* Simple telnet server
* Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
*
- * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
*
* ---------------------------------------------------------------------------
* (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
* 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
+# 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;*/
const char *loginpath;
const char *issuefile;
int maxfd;
-};
-#define G (*(struct globals*)&bb_common_bufsiz1)
+} 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)
-/*
- 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.
-
- CR-LF ->'s CR mapping is also done here, for convenience.
-
- NB: may fail to remove iacs which wrap around buffer!
+/* 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 unsigned char *
-remove_iacs(struct tsession *ts, int *pnum_totty)
+static ssize_t
+safe_write_to_pty_decode_iac(struct tsession *ts)
{
- unsigned char *ptr0 = TS_BUF1(ts) + ts->wridx1;
- unsigned char *ptr = ptr0;
- unsigned char *totty = ptr;
- unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
- int num_totty;
-
- while (ptr < end) {
- if (*ptr != IAC) {
- char c = *ptr;
-
- *totty++ = c;
- ptr++;
- /* We map \r\n ==> \r for pragmatic reasons.
- * Many client implementations send \r\n when
- * the user hits the CarriageReturn key.
- */
- if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
- ptr++;
- continue;
- }
+ 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;
+ }
- if ((ptr+1) >= end)
- break;
- if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */
- ptr += 2;
- continue;
- }
- if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */
- *totty++ = ptr[1];
- ptr += 2;
- continue;
- }
+ 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;
- /*
- * TELOPT_NAWS support!
+ /* 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.
*/
- 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;
+ 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);
/*
- * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
+ * 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 (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
+#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 ((ptr+8) >= end)
- break; /* incomplete, can't process */
- ws.ws_col = (ptr[3] << 8) | ptr[4];
- ws.ws_row = (ptr[5] << 8) | ptr[6];
+ 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);
- ptr += 9;
- continue;
+ rc = 7;
+ /* trailing IAC SE will be eaten separately, as 2-byte NOP */
+ goto update_and_return;
}
- /* skip 3-byte IAC non-SB cmd */
+ /* 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(ptr[1]), TELOPT(ptr[2]));
+ fprintf(stderr, "Ignoring IAC %s,%s\n",
+ TELCMD(buf[1]), TELOPT(buf[2]));
#endif
- ptr += 3;
+ 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;
}
-
- num_totty = totty - ptr0;
- *pnum_totty = num_totty;
- /* The difference between ptr and totty is number of iacs
- we removed from the stream. Adjust buf1 accordingly */
- if ((ptr - totty) == 0) /* 99.999% of cases */
- return ptr0;
- ts->wridx1 += ptr - totty;
- ts->size1 -= ptr - totty;
- /* Move chars meant for the terminal towards the end of the buffer */
- return memmove(ptr - num_totty, ptr0, num_totty);
+ 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 iac_safe_write(int fd, const char *buf, size_t count)
+static size_t safe_write_double_iac(int fd, const char *buf, size_t count)
{
const char *IACptr;
size_t wr, rc, 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++;
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;
ndelay_on(fd);
close_on_exec_on(fd);
-#if ENABLE_FEATURE_TELNETD_STANDALONE
/* SO_KEEPALIVE by popular demand */
- setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
+ 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 */
if (sock > G.maxfd)
G.maxfd = sock;
#else
- /* SO_KEEPALIVE by popular demand */
- setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
/* ts->sockfd_read = 0; - done by xzalloc */
ts->sockfd_write = 1;
ndelay_on(0);
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, */
+ /* This requires telnetd.ctrlSQ.patch (incomplete) */
+ /*IAC, DO, TELOPT_LFLOW,*/
IAC, WILL, TELOPT_ECHO,
IAC, WILL, TELOPT_SGA
};
- /* This confuses iac_safe_write(), it will try to duplicate
+ /* 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);
/* 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();
xopen(tty_name, O_RDWR); /* becomes our ctty */
xdup2(0, 1);
xdup2(0, 2);
- tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
+ 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)) */
static void
free_session(struct tsession *ts)
{
- struct tsession *t = G.sessions;
+ 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 {
{
pid_t pid;
struct tsession *ts;
+ int save_errno = errno;
/* Looping: more than one child may have exited */
while (1) {
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;
#endif
INIT_G();
- /* -w NUM, and implies -F. -w and -i don't mix */
- IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:w+: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"
+ opt = getopt32(argv, "^"
+ "f:l:Ki"
IF_FEATURE_TELNETD_STANDALONE("p:b:F")
- IF_FEATURE_TELNETD_INETD_WAIT("Sw:"),
+ 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)
struct tsession *next = ts->next; /* in case we free ts */
if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
- int num_totty;
- unsigned char *ptr;
/* Write to pty from buffer 1 */
- ptr = remove_iacs(ts, &num_totty);
- count = safe_write(ts->ptyfd, ptr, num_totty);
+ count = safe_write_to_pty_decode_iac(ts);
if (count < 0) {
if (errno == EAGAIN)
goto skip1;
goto kill_session;
}
- ts->size1 -= count;
- ts->wridx1 += count;
- 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 */
count = MIN(BUFSIZE - ts->wridx2, ts->size2);
- count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
+ 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->size2 -= count;
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:
- /* Should not be needed, but... remove_iacs is actually buggy
- * (it 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) {
- ts->rdidx1 = 0;
- ts->wridx1 = 0;
- }
- if (ts->size2 == 0) {
- ts->rdidx2 = 0;
- ts->wridx2 = 0;
- }
if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
/* Read from socket to buffer 1 */
ts = next;
continue;
kill_session:
+ if (ts->shell_pid > 0)
+ update_utmp_DEAD_PROCESS(ts->shell_pid);
free_session(ts);
ts = next;
}
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