/* vi: set sw=4 ts=4: */ /* * Simple telnet server * Bjorn Wesen, Axis Communications AB (bjornw@axis.com) * * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. * * --------------------------------------------------------------------------- * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN **************************************************************************** * * The telnetd manpage says it all: * * Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for * a client, then creating a login process which has the slave side of the * pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the * master side of the pseudo-terminal, implementing the telnet protocol and * passing characters between the remote client and the login process. * * Vladimir Oleynik 2001 * Set process group corrections, initial busybox port */ #define DEBUG 0 #include "libbb.h" #if DEBUG #define TELCMDS #define TELOPTS #endif #include #include /* Structure that describes a session */ struct tsession { struct tsession *next; int sockfd_read, sockfd_write, ptyfd; /*int shell_pid;*/ /* two circular buffers */ /*char *buf1, *buf2;*/ /*#define TS_BUF1 ts->buf1*/ /*#define TS_BUF2 TS_BUF2*/ #define TS_BUF1 ((char*)(ts + 1)) #define TS_BUF2 (((char*)(ts + 1)) + BUFSIZE) int rdidx1, wridx1, size1; int rdidx2, wridx2, size2; }; /* Two buffers are directly after tsession in malloced memory. * Make whole thing fit in 4k */ enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 }; /* Globals */ static int maxfd; static struct tsession *sessions; #if ENABLE_LOGIN static const char *loginpath = "/bin/login"; #else static const char *loginpath = DEFAULT_SHELL; #endif static const char *issuefile = "/etc/issue.net"; /* Remove all IAC's from buf1 (received IACs are ignored and must be removed so as to not be interpreted by the terminal). Make an uninterrupted string of characters fit for the terminal. Do this by packing all characters meant for the terminal sequentially towards the end of buf. Return a pointer to the beginning of the characters meant for the terminal. and make *num_totty the number of characters that should be sent to the terminal. Note - If an IAC (3 byte quantity) starts before (bf + len) but extends past (bf + len) then that IAC will be left unprocessed and *processed will be less than len. FIXME - if we mean to send 0xFF to the terminal then it will be escaped, what is the escape character? We aren't handling that situation here. CR-LF ->'s CR mapping is also done here, for convenience */ static char * remove_iacs(struct tsession *ts, int *pnum_totty) { unsigned char *ptr0 = (unsigned char *)TS_BUF1 + ts->wridx1; unsigned char *ptr = ptr0; unsigned char *totty = ptr; unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1); int processed; int num_totty; while (ptr < end) { if (*ptr != IAC) { int c = *ptr; *totty++ = *ptr++; /* We now map \r\n ==> \r for pragmatic reasons. * Many client implementations send \r\n when * the user hits the CarriageReturn key. */ if (c == '\r' && (*ptr == '\n' || *ptr == 0) && ptr < end) ptr++; } else { /* * TELOPT_NAWS support! */ if ((ptr+2) >= end) { /* only the beginning of the IAC is in the buffer we were asked to process, we can't process this char. */ break; } /* * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE */ else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) { struct winsize ws; if ((ptr+8) >= end) break; /* incomplete, can't process */ ws.ws_col = (ptr[3] << 8) | ptr[4]; ws.ws_row = (ptr[5] << 8) | ptr[6]; ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws); ptr += 9; } else { /* skip 3-byte IAC non-SB cmd */ #if DEBUG fprintf(stderr, "Ignoring IAC %s,%s\n", TELCMD(ptr[1]), TELOPT(ptr[2])); #endif ptr += 3; } } } processed = ptr - ptr0; num_totty = totty - ptr0; /* the difference between processed and num_to tty is all the iacs we removed from the stream. Adjust buf1 accordingly. */ ts->wridx1 += processed - num_totty; ts->size1 -= processed - num_totty; *pnum_totty = num_totty; /* move the chars meant for the terminal towards the end of the buffer. */ return memmove(ptr - num_totty, ptr0, num_totty); } static int getpty(char *line, int size) { int p; #if ENABLE_FEATURE_DEVPTS p = open("/dev/ptmx", O_RDWR); if (p > 0) { const char *name; grantpt(p); unlockpt(p); name = ptsname(p); if (!name) { bb_perror_msg("ptsname error (is /dev/pts mounted?)"); return -1; } safe_strncpy(line, name, size); return p; } #else struct stat stb; int i; int j; strcpy(line, "/dev/ptyXX"); for (i = 0; i < 16; i++) { line[8] = "pqrstuvwxyzabcde"[i]; line[9] = '0'; if (stat(line, &stb) < 0) { continue; } for (j = 0; j < 16; j++) { line[9] = j < 10 ? j + '0' : j - 10 + 'a'; if (DEBUG) fprintf(stderr, "Trying to open device: %s\n", line); p = open(line, O_RDWR | O_NOCTTY); if (p >= 0) { line[5] = 't'; return p; } } } #endif /* FEATURE_DEVPTS */ return -1; } static struct tsession * make_new_session( USE_FEATURE_TELNETD_STANDALONE(int sock_r, int sock_w) SKIP_FEATURE_TELNETD_STANDALONE(void) ) { const char *login_argv[2]; struct termios termbuf; int fd, pid; char tty_name[32]; struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2); /*ts->buf1 = (char *)(ts + 1);*/ /*ts->buf2 = ts->buf1 + BUFSIZE;*/ /* Got a new connection, set up a tty. */ fd = getpty(tty_name, 32); if (fd < 0) { bb_error_msg("can't create pty"); return NULL; } if (fd > maxfd) maxfd = fd; ts->ptyfd = fd; ndelay_on(fd); #if ENABLE_FEATURE_TELNETD_STANDALONE if (sock_w > maxfd) maxfd = sock_w; ts->sockfd_write = sock_w; ndelay_on(sock_w); if (sock_r > maxfd) maxfd = sock_r; ts->sockfd_read = sock_r; ndelay_on(sock_r); #else ts->sockfd_write = 1; /* ts->sockfd_read = 0; - done by xzalloc */ ndelay_on(0); ndelay_on(1); #endif /* Make the telnet client understand we will echo characters so it * should not do it locally. We don't tell the client to run linemode, * because we want to handle line editing and tab completion and other * stuff that requires char-by-char support. */ { static const char iacs_to_send[] ALIGN1 = { IAC, DO, TELOPT_ECHO, IAC, DO, TELOPT_NAWS, IAC, DO, TELOPT_LFLOW, IAC, WILL, TELOPT_ECHO, IAC, WILL, TELOPT_SGA }; memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send)); ts->rdidx2 = sizeof(iacs_to_send); ts->size2 = sizeof(iacs_to_send); } fflush(NULL); /* flush all streams */ pid = vfork(); /* NOMMU-friendly */ if (pid < 0) { free(ts); close(fd); /* sock_r and sock_w will be closed by caller */ bb_perror_msg("vfork"); return NULL; } if (pid > 0) { /* Parent */ /*ts->shell_pid = pid;*/ return ts; } /* Child */ /* Careful - we are after vfork! */ /* make new session and process group */ setsid(); /* open the child's side of the tty. */ /* NB: setsid() disconnects from any previous ctty's. Therefore * we must open child's side of the tty AFTER setsid! */ fd = xopen(tty_name, O_RDWR); /* becomes our ctty */ dup2(fd, 0); dup2(fd, 1); dup2(fd, 2); while (fd > 2) close(fd--); tcsetpgrp(0, getpid()); /* switch this tty's process group to us */ /* The pseudo-terminal allocated to the client is configured to operate in * cooked mode, and with XTABS CRMOD enabled (see tty(4)). */ tcgetattr(0, &termbuf); termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */ termbuf.c_oflag |= ONLCR | XTABS; termbuf.c_iflag |= ICRNL; termbuf.c_iflag &= ~IXOFF; /*termbuf.c_lflag &= ~ICANON;*/ tcsetattr(0, TCSANOW, &termbuf); /* Uses FILE-based I/O to stdout, but does fflush(stdout), * so should be safe with vfork. * I fear, though, that some users will have ridiculously big * issue files, and they may block writing to fd 1. */ print_login_issue(issuefile, NULL); /* Exec shell / login / whatever */ login_argv[0] = loginpath; login_argv[1] = NULL; execvp(loginpath, (char **)login_argv); /* Safer with vfork, and we shouldn't send this to the client anyway */ _exit(1); /*bb_perror_msg_and_die("execv %s", loginpath);*/ } #if ENABLE_FEATURE_TELNETD_STANDALONE static void free_session(struct tsession *ts) { struct tsession *t = sessions; /* Unlink this telnet session from the session list */ if (t == ts) sessions = ts->next; else { while (t->next != ts) t = t->next; t->next = ts->next; } /* It was said that "normal" telnetd just closes ptyfd, * doesn't send SIGKILL. When we close ptyfd, * kernel sends SIGHUP to processes having slave side opened. */ /*kill(ts->shell_pid, SIGKILL); wait4(ts->shell_pid, NULL, 0, NULL);*/ close(ts->ptyfd); close(ts->sockfd_read); /* error if ts->sockfd_read == ts->sockfd_write. So what? ;) */ close(ts->sockfd_write); free(ts); /* Scan all sessions and find new maxfd */ ts = sessions; maxfd = 0; while (ts) { if (maxfd < ts->ptyfd) maxfd = ts->ptyfd; if (maxfd < ts->sockfd_read) maxfd = ts->sockfd_read; if (maxfd < ts->sockfd_write) maxfd = ts->sockfd_write; ts = ts->next; } } #else /* !FEATURE_TELNETD_STANDALONE */ /* Never actually called */ void free_session(struct tsession *ts); #endif int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; int telnetd_main(int argc, char **argv) { fd_set rdfdset, wrfdset; unsigned opt; int selret, maxlen, w, r; struct tsession *ts; #if ENABLE_FEATURE_TELNETD_STANDALONE #define IS_INETD (opt & OPT_INETD) int master_fd = master_fd; /* be happy, gcc */ unsigned portnbr = 23; char *opt_bindaddr = NULL; char *opt_portnbr; #else enum { IS_INETD = 1, master_fd = -1, portnbr = 23, }; #endif enum { OPT_INETD = (1 << 2) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */ OPT_PORT = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */ OPT_FOREGROUND = (1 << 5) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */ }; /* If !STANDALONE, we accept (and ignore) -i, thus people * don't need to guess whether it's ok to pass -i to us */ opt = getopt32(argv, "f:l:i" USE_FEATURE_TELNETD_STANDALONE("p:b:F"), &issuefile, &loginpath USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)); /* Redirect log to syslog early, if needed */ if (IS_INETD || !(opt & OPT_FOREGROUND)) { openlog(applet_name, 0, LOG_USER); logmode = LOGMODE_SYSLOG; } //if (opt & 1) // -f //if (opt & 2) // -l USE_FEATURE_TELNETD_STANDALONE( if (opt & OPT_PORT) // -p portnbr = xatou16(opt_portnbr); //if (opt & 8) // -b //if (opt & 0x10) // -F //if (opt & 0x20) // -i ); /* Used to check access(loginpath, X_OK) here. Pointless. * exec will do this for us for free later. */ #if ENABLE_FEATURE_TELNETD_STANDALONE if (IS_INETD) { sessions = make_new_session(0, 1); if (!sessions) /* pty opening or vfork problem, exit */ return 1; /* make_new_session prints error message */ } else { //vda: inform that we start in standalone mode? master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr); xlisten(master_fd, 1); if (!(opt & OPT_FOREGROUND)) //vda: NOMMU? bb_daemonize(DAEMON_CHDIR_ROOT); } #else sessions = make_new_session(); if (!sessions) /* pty opening or vfork problem, exit */ return 1; /* make_new_session prints error message */ #endif /* We don't want to die if just one session is broken */ signal(SIGPIPE, SIG_IGN); /* This is how the buffers are used. The arrows indicate the movement of data. +-------+ wridx1++ +------+ rdidx1++ +----------+ | | <-------------- | buf1 | <-------------- | | | | size1-- +------+ size1++ | | | pty | | socket | | | rdidx2++ +------+ wridx2++ | | | | --------------> | buf2 | --------------> | | +-------+ size2++ +------+ size2-- +----------+ size1: "how many bytes are buffered for pty between rdidx1 and wridx1?" size2: "how many bytes are buffered for socket between rdidx2 and wridx2?" Each session has got two buffers. Buffers are circular. If sizeN == 0, buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases rdidxN == wridxN. */ again: FD_ZERO(&rdfdset); FD_ZERO(&wrfdset); if (!IS_INETD) { FD_SET(master_fd, &rdfdset); /* This is needed because free_session() does not * take into account master_fd when it finds new * maxfd among remaining fd's: */ if (master_fd > maxfd) maxfd = master_fd; } /* Select on the master socket, all telnet sockets and their * ptys if there is room in their session buffers. * NB: scalability problem: we recalculate entire bitmap * before each select. Can be a problem with 500+ connections. */ ts = sessions; while (ts) { if (ts->size1 > 0) /* can write to pty */ FD_SET(ts->ptyfd, &wrfdset); if (ts->size1 < BUFSIZE) /* can read from socket */ FD_SET(ts->sockfd_read, &rdfdset); if (ts->size2 > 0) /* can write to socket */ FD_SET(ts->sockfd_write, &wrfdset); if (ts->size2 < BUFSIZE) /* can read from pty */ FD_SET(ts->ptyfd, &rdfdset); ts = ts->next; } selret = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL); if (selret < 0) goto again; /* EINTR or ENOMEM */ #if ENABLE_FEATURE_TELNETD_STANDALONE /* First check for and accept new sessions. */ if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) { int fd; struct tsession *new_ts; fd = accept(master_fd, NULL, NULL); if (fd < 0) goto again; /* Create a new session and link it into our active list */ new_ts = make_new_session(fd, fd); if (new_ts) { new_ts->next = sessions; sessions = new_ts; } else { close(fd); } } #endif /* Then check for data tunneling. */ ts = sessions; while (ts) { /* For all sessions... */ struct tsession *next = ts->next; /* in case we free ts. */ if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) { int num_totty; char *ptr; /* Write to pty from buffer 1. */ ptr = remove_iacs(ts, &num_totty); w = safe_write(ts->ptyfd, ptr, num_totty); if (w < 0) { if (errno == EAGAIN) goto skip1; if (IS_INETD) return 0; free_session(ts); ts = next; continue; } ts->size1 -= w; ts->wridx1 += w; if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */ ts->wridx1 = 0; } skip1: if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) { /* Write to socket from buffer 2. */ maxlen = MIN(BUFSIZE - ts->wridx2, ts->size2); w = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, maxlen); if (w < 0) { if (errno == EAGAIN) goto skip2; if (IS_INETD) return 0; free_session(ts); ts = next; continue; } ts->size2 -= w; ts->wridx2 += w; if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */ ts->wridx2 = 0; } skip2: #if 0 /* Not strictly needed, but allows for bigger reads in common case */ if (ts->size1 == 0) { ts->rdidx1 = 0; ts->wridx1 = 0; } if (ts->size2 == 0) { ts->rdidx2 = 0; ts->wridx2 = 0; } #endif if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) { /* Read from socket to buffer 1. */ maxlen = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1); r = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, maxlen); if (r <= 0) { if (r < 0 && errno == EAGAIN) goto skip3; if (IS_INETD) return 0; free_session(ts); ts = next; continue; } /* Ignore trailing NUL if it is there */ if (!TS_BUF1[ts->rdidx1 + r - 1]) { if (!--r) goto skip3; } ts->size1 += r; ts->rdidx1 += r; if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */ ts->rdidx1 = 0; } skip3: if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) { /* Read from pty to buffer 2. */ maxlen = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2); r = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, maxlen); if (r <= 0) { if (r < 0 && errno == EAGAIN) goto skip4; if (IS_INETD) return 0; free_session(ts); ts = next; continue; } ts->size2 += r; ts->rdidx2 += r; if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */ ts->rdidx2 = 0; } skip4: ts = next; } goto again; }