/*      $NetBSD: rfc931.c,v 1.12 2016/03/16 22:32:32 christos Exp $     */

 /*
  * rfc931() speaks a common subset of the RFC 931, AUTH, TAP, IDENT and RFC
  * 1413 protocols. It 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.
  */

#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#) rfc931.c 1.10 95/01/02 16:11:34";
#else
__RCSID("$NetBSD: rfc931.c,v 1.12 2016/03/16 22:32:32 christos Exp $");
#endif
#endif

/* System libraries. */

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

/* Local stuff. */

#include "tcpd.h"

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

int     rfc931_timeout = RFC931_TIMEOUT;/* Global so it can be changed */

static jmp_buf timebuf;

static FILE *fsocket(int, int, int);
static void timeout(int) __dead;

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

static FILE *
fsocket(int domain, int type, int protocol)
{
    int     s;
    FILE   *fp;

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

/* timeout - handle timeouts */

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

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

void
rfc931(struct sockaddr *rmt_sin, struct sockaddr *our_sin, char *dest)
{
    unsigned rmt_port;
    unsigned our_port;
    struct sockaddr_storage rmt_query_sin;
    struct sockaddr_storage our_query_sin;
    char    user[256];                  /* XXX */
    char    buffer[512];                /* XXX */
    char   *cp;
    char   * volatile result = unknown;
    FILE   *fp;
    volatile int salen;
    u_short * volatile rmt_portp;
    u_short * volatile our_portp;

    /* address family must be the same */
    if (rmt_sin->sa_family != our_sin->sa_family) {
        strlcpy(dest, unknown, STRING_LENGTH);
        return;
    }
    switch (rmt_sin->sa_family) {
    case AF_INET:
        salen = sizeof(struct sockaddr_in);
        rmt_portp = &(((struct sockaddr_in *)rmt_sin)->sin_port);
        break;
#ifdef INET6
    case AF_INET6:
        salen = sizeof(struct sockaddr_in6);
        rmt_portp = &(((struct sockaddr_in6 *)rmt_sin)->sin6_port);
        break;
#endif
    default:
        strlcpy(dest, unknown, STRING_LENGTH);
        return;
    }
    switch (our_sin->sa_family) {
    case AF_INET:
        our_portp = &(((struct sockaddr_in *)our_sin)->sin_port);
        break;
#ifdef INET6
    case AF_INET6:
        our_portp = &(((struct sockaddr_in6 *)our_sin)->sin6_port);
        break;
#endif
    default:
        strlcpy(dest, unknown, STRING_LENGTH);
        return;
    }

    /*
     * Use one unbuffered stdio stream 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, buffered, 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 ((fp = fsocket(rmt_sin->sa_family, SOCK_STREAM, 0)) != 0) {
        setbuf(fp, (char *) 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.
             */

            memcpy(&our_query_sin, our_sin, salen);
            switch (our_query_sin.ss_family) {
            case AF_INET:
                ((struct sockaddr_in *)&our_query_sin)->sin_port =
                        htons(ANY_PORT);
                break;
#ifdef INET6
            case AF_INET6:
                ((struct sockaddr_in6 *)&our_query_sin)->sin6_port =
                        htons(ANY_PORT);
                break;
#endif
            }
            memcpy(&rmt_query_sin, rmt_sin, salen);
            switch (rmt_query_sin.ss_family) {
            case AF_INET:
                ((struct sockaddr_in *)&rmt_query_sin)->sin_port =
                        htons(RFC931_PORT);
                break;
#ifdef INET6
            case AF_INET6:
                ((struct sockaddr_in6 *)&rmt_query_sin)->sin6_port = 
                        htons(RFC931_PORT);
                break;
#endif
            }

            if (bind(fileno(fp), (struct sockaddr *) & our_query_sin,
                     salen) >= 0 &&
                connect(fileno(fp), (struct sockaddr *) & rmt_query_sin,
                        salen) >= 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(fp, "%u,%u\r\n",
                        ntohs(*rmt_portp),
                        ntohs(*our_portp));
                fflush(fp);

                /*
                 * 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), fp) != 0
                    && ferror(fp) == 0 && feof(fp) == 0
                    && sscanf(buffer, "%u , %u : USERID :%*[^:]:%255s",
                              &rmt_port, &our_port, user) == 3
                    && ntohs(*rmt_portp) == rmt_port
                    && ntohs(*our_portp) == our_port) {

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

                    if ((cp = strchr(user, '\r')) != NULL)
                        *cp = '\0';
                    result = user;
                }
            }
            alarm(0);
        }
        fclose(fp);
    }
    strlcpy(dest, result, STRING_LENGTH);
}