busybox/networking/telnetd.c
Denys Vlasenko 47367e1d50 Convert all networking/* applets to "new style" applet definitions
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2016-11-23 09:05:14 +01:00

890 lines
26 KiB
C

/* 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"
//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();
/* -w NUM, and implies -F. -w and -i don't mix */
IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:i--w:w--i";)
/* 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:+"),
&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;
}