[BusyBox] [PATCH] : telnetd
David Kimdon
dwhedon at gordian.com
Sun Aug 5 22:31:28 MDT 2001
Hi,
I incorporated most of Vladamir's changes. With the funky control character
fixes and better busybox integration I think this gives us a rather nice
telnetd. If okay to commit to CVS head I'll do so, I'm open to
suggestions for improvement.
One rather cute feature is that you can set the login program, so you can
do fun things like :
# /usr/sbin/telnetd -l /bin/dmesg
If you want some status available from the host but don't have a shell
installed.
Another entertaining use is:
# /usr/sbin/telnetd -l /bin/vi
-David
Index: Config.h
===================================================================
RCS file: /var/cvs/busybox/Config.h,v
retrieving revision 1.98
diff -u -r1.98 Config.h
--- Config.h 2001/08/02 09:21:17 1.98
+++ Config.h 2001/08/06 02:56:21
@@ -116,6 +116,7 @@
//#define BB_TEE
//#define BB_TEST
//#define BB_TELNET
+//#define BB_TELNETD
//#define BB_TFTP
#define BB_TOUCH
//#define BB_TR
Index: applets.h
===================================================================
RCS file: /var/cvs/busybox/applets.h,v
retrieving revision 1.38
diff -u -r1.38 applets.h
--- applets.h 2001/08/02 08:48:03 1.38
+++ applets.h 2001/08/06 02:56:22
@@ -398,6 +398,9 @@
#ifdef BB_TELNET
APPLET(telnet, telnet_main, _BB_DIR_USR_BIN)
#endif
+#ifdef BB_TELNETD
+ APPLET(telnetd, telnetd_main, _BB_DIR_USR_SBIN)
+#endif
#ifdef BB_TEST
APPLET(test, test_main, _BB_DIR_USR_BIN)
#endif
Index: usage.h
===================================================================
RCS file: /var/cvs/busybox/usage.h,v
retrieving revision 1.60
diff -u -r1.60 usage.h
--- usage.h 2001/08/01 17:21:34 1.60
+++ usage.h 2001/08/06 02:56:32
@@ -1544,6 +1544,14 @@
"Telnet is used to establish interactive communication with another\n"\
"computer over a network using the TELNET protocol."
+#define telnetd_trivial_usage \
+ "[OPTION]"
+#define telnetd_full_usage \
+ "Telnetd listens for incoming TELNET connections on PORT.\n"\
+ "Options:\n" \
+ "\t-p PORT\tlisten for connections on PORT (default 23)\n"\
+ "\t-l LOGIN\texec LOGIN on connect (default /bin/sh)"
+
#define test_trivial_usage \
"EXPRESSION\n or [ EXPRESSION ]"
#define test_full_usage \
--- /dev/null Thu Nov 30 07:25:58 2000
+++ telnetd.c Sun Aug 5 20:28:29 2001
@@ -0,0 +1,551 @@
+/* $Id: telnetd.c,v 1.5 2001/08/06 01:40:57 davidw Exp $
+ *
+ * Simple telnet server
+ * Bjorn Wesen, Axis Communications AB (bjornw at axis.com)
+ *
+ * This file is distributed under the Gnu Public License (GPL),
+ * please see the file LICENSE for further information.
+ *
+ * ---------------------------------------------------------------------------
+ * (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 at simtreas.ru> 2001
+ * Set process group corrections, initial busybox port
+ */
+
+/*#define DEBUG 1 */
+
+#include <sys/time.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <netinet/in.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <signal.h>
+#include <termios.h>
+#ifdef DEBUG
+#define TELCMDS
+#define TELOPTS
+#endif
+#include <arpa/telnet.h>
+#include <ctype.h>
+
+#include "busybox.h"
+
+#define BUFSIZE 4000
+
+static char *loginpath = NULL;
+
+/* shell name and arguments */
+
+static char *argv_init[] = {NULL, NULL};
+
+/* structure that describes a session */
+
+struct tsession {
+ struct tsession *next;
+ int sockfd, ptyfd;
+ int shell_pid;
+ /* two circular buffers */
+ char *buf1, *buf2;
+ int rdidx1, wridx1, size1;
+ int rdidx2, wridx2, size2;
+};
+
+/*
+
+ 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-- +----------+
+
+ Each session has got two buffers.
+
+*/
+
+static int maxfd;
+
+static struct tsession *sessions;
+
+
+/*
+
+ Remove all IAC's from the buffer pointed to by bf (recieved 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 bf.
+
+ Return a pointer to the beginning of the characters meant for the terminal.
+ and make *processed equal to the number of characters that were actually
+ processed and *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.
+
+ */
+static char *
+remove_iacs(unsigned char *bf, int len, int *processed, int *num_totty) {
+ unsigned char *ptr = bf;
+ unsigned char *totty = bf;
+ unsigned char *end = bf + len;
+
+ while (ptr < end) {
+ if (*ptr != IAC) {
+ *totty++ = *ptr++;
+ }
+ else {
+ if ((ptr+2) < end) {
+ /* the entire IAC is contained in the buffer
+ we were asked to process. */
+#ifdef DEBUG
+ fprintf(stderr, "Ignoring IAC %s,%s\n",
+ *ptr, TELCMD(*(ptr+1)), TELOPT(*(ptr+2)));
+#endif
+ ptr += 3;
+ } else {
+ /* only the beginning of the IAC is in the
+ buffer we were asked to process, we can't
+ process this char. */
+ break;
+ }
+ }
+ }
+
+ *processed = ptr - bf;
+ *num_totty = totty - bf;
+ /* move the chars meant for the terminal towards the end of the
+ buffer. */
+ return memmove(ptr - *num_totty, bf, *num_totty);
+}
+
+
+static int
+getpty(char *line)
+{
+ int p;
+#ifdef HAVE_DEVPTS_FS
+ p = open("/dev/ptmx", 2);
+ if (p > 0) {
+ grantpt(p);
+ unlockpt(p);
+ strcpy(line, ptsname(p));
+ 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] = "0123456789abcdef"[j];
+ if ((p = open(line, O_RDWR | O_NOCTTY)) >= 0) {
+ line[5] = 't';
+ return p;
+ }
+ }
+ }
+#endif /* HAVE_DEVPTS_FS */
+ return -1;
+}
+
+
+static void
+send_iac(struct tsession *ts, unsigned char command, int option)
+{
+ /* We rely on that there is space in the buffer for now. */
+ char *b = ts->buf2 + ts->rdidx2;
+ *b++ = IAC;
+ *b++ = command;
+ *b++ = option;
+ ts->rdidx2 += 3;
+ ts->size2 += 3;
+}
+
+
+static struct tsession *
+make_new_session(int sockfd)
+{
+ struct termios termbuf;
+ int pty, pid;
+ static char tty_name[32];
+ struct tsession *ts = (struct tsession *)malloc(sizeof(struct tsession));
+
+ ts->buf1 = (char *)malloc(BUFSIZE);
+ ts->buf2 = (char *)malloc(BUFSIZE);
+
+ ts->sockfd = sockfd;
+
+ ts->rdidx1 = ts->wridx1 = ts->size1 = 0;
+ ts->rdidx2 = ts->wridx2 = ts->size2 = 0;
+
+ /* Got a new connection, set up a tty and spawn a shell. */
+
+ pty = getpty(tty_name);
+
+ if (pty < 0) {
+ fprintf(stderr, "All network ports in use!\n");
+ return 0;
+ }
+
+ if (pty > maxfd)
+ maxfd = pty;
+
+ ts->ptyfd = pty;
+
+ /* 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.
+ */
+
+ send_iac(ts, DO, TELOPT_ECHO);
+ send_iac(ts, DO, TELOPT_LFLOW);
+ send_iac(ts, WILL, TELOPT_ECHO);
+ send_iac(ts, WILL, TELOPT_SGA);
+
+
+ if ((pid = fork()) < 0) {
+ perror("fork");
+ }
+ if (pid == 0) {
+ /* In child, open the child's side of the tty. */
+ int i, t;
+
+ for(i = 0; i <= maxfd; i++)
+ close(i);
+ /* make new process group */
+ if (setsid() < 0)
+ perror_msg_and_die("setsid");
+
+ t = open(tty_name, O_RDWR | O_NOCTTY);
+ if (t < 0)
+ perror_msg_and_die("Could not open tty");
+ dup(0);
+ dup(1);
+
+ tcsetpgrp(0, getpid());
+
+ /* The pseudo-terminal allocated to the client is configured to operate in
+ * cooked mode, and with XTABS CRMOD enabled (see tty(4)).
+ */
+
+ tcgetattr(t, &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(t, TCSANOW, &termbuf);
+
+ /* exec shell, with correct argv and env */
+ execv(loginpath, argv_init);
+
+ /* NOT REACHED */
+ perror_msg_and_die("execv");
+ }
+
+ ts->shell_pid = pid;
+
+ return ts;
+}
+
+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;
+ }
+
+ free(ts->buf1);
+ free(ts->buf2);
+
+ kill(ts->shell_pid, SIGKILL);
+
+ wait4(ts->shell_pid, NULL, 0, NULL);
+
+ close(ts->ptyfd);
+ close(ts->sockfd);
+
+ if(ts->ptyfd == maxfd || ts->sockfd == maxfd)
+ maxfd--;
+ if(ts->ptyfd == maxfd || ts->sockfd == maxfd)
+ maxfd--;
+
+ free(ts);
+}
+
+int
+telnetd_main(int argc, char **argv)
+{
+ struct sockaddr_in sa;
+ int master_fd;
+ fd_set rdfdset, wrfdset;
+ int selret;
+ int on = 1;
+ int portnbr = 23;
+ int c;
+
+ /* check if user supplied a port number */
+
+ for (;;) {
+ c = getopt( argc, argv, "p:l:");
+ if (c == EOF) break;
+ switch (c) {
+ case 'p':
+ portnbr = atoi(optarg);
+ break;
+ case 'l':
+ loginpath = strdup (optarg);
+ break;
+ default:
+ show_usage();
+ exit(1);
+ }
+ }
+
+ if (!loginpath)
+ loginpath = "/bin/sh";
+
+ if (access(loginpath, X_OK) < 0) {
+ error_msg_and_die ("'%s' unavailable.", loginpath);
+ }
+
+ argv_init[0] = loginpath;
+ sessions = 0;
+
+ /* Grab a TCP socket. */
+
+ master_fd = socket(AF_INET, SOCK_STREAM, 0);
+ if (master_fd < 0) {
+ perror("socket");
+ return 1;
+ }
+ (void)setsockopt(master_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on));
+
+ /* Set it to listen to specified port. */
+
+ memset((void *)&sa, 0, sizeof(sa));
+ sa.sin_family = AF_INET;
+ sa.sin_port = htons(portnbr);
+
+ if (bind(master_fd, (struct sockaddr *) &sa, sizeof(sa)) < 0) {
+ perror("bind");
+ return 1;
+ }
+
+ if (listen(master_fd, 1) < 0) {
+ perror("listen");
+ return 1;
+ }
+
+ if (daemon(0, 1) < 0)
+ perror_msg_and_die("daemon");
+
+
+ maxfd = master_fd;
+
+ do {
+ struct tsession *ts;
+
+ FD_ZERO(&rdfdset);
+ FD_ZERO(&wrfdset);
+
+ /* select on the master socket, all telnet sockets and their
+ * ptys if there is room in their respective session buffers.
+ */
+
+ FD_SET(master_fd, &rdfdset);
+
+ ts = sessions;
+ while (ts) {
+ /* buf1 is used from socket to pty
+ * buf2 is used from pty to socket
+ */
+ if (ts->size1 > 0) {
+ FD_SET(ts->ptyfd, &wrfdset); /* can write to pty */
+ }
+ if (ts->size1 < BUFSIZE) {
+ FD_SET(ts->sockfd, &rdfdset); /* can read from socket */
+ }
+ if (ts->size2 > 0) {
+ FD_SET(ts->sockfd, &wrfdset); /* can write to socket */
+ }
+ if (ts->size2 < BUFSIZE) {
+ FD_SET(ts->ptyfd, &rdfdset); /* can read from pty */
+ }
+ ts = ts->next;
+ }
+
+ selret = select(maxfd + 1, &rdfdset, &wrfdset, 0, 0);
+
+ if (!selret)
+ break;
+
+ /* First check for and accept new sessions. */
+ if (FD_ISSET(master_fd, &rdfdset)) {
+ int fd, salen;
+
+ salen = sizeof(sa);
+ if ((fd = accept(master_fd, (struct sockaddr *)&sa,
+ &salen)) < 0) {
+ continue;
+ } else {
+ /* Create a new session and link it into
+ our active list. */
+ struct tsession *new_ts = make_new_session(fd);
+ if (new_ts) {
+ new_ts->next = sessions;
+ sessions = new_ts;
+ if (fd > maxfd)
+ maxfd = fd;
+ } else {
+ close(fd);
+ }
+ }
+ }
+
+ /* Then check for data tunneling. */
+
+ ts = sessions;
+ while (ts) { /* For all sessions... */
+ int maxlen, w, r;
+ struct tsession *next = ts->next; /* in case we free ts. */
+
+ if (ts->size1 && FD_ISSET(ts->ptyfd, &wrfdset)) {
+ int processed, num_totty;
+ char *ptr;
+ /* Write to pty from buffer 1. */
+
+ maxlen = MIN(BUFSIZE - ts->wridx1,
+ ts->size1);
+ ptr = remove_iacs(ts->buf1 + ts->wridx1, maxlen,
+ &processed, &num_totty);
+
+ /* the difference between processed and num_totty
+ is all the iacs we removed from the stream.
+ Adjust buf1 accordingly. */
+ ts->wridx1 += processed - num_totty;
+ ts->size1 -= processed - num_totty;
+
+ w = write(ts->ptyfd, ptr, num_totty);
+ if (w < 0) {
+ perror("write");
+ free_session(ts);
+ ts = next;
+ continue;
+ }
+ ts->wridx1 += w;
+ ts->size1 -= w;
+ if (ts->wridx1 == BUFSIZE)
+ ts->wridx1 = 0;
+ }
+
+ if (ts->size2 && FD_ISSET(ts->sockfd, &wrfdset)) {
+ /* Write to socket from buffer 2. */
+ maxlen = MIN(BUFSIZE - ts->wridx2,
+ ts->size2);
+ w = write(ts->sockfd, ts->buf2 + ts->wridx2, maxlen);
+ if (w < 0) {
+ perror("write");
+ free_session(ts);
+ ts = next;
+ continue;
+ }
+ ts->wridx2 += w;
+ ts->size2 -= w;
+ if (ts->wridx2 == BUFSIZE)
+ ts->wridx2 = 0;
+ }
+
+ if (ts->size1 < BUFSIZE && FD_ISSET(ts->sockfd, &rdfdset)) {
+ /* Read from socket to buffer 1. */
+ maxlen = MIN(BUFSIZE - ts->rdidx1,
+ BUFSIZE - ts->size1);
+ r = read(ts->sockfd, ts->buf1 + ts->rdidx1, maxlen);
+ if (!r || (r < 0 && errno != EINTR)) {
+ free_session(ts);
+ ts = next;
+ continue;
+ }
+ if(!*(ts->buf1 + ts->rdidx1 + r - 1)) {
+ r--;
+ if(!r)
+ continue;
+ }
+ ts->rdidx1 += r;
+ ts->size1 += r;
+ if (ts->rdidx1 == BUFSIZE)
+ ts->rdidx1 = 0;
+ }
+
+ if (ts->size2 < BUFSIZE && FD_ISSET(ts->ptyfd, &rdfdset)) {
+ /* Read from pty to buffer 2. */
+ maxlen = MIN(BUFSIZE - ts->rdidx2,
+ BUFSIZE - ts->size2);
+ r = read(ts->ptyfd, ts->buf2 + ts->rdidx2, maxlen);
+ if (!r || (r < 0 && errno != EINTR)) {
+ free_session(ts);
+ ts = next;
+ continue;
+ }
+ ts->rdidx2 += r;
+ ts->size2 += r;
+ if (ts->rdidx2 == BUFSIZE)
+ ts->rdidx2 = 0;
+ }
+
+ if (ts->size1 == 0) {
+ ts->rdidx1 = 0;
+ ts->wridx1 = 0;
+ }
+ if (ts->size2 == 0) {
+ ts->rdidx2 = 0;
+ ts->wridx2 = 0;
+ }
+ ts = next;
+ }
+
+ } while (1);
+
+ return 0;
+}
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