source: MondoRescue/trunk/mindi-busybox/networking/fakeidentd.c@ 904

/* vi: set sw=4 ts=4: */
/*
 * A fake identd server
 *
 * Adapted to busybox by Thomas Lundquist <thomasez@zelow.no>
 * Original Author: Tomi Ollila <too@iki.fi>
 *                  http://www.guru-group.fi/~too/sw/
 *
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include "busybox.h"

#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/syslog.h>

#include <pwd.h>

#include <sys/syslog.h>
#include <time.h>
#include <sys/socket.h>
#include <errno.h>
#include <sys/uio.h>


#define IDENT_PORT  113
#define MAXCONNS    20
#define MAXIDLETIME 45

static const char ident_substr[] = " : USERID : UNIX : ";
enum { ident_substr_len = sizeof(ident_substr) - 1 };
#define PIDFILE "/var/run/identd.pid"

/*
 * We have to track the 'first connection socket' so that we
 * don't go around closing file descriptors for non-clients.
 *
 * descriptor setup normally
 *  0 = server socket
 *  1 = syslog fd (hopefully -- otherwise this won't work)
 *  2 = connection socket after detached from tty. standard error before that
 *  3 - 2 + MAXCONNS = rest connection sockets
 *
 * To try to make sure that syslog fd is what is "requested", the that fd
 * is closed before openlog() call.  It can only severely fail if fd 0
 * is initially closed.
 */
#define FCS 2

/*
 * FD of the connection is always the index of the connection structure
 * in `conns' array + FCS
 */
static struct {
    char buf[20];
    int len;
    time_t lasttime;
} conns[MAXCONNS];

/* When using global variables, bind those at least to a structure. */
static struct {
    const char *identuser;
    fd_set readfds;
    int conncnt;
} G;

/*
 * Prototypes
 */
static void reply(int s, char *buf);
static void replyError(int s, char *buf);

static const char *nobodystr = "nobody"; /* this needs to be declared like this */
static char *bind_ip_address = "0.0.0.0";

static inline void movefd(int from, int to)
{
    if (from != to) {
        dup2(from, to);
        close(from);
    }
}

static void inetbind(void)
{
    int s, port;
    struct sockaddr_in addr;
    int len = sizeof(addr);
    int one = 1;
    struct servent *se;

    if ((se = getservbyname("identd", "tcp")) == NULL)
        port = IDENT_PORT;
    else
        port = se->s_port;

    s = bb_xsocket(AF_INET, SOCK_STREAM, 0);

    setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));

    memset(&addr, 0, sizeof(addr));
    addr.sin_addr.s_addr = inet_addr(bind_ip_address);
    addr.sin_family = AF_INET;
    addr.sin_port = htons(port);

    bb_xbind(s, (struct sockaddr *)&addr, len);
    bb_xlisten(s, 5);

    movefd(s, 0);
}

static void handlexitsigs(int signum)
{
    if (unlink(PIDFILE) < 0)
        close(open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0644));
    exit(0);
}

/* May succeed. If not, won't care. */
static inline void writepid(uid_t nobody, uid_t nogrp)
{
    char buf[24];
    int fd = open(PIDFILE, O_WRONLY|O_CREAT|O_TRUNC, 0664);

    if (fd < 0)
        return;

    snprintf(buf, 23, "%d\n", getpid());
    write(fd, buf, strlen(buf));
    fchown(fd, nobody, nogrp);
    close(fd);

    /* should this handle ILL, ... (see signal(7)) */
    signal(SIGTERM, handlexitsigs);
    signal(SIGINT,  handlexitsigs);
    signal(SIGQUIT, handlexitsigs);
}

/* return 0 as parent, 1 as child */
static int godaemon(void)
{
    uid_t nobody, nogrp;
    struct passwd *pw;

    switch (fork()) {
    case -1:
        bb_perror_msg_and_die("Could not fork");

    case 0:
        pw = getpwnam(nobodystr);
        if (pw == NULL)
            bb_error_msg_and_die("Cannot find uid/gid of user '%s'", nobodystr);
        nobody = pw->pw_uid;
        nogrp = pw->pw_gid;
        writepid(nobody, nogrp);

        close(0);
        inetbind();
        xsetgid(nogrp);
        xsetuid(nobody);
        close(1);
        close(2);

        signal(SIGHUP, SIG_IGN);
        signal(SIGPIPE, SIG_IGN); /* connection closed when writing (raises ???) */

        setsid();

        openlog(bb_applet_name, 0, LOG_DAEMON);
        return 1;
    }

    return 0;
}

static void deleteConn(int s)
{
    int i = s - FCS;

    close(s);

    G.conncnt--;

    /*
     * Most of the time there is 0 connections. Most often that there
     * is connections, there is just one connection. When this one connection
     * closes, i == G.conncnt = 0 -> no copying.
     * When there is more than one connection, the oldest connections closes
     * earlier on average. When this happens, the code below starts copying
     * the connection structure w/ highest index to the place which which is
     * just deleted. This means that the connection structures are no longer
     * in chronological order. I'd quess this means that when there is more
     * than 1 connection, on average every other connection structure needs
     * to be copied over the time all these connections are deleted.
     */
    if (i != G.conncnt) {
        memcpy(&conns[i], &conns[G.conncnt], sizeof(conns[0]));
        movefd(G.conncnt + FCS, s);
    }

    FD_CLR(G.conncnt + FCS, &G.readfds);
}

static int closeOldest(void)
{
    time_t min = conns[0].lasttime;
    int idx = 0;
    int i;

    for (i = 1; i < MAXCONNS; i++)
        if (conns[i].lasttime < min)
            idx = i;

    replyError(idx + FCS, "X-SERVER-TOO-BUSY");
    close(idx + FCS);

    return idx;
}

static int checkInput(char *buf, int len, int l)
{
    int i;
    for (i = len; i < len + l; ++i)
        if (buf[i] == '\n')
            return 1;
    return 0;
}

int fakeidentd_main(int argc, char **argv)
{
    memset(conns, 0, sizeof(conns));
    memset(&G, 0, sizeof(G));
    FD_ZERO(&G.readfds);
    FD_SET(0, &G.readfds);

    /* handle -b <ip> parameter */
    bb_getopt_ulflags(argc, argv, "b:", &bind_ip_address);
    /* handle optional REPLY STRING */
    if (optind < argc)
        G.identuser = argv[optind];
    else
        G.identuser = nobodystr;

    /* daemonize and have the parent return */
    if (godaemon() == 0)
        return 0;

    /* main loop where we process all events and never exit */
    while (1) {
    fd_set rfds = G.readfds;
    struct timeval tv = { 15, 0 };
    int i;
    int tim = time(NULL);

    select(G.conncnt + FCS, &rfds, NULL, NULL, G.conncnt? &tv: NULL);

    for (i = G.conncnt - 1; i >= 0; i--) {
        int s = i + FCS;

        if (FD_ISSET(s, &rfds)) {
            char *buf = conns[i].buf;
            unsigned int len = conns[i].len;
            unsigned int l;

            if ((l = read(s, buf + len, sizeof(conns[0].buf) - len)) > 0) {
                if (checkInput(buf, len, l)) {
                    reply(s, buf);
                    goto deleteconn;
                } else if (len + l >= sizeof(conns[0].buf)) {
                    replyError(s, "X-INVALID-REQUEST");
                    goto deleteconn;
                } else {
                    conns[i].len += l;
                }
            } else {
                goto deleteconn;
            }

            conns[i].lasttime = tim;
            continue;

deleteconn:
            deleteConn(s);
        } else {
            /* implement as time_after() in linux kernel sources ... */
            if (conns[i].lasttime + MAXIDLETIME <= tim) {
                replyError(s, "X-TIMEOUT");
                deleteConn(s);
            }
        }
    }

    if (FD_ISSET(0, &rfds)) {
        int s = accept(0, NULL, 0);

        if (s < 0) {
            if (errno != EINTR) /* EINTR */
                syslog(LOG_ERR, "accept: %s", strerror(errno));
        } else {
            if (G.conncnt == MAXCONNS)
                i = closeOldest();
            else
                i = G.conncnt++;

            movefd(s, i + FCS); /* move if not already there */
            FD_SET(i + FCS, &G.readfds);

            conns[i].len = 0;
            conns[i].lasttime = time(NULL);
        }
    }
    } /* end of while(1) */

    return 0;
}

static int parseAddrs(char *ptr, char **myaddr, char **heraddr);
static void reply(int s, char *buf)
{
    char *myaddr, *heraddr;

    myaddr = heraddr = NULL;

    if (parseAddrs(buf, &myaddr, &heraddr))
        replyError(s, "X-INVALID-REQUEST");
    else {
        struct iovec iv[6];
        iv[0].iov_base = myaddr;               iv[0].iov_len = strlen(myaddr);
        iv[1].iov_base = ", ";                 iv[1].iov_len = 2;
        iv[2].iov_base = heraddr;              iv[2].iov_len = strlen(heraddr);
        iv[3].iov_base = (void *)ident_substr; iv[3].iov_len = ident_substr_len;
        iv[4].iov_base = (void *)G.identuser;  iv[4].iov_len = strlen(G.identuser);
        iv[5].iov_base = "\r\n";               iv[5].iov_len = 2;
        writev(s, iv, 6);
    }
}

static void replyError(int s, char *buf)
{
    struct iovec iv[3];
    iv[0].iov_base = "0, 0 : ERROR : ";   iv[0].iov_len = 15;
    iv[1].iov_base = buf;                 iv[1].iov_len = strlen(buf);
    iv[2].iov_base = "\r\n";              iv[2].iov_len = 2;
    writev(s, iv, 3);
}

static int chmatch(char c, char *chars)
{
    for (; *chars; chars++)
        if (c == *chars)
            return 1;
    return 0;
}

static int skipchars(char **p, char *chars)
{
    while (chmatch(**p, chars))
        (*p)++;
    if (**p == '\r' || **p == '\n')
        return 0;
    return 1;
}

static int parseAddrs(char *ptr, char **myaddr, char **heraddr)
{
    /* parse <port-on-server> , <port-on-client> */

    if (!skipchars(&ptr, " \t"))
        return -1;

    *myaddr = ptr;

    if (!skipchars(&ptr, "1234567890"))
        return -1;

    if (!chmatch(*ptr, " \t,"))
        return -1;

    *ptr++ = '\0';

    if (!skipchars(&ptr, " \t,") )
        return -1;

    *heraddr = ptr;

    skipchars(&ptr, "1234567890");

    if (!chmatch(*ptr, " \n\r"))
        return -1;

    *ptr = '\0';

    return 0;
}