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- /* 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 source tree.
- *
- * ---------------------------------------------------------------------------
- * (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 <dzo@simtreas.ru> 2001
- * Set process group corrections, initial busybox port
- */
- //config:config TELNETD
- //config: bool "telnetd (12 kb)"
- //config: default y
- //config: select FEATURE_SYSLOG
- //config: help
- //config: A daemon for the TELNET protocol, allowing you to log onto the host
- //config: running the daemon. Please keep in mind that the TELNET protocol
- //config: sends passwords in plain text. If you can't afford the space for an
- //config: SSH daemon and you trust your network, you may say 'y' here. As a
- //config: more secure alternative, you should seriously consider installing the
- //config: very small Dropbear SSH daemon instead:
- //config: http://matt.ucc.asn.au/dropbear/dropbear.html
- //config:
- //config: Note that for busybox telnetd to work you need several things:
- //config: First of all, your kernel needs:
- //config: CONFIG_UNIX98_PTYS=y
- //config:
- //config: Next, you need a /dev/pts directory on your root filesystem:
- //config:
- //config: $ ls -ld /dev/pts
- //config: drwxr-xr-x 2 root root 0 Sep 23 13:21 /dev/pts/
- //config:
- //config: Next you need the pseudo terminal master multiplexer /dev/ptmx:
- //config:
- //config: $ ls -la /dev/ptmx
- //config: crw-rw-rw- 1 root tty 5, 2 Sep 23 13:55 /dev/ptmx
- //config:
- //config: Any /dev/ttyp[0-9]* files you may have can be removed.
- //config: Next, you need to mount the devpts filesystem on /dev/pts using:
- //config:
- //config: mount -t devpts devpts /dev/pts
- //config:
- //config: You need to be sure that busybox has LOGIN and
- //config: FEATURE_SUID enabled. And finally, you should make
- //config: certain that busybox has been installed setuid root:
- //config:
- //config: chown root.root /bin/busybox
- //config: chmod 4755 /bin/busybox
- //config:
- //config: with all that done, telnetd _should_ work....
- //config:
- //config:config FEATURE_TELNETD_STANDALONE
- //config: bool "Support standalone telnetd (not inetd only)"
- //config: default y
- //config: depends on TELNETD
- //config: help
- //config: Selecting this will make telnetd able to run standalone.
- //config:
- //config:config FEATURE_TELNETD_INETD_WAIT
- //config: bool "Support -w SEC option (inetd wait mode)"
- //config: default y
- //config: depends on FEATURE_TELNETD_STANDALONE
- //config: help
- //config: This option allows you to run telnetd in "inet wait" mode.
- //config: Example inetd.conf line (note "wait", not usual "nowait"):
- //config:
- //config: telnet stream tcp wait root /bin/telnetd telnetd -w10
- //config:
- //config: In this example, inetd passes _listening_ socket_ as fd 0
- //config: to telnetd when connection appears.
- //config: telnetd will wait for connections until all existing
- //config: connections are closed, and no new connections
- //config: appear during 10 seconds. Then it exits, and inetd continues
- //config: to listen for new connections.
- //config:
- //config: This option is rarely used. "tcp nowait" is much more usual
- //config: way of running tcp services, including telnetd.
- //config: You most probably want to say N here.
- //applet:IF_TELNETD(APPLET(telnetd, BB_DIR_USR_SBIN, BB_SUID_DROP))
- //kbuild:lib-$(CONFIG_TELNETD) += telnetd.o
- //usage:#define telnetd_trivial_usage
- //usage: "[OPTIONS]"
- //usage:#define telnetd_full_usage "\n\n"
- //usage: "Handle incoming telnet connections"
- //usage: IF_NOT_FEATURE_TELNETD_STANDALONE(" via inetd") "\n"
- //usage: "\n -l LOGIN Exec LOGIN on connect"
- //usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue"
- //usage: "\n -K Close connection as soon as login exits"
- //usage: "\n (normally wait until all programs close slave pty)"
- //usage: IF_FEATURE_TELNETD_STANDALONE(
- //usage: "\n -p PORT Port to listen on"
- //usage: "\n -b ADDR[:PORT] Address to bind to"
- //usage: "\n -F Run in foreground"
- //usage: "\n -i Inetd mode"
- //usage: IF_FEATURE_TELNETD_INETD_WAIT(
- //usage: "\n -w SEC Inetd 'wait' mode, linger time SEC"
- //usage: "\n -S Log to syslog (implied by -i or without -F and -w)"
- //usage: )
- //usage: )
- #define DEBUG 0
- #include "libbb.h"
- #include "common_bufsiz.h"
- #include <syslog.h>
- #if DEBUG
- # define TELCMDS
- # define TELOPTS
- #endif
- #include <arpa/telnet.h>
- struct tsession {
- struct tsession *next;
- pid_t shell_pid;
- int sockfd_read;
- int sockfd_write;
- int ptyfd;
- smallint buffered_IAC_for_pty;
- /* two circular buffers */
- /*char *buf1, *buf2;*/
- /*#define TS_BUF1(ts) ts->buf1*/
- /*#define TS_BUF2(ts) TS_BUF2(ts)*/
- #define TS_BUF1(ts) ((unsigned char*)(ts + 1))
- #define TS_BUF2(ts) (((unsigned 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 */
- struct globals {
- struct tsession *sessions;
- const char *loginpath;
- const char *issuefile;
- int maxfd;
- } FIX_ALIASING;
- #define G (*(struct globals*)bb_common_bufsiz1)
- #define INIT_G() do { \
- setup_common_bufsiz(); \
- G.loginpath = "/bin/login"; \
- G.issuefile = "/etc/issue.net"; \
- } while (0)
- /* Write some buf1 data to pty, processing IACs.
- * Update wridx1 and size1. Return < 0 on error.
- * Buggy if IAC is present but incomplete: skips them.
- */
- static ssize_t
- safe_write_to_pty_decode_iac(struct tsession *ts)
- {
- unsigned wr;
- ssize_t rc;
- unsigned char *buf;
- unsigned char *found;
- buf = TS_BUF1(ts) + ts->wridx1;
- wr = MIN(BUFSIZE - ts->wridx1, ts->size1);
- /* wr is at least 1 here */
- if (ts->buffered_IAC_for_pty) {
- /* Last time we stopped on a "dangling" IAC byte.
- * We removed it from the buffer back then.
- * Now pretend it's still there, and jump to IAC processing.
- */
- ts->buffered_IAC_for_pty = 0;
- wr++;
- ts->size1++;
- buf--; /* Yes, this can point before the buffer. It's ok */
- ts->wridx1--;
- goto handle_iac;
- }
- found = memchr(buf, IAC, wr);
- if (found != buf) {
- /* There is a "prefix" of non-IAC chars.
- * Write only them, and return.
- */
- if (found)
- wr = found - buf;
- /* We map \r\n ==> \r for pragmatic reasons:
- * many client implementations send \r\n when
- * the user hits the CarriageReturn key.
- * See RFC 1123 3.3.1 Telnet End-of-Line Convention.
- */
- rc = wr;
- found = memchr(buf, '\r', wr);
- if (found)
- rc = found - buf + 1;
- rc = safe_write(ts->ptyfd, buf, rc);
- if (rc <= 0)
- return rc;
- if (rc < wr /* don't look past available data */
- && buf[rc-1] == '\r' /* need this: imagine that write was _short_ */
- && (buf[rc] == '\n' || buf[rc] == '\0')
- ) {
- rc++;
- }
- goto update_and_return;
- }
- /* buf starts with IAC char. Process that sequence.
- * Example: we get this from our own (bbox) telnet client:
- * read(5, "\377\374\1""\377\373\37""\377\372\37\0\262\0@\377\360""\377\375\1""\377\375\3"):
- * IAC WONT ECHO, IAC WILL NAWS, IAC SB NAWS <cols> <rows> IAC SE, IAC DO SGA
- * Another example (telnet-0.17 from old-netkit):
- * read(4, "\377\375\3""\377\373\30""\377\373\37""\377\373 ""\377\373!""\377\373\"""\377\373'"
- * "\377\375\5""\377\373#""\377\374\1""\377\372\37\0\257\0I\377\360""\377\375\1"):
- * IAC DO SGA, IAC WILL TTYPE, IAC WILL NAWS, IAC WILL TSPEED, IAC WILL LFLOW, IAC WILL LINEMODE, IAC WILL NEW_ENVIRON,
- * IAC DO STATUS, IAC WILL XDISPLOC, IAC WONT ECHO, IAC SB NAWS <cols> <rows> IAC SE, IAC DO ECHO
- */
- if (wr <= 1) {
- /* Only the single IAC byte is in the buffer, eat it
- * and set a flag "process the rest of the sequence
- * next time we are here".
- */
- //bb_error_msg("dangling IAC!");
- ts->buffered_IAC_for_pty = 1;
- rc = 1;
- goto update_and_return;
- }
- handle_iac:
- /* 2-byte commands (240..250 and 255):
- * IAC IAC (255) Literal 255. Supported.
- * IAC SE (240) End of subnegotiation. Treated as NOP.
- * IAC NOP (241) NOP. Supported.
- * IAC BRK (243) Break. Like serial line break. TODO via tcsendbreak()?
- * IAC AYT (246) Are you there. Send back evidence that AYT was seen. TODO (send NOP back)?
- * These don't look useful:
- * IAC DM (242) Data mark. What is this?
- * IAC IP (244) Suspend, interrupt or abort the process. (Ancient cousin of ^C).
- * IAC AO (245) Abort output. "You can continue running, but do not send me the output".
- * IAC EC (247) Erase character. The receiver should delete the last received char.
- * IAC EL (248) Erase line. The receiver should delete everything up tp last newline.
- * IAC GA (249) Go ahead. For half-duplex lines: "now you talk".
- * Implemented only as part of NAWS:
- * IAC SB (250) Subnegotiation of an option follows.
- */
- if (buf[1] == IAC) {
- /* Literal 255 (emacs M-DEL) */
- //bb_error_msg("255!");
- rc = safe_write(ts->ptyfd, &buf[1], 1);
- /*
- * If we went through buffered_IAC_for_pty==1 path,
- * bailing out on error like below messes up the buffer.
- * EAGAIN is highly unlikely here, other errors will be
- * repeated on next write, let's just skip error check.
- */
- #if 0
- if (rc <= 0)
- return rc;
- #endif
- rc = 2;
- goto update_and_return;
- }
- if (buf[1] >= 240 && buf[1] <= 249) {
- /* NOP (241). Ignore (putty keepalive, etc) */
- /* All other 2-byte commands also treated as NOPs here */
- rc = 2;
- goto update_and_return;
- }
- if (wr <= 2) {
- /* BUG: only 2 bytes of the IAC is in the buffer, we just eat them.
- * This is not a practical problem since >2 byte IACs are seen only
- * in initial negotiation, when buffer is empty
- */
- rc = 2;
- goto update_and_return;
- }
- if (buf[1] == SB) {
- if (buf[2] == TELOPT_NAWS) {
- /* IAC SB, TELOPT_NAWS, 4-byte, IAC SE */
- struct winsize ws;
- if (wr <= 6) {
- /* BUG: incomplete, can't process */
- rc = wr;
- goto update_and_return;
- }
- memset(&ws, 0, sizeof(ws)); /* pixel sizes are set to 0 */
- ws.ws_col = (buf[3] << 8) | buf[4];
- ws.ws_row = (buf[5] << 8) | buf[6];
- ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
- rc = 7;
- /* trailing IAC SE will be eaten separately, as 2-byte NOP */
- goto update_and_return;
- }
- /* else: other subnegs not supported yet */
- }
- /* Assume it is a 3-byte WILL/WONT/DO/DONT 251..254 command and skip it */
- #if DEBUG
- fprintf(stderr, "Ignoring IAC %s,%s\n",
- TELCMD(buf[1]), TELOPT(buf[2]));
- #endif
- rc = 3;
- update_and_return:
- ts->wridx1 += rc;
- if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
- ts->wridx1 = 0;
- ts->size1 -= rc;
- /*
- * Hack. We cannot process IACs which wrap around buffer's end.
- * Since properly fixing it requires writing bigger code,
- * we rely instead on this code making it virtually impossible
- * to have wrapped IAC (people don't type at 2k/second).
- * It also allows for bigger reads in common case.
- */
- if (ts->size1 == 0) { /* very typical */
- //bb_error_msg("zero size1");
- ts->rdidx1 = 0;
- ts->wridx1 = 0;
- return rc;
- }
- wr = ts->wridx1;
- if (wr != 0 && wr < ts->rdidx1) {
- /* Buffer is not wrapped yet.
- * We can easily move it to the beginning.
- */
- //bb_error_msg("moved %d", wr);
- memmove(TS_BUF1(ts), TS_BUF1(ts) + wr, ts->size1);
- ts->rdidx1 -= wr;
- ts->wridx1 = 0;
- }
- return rc;
- }
- /*
- * Converting single IAC into double on output
- */
- static size_t safe_write_double_iac(int fd, const char *buf, size_t count)
- {
- const char *IACptr;
- size_t wr, rc, total;
- total = 0;
- while (1) {
- if (count == 0)
- return total;
- if (*buf == (char)IAC) {
- static const char IACIAC[] ALIGN1 = { IAC, IAC };
- rc = safe_write(fd, IACIAC, 2);
- /* BUG: if partial write was only 1 byte long, we end up emitting just one IAC */
- if (rc != 2)
- break;
- buf++;
- total++;
- count--;
- continue;
- }
- /* count != 0, *buf != IAC */
- IACptr = memchr(buf, IAC, count);
- wr = count;
- if (IACptr)
- wr = IACptr - buf;
- rc = safe_write(fd, buf, wr);
- if (rc != wr)
- break;
- buf += rc;
- total += rc;
- count -= rc;
- }
- /* here: rc - result of last short write */
- if ((ssize_t)rc < 0) { /* error? */
- if (total == 0)
- return rc;
- rc = 0;
- }
- return total + rc;
- }
- /* Must match getopt32 string */
- enum {
- OPT_WATCHCHILD = (1 << 2), /* -K */
- OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
- OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */
- OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
- OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */
- OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */
- };
- static struct tsession *
- make_new_session(
- IF_FEATURE_TELNETD_STANDALONE(int sock)
- IF_NOT_FEATURE_TELNETD_STANDALONE(void)
- ) {
- #if !ENABLE_FEATURE_TELNETD_STANDALONE
- enum { sock = 0 };
- #endif
- const char *login_argv[2];
- struct termios termbuf;
- int fd, pid;
- char tty_name[GETPTY_BUFSIZE];
- 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 = xgetpty(tty_name);
- if (fd > G.maxfd)
- G.maxfd = fd;
- ts->ptyfd = fd;
- ndelay_on(fd);
- close_on_exec_on(fd);
- /* SO_KEEPALIVE by popular demand */
- setsockopt_keepalive(sock);
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- ts->sockfd_read = sock;
- ndelay_on(sock);
- if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */
- sock++; /* so use fd 1 for output */
- ndelay_on(sock);
- }
- ts->sockfd_write = sock;
- if (sock > G.maxfd)
- G.maxfd = sock;
- #else
- /* ts->sockfd_read = 0; - done by xzalloc */
- ts->sockfd_write = 1;
- 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,
- /* This requires telnetd.ctrlSQ.patch (incomplete) */
- /*IAC, DO, TELOPT_LFLOW,*/
- IAC, WILL, TELOPT_ECHO,
- IAC, WILL, TELOPT_SGA
- };
- /* This confuses safe_write_double_iac(), it will try to duplicate
- * each IAC... */
- //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send));
- //ts->rdidx2 = sizeof(iacs_to_send);
- //ts->size2 = sizeof(iacs_to_send);
- /* So just stuff it into TCP stream! (no error check...) */
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- safe_write(sock, iacs_to_send, sizeof(iacs_to_send));
- #else
- safe_write(1, iacs_to_send, sizeof(iacs_to_send));
- #endif
- /*ts->rdidx2 = 0; - xzalloc did it */
- /*ts->size2 = 0;*/
- }
- fflush_all();
- pid = vfork(); /* NOMMU-friendly */
- if (pid < 0) {
- free(ts);
- close(fd);
- /* sock 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! */
- /* Restore default signal handling ASAP */
- bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
- pid = getpid();
- if (ENABLE_FEATURE_UTMP) {
- len_and_sockaddr *lsa = get_peer_lsa(sock);
- char *hostname = NULL;
- if (lsa) {
- hostname = xmalloc_sockaddr2dotted(&lsa->u.sa);
- free(lsa);
- }
- write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname);
- free(hostname);
- }
- /* 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! */
- close(0);
- xopen(tty_name, O_RDWR); /* becomes our ctty */
- xdup2(0, 1);
- xdup2(0, 2);
- tcsetpgrp(0, pid); /* 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_stdin_TCSANOW(&termbuf);
- /* Uses FILE-based I/O to stdout, but does fflush_all(),
- * 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,
- * (parent is supposed to read it, but parent waits
- * for vforked child to exec!) */
- print_login_issue(G.issuefile, tty_name);
- /* Exec shell / login / whatever */
- login_argv[0] = G.loginpath;
- login_argv[1] = NULL;
- /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
- * exec external program.
- * NB: sock is either 0 or has CLOEXEC set on it.
- * fd has CLOEXEC set on it too. These two fds will be closed here.
- */
- BB_EXECVP(G.loginpath, (char **)login_argv);
- /* _exit is safer with vfork, and we shouldn't send message
- * to remote clients anyway */
- _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
- }
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- static void
- free_session(struct tsession *ts)
- {
- struct tsession *t;
- if (option_mask32 & OPT_INETD)
- exit(EXIT_SUCCESS);
- /* Unlink this telnet session from the session list */
- t = G.sessions;
- if (t == ts)
- G.sessions = ts->next;
- else {
- while (t->next != ts)
- t = t->next;
- t->next = ts->next;
- }
- #if 0
- /* 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);
- waitpid(ts->shell_pid, NULL, 0);
- #endif
- close(ts->ptyfd);
- close(ts->sockfd_read);
- /* We do not need to close(ts->sockfd_write), it's the same
- * as sockfd_read unless we are in inetd mode. But in inetd mode
- * we do not reach this */
- free(ts);
- /* Scan all sessions and find new maxfd */
- G.maxfd = 0;
- ts = G.sessions;
- while (ts) {
- if (G.maxfd < ts->ptyfd)
- G.maxfd = ts->ptyfd;
- if (G.maxfd < ts->sockfd_read)
- G.maxfd = ts->sockfd_read;
- #if 0
- /* Again, sockfd_write == sockfd_read here */
- if (G.maxfd < ts->sockfd_write)
- G.maxfd = ts->sockfd_write;
- #endif
- ts = ts->next;
- }
- }
- #else /* !FEATURE_TELNETD_STANDALONE */
- /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
- #define free_session(ts) return 0
- #endif
- static void handle_sigchld(int sig UNUSED_PARAM)
- {
- pid_t pid;
- struct tsession *ts;
- int save_errno = errno;
- /* Looping: more than one child may have exited */
- while (1) {
- pid = wait_any_nohang(NULL);
- if (pid <= 0)
- break;
- ts = G.sessions;
- while (ts) {
- if (ts->shell_pid == pid) {
- ts->shell_pid = -1;
- update_utmp_DEAD_PROCESS(pid);
- break;
- }
- ts = ts->next;
- }
- }
- errno = save_errno;
- }
- int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
- int telnetd_main(int argc UNUSED_PARAM, char **argv)
- {
- fd_set rdfdset, wrfdset;
- unsigned opt;
- int count;
- struct tsession *ts;
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- #define IS_INETD (opt & OPT_INETD)
- int master_fd = master_fd; /* for compiler */
- int sec_linger = sec_linger;
- char *opt_bindaddr = NULL;
- char *opt_portnbr;
- #else
- enum {
- IS_INETD = 1,
- master_fd = -1,
- };
- #endif
- INIT_G();
- /* Even 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:Ki"
- IF_FEATURE_TELNETD_STANDALONE("p:b:F")
- IF_FEATURE_TELNETD_INETD_WAIT("Sw:+") /* -w NUM */
- "\0"
- /* -w implies -F. -w and -i don't mix */
- IF_FEATURE_TELNETD_INETD_WAIT("wF:i--w:w--i"),
- &G.issuefile, &G.loginpath
- IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)
- IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger)
- );
- if (!IS_INETD /*&& !re_execed*/) {
- /* inform that we start in standalone mode?
- * May be useful when people forget to give -i */
- /*bb_error_msg("listening for connections");*/
- if (!(opt & OPT_FOREGROUND)) {
- /* DAEMON_CHDIR_ROOT was giving inconsistent
- * behavior with/without -F, -i */
- bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
- }
- }
- /* Redirect log to syslog early, if needed */
- if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
- openlog(applet_name, LOG_PID, LOG_DAEMON);
- logmode = LOGMODE_SYSLOG;
- }
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- if (IS_INETD) {
- G.sessions = make_new_session(0);
- if (!G.sessions) /* pty opening or vfork problem, exit */
- return 1; /* make_new_session printed error message */
- } else {
- master_fd = 0;
- if (!(opt & OPT_WAIT)) {
- unsigned portnbr = 23;
- if (opt & OPT_PORT)
- portnbr = xatou16(opt_portnbr);
- master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
- xlisten(master_fd, 1);
- }
- close_on_exec_on(master_fd);
- }
- #else
- G.sessions = make_new_session();
- if (!G.sessions) /* pty opening or vfork problem, exit */
- return 1; /* make_new_session printed error message */
- #endif
- /* We don't want to die if just one session is broken */
- signal(SIGPIPE, SIG_IGN);
- if (opt & OPT_WATCHCHILD)
- signal(SIGCHLD, handle_sigchld);
- else /* prevent dead children from becoming zombies */
- signal(SIGCHLD, SIG_IGN);
- /*
- This is how the buffers are used. The arrows indicate data flow.
- +-------+ 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);
- /* 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 = G.sessions;
- while (ts) {
- struct tsession *next = ts->next; /* in case we free ts */
- if (ts->shell_pid == -1) {
- /* Child died and we detected that */
- free_session(ts);
- } else {
- 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 = next;
- }
- if (!IS_INETD) {
- FD_SET(master_fd, &rdfdset);
- /* This is needed because free_session() does not
- * take master_fd into account when it finds new
- * maxfd among remaining fd's */
- if (master_fd > G.maxfd)
- G.maxfd = master_fd;
- }
- {
- struct timeval *tv_ptr = NULL;
- #if ENABLE_FEATURE_TELNETD_INETD_WAIT
- struct timeval tv;
- if ((opt & OPT_WAIT) && !G.sessions) {
- tv.tv_sec = sec_linger;
- tv.tv_usec = 0;
- tv_ptr = &tv;
- }
- #endif
- count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr);
- }
- if (count == 0) /* "telnetd -w SEC" timed out */
- return 0;
- if (count < 0)
- goto again; /* EINTR or ENOMEM */
- #if ENABLE_FEATURE_TELNETD_STANDALONE
- /* 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;
- close_on_exec_on(fd);
- /* Create a new session and link it into active list */
- new_ts = make_new_session(fd);
- if (new_ts) {
- new_ts->next = G.sessions;
- G.sessions = new_ts;
- } else {
- close(fd);
- }
- }
- #endif
- /* Then check for data tunneling */
- ts = G.sessions;
- while (ts) { /* For all sessions... */
- struct tsession *next = ts->next; /* in case we free ts */
- if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
- /* Write to pty from buffer 1 */
- count = safe_write_to_pty_decode_iac(ts);
- if (count < 0) {
- if (errno == EAGAIN)
- goto skip1;
- goto kill_session;
- }
- }
- skip1:
- if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
- /* Write to socket from buffer 2 */
- count = MIN(BUFSIZE - ts->wridx2, ts->size2);
- count = safe_write_double_iac(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
- if (count < 0) {
- if (errno == EAGAIN)
- goto skip2;
- goto kill_session;
- }
- ts->wridx2 += count;
- if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
- ts->wridx2 = 0;
- ts->size2 -= count;
- if (ts->size2 == 0) {
- ts->rdidx2 = 0;
- ts->wridx2 = 0;
- }
- }
- skip2:
- if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
- /* Read from socket to buffer 1 */
- count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
- count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count);
- if (count <= 0) {
- if (count < 0 && errno == EAGAIN)
- goto skip3;
- goto kill_session;
- }
- /* Ignore trailing NUL if it is there */
- if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
- --count;
- }
- ts->size1 += count;
- ts->rdidx1 += count;
- 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 */
- count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
- count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
- if (count <= 0) {
- if (count < 0 && errno == EAGAIN)
- goto skip4;
- goto kill_session;
- }
- ts->size2 += count;
- ts->rdidx2 += count;
- if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
- ts->rdidx2 = 0;
- }
- skip4:
- ts = next;
- continue;
- kill_session:
- if (ts->shell_pid > 0)
- update_utmp_DEAD_PROCESS(ts->shell_pid);
- free_session(ts);
- ts = next;
- }
- goto again;
- }
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