
    return (result);
}