lbbs/src/net_server.c

/* SPDX-License-Identifier: GPL-3.0-or-later */
/*
 * net_server
 *   - network server with SSH support
 *
 * Copyright (C) 2004-2025  Leaflet <leaflet@leafok.com>
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "bbs.h"
#include "bbs_main.h"
#include "bwf.h"
#include "common.h"
#include "database.h"
#include "file_loader.h"
#include "hash_dict.h"
#include "io.h"
#include "init.h"
#include "log.h"
#include "login.h"
#include "menu.h"
#include "net_server.h"
#include "section_list.h"
#include "section_list_loader.h"
#include <errno.h>
#include <fcntl.h>
#include <pty.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <utmp.h>
#include <arpa/inet.h>
#include <libssh/callbacks.h>
#include <libssh/libssh.h>
#include <libssh/server.h>
#include <netinet/in.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

#ifdef HAVE_SYS_EPOLL_H
#include <sys/epoll.h>
#else
#include <poll.h>
#endif

#ifdef HAVE_SYSTEMD_SD_DAEMON_H
#include <systemd/sd-daemon.h>
#endif

enum _net_server_constant_t
{
        WAIT_CHILD_PROCESS_EXIT_TIMEOUT = 5, // second
        WAIT_CHILD_PROCESS_KILL_TIMEOUT = 1, // second

        SSH_AUTH_MAX_DURATION = 60 * 1000, // milliseconds
};

/* A userdata struct for session. */
struct session_data_struct
{
        int tries;
        int error;
};

/* A userdata struct for channel. */
struct channel_data_struct
{
        /* pid of the child process the channel will spawn. */
        pid_t pid;
        /* For PTY allocation */
        socket_t pty_master;
        socket_t pty_slave;
        /* For communication with the child process. */
        socket_t child_stdin;
        socket_t child_stdout;
        /* Only used for subsystem and exec requests. */
        socket_t child_stderr;
        /* Event which is used to poll the above descriptors. */
        ssh_event event;
        /* Terminal size struct. */
        struct winsize *winsize;
};

static int socket_server[2];
static int socket_client;

#ifdef HAVE_SYS_EPOLL_H
static int epollfd_server = -1;
#endif

static ssh_bind sshbind;

static HASH_DICT *hash_dict_pid_sockaddr = NULL;
static HASH_DICT *hash_dict_sockaddr_count = NULL;

static const char SFTP_SERVER_PATH[] = "/usr/lib/sftp-server";

static int auth_password(ssh_session session, const char *user,
                                                 const char *password, void *userdata)
{
        struct session_data_struct *sdata = (struct session_data_struct *)userdata;
        int ret;

        if (strcmp(user, "guest") == 0)
        {
                ret = load_guest_info();
        }
        else
        {
                ret = check_user(user, password);
                if (ret == 2) // Enforce update user agreement
                {
                        BBS_update_eula = 1;
                        ret = 0;
                }
        }

        if (ret == 0)
        {
                return SSH_AUTH_SUCCESS;
        }

        if ((++(sdata->tries)) >= BBS_login_retry_times)
        {
                sdata->error = 1;
        }

        return SSH_AUTH_DENIED;
}

static int pty_request(ssh_session session, ssh_channel channel, const char *term,
                                           int cols, int rows, int px, int py, void *userdata)
{
        struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;
        int rc;

        (void)session;
        (void)channel;
        (void)term;

        cdata->winsize->ws_row = (unsigned short int)rows;
        cdata->winsize->ws_col = (unsigned short int)cols;
        cdata->winsize->ws_xpixel = (unsigned short int)px;
        cdata->winsize->ws_ypixel = (unsigned short int)py;

        rc = openpty(&cdata->pty_master, &cdata->pty_slave, NULL, NULL, cdata->winsize);
        if (rc != 0)
        {
                log_error("Failed to open pty");
                return SSH_ERROR;
        }

        return SSH_OK;
}

static int pty_resize(ssh_session session, ssh_channel channel, int cols, int rows,
                                          int py, int px, void *userdata)
{
        struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;

        (void)session;
        (void)channel;

        cdata->winsize->ws_row = (unsigned short int)rows;
        cdata->winsize->ws_col = (unsigned short int)cols;
        cdata->winsize->ws_xpixel = (unsigned short int)px;
        cdata->winsize->ws_ypixel = (unsigned short int)py;

        if (cdata->pty_master != -1)
        {
                return ioctl(cdata->pty_master, TIOCSWINSZ, cdata->winsize);
        }

        return SSH_ERROR;
}

static int exec_pty(const char *mode, const char *command, struct channel_data_struct *cdata)
{
        (void)cdata;

        if (command != NULL)
        {
                log_error("Forbid exec /bin/sh %s %s)", mode, command);
        }

        return SSH_OK;
}

static int exec_nopty(const char *command, struct channel_data_struct *cdata)
{
        (void)cdata;

        if (command != NULL)
        {
                log_error("Forbid exec /bin/sh -c %s)", command);
        }

        return SSH_OK;
}

static int exec_request(ssh_session session, ssh_channel channel, const char *command, void *userdata)
{
        struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;

        (void)session;
        (void)channel;

        if (cdata->pid > 0)
        {
                return SSH_ERROR;
        }

        if (cdata->pty_master != -1 && cdata->pty_slave != -1)
        {
                return exec_pty("-c", command, cdata);
        }
        return exec_nopty(command, cdata);
}

static int shell_request(ssh_session session, ssh_channel channel, void *userdata)
{
        struct channel_data_struct *cdata = (struct channel_data_struct *)userdata;

        (void)session;
        (void)channel;

        if (cdata->pid > 0)
        {
                return SSH_ERROR;
        }

        if (cdata->pty_master != -1 && cdata->pty_slave != -1)
        {
                return exec_pty("-l", NULL, cdata);
        }
        /* Client requested a shell without a pty, let's pretend we allow that */
        return SSH_OK;
}

static int subsystem_request(ssh_session session, ssh_channel channel, const char *subsystem, void *userdata)
{
        (void)session;
        (void)channel;

        log_error("subsystem_request(subsystem=%s)", subsystem);

        /* subsystem requests behave similarly to exec requests. */
        if (strcmp(subsystem, "sftp") == 0)
        {
                return exec_request(session, channel, SFTP_SERVER_PATH, userdata);
        }
        return SSH_ERROR;
}

static ssh_channel channel_open(ssh_session session, void *userdata)
{
        (void)userdata;

        if (SSH_channel != NULL)
        {
                return NULL;
        }

        SSH_channel = ssh_channel_new(session);

        return SSH_channel;
}

static int fork_server(void)
{
        ssh_event event;
        long int ssh_timeout = 0;
        int pid;
        int i;
        int ret;

        /* Structure for storing the pty size. */
        struct winsize wsize = {
                .ws_row = 0,
                .ws_col = 0,
                .ws_xpixel = 0,
                .ws_ypixel = 0};

        /* Our struct holding information about the channel. */
        struct channel_data_struct cdata = {
                .pid = 0,
                .pty_master = -1,
                .pty_slave = -1,
                .child_stdin = -1,
                .child_stdout = -1,
                .child_stderr = -1,
                .event = NULL,
                .winsize = &wsize};

        struct session_data_struct cb_data = {
                .tries = 0,
                .error = 0,
        };

        struct ssh_channel_callbacks_struct channel_cb = {
                .userdata = &cdata,
                .channel_pty_request_function = pty_request,
                .channel_pty_window_change_function = pty_resize,
                .channel_shell_request_function = shell_request,
                .channel_exec_request_function = exec_request,
                .channel_subsystem_request_function = subsystem_request};

        struct ssh_server_callbacks_struct server_cb = {
                .userdata = &cb_data,
                .auth_password_function = auth_password,
                .channel_open_request_session_function = channel_open,
        };

        pid = fork();

        if (pid > 0) // Parent process
        {
                SYS_child_process_count++;
                log_common("Child process (%d) start", pid);
                return pid;
        }
        else if (pid < 0) // Error
        {
                log_error("fork() error (%d)", errno);
                return -1;
        }

        // Child process
#ifdef HAVE_SYS_EPOLL_H
        if (close(epollfd_server) < 0)
        {
                log_error("close(epollfd_server) error (%d)");
        }
#endif

        for (i = 0; i < 2; i++)
        {
                if (close(socket_server[i]) == -1)
                {
                        log_error("Close server socket failed");
                }
        }

        hash_dict_destroy(hash_dict_pid_sockaddr);
        hash_dict_destroy(hash_dict_sockaddr_count);

        SSH_session = ssh_new();

        if (SSH_v2)
        {
                if (ssh_bind_accept_fd(sshbind, SSH_session, socket_client) != SSH_OK)
                {
                        log_error("ssh_bind_accept_fd() error: %s", ssh_get_error(SSH_session));
                        goto cleanup;
                }

                ssh_bind_free(sshbind);

                ssh_timeout = 60; // second
                if (ssh_options_set(SSH_session, SSH_OPTIONS_TIMEOUT, &ssh_timeout) < 0)
                {
                        log_error("Error setting SSH options: %s", ssh_get_error(SSH_session));
                        goto cleanup;
                }

                ssh_set_auth_methods(SSH_session, SSH_AUTH_METHOD_PASSWORD);

                ssh_callbacks_init(&server_cb);
                ssh_callbacks_init(&channel_cb);

                ssh_set_server_callbacks(SSH_session, &server_cb);

                if (ssh_handle_key_exchange(SSH_session))
                {
                        log_error("ssh_handle_key_exchange() error: %s", ssh_get_error(SSH_session));
                        goto cleanup;
                }

                event = ssh_event_new();
                ssh_event_add_session(event, SSH_session);

                for (i = 0; i < SSH_AUTH_MAX_DURATION && !SYS_server_exit && !cb_data.error && SSH_channel == NULL; i += 100)
                {
                        ret = ssh_event_dopoll(event, 100); // 0.1 second
                        if (ret == SSH_ERROR)
                        {
                                log_debug("ssh_event_dopoll() error: %s", ssh_get_error(SSH_session));
                                goto cleanup;
                        }
                }

                if (cb_data.error)
                {
                        log_error("SSH auth error, tried %d times", cb_data.tries);
                        goto cleanup;
                }

                ssh_set_channel_callbacks(SSH_channel, &channel_cb);

                do
                {
                        ret = ssh_event_dopoll(event, 100); // 0.1 second
                        if (ret == SSH_ERROR)
                        {
                                ssh_channel_close(SSH_channel);
                        }

                        if (ret == SSH_AGAIN) // loop until SSH connection is fully established
                        {
                                /* Executed only once, once the child process starts. */
                                cdata.event = event;
                                break;
                        }
                } while (ssh_channel_is_open(SSH_channel));

                ssh_timeout = 0;
                if (ssh_options_set(SSH_session, SSH_OPTIONS_TIMEOUT, &ssh_timeout) < 0)
                {
                        log_error("Error setting SSH options: %s", ssh_get_error(SSH_session));
                        goto cleanup;
                }

                ssh_set_blocking(SSH_session, 0);
        }

        // Redirect Input
        if (dup2(socket_client, STDIN_FILENO) == -1)
        {
                log_error("Redirect stdin to client socket failed");
                goto cleanup;
        }

        // Redirect Output
        if (dup2(socket_client, STDOUT_FILENO) == -1)
        {
                log_error("Redirect stdout to client socket failed");
                goto cleanup;
        }

        if (io_init() < 0)
        {
                log_error("io_init() error");
                goto cleanup;
        }

        SYS_child_process_count = 0;

        // BWF compile
        if (bwf_compile() < 0)
        {
                log_error("bwf_compile() error");
                goto cleanup;
        }

        bbs_main();

cleanup:
        // Child process exit
        SYS_server_exit = 1;

        if (SSH_v2)
        {
                if (cdata.pty_master != -1)
                {
                        close(cdata.pty_master);
                }
                if (cdata.child_stdin != -1)
                {
                        close(cdata.child_stdin);
                }
                if (cdata.child_stdout != -1)
                {
                        close(cdata.child_stdout);
                }
                if (cdata.child_stderr != -1)
                {
                        close(cdata.child_stderr);
                }

                ssh_channel_free(SSH_channel);
                ssh_disconnect(SSH_session);
        }
        else if (close(socket_client) == -1)
        {
                log_error("Close client socket failed");
        }

        ssh_free(SSH_session);
        ssh_finalize();

        // BWF cleanup
        bwf_cleanup();

        // Close Input and Output for client
        io_cleanup();
        close(STDIN_FILENO);
        close(STDOUT_FILENO);

        log_common("Process exit normally");
        log_end();

        _exit(0);

        return 0;
}

int net_server(const char *hostaddr, in_port_t port[])
{
        struct stat file_stat;
        unsigned int addrlen;
        int ret;
        int flags_server[2];
        struct sockaddr_in sin;

#ifdef HAVE_SYS_EPOLL_H
        struct epoll_event ev, events[MAX_EVENTS];
#else
        struct pollfd pfds[2];
#endif

        int nfds;
        int notify_child_exit = 0;
        time_t tm_notify_child_exit = time(NULL);
        pid_t pid;
        int ssh_key_valid = 0;
        int ssh_log_level = SSH_LOG_NOLOG;

#ifdef HAVE_SYSTEMD_SD_DAEMON_H
        int sd_notify_stopping = 0;
#endif

        ssh_init();

        sshbind = ssh_bind_new();

        if (ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_HOSTKEY, SSH_HOST_RSA_KEY_FILE) < 0)
        {
                log_error("Error loading SSH RSA key: %s", SSH_HOST_RSA_KEY_FILE);
        }
        else
        {
                ssh_key_valid = 1;
        }
        if (ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_HOSTKEY, SSH_HOST_ED25519_KEY_FILE) < 0)
        {
                log_error("Error loading SSH ED25519 key: %s", SSH_HOST_ED25519_KEY_FILE);
        }
        else
        {
                ssh_key_valid = 1;
        }
        if (ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_HOSTKEY, SSH_HOST_ECDSA_KEY_FILE) < 0)
        {
                log_error("Error loading SSH ECDSA key: %s", SSH_HOST_ECDSA_KEY_FILE);
        }
        else
        {
                ssh_key_valid = 1;
        }

        if (!ssh_key_valid)
        {
                log_error("Error: no valid SSH host key");
                ssh_bind_free(sshbind);
                return -1;
        }

        if (ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_BINDADDR, hostaddr) < 0 ||
                ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_BINDPORT, &port) < 0 ||
                ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_HOSTKEY_ALGORITHMS, "+ssh-ed25519,ecdsa-sha2-nistp256,ssh-rsa") < 0 ||
                ssh_bind_options_set(sshbind, SSH_BIND_OPTIONS_LOG_VERBOSITY, &ssh_log_level) < 0)
        {
                log_error("Error setting SSH bind options: %s", ssh_get_error(sshbind));
                ssh_bind_free(sshbind);
                return -1;
        }

#ifdef HAVE_SYS_EPOLL_H
        epollfd_server = epoll_create1(0);
        if (epollfd_server == -1)
        {
                log_error("epoll_create1() error (%d)", errno);
                return -1;
        }
#endif

        // Server socket
        for (int i = 0; i < 2; i++)
        {
                socket_server[i] = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

                if (socket_server[i] < 0)
                {
                        log_error("Create socket_server error (%d)", errno);
                        return -1;
                }

                sin.sin_family = AF_INET;
                sin.sin_addr.s_addr = (hostaddr[0] != '\0' ? inet_addr(hostaddr) : INADDR_ANY);
                sin.sin_port = htons(port[i]);

                // Reuse address and port
                flags_server[i] = 1;
                if (setsockopt(socket_server[i], SOL_SOCKET, SO_REUSEADDR, &flags_server[i], sizeof(flags_server[i])) < 0)
                {
                        log_error("setsockopt SO_REUSEADDR error (%d)", errno);
                }
#if defined(SO_REUSEPORT)
                if (setsockopt(socket_server[i], SOL_SOCKET, SO_REUSEPORT, &flags_server[i], sizeof(flags_server[i])) < 0)
                {
                        log_error("setsockopt SO_REUSEPORT error (%d)", errno);
                }
#endif

                if (bind(socket_server[i], (struct sockaddr *)&sin, sizeof(sin)) < 0)
                {
                        log_error("Bind address %s:%u error (%d)",
                                          inet_ntoa(sin.sin_addr), ntohs(sin.sin_port), errno);
                        return -1;
                }

                if (listen(socket_server[i], 10) < 0)
                {
                        log_error("Telnet socket listen error (%d)", errno);
                        return -1;
                }

                log_common("Listening at %s:%u", inet_ntoa(sin.sin_addr), ntohs(sin.sin_port));

#ifdef HAVE_SYS_EPOLL_H
                ev.events = EPOLLIN;
                ev.data.fd = socket_server[i];
                if (epoll_ctl(epollfd_server, EPOLL_CTL_ADD, socket_server[i], &ev) == -1)
                {
                        log_error("epoll_ctl(socket_server[%d]) error (%d)", i, errno);
                        if (close(epollfd_server) < 0)
                        {
                                log_error("close(epoll) error (%d)");
                        }
                        return -1;
                }
#endif

                flags_server[i] = fcntl(socket_server[i], F_GETFL, 0);
                fcntl(socket_server[i], F_SETFL, flags_server[i] | O_NONBLOCK);
        }

        ssh_bind_set_blocking(sshbind, 0);

        hash_dict_pid_sockaddr = hash_dict_create(MAX_CLIENT_LIMIT);
        if (hash_dict_pid_sockaddr == NULL)
        {
                log_error("hash_dict_create(hash_dict_pid_sockaddr) error");
                return -1;
        }
        hash_dict_sockaddr_count = hash_dict_create(MAX_CLIENT_LIMIT);
        if (hash_dict_sockaddr_count == NULL)
        {
                log_error("hash_dict_create(hash_dict_sockaddr_count) error");
                return -1;
        }

        // Startup complete
#ifdef HAVE_SYSTEMD_SD_DAEMON_H
        sd_notifyf(0, "READY=1\n"
                                  "STATUS=Listening at %s:%d (Telnet) and %s:%d (SSH2)\n"
                                  "MAINPID=%d",
                           hostaddr, port[0], hostaddr, port[1], getpid());
#endif

        while (!SYS_server_exit || SYS_child_process_count > 0)
        {
#ifdef HAVE_SYSTEMD_SD_DAEMON_H
                if (SYS_server_exit && !sd_notify_stopping)
                {
                        sd_notify(0, "STOPPING=1");
                        sd_notify_stopping = 1;
                }
#endif

                while ((SYS_child_exit || SYS_server_exit) && SYS_child_process_count > 0)
                {
                        SYS_child_exit = 0;

                        pid = waitpid(-1, &ret, WNOHANG);
                        if (pid > 0)
                        {
                                SYS_child_exit = 1; // Retry waitid
                                SYS_child_process_count--;

                                if (WIFEXITED(ret))
                                {
                                        log_common("Child process (%d) exited, status=%d", pid, WEXITSTATUS(ret));
                                }
                                else if (WIFSIGNALED(ret))
                                {
                                        log_common("Child process (%d) is killed, status=%d", pid, WTERMSIG(ret));
                                }
                                else
                                {
                                        log_common("Child process (%d) exited abnormally, status=%d", pid, ret);
                                }

                                if (pid != section_list_loader_pid)
                                {
                                        int64_t j = 0;
                                        ret = hash_dict_get(hash_dict_pid_sockaddr, (uint64_t)pid, &j);
                                        if (ret < 0)
                                        {
                                                log_error("hash_dict_get(hash_dict_pid_sockaddr, %d) error", pid);
                                        }
                                        else
                                        {
                                                ret = hash_dict_inc(hash_dict_sockaddr_count, (in_addr_t)j, -1);
                                                if (ret <= 0)
                                                {
                                                        log_error("hash_dict_inc(hash_dict_sockaddr_count, %lu, -1) error: %d", (in_addr_t)j, ret);
                                                }

                                                ret = hash_dict_del(hash_dict_pid_sockaddr, (uint64_t)pid);
                                                if (ret < 0)
                                                {
                                                        log_error("hash_dict_del(hash_dict_pid_sockaddr, %lu) error", (uint64_t)pid);
                                                }
                                        }
                                }
                        }
                        else if (pid == 0)
                        {
                                break;
                        }
                        else if (pid < 0)
                        {
                                log_error("Error in waitpid(): %d", errno);
                                break;
                        }
                }

                if (SYS_server_exit && !SYS_child_exit && SYS_child_process_count > 0)
                {
                        if (notify_child_exit == 0)
                        {
#ifdef HAVE_SYSTEMD_SD_DAEMON_H
                                sd_notifyf(0, "STATUS=Notify %d child process to exit", SYS_child_process_count);
                                log_common("Notify %d child process to exit", SYS_child_process_count);
#endif

                                if (kill(0, SIGTERM) < 0)
                                {
                                        log_error("Send SIGTERM signal failed (%d)", errno);
                                }

                                notify_child_exit = 1;
                                tm_notify_child_exit = time(NULL);
                        }
                        else if (notify_child_exit == 1 && time(NULL) - tm_notify_child_exit >= WAIT_CHILD_PROCESS_EXIT_TIMEOUT)
                        {
#ifdef HAVE_SYSTEMD_SD_DAEMON_H
                                sd_notifyf(0, "STATUS=Kill %d child process", SYS_child_process_count);
#endif

                                if (kill(0, SIGKILL) < 0)
                                {
                                        log_error("Send SIGKILL signal failed (%d)", errno);
                                }

                                notify_child_exit = 2;
                                tm_notify_child_exit = time(NULL);
                        }
                        else if (notify_child_exit == 2 && time(NULL) - tm_notify_child_exit >= WAIT_CHILD_PROCESS_KILL_TIMEOUT)
                        {
                                log_error("Main process prepare to exit without waiting for %d child process any longer", SYS_child_process_count);
                                SYS_child_process_count = 0;
                        }
                }

                if (SYS_conf_reload && !SYS_server_exit)
                {
                        SYS_conf_reload = 0;

#ifdef HAVE_SYSTEMD_SD_DAEMON_H
                        sd_notify(0, "RELOADING=1");
#endif

                        log_common("Reload configuration");
                        
                        // Restart log
                        if (log_restart() < 0)
                        {
                                log_error("Restart logging failed");
                        }

                        // Reload configuration
                        if (load_conf(CONF_BBSD) < 0)
                        {
                                log_error("Reload conf failed");
                        }

                        // Reload BWF config
                        if (bwf_load(CONF_BWF) < 0)
                        {
                                log_error("Reload BWF conf failed");
                        }

                        // Get EULA modification tm
                        if (stat(DATA_EULA, &file_stat) == -1)
                        {
                                log_error("stat(%s) error", DATA_EULA, errno);
                        }
                        else
                        {
                                BBS_eula_tm = file_stat.st_mtim.tv_sec;
                        }

                        if (detach_menu_shm(&bbs_menu) < 0)
                        {
                                log_error("detach_menu_shm(bbs_menu) error");
                        }
                        if (load_menu(&bbs_menu, CONF_MENU) < 0)
                        {
                                log_error("load_menu(bbs_menu) error");
                                unload_menu(&bbs_menu);
                        }

                        if (detach_menu_shm(&top10_menu) < 0)
                        {
                                log_error("detach_menu_shm(top10_menu) error");
                        }
                        if (load_menu(&top10_menu, CONF_TOP10_MENU) < 0)
                        {
                                log_error("load_menu(top10_menu) error");
                                unload_menu(&top10_menu);
                        }
                        top10_menu.allow_exit = 1;

                        for (int i = 0; i < data_files_load_startup_count; i++)
                        {
                                if (load_file(data_files_load_startup[i]) < 0)
                                {
                                        log_error("load_file(%s) error", data_files_load_startup[i]);
                                }
                        }

                        // Load section config and gen_ex
                        if (load_section_config_from_db(1) < 0)
                        {
                                log_error("load_section_config_from_db(1) error");
                        }

                        // Notify child processes to reload configuration
                        if (kill(0, SIGUSR1) < 0)
                        {
                                log_error("Send SIGUSR1 signal failed (%d)", errno);
                        }

#ifdef HAVE_SYSTEMD_SD_DAEMON_H
                        sd_notify(0, "READY=1");
#endif
                }

#ifdef HAVE_SYS_EPOLL_H
                nfds = epoll_wait(epollfd_server, events, MAX_EVENTS, 100); // 0.1 second
                ret = nfds;
#else
                pfds[0].fd = socket_server[0];
                pfds[0].events = POLLIN;
                pfds[1].fd = socket_server[1];
                pfds[1].events = POLLIN;
                nfds = 2;
                ret = poll(pfds, (nfds_t)nfds, 100); // 0.1 second
#endif
                if (ret < 0)
                {
                        if (errno != EINTR)
                        {
#ifdef HAVE_SYS_EPOLL_H
                                log_error("epoll_wait() error (%d)", errno);
#else
                                log_error("poll() error (%d)", errno);
#endif
                                break;
                        }
                        continue;
                }

                // Stop accept new connection on exit
                if (SYS_server_exit)
                {
                        continue;
                }

                for (int i = 0; i < nfds; i++)
                {
#ifdef HAVE_SYS_EPOLL_H
                        if (events[i].data.fd == socket_server[0] || events[i].data.fd == socket_server[1])
#else
                        if ((pfds[i].fd == socket_server[0] || pfds[i].fd == socket_server[1]) && (pfds[i].revents & POLLIN))
#endif
                        {
#ifdef HAVE_SYS_EPOLL_H
                                SSH_v2 = (events[i].data.fd == socket_server[1] ? 1 : 0);
#else
                                SSH_v2 = (pfds[i].fd == socket_server[1] ? 1 : 0);
#endif

                                while (!SYS_server_exit) // Accept all incoming connections until error
                                {
                                        addrlen = sizeof(sin);
                                        socket_client = accept(socket_server[SSH_v2], (struct sockaddr *)&sin, (socklen_t *)&addrlen);
                                        if (socket_client < 0)
                                        {
                                                if (errno == EAGAIN || errno == EWOULDBLOCK)
                                                {
                                                        break;
                                                }
                                                else if (errno == EINTR)
                                                {
                                                        continue;
                                                }
                                                else
                                                {
                                                        log_error("accept(socket_server) error (%d)", errno);
                                                        break;
                                                }
                                        }

                                        strncpy(hostaddr_client, inet_ntoa(sin.sin_addr), sizeof(hostaddr_client) - 1);
                                        hostaddr_client[sizeof(hostaddr_client) - 1] = '\0';

                                        port_client = ntohs(sin.sin_port);

                                        if (SYS_child_process_count - 1 < BBS_max_client)
                                        {
                                                int64_t j = 0;
                                                ret = hash_dict_get(hash_dict_sockaddr_count, sin.sin_addr.s_addr, &j);
                                                if (ret < 0)
                                                {
                                                        log_error("hash_dict_get(hash_dict_sockaddr_count, %s) error", hostaddr_client);
                                                }

                                                if (j < BBS_max_client_per_ip)
                                                {
                                                        if ((pid = fork_server()) < 0)
                                                        {
                                                                log_error("fork_server() error");
                                                        }
                                                        else if (pid > 0)
                                                        {
                                                                ret = hash_dict_set(hash_dict_pid_sockaddr, (uint64_t)pid, sin.sin_addr.s_addr);
                                                                if (ret < 0)
                                                                {
                                                                        log_error("hash_dict_set(hash_dict_pid_sockaddr, %lu, %s) error", (uint64_t)pid, hostaddr_client);
                                                                }

                                                                if (j == 0)
                                                                {
                                                                        // First connection from this IP
                                                                        log_common("Accept %s connection from %s:%d",
                                                                                           (SSH_v2 ? "SSH" : "telnet"), hostaddr_client, port_client);

                                                                        ret = hash_dict_set(hash_dict_sockaddr_count, (uint64_t)sin.sin_addr.s_addr, 1);
                                                                        if (ret < 0)
                                                                        {
                                                                                log_error("hash_dict_set(hash_dict_sockaddr_count, %s, 1) error", hostaddr_client);
                                                                        }
                                                                }
                                                                else
                                                                {
                                                                        // Increase connection count from this IP
                                                                        log_common("Accept %s connection from %s:%d, already have %d connections",
                                                                                           (SSH_v2 ? "SSH" : "telnet"), hostaddr_client, port_client, j);

                                                                        ret = hash_dict_inc(hash_dict_sockaddr_count, (uint64_t)sin.sin_addr.s_addr, 1);
                                                                        if (ret <= 0)
                                                                        {
                                                                                log_error("hash_dict_inc(hash_dict_sockaddr_count, %s, 1) error: %d", hostaddr_client, ret);
                                                                        }
                                                                }
                                                        }
                                                }
                                                else
                                                {
                                                        log_error("Rejected %s connection from %s:%d over limit per IP (%d >= %d)",
                                                                          (SSH_v2 ? "SSH" : "telnet"), hostaddr_client, port_client, j, BBS_max_client_per_ip);
                                                }
                                        }
                                        else
                                        {
                                                log_error("Rejected %s connection from %s:%d over limit (%d >= %d)",
                                                                  (SSH_v2 ? "SSH" : "telnet"), hostaddr_client, port_client, SYS_child_process_count - 1, BBS_max_client);
                                        }

                                        if (close(socket_client) == -1)
                                        {
                                                log_error("close(socket_lient) error (%d)", errno);
                                        }
                                }
                        }
                }
        }

#ifdef HAVE_SYS_EPOLL_H
        if (close(epollfd_server) < 0)
        {
                log_error("close(epollfd_server) error (%d)");
        }
#endif

        for (int i = 0; i < 2; i++)
        {
                if (close(socket_server[i]) == -1)
                {
                        log_error("Close server socket failed");
                }
        }

        hash_dict_destroy(hash_dict_pid_sockaddr);
        hash_dict_destroy(hash_dict_sockaddr_count);

        ssh_bind_free(sshbind);
        ssh_finalize();

        return 0;
}
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