Fix crash when --backup-dir is excessively long.

[rsync/qnx.git] / clientserver.c

/*
 * The socket based protocol for setting up a connection with rsyncd.
 *
 * Copyright (C) 1998-2001 Andrew Tridgell <tridge@samba.org>
 * Copyright (C) 2001-2002 Martin Pool <mbp@samba.org>
 * Copyright (C) 2002-2009 Wayne Davison
 *
 * 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 3 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, visit the http://fsf.org website.
 */

#include "rsync.h"
#include "itypes.h"

extern int quiet;
extern int dry_run;
extern int output_motd;
extern int list_only;
extern int am_sender;
extern int am_server;
extern int am_daemon;
extern int am_root;
extern int rsync_port;
extern int protect_args;
extern int ignore_errors;
extern int preserve_xattrs;
extern int kluge_around_eof;
extern int daemon_over_rsh;
extern int munge_symlinks;
extern int sanitize_paths;
extern int numeric_ids;
extern int filesfrom_fd;
extern int remote_protocol;
extern int protocol_version;
extern int io_timeout;
extern int no_detach;
extern int write_batch;
extern int default_af_hint;
extern int logfile_format_has_i;
extern int logfile_format_has_o_or_i;
extern char *bind_address;
extern char *config_file;
extern char *logfile_format;
extern char *files_from;
extern char *tmpdir;
extern struct chmod_mode_struct *chmod_modes;
extern filter_rule_list daemon_filter_list;
#ifdef ICONV_OPTION
extern char *iconv_opt;
extern iconv_t ic_send, ic_recv;
#endif

#define MAX_GID_LIST 32

char *auth_user;
int read_only = 0;
int module_id = -1;
struct chmod_mode_struct *daemon_chmod_modes;

/* module_dirlen is the length of the module_dir string when in daemon
 * mode and module_dir is not "/"; otherwise 0.  (Note that a chroot-
 * enabled module can have a non-"/" module_dir these days.) */
char *module_dir = NULL;
unsigned int module_dirlen = 0;

char *full_module_path;

static int rl_nulls = 0;

#ifdef HAVE_SIGACTION
static struct sigaction sigact;
#endif

static gid_t gid_list[MAX_GID_LIST];
static int gid_count = 0;

/* Used when "reverse lookup" is off. */
const char undetermined_hostname[] = "UNDETERMINED";

/**
 * Run a client connected to an rsyncd.  The alternative to this
 * function for remote-shell connections is do_cmd().
 *
 * After negotiating which module to use and reading the server's
 * motd, this hands over to client_run().  Telling the server the
 * module will cause it to chroot/setuid/etc.
 *
 * Instead of doing a transfer, the client may at this stage instead
 * get a listing of remote modules and exit.
 *
 * @return -1 for error in startup, or the result of client_run().
 * Either way, it eventually gets passed to exit_cleanup().
 **/
int start_socket_client(char *host, int remote_argc, char *remote_argv[],
                        int argc, char *argv[])
{
        int fd, ret;
        char *p, *user = NULL;

        /* This is redundant with code in start_inband_exchange(), but this
         * short-circuits a problem in the client before we open a socket,
         * and the extra check won't hurt. */
        if (**remote_argv == '/') {
                rprintf(FERROR,
                        "ERROR: The remote path must start with a module name not a /\n");
                return -1;
        }

        if ((p = strrchr(host, '@')) != NULL) {
                user = host;
                host = p+1;
                *p = '\0';
        }

        fd = open_socket_out_wrapped(host, rsync_port, bind_address,
                                     default_af_hint);
        if (fd == -1)
                exit_cleanup(RERR_SOCKETIO);

#ifdef ICONV_CONST
        setup_iconv();
#endif

        ret = start_inband_exchange(fd, fd, user, remote_argc, remote_argv);

        return ret ? ret : client_run(fd, fd, -1, argc, argv);
}

static int exchange_protocols(int f_in, int f_out, char *buf, size_t bufsiz, int am_client)
{
        int remote_sub = -1;
#if SUBPROTOCOL_VERSION != 0
        int our_sub = protocol_version < PROTOCOL_VERSION ? 0 : SUBPROTOCOL_VERSION;
#else
        int our_sub = 0;
#endif
        char *motd;

        io_printf(f_out, "@RSYNCD: %d.%d\n", protocol_version, our_sub);

        if (!am_client) {
                motd = lp_motd_file();
                if (motd && *motd) {
                        FILE *f = fopen(motd,"r");
                        while (f && !feof(f)) {
                                int len = fread(buf, 1, bufsiz - 1, f);
                                if (len > 0)
                                        write_buf(f_out, buf, len);
                        }
                        if (f)
                                fclose(f);
                        write_sbuf(f_out, "\n");
                }
        }

        /* This strips the \n. */
        if (!read_line_old(f_in, buf, bufsiz, 0)) {
                if (am_client)
                        rprintf(FERROR, "rsync: did not see server greeting\n");
                return -1;
        }

        if (sscanf(buf, "@RSYNCD: %d.%d", &remote_protocol, &remote_sub) < 1) {
                if (am_client)
                        rprintf(FERROR, "rsync: server sent \"%s\" rather than greeting\n", buf);
                else
                        io_printf(f_out, "@ERROR: protocol startup error\n");
                return -1;
        }

        if (remote_sub < 0) {
                if (remote_protocol == 30) {
                        if (am_client)
                                rprintf(FERROR, "rsync: server is speaking an incompatible beta of protocol 30\n");
                        else
                                io_printf(f_out, "@ERROR: your client is speaking an incompatible beta of protocol 30\n");
                        return -1;
                }
                remote_sub = 0;
        }

        if (protocol_version > remote_protocol) {
                protocol_version = remote_protocol;
                if (remote_sub)
                        protocol_version--;
        } else if (protocol_version == remote_protocol) {
                if (remote_sub != our_sub)
                        protocol_version--;
        }
#if SUBPROTOCOL_VERSION != 0
        else if (protocol_version < remote_protocol) {
                if (our_sub)
                        protocol_version--;
        }
#endif

        if (protocol_version >= 30)
                rl_nulls = 1;

        return 0;
}

int start_inband_exchange(int f_in, int f_out, const char *user, int argc, char *argv[])
{
        int i, modlen;
        char line[BIGPATHBUFLEN];
        char *sargs[MAX_ARGS];
        int sargc = 0;
        char *p, *modname;

        assert(argc > 0 && *argv != NULL);

        if (**argv == '/') {
                rprintf(FERROR,
                        "ERROR: The remote path must start with a module name\n");
                return -1;
        }

        if (!(p = strchr(*argv, '/')))
                modlen = strlen(*argv);
        else
                modlen = p - *argv;

        if (!(modname = new_array(char, modlen+1+1))) /* room for '/' & '\0' */
                out_of_memory("start_inband_exchange");
        strlcpy(modname, *argv, modlen + 1);
        modname[modlen] = '/';
        modname[modlen+1] = '\0';

        if (!user)
                user = getenv("USER");
        if (!user)
                user = getenv("LOGNAME");

        if (exchange_protocols(f_in, f_out, line, sizeof line, 1) < 0)
                return -1;

        /* set daemon_over_rsh to false since we need to build the
         * true set of args passed through the rsh/ssh connection;
         * this is a no-op for direct-socket-connection mode */
        daemon_over_rsh = 0;
        server_options(sargs, &sargc);

        if (sargc >= MAX_ARGS - 2)
                goto arg_overflow;

        sargs[sargc++] = ".";

        while (argc > 0) {
                if (sargc >= MAX_ARGS - 1) {
                  arg_overflow:
                        rprintf(FERROR, "internal: args[] overflowed in do_cmd()\n");
                        exit_cleanup(RERR_SYNTAX);
                }
                if (strncmp(*argv, modname, modlen) == 0
                 && argv[0][modlen] == '\0')
                        sargs[sargc++] = modname; /* we send "modname/" */
                else
                        sargs[sargc++] = *argv;
                argv++;
                argc--;
        }

        sargs[sargc] = NULL;

        if (DEBUG_GTE(CMD, 1))
                print_child_argv("sending daemon args:", sargs);

        io_printf(f_out, "%.*s\n", modlen, modname);

        /* Old servers may just drop the connection here,
         rather than sending a proper EXIT command.  Yuck. */
        kluge_around_eof = list_only && protocol_version < 25 ? 1 : 0;

        while (1) {
                if (!read_line_old(f_in, line, sizeof line, 0)) {
                        rprintf(FERROR, "rsync: didn't get server startup line\n");
                        return -1;
                }

                if (strncmp(line,"@RSYNCD: AUTHREQD ",18) == 0) {
                        auth_client(f_out, user, line+18);
                        continue;
                }

                if (strcmp(line,"@RSYNCD: OK") == 0)
                        break;

                if (strcmp(line,"@RSYNCD: EXIT") == 0) {
                        /* This is sent by recent versions of the
                         * server to terminate the listing of modules.
                         * We don't want to go on and transfer
                         * anything; just exit. */
                        exit(0);
                }

                if (strncmp(line, "@ERROR", 6) == 0) {
                        rprintf(FERROR, "%s\n", line);
                        /* This is always fatal; the server will now
                         * close the socket. */
                        return -1;
                }

                /* This might be a MOTD line or a module listing, but there is
                 * no way to differentiate it.  The manpage mentions this. */
                if (output_motd)
                        rprintf(FINFO, "%s\n", line);
        }
        kluge_around_eof = 0;

        if (rl_nulls) {
                for (i = 0; i < sargc; i++) {
                        if (!sargs[i]) /* stop at --protect-args NULL */
                                break;
                        write_sbuf(f_out, sargs[i]);
                        write_byte(f_out, 0);
                }
                write_byte(f_out, 0);
        } else {
                for (i = 0; i < sargc; i++)
                        io_printf(f_out, "%s\n", sargs[i]);
                write_sbuf(f_out, "\n");
        }

        if (protect_args)
                send_protected_args(f_out, sargs);

        if (protocol_version < 23) {
                if (protocol_version == 22 || !am_sender)
                        io_start_multiplex_in(f_in);
        }

        free(modname);

        return 0;
}

static char *finish_pre_exec(pid_t pid, int fd, char *request,
                             char **early_argv, char **argv)
{
        int j = 0, status = -1;

        if (!request)
                request = "(NONE)";

        write_buf(fd, request, strlen(request)+1);
        if (early_argv) {
                for ( ; *early_argv; early_argv++)
                        write_buf(fd, *early_argv, strlen(*early_argv)+1);
                j = 1; /* Skip arg0 name in argv. */
        }
        for ( ; argv[j]; j++) {
                write_buf(fd, argv[j], strlen(argv[j])+1);
                if (argv[j][0] == '.' && argv[j][1] == '\0')
                        break;
        }
        write_byte(fd, 0);

        close(fd);

        if (wait_process(pid, &status, 0) < 0
         || !WIFEXITED(status) || WEXITSTATUS(status) != 0) {
                char *e;
                if (asprintf(&e, "pre-xfer exec returned failure (%d)%s%s\n",
                             status, status < 0 ? ": " : "",
                             status < 0 ? strerror(errno) : "") < 0)
                        out_of_memory("finish_pre_exec");
                return e;
        }
        return NULL;
}

#ifdef HAVE_PUTENV
static int read_arg_from_pipe(int fd, char *buf, int limit)
{
        char *bp = buf, *eob = buf + limit - 1;

        while (1) {
                int got = read(fd, bp, 1);
                if (got != 1) {
                        if (got < 0 && errno == EINTR)
                                continue;
                        return -1;
                }
                if (*bp == '\0')
                        break;
                if (bp < eob)
                        bp++;
        }
        *bp = '\0';

        return bp - buf;
}
#endif

static int path_failure(int f_out, const char *dir, BOOL was_chdir)
{
        if (was_chdir)
                rsyserr(FLOG, errno, "chdir %s failed\n", dir);
        else
                rprintf(FLOG, "normalize_path(%s) failed\n", dir);
        io_printf(f_out, "@ERROR: chdir failed\n");
        return -1;
}

static int add_a_group(int f_out, const char *gname)
{
        gid_t gid;
        if (!group_to_gid(gname, &gid, True)) {
                rprintf(FLOG, "Invalid gid %s\n", gname);
                io_printf(f_out, "@ERROR: invalid gid %s\n", gname);
                return -1;
        }
        if (gid_count == MAX_GID_LIST) {
                rprintf(FLOG, "Too many groups specified via gid parameter.\n");
                io_printf(f_out, "@ERROR: too many groups\n");
                return -1;
        }
        gid_list[gid_count++] = gid;
        return 0;
}

#ifdef HAVE_GETGROUPLIST
static int want_all_groups(int f_out, uid_t uid)
{
        const char *err;
        gid_count = MAX_GID_LIST;
        if ((err = getallgroups(uid, gid_list, &gid_count)) != NULL) {
                rsyserr(FLOG, errno, "%s", err);
                io_printf(f_out, "@ERROR: %s\n", err);
                return -1;
        }
        return 0;
}
#elif defined HAVE_INITGROUPS
static struct passwd *want_all_groups(int f_out, uid_t uid)
{
        struct passwd *pw;
        if ((pw = getpwuid(uid)) == NULL) {
                rsyserr(FLOG, errno, "getpwuid failed");
                io_printf(f_out, "@ERROR: getpwuid failed\n");
                return NULL;
        }
        /* Start with the default group and initgroups() will add the reset. */
        gid_count = 1;
        gid_list[0] = pw->pw_gid;
        return pw;
}
#endif

static void set_env_str(const char *var, const char *str)
{
#ifdef HAVE_PUTENV
        char *mem;
        if (asprintf(&mem, "%s=%s", var, str) < 0)
                out_of_memory("set_env_str");
        putenv(mem);
#endif
}

#ifdef HAVE_PUTENV
static void set_env_num(const char *var, long num)
{
        char *mem;
        if (asprintf(&mem, "%s=%ld", var, num) < 0)
                out_of_memory("set_env_num");
        putenv(mem);
}
#endif

static int rsync_module(int f_in, int f_out, int i, const char *addr, const char *host)
{
        int argc;
        char **argv, **orig_argv, **orig_early_argv, *module_chdir;
        char line[BIGPATHBUFLEN];
#if defined HAVE_INITGROUPS && !defined HAVE_GETGROUPLIST
        struct passwd *pw = NULL;
#endif
        uid_t uid;
        int set_uid;
        char *p, *err_msg = NULL;
        char *name = lp_name(i);
        int use_chroot = lp_use_chroot(i);
        int ret, pre_exec_fd = -1;
        int save_munge_symlinks;
        pid_t pre_exec_pid = 0;
        char *request = NULL;

        set_env_str("RSYNC_MODULE_NAME", name);

#ifdef ICONV_OPTION
        iconv_opt = lp_charset(i);
        if (*iconv_opt)
                setup_iconv();
        iconv_opt = NULL;
#endif

        /* If reverse lookup is disabled globally but enabled for this module,
         * we need to do it now before the access check. */
        if (host == undetermined_hostname && lp_reverse_lookup(i))
                host = client_name(f_in);
        set_env_str("RSYNC_HOST_NAME", host);
        set_env_str("RSYNC_HOST_ADDR", addr);

        if (!allow_access(addr, host, lp_hosts_allow(i), lp_hosts_deny(i))) {
                rprintf(FLOG, "rsync denied on module %s from %s (%s)\n",
                        name, host, addr);
                if (!lp_list(i))
                        io_printf(f_out, "@ERROR: Unknown module '%s'\n", name);
                else {
                        io_printf(f_out,
                                  "@ERROR: access denied to %s from %s (%s)\n",
                                  name, host, addr);
                }
                return -1;
        }

        if (am_daemon && am_server) {
                rprintf(FLOG, "rsync allowed access on module %s from %s (%s)\n",
                        name, host, addr);
        }

        if (!claim_connection(lp_lock_file(i), lp_max_connections(i))) {
                if (errno) {
                        rsyserr(FLOG, errno, "failed to open lock file %s",
                                lp_lock_file(i));
                        io_printf(f_out, "@ERROR: failed to open lock file\n");
                } else {
                        rprintf(FLOG, "max connections (%d) reached\n",
                                lp_max_connections(i));
                        io_printf(f_out, "@ERROR: max connections (%d) reached -- try again later\n",
                                lp_max_connections(i));
                }
                return -1;
        }

        read_only = lp_read_only(i); /* may also be overridden by auth_server() */
        auth_user = auth_server(f_in, f_out, i, host, addr, "@RSYNCD: AUTHREQD ");

        if (!auth_user) {
                io_printf(f_out, "@ERROR: auth failed on module %s\n", name);
                return -1;
        }
        set_env_str("RSYNC_USER_NAME", auth_user);

        module_id = i;

        if (lp_transfer_logging(i) && !logfile_format)
                logfile_format = lp_log_format(i);
        if (log_format_has(logfile_format, 'i'))
                logfile_format_has_i = 1;
        if (logfile_format_has_i || log_format_has(logfile_format, 'o'))
                logfile_format_has_o_or_i = 1;

        uid = MY_UID();
        am_root = (uid == 0);

        p = *lp_uid(i) ? lp_uid(i) : am_root ? NOBODY_USER : NULL;
        if (p) {
                if (!user_to_uid(p, &uid, True)) {
                        rprintf(FLOG, "Invalid uid %s\n", p);
                        io_printf(f_out, "@ERROR: invalid uid %s\n", p);
                        return -1;
                }
                set_uid = 1;
        } else
                set_uid = 0;

        p = *lp_gid(i) ? strtok(lp_gid(i), ", ") : NULL;
        if (p) {
                /* The "*" gid must be the first item in the list. */
                if (strcmp(p, "*") == 0) {
#ifdef HAVE_GETGROUPLIST
                        if (want_all_groups(f_out, uid) < 0)
                                return -1;
#elif defined HAVE_INITGROUPS
                        if ((pw = want_all_groups(f_out, uid)) == NULL)
                                return -1;
#else
                        rprintf(FLOG, "This rsync does not support a gid of \"*\"\n");
                        io_printf(f_out, "@ERROR: invalid gid setting.\n");
                        return -1;
#endif
                } else if (add_a_group(f_out, p) < 0)
                        return -1;
                while ((p = strtok(NULL, ", ")) != NULL) {
#if defined HAVE_INITGROUPS && !defined HAVE_GETGROUPLIST
                        if (pw) {
                                rprintf(FLOG, "This rsync cannot add groups after \"*\".\n");
                                io_printf(f_out, "@ERROR: invalid gid setting.\n");
                                return -1;
                        }
#endif
                        if (add_a_group(f_out, p) < 0)
                                return -1;
                }
        } else if (am_root) {
                if (add_a_group(f_out, NOBODY_GROUP) < 0)
                        return -1;
        }

        module_dir = lp_path(i);
        if (*module_dir == '\0') {
                rprintf(FLOG, "No path specified for module %s\n", name);
                io_printf(f_out, "@ERROR: no path setting.\n");
                return -1;
        }
        if (use_chroot) {
                if ((p = strstr(module_dir, "/./")) != NULL) {
                        *p = '\0'; /* Temporary... */
                        if (!(module_chdir = normalize_path(module_dir, True, NULL)))
                                return path_failure(f_out, module_dir, False);
                        *p = '/';
                        if (!(p = normalize_path(p + 2, True, &module_dirlen)))
                                return path_failure(f_out, strstr(module_dir, "/./"), False);
                        if (!(full_module_path = normalize_path(module_dir, False, NULL)))
                                full_module_path = module_dir;
                        module_dir = p;
                } else {
                        if (!(module_chdir = normalize_path(module_dir, False, NULL)))
                                return path_failure(f_out, module_dir, False);
                        full_module_path = module_chdir;
                        module_dir = "/";
                        module_dirlen = 1;
                }
        } else {
                if (!(module_chdir = normalize_path(module_dir, False, &module_dirlen)))
                        return path_failure(f_out, module_dir, False);
                full_module_path = module_dir = module_chdir;
        }
        set_env_str("RSYNC_MODULE_PATH", full_module_path);

        if (module_dirlen == 1) {
                module_dirlen = 0;
                set_filter_dir("/", 1);
        } else
                set_filter_dir(module_dir, module_dirlen);

        p = lp_filter(i);
        parse_filter_str(&daemon_filter_list, p, rule_template(FILTRULE_WORD_SPLIT),
                   XFLG_ABS_IF_SLASH | XFLG_DIR2WILD3);

        p = lp_include_from(i);
        parse_filter_file(&daemon_filter_list, p, rule_template(FILTRULE_INCLUDE),
            XFLG_ABS_IF_SLASH | XFLG_DIR2WILD3 | XFLG_OLD_PREFIXES | XFLG_FATAL_ERRORS);

        p = lp_include(i);
        parse_filter_str(&daemon_filter_list, p,
                   rule_template(FILTRULE_INCLUDE | FILTRULE_WORD_SPLIT),
                   XFLG_ABS_IF_SLASH | XFLG_DIR2WILD3 | XFLG_OLD_PREFIXES);

        p = lp_exclude_from(i);
        parse_filter_file(&daemon_filter_list, p, rule_template(0),
            XFLG_ABS_IF_SLASH | XFLG_DIR2WILD3 | XFLG_OLD_PREFIXES | XFLG_FATAL_ERRORS);

        p = lp_exclude(i);
        parse_filter_str(&daemon_filter_list, p, rule_template(FILTRULE_WORD_SPLIT),
                   XFLG_ABS_IF_SLASH | XFLG_DIR2WILD3 | XFLG_OLD_PREFIXES);

        log_init(1);

#ifdef HAVE_PUTENV
        if (*lp_prexfer_exec(i) || *lp_postxfer_exec(i)) {
                int status;

                /* For post-xfer exec, fork a new process to run the rsync
                 * daemon while this process waits for the exit status and
                 * runs the indicated command at that point. */
                if (*lp_postxfer_exec(i)) {
                        pid_t pid = fork();
                        if (pid < 0) {
                                rsyserr(FLOG, errno, "fork failed");
                                io_printf(f_out, "@ERROR: fork failed\n");
                                return -1;
                        }
                        if (pid) {
                                close(f_in);
                                if (f_out != f_in)
                                        close(f_out);
                                set_env_num("RSYNC_PID", (long)pid);
                                if (wait_process(pid, &status, 0) < 0)
                                        status = -1;
                                set_env_num("RSYNC_RAW_STATUS", status);
                                if (WIFEXITED(status))
                                        status = WEXITSTATUS(status);
                                else
                                        status = -1;
                                set_env_num("RSYNC_EXIT_STATUS", status);
                                if (system(lp_postxfer_exec(i)) < 0)
                                        status = -1;
                                _exit(status);
                        }
                }
                /* For pre-xfer exec, fork a child process to run the indicated
                 * command, though it first waits for the parent process to
                 * send us the user's request via a pipe. */
                if (*lp_prexfer_exec(i)) {
                        int fds[2];
                        set_env_num("RSYNC_PID", (long)getpid());
                        if (pipe(fds) < 0 || (pre_exec_pid = fork()) < 0) {
                                rsyserr(FLOG, errno, "pre-xfer exec preparation failed");
                                io_printf(f_out, "@ERROR: pre-xfer exec preparation failed\n");
                                return -1;
                        }
                        if (pre_exec_pid == 0) {
                                char buf[BIGPATHBUFLEN];
                                int j, len;
                                close(fds[1]);
                                set_blocking(fds[0]);
                                len = read_arg_from_pipe(fds[0], buf, BIGPATHBUFLEN);
                                if (len <= 0)
                                        _exit(1);
                                set_env_str("RSYNC_REQUEST", buf);
                                for (j = 0; ; j++) {
                                        len = read_arg_from_pipe(fds[0], buf,
                                                                 BIGPATHBUFLEN);
                                        if (len <= 0) {
                                                if (!len)
                                                        break;
                                                _exit(1);
                                        }
                                        if (asprintf(&p, "RSYNC_ARG%d=%s", j, buf) > 0)
                                                putenv(p);
                                }
                                close(fds[0]);
                                close(STDIN_FILENO);
                                close(STDOUT_FILENO);
                                status = system(lp_prexfer_exec(i));
                                if (!WIFEXITED(status))
                                        _exit(1);
                                _exit(WEXITSTATUS(status));
                        }
                        close(fds[0]);
                        set_blocking(fds[1]);
                        pre_exec_fd = fds[1];
                }
        }
#endif

        if (use_chroot) {
                /*
                 * XXX: The 'use chroot' flag is a fairly reliable
                 * source of confusion, because it fails under two
                 * important circumstances: running as non-root,
                 * running on Win32 (or possibly others).  On the
                 * other hand, if you are running as root, then it
                 * might be better to always use chroot.
                 *
                 * So, perhaps if we can't chroot we should just issue
                 * a warning, unless a "require chroot" flag is set,
                 * in which case we fail.
                 */
                if (chroot(module_chdir)) {
                        rsyserr(FLOG, errno, "chroot %s failed", module_chdir);
                        io_printf(f_out, "@ERROR: chroot failed\n");
                        return -1;
                }
                module_chdir = module_dir;
        }

        if (!change_dir(module_chdir, CD_NORMAL))
                return path_failure(f_out, module_chdir, True);
        if (module_dirlen || !use_chroot)
                sanitize_paths = 1;

        if ((munge_symlinks = lp_munge_symlinks(i)) < 0)
                munge_symlinks = !use_chroot || module_dirlen;
        if (munge_symlinks) {
                STRUCT_STAT st;
                char prefix[SYMLINK_PREFIX_LEN]; /* NOT +1 ! */
                strlcpy(prefix, SYMLINK_PREFIX, sizeof prefix); /* trim the trailing slash */
                if (do_stat(prefix, &st) == 0 && S_ISDIR(st.st_mode)) {
                        rprintf(FLOG, "Symlink munging is unsafe when a %s directory exists.\n",
                                prefix);
                        io_printf(f_out, "@ERROR: daemon security issue -- contact admin\n", name);
                        exit_cleanup(RERR_UNSUPPORTED);
                }
        }

        if (gid_count) {
                if (setgid(gid_list[0])) {
                        rsyserr(FLOG, errno, "setgid %ld failed", (long)gid_list[0]);
                        io_printf(f_out, "@ERROR: setgid failed\n");
                        return -1;
                }
#ifdef HAVE_SETGROUPS
                /* Set the group(s) we want to be active. */
                if (setgroups(gid_count, gid_list)) {
                        rsyserr(FLOG, errno, "setgroups failed");
                        io_printf(f_out, "@ERROR: setgroups failed\n");
                        return -1;
                }
#endif
#if defined HAVE_INITGROUPS && !defined HAVE_GETGROUPLIST
                /* pw is set if the user wants all the user's groups. */
                if (pw && initgroups(pw->pw_name, pw->pw_gid) < 0) {
                        rsyserr(FLOG, errno, "initgroups failed");
                        io_printf(f_out, "@ERROR: initgroups failed\n");
                        return -1;
                }
#endif
        }

        if (set_uid) {
                if (setuid(uid) < 0
#ifdef HAVE_SETEUID
                 || seteuid(uid) < 0
#endif
                ) {
                        rsyserr(FLOG, errno, "setuid %ld failed", (long)uid);
                        io_printf(f_out, "@ERROR: setuid failed\n");
                        return -1;
                }

                am_root = (MY_UID() == 0);
        }

        if (lp_temp_dir(i) && *lp_temp_dir(i)) {
                tmpdir = lp_temp_dir(i);
                if (strlen(tmpdir) >= MAXPATHLEN - 10) {
                        rprintf(FLOG,
                                "the 'temp dir' value for %s is WAY too long -- ignoring.\n",
                                name);
                        tmpdir = NULL;
                }
        }

        io_printf(f_out, "@RSYNCD: OK\n");

        read_args(f_in, name, line, sizeof line, rl_nulls, &argv, &argc, &request);
        orig_argv = argv;

        save_munge_symlinks = munge_symlinks;

        reset_output_levels(); /* future verbosity is controlled by client options */
        ret = parse_arguments(&argc, (const char ***) &argv);
        if (protect_args && ret) {
                orig_early_argv = orig_argv;
                protect_args = 2;
                read_args(f_in, name, line, sizeof line, 1, &argv, &argc, &request);
                orig_argv = argv;
                ret = parse_arguments(&argc, (const char ***) &argv);
        } else
                orig_early_argv = NULL;

        munge_symlinks = save_munge_symlinks; /* The client mustn't control this. */

        if (pre_exec_pid) {
                err_msg = finish_pre_exec(pre_exec_pid, pre_exec_fd, request,
                                          orig_early_argv, orig_argv);
        }

        if (orig_early_argv)
                free(orig_early_argv);

        am_server = 1; /* Don't let someone try to be tricky. */
        quiet = 0;
        if (lp_ignore_errors(module_id))
                ignore_errors = 1;
        if (write_batch < 0)
                dry_run = 1;

        if (lp_fake_super(i)) {
                if (preserve_xattrs > 1)
                        preserve_xattrs = 1;
                am_root = -1;
        } else if (am_root < 0) /* Treat --fake-super from client as --super. */
                am_root = 2;

        if (filesfrom_fd == 0)
                filesfrom_fd = f_in;

        if (request) {
                if (*auth_user) {
                        rprintf(FLOG, "rsync %s %s from %s@%s (%s)\n",
                                am_sender ? "on" : "to",
                                request, auth_user, host, addr);
                } else {
                        rprintf(FLOG, "rsync %s %s from %s (%s)\n",
                                am_sender ? "on" : "to",
                                request, host, addr);
                }
                free(request);
        }

#ifndef DEBUG
        /* don't allow the logs to be flooded too fast */
        limit_output_verbosity(lp_max_verbosity(i));
#endif

        if (protocol_version < 23
            && (protocol_version == 22 || am_sender))
                io_start_multiplex_out(f_out);
        else if (!ret || err_msg) {
                /* We have to get I/O multiplexing started so that we can
                 * get the error back to the client.  This means getting
                 * the protocol setup finished first in later versions. */
                setup_protocol(f_out, f_in);
                if (!am_sender) {
                        /* Since we failed in our option parsing, we may not
                         * have finished parsing that the client sent us a
                         * --files-from option, so look for it manually.
                         * Without this, the socket would be in the wrong
                         * state for the upcoming error message. */
                        if (!files_from) {
                                int i;
                                for (i = 0; i < argc; i++) {
                                        if (strncmp(argv[i], "--files-from", 12) == 0) {
                                                files_from = "";
                                                break;
                                        }
                                }
                        }
                        if (files_from)
                                write_byte(f_out, 0);
                }
                io_start_multiplex_out(f_out);
        }

        if (!ret || err_msg) {
                if (err_msg)
                        rwrite(FERROR, err_msg, strlen(err_msg), 0);
                else
                        option_error();
                msleep(400);
                exit_cleanup(RERR_UNSUPPORTED);
        }

#ifdef ICONV_OPTION
        if (!iconv_opt) {
                if (ic_send != (iconv_t)-1) {
                        iconv_close(ic_send);
                        ic_send = (iconv_t)-1;
                }
                if (ic_recv != (iconv_t)-1) {
                        iconv_close(ic_recv);
                        ic_recv = (iconv_t)-1;
                }
        }
#endif

        if (!numeric_ids
         && (use_chroot ? lp_numeric_ids(i) != False : lp_numeric_ids(i) == True))
                numeric_ids = -1; /* Set --numeric-ids w/o breaking protocol. */

        if (lp_timeout(i) && (!io_timeout || lp_timeout(i) < io_timeout))
                set_io_timeout(lp_timeout(i));

        /* If we have some incoming/outgoing chmod changes, append them to
         * any user-specified changes (making our changes have priority).
         * We also get a pointer to just our changes so that a receiver
         * process can use them separately if --perms wasn't specified. */
        if (am_sender)
                p = lp_outgoing_chmod(i);
        else
                p = lp_incoming_chmod(i);
        if (*p && !(daemon_chmod_modes = parse_chmod(p, &chmod_modes))) {
                rprintf(FLOG, "Invalid \"%sing chmod\" directive: %s\n",
                        am_sender ? "outgo" : "incom", p);
        }

        start_server(f_in, f_out, argc, argv);

        return 0;
}

/* send a list of available modules to the client. Don't list those
   with "list = False". */
static void send_listing(int fd)
{
        int n = lp_num_modules();
        int i;

        for (i = 0; i < n; i++) {
                if (lp_list(i))
                        io_printf(fd, "%-15s\t%s\n", lp_name(i), lp_comment(i));
        }

        if (protocol_version >= 25)
                io_printf(fd,"@RSYNCD: EXIT\n");
}

static int load_config(int globals_only)
{
        if (!config_file) {
                if (am_server && am_root <= 0)
                        config_file = RSYNCD_USERCONF;
                else
                        config_file = RSYNCD_SYSCONF;
        }
        return lp_load(config_file, globals_only);
}

/* this is called when a connection is established to a client
   and we want to start talking. The setup of the system is done from
   here */
int start_daemon(int f_in, int f_out)
{
        char line[1024];
        const char *addr, *host;
        int i;

        io_set_sock_fds(f_in, f_out);

        /* We must load the config file before calling any function that
         * might cause log-file output to occur.  This ensures that the
         * "log file" param gets honored for the 2 non-forked use-cases
         * (when rsync is run by init and run by a remote shell). */
        if (!load_config(0))
                exit_cleanup(RERR_SYNTAX);

        addr = client_addr(f_in);
        host = lp_reverse_lookup(-1) ? client_name(f_in) : undetermined_hostname;
        rprintf(FLOG, "connect from %s (%s)\n", host, addr);

        if (!am_server) {
                set_socket_options(f_in, "SO_KEEPALIVE");
                set_nonblocking(f_in);
        }

        if (exchange_protocols(f_in, f_out, line, sizeof line, 0) < 0)
                return -1;

        line[0] = 0;
        if (!read_line_old(f_in, line, sizeof line, 0))
                return -1;

        if (!*line || strcmp(line, "#list") == 0) {
                rprintf(FLOG, "module-list request from %s (%s)\n",
                        host, addr);
                send_listing(f_out);
                return -1;
        }

        if (*line == '#') {
                /* it's some sort of command that I don't understand */
                io_printf(f_out, "@ERROR: Unknown command '%s'\n", line);
                return -1;
        }

        if ((i = lp_number(line)) < 0) {
                rprintf(FLOG, "unknown module '%s' tried from %s (%s)\n",
                        line, host, addr);
                io_printf(f_out, "@ERROR: Unknown module '%s'\n", line);
                return -1;
        }

#ifdef HAVE_SIGACTION
        sigact.sa_flags = SA_NOCLDSTOP;
#endif
        SIGACTION(SIGCHLD, remember_children);

        return rsync_module(f_in, f_out, i, addr, host);
}

static void create_pid_file(void)
{
        char *pid_file = lp_pid_file();
        char pidbuf[16];
        pid_t pid = getpid();
        int fd, len;

        if (!pid_file || !*pid_file)
                return;

        cleanup_set_pid(pid);
        if ((fd = do_open(pid_file, O_WRONLY|O_CREAT|O_EXCL, 0666)) == -1) {
          failure:
                cleanup_set_pid(0);
                fprintf(stderr, "failed to create pid file %s: %s\n", pid_file, strerror(errno));
                rsyserr(FLOG, errno, "failed to create pid file %s", pid_file);
                exit_cleanup(RERR_FILEIO);
        }
        snprintf(pidbuf, sizeof pidbuf, "%ld\n", (long)pid);
        len = strlen(pidbuf);
        if (write(fd, pidbuf, len) != len)
                goto failure;
        close(fd);
}

/* Become a daemon, discarding the controlling terminal. */
static void become_daemon(void)
{
        int i;
        pid_t pid = fork();

        if (pid) {
                if (pid < 0) {
                        fprintf(stderr, "failed to fork: %s\n", strerror(errno));
                        exit_cleanup(RERR_FILEIO);
                }
                _exit(0);
        }

        create_pid_file();

        /* detach from the terminal */
#ifdef HAVE_SETSID
        setsid();
#elif defined TIOCNOTTY
        i = open("/dev/tty", O_RDWR);
        if (i >= 0) {
                ioctl(i, (int)TIOCNOTTY, (char *)0);
                close(i);
        }
#endif
        /* make sure that stdin, stdout an stderr don't stuff things
         * up (library functions, for example) */
        for (i = 0; i < 3; i++) {
                close(i);
                open("/dev/null", O_RDWR);
        }
}

int daemon_main(void)
{
        if (is_a_socket(STDIN_FILENO)) {
                int i;

                /* we are running via inetd - close off stdout and
                 * stderr so that library functions (and getopt) don't
                 * try to use them. Redirect them to /dev/null */
                for (i = 1; i < 3; i++) {
                        close(i);
                        open("/dev/null", O_RDWR);
                }

                return start_daemon(STDIN_FILENO, STDIN_FILENO);
        }

        if (!load_config(1)) {
                fprintf(stderr, "Failed to parse config file: %s\n", config_file);
                exit_cleanup(RERR_SYNTAX);
        }
        set_dparams(0);

        if (no_detach)
                create_pid_file();
        else
                become_daemon();

        if (rsync_port == 0 && (rsync_port = lp_rsync_port()) == 0)
                rsync_port = RSYNC_PORT;
        if (bind_address == NULL && *lp_bind_address())
                bind_address = lp_bind_address();

        log_init(0);

        rprintf(FLOG, "rsyncd version %s starting, listening on port %d\n",
                RSYNC_VERSION, rsync_port);
        /* TODO: If listening on a particular address, then show that
         * address too.  In fact, why not just do inet_ntop on the
         * local address??? */

        start_accept_loop(rsync_port, start_daemon);
        return -1;
}