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597 lines
17 KiB
C
597 lines
17 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Simple telnet server
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* Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*
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* ---------------------------------------------------------------------------
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* (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
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****************************************************************************
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*
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* The telnetd manpage says it all:
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*
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* Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for
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* a client, then creating a login process which has the slave side of the
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* pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the
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* master side of the pseudo-terminal, implementing the telnet protocol and
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* passing characters between the remote client and the login process.
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*
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* Vladimir Oleynik <dzo@simtreas.ru> 2001
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* Set process group corrections, initial busybox port
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*/
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#define DEBUG 0
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#include "libbb.h"
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#include <syslog.h>
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#if DEBUG
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#define TELCMDS
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#define TELOPTS
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#endif
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#include <arpa/telnet.h>
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/* Structure that describes a session */
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struct tsession {
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struct tsession *next;
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int sockfd_read, sockfd_write, ptyfd;
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int shell_pid;
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/* two circular buffers */
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/*char *buf1, *buf2;*/
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/*#define TS_BUF1 ts->buf1*/
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/*#define TS_BUF2 TS_BUF2*/
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#define TS_BUF1 ((unsigned char*)(ts + 1))
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#define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
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int rdidx1, wridx1, size1;
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int rdidx2, wridx2, size2;
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};
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/* Two buffers are directly after tsession in malloced memory.
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* Make whole thing fit in 4k */
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enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
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/* Globals */
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static int maxfd;
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static struct tsession *sessions;
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static const char *loginpath = "/bin/login";
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static const char *issuefile = "/etc/issue.net";
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/*
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Remove all IAC's from buf1 (received IACs are ignored and must be removed
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so as to not be interpreted by the terminal). Make an uninterrupted
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string of characters fit for the terminal. Do this by packing
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all characters meant for the terminal sequentially towards the end of buf.
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Return a pointer to the beginning of the characters meant for the terminal.
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and make *num_totty the number of characters that should be sent to
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the terminal.
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Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
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past (bf + len) then that IAC will be left unprocessed and *processed
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will be less than len.
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FIXME - if we mean to send 0xFF to the terminal then it will be escaped,
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what is the escape character? We aren't handling that situation here.
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CR-LF ->'s CR mapping is also done here, for convenience.
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NB: may fail to remove iacs which wrap around buffer!
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*/
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static unsigned char *
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remove_iacs(struct tsession *ts, int *pnum_totty)
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{
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unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
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unsigned char *ptr = ptr0;
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unsigned char *totty = ptr;
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unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
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int num_totty;
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while (ptr < end) {
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if (*ptr != IAC) {
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char c = *ptr;
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*totty++ = c;
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ptr++;
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/* We now map \r\n ==> \r for pragmatic reasons.
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* Many client implementations send \r\n when
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* the user hits the CarriageReturn key.
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*/
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if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
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ptr++;
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} else {
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/*
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* TELOPT_NAWS support!
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*/
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if ((ptr+2) >= end) {
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/* only the beginning of the IAC is in the
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buffer we were asked to process, we can't
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process this char. */
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break;
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}
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/*
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* IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
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*/
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else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
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struct winsize ws;
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if ((ptr+8) >= end)
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break; /* incomplete, can't process */
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ws.ws_col = (ptr[3] << 8) | ptr[4];
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ws.ws_row = (ptr[5] << 8) | ptr[6];
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ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
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ptr += 9;
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} else {
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/* skip 3-byte IAC non-SB cmd */
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#if DEBUG
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fprintf(stderr, "Ignoring IAC %s,%s\n",
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TELCMD(ptr[1]), TELOPT(ptr[2]));
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#endif
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ptr += 3;
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}
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}
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}
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num_totty = totty - ptr0;
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*pnum_totty = num_totty;
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/* the difference between ptr and totty is number of iacs
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we removed from the stream. Adjust buf1 accordingly. */
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if ((ptr - totty) == 0) /* 99.999% of cases */
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return ptr0;
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ts->wridx1 += ptr - totty;
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ts->size1 -= ptr - totty;
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/* move chars meant for the terminal towards the end of the buffer */
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return memmove(ptr - num_totty, ptr0, num_totty);
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}
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static struct tsession *
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make_new_session(
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USE_FEATURE_TELNETD_STANDALONE(int sock)
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SKIP_FEATURE_TELNETD_STANDALONE(void)
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) {
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const char *login_argv[2];
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struct termios termbuf;
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int fd, pid;
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char tty_name[GETPTY_BUFSIZE];
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struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
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/*ts->buf1 = (char *)(ts + 1);*/
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/*ts->buf2 = ts->buf1 + BUFSIZE;*/
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/* Got a new connection, set up a tty. */
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fd = xgetpty(tty_name);
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if (fd > maxfd)
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maxfd = fd;
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ts->ptyfd = fd;
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ndelay_on(fd);
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#if ENABLE_FEATURE_TELNETD_STANDALONE
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ts->sockfd_read = sock;
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ndelay_on(sock);
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if (!sock) { /* We are called with fd 0 - we are in inetd mode */
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sock++; /* so use fd 1 for output */
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ndelay_on(sock);
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}
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ts->sockfd_write = sock;
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if (sock > maxfd)
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maxfd = sock;
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#else
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/* ts->sockfd_read = 0; - done by xzalloc */
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ts->sockfd_write = 1;
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ndelay_on(0);
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ndelay_on(1);
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#endif
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/* Make the telnet client understand we will echo characters so it
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* should not do it locally. We don't tell the client to run linemode,
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* because we want to handle line editing and tab completion and other
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* stuff that requires char-by-char support. */
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{
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static const char iacs_to_send[] ALIGN1 = {
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IAC, DO, TELOPT_ECHO,
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IAC, DO, TELOPT_NAWS,
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IAC, DO, TELOPT_LFLOW,
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IAC, WILL, TELOPT_ECHO,
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IAC, WILL, TELOPT_SGA
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};
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memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
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ts->rdidx2 = sizeof(iacs_to_send);
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ts->size2 = sizeof(iacs_to_send);
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}
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fflush(NULL); /* flush all streams */
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pid = vfork(); /* NOMMU-friendly */
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if (pid < 0) {
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free(ts);
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close(fd);
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/* sock will be closed by caller */
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bb_perror_msg("vfork");
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return NULL;
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}
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if (pid > 0) {
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/* Parent */
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ts->shell_pid = pid;
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return ts;
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}
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/* Child */
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/* Careful - we are after vfork! */
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/* make new session and process group */
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setsid();
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/* Restore default signal handling */
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bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
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/* open the child's side of the tty. */
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/* NB: setsid() disconnects from any previous ctty's. Therefore
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* we must open child's side of the tty AFTER setsid! */
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fd = xopen(tty_name, O_RDWR); /* becomes our ctty */
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dup2(fd, 0);
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dup2(fd, 1);
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dup2(fd, 2);
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while (fd > 2) close(fd--);
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tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
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/* The pseudo-terminal allocated to the client is configured to operate in
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* cooked mode, and with XTABS CRMOD enabled (see tty(4)). */
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tcgetattr(0, &termbuf);
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termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
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termbuf.c_oflag |= ONLCR | XTABS;
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termbuf.c_iflag |= ICRNL;
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termbuf.c_iflag &= ~IXOFF;
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/*termbuf.c_lflag &= ~ICANON;*/
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tcsetattr(0, TCSANOW, &termbuf);
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/* Uses FILE-based I/O to stdout, but does fflush(stdout),
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* so should be safe with vfork.
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* I fear, though, that some users will have ridiculously big
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* issue files, and they may block writing to fd 1,
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* (parent is supposed to read it, but parent waits
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* for vforked child to exec!) */
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print_login_issue(issuefile, NULL);
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/* Exec shell / login / whatever */
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login_argv[0] = loginpath;
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login_argv[1] = NULL;
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/* exec busybox applet (if PREFER_APPLETS=y), if that fails,
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* exec external program */
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BB_EXECVP(loginpath, (char **)login_argv);
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/* _exit is safer with vfork, and we shouldn't send message
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* to remote clients anyway */
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_exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", loginpath);*/
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}
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/* Must match getopt32 string */
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enum {
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OPT_WATCHCHILD = (1 << 2), /* -K */
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OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */
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OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p */
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OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
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};
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#if ENABLE_FEATURE_TELNETD_STANDALONE
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static void
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free_session(struct tsession *ts)
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{
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struct tsession *t = sessions;
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if (option_mask32 & OPT_INETD)
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exit(EXIT_SUCCESS);
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/* Unlink this telnet session from the session list */
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if (t == ts)
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sessions = ts->next;
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else {
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while (t->next != ts)
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t = t->next;
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t->next = ts->next;
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}
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#if 0
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/* It was said that "normal" telnetd just closes ptyfd,
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* doesn't send SIGKILL. When we close ptyfd,
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* kernel sends SIGHUP to processes having slave side opened. */
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kill(ts->shell_pid, SIGKILL);
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wait4(ts->shell_pid, NULL, 0, NULL);
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#endif
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close(ts->ptyfd);
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close(ts->sockfd_read);
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/* We do not need to close(ts->sockfd_write), it's the same
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* as sockfd_read unless we are in inetd mode. But in inetd mode
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* we do not reach this */
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free(ts);
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/* Scan all sessions and find new maxfd */
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maxfd = 0;
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ts = sessions;
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while (ts) {
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if (maxfd < ts->ptyfd)
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maxfd = ts->ptyfd;
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if (maxfd < ts->sockfd_read)
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maxfd = ts->sockfd_read;
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#if 0
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/* Again, sockfd_write == sockfd_read here */
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if (maxfd < ts->sockfd_write)
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maxfd = ts->sockfd_write;
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#endif
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ts = ts->next;
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}
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}
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#else /* !FEATURE_TELNETD_STANDALONE */
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/* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
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#define free_session(ts) return 0
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#endif
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static void handle_sigchld(int sig ATTRIBUTE_UNUSED)
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{
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pid_t pid;
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struct tsession *ts;
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/* Looping: more than one child may have exited */
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while (1) {
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pid = wait_any_nohang(NULL);
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if (pid <= 0)
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break;
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ts = sessions;
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while (ts) {
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if (ts->shell_pid == pid) {
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ts->shell_pid = -1;
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break;
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}
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ts = ts->next;
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}
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}
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}
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int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
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{
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fd_set rdfdset, wrfdset;
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unsigned opt;
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int count;
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struct tsession *ts;
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#if ENABLE_FEATURE_TELNETD_STANDALONE
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#define IS_INETD (opt & OPT_INETD)
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int master_fd = master_fd; /* be happy, gcc */
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unsigned portnbr = 23;
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char *opt_bindaddr = NULL;
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char *opt_portnbr;
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#else
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enum {
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IS_INETD = 1,
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master_fd = -1,
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portnbr = 23,
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};
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#endif
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/* Even if !STANDALONE, we accept (and ignore) -i, thus people
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* don't need to guess whether it's ok to pass -i to us */
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opt = getopt32(argv, "f:l:Ki" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
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&issuefile, &loginpath
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USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
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if (!IS_INETD /*&& !re_execed*/) {
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/* inform that we start in standalone mode?
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* May be useful when people forget to give -i */
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/*bb_error_msg("listening for connections");*/
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if (!(opt & OPT_FOREGROUND)) {
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/* DAEMON_CHDIR_ROOT was giving inconsistent
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* behavior with/without -F, -i */
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bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
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}
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}
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/* Redirect log to syslog early, if needed */
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if (IS_INETD || !(opt & OPT_FOREGROUND)) {
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openlog(applet_name, 0, LOG_USER);
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logmode = LOGMODE_SYSLOG;
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}
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USE_FEATURE_TELNETD_STANDALONE(
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if (opt & OPT_PORT)
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portnbr = xatou16(opt_portnbr);
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);
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/* Used to check access(loginpath, X_OK) here. Pointless.
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* exec will do this for us for free later. */
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#if ENABLE_FEATURE_TELNETD_STANDALONE
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if (IS_INETD) {
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sessions = make_new_session(0);
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if (!sessions) /* pty opening or vfork problem, exit */
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return 1; /* make_new_session prints error message */
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} else {
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master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
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xlisten(master_fd, 1);
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}
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#else
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sessions = make_new_session();
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if (!sessions) /* pty opening or vfork problem, exit */
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return 1; /* make_new_session prints error message */
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#endif
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/* We don't want to die if just one session is broken */
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signal(SIGPIPE, SIG_IGN);
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if (opt & OPT_WATCHCHILD)
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signal(SIGCHLD, handle_sigchld);
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else /* prevent dead children from becoming zombies */
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signal(SIGCHLD, SIG_IGN);
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/*
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This is how the buffers are used. The arrows indicate the movement
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of data.
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+-------+ wridx1++ +------+ rdidx1++ +----------+
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| | <-------------- | buf1 | <-------------- | |
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| | size1-- +------+ size1++ | |
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| pty | | socket |
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| | rdidx2++ +------+ wridx2++ | |
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| | --------------> | buf2 | --------------> | |
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+-------+ size2++ +------+ size2-- +----------+
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size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
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size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
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Each session has got two buffers. Buffers are circular. If sizeN == 0,
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buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
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rdidxN == wridxN.
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*/
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again:
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FD_ZERO(&rdfdset);
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FD_ZERO(&wrfdset);
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/* Select on the master socket, all telnet sockets and their
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* ptys if there is room in their session buffers.
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* NB: scalability problem: we recalculate entire bitmap
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* before each select. Can be a problem with 500+ connections. */
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ts = sessions;
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while (ts) {
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struct tsession *next = ts->next; /* in case we free ts. */
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if (ts->shell_pid == -1) {
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/* Child died and we detected that */
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free_session(ts);
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} else {
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if (ts->size1 > 0) /* can write to pty */
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FD_SET(ts->ptyfd, &wrfdset);
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if (ts->size1 < BUFSIZE) /* can read from socket */
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FD_SET(ts->sockfd_read, &rdfdset);
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if (ts->size2 > 0) /* can write to socket */
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FD_SET(ts->sockfd_write, &wrfdset);
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if (ts->size2 < BUFSIZE) /* can read from pty */
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FD_SET(ts->ptyfd, &rdfdset);
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}
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ts = next;
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}
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if (!IS_INETD) {
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FD_SET(master_fd, &rdfdset);
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/* This is needed because free_session() does not
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* take master_fd into account when it finds new
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* maxfd among remaining fd's */
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if (master_fd > maxfd)
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maxfd = master_fd;
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}
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count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
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if (count < 0)
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goto again; /* EINTR or ENOMEM */
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#if ENABLE_FEATURE_TELNETD_STANDALONE
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/* First check for and accept new sessions. */
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if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
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int fd;
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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);
|
|
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;
|
|
unsigned char *ptr;
|
|
/* Write to pty from buffer 1. */
|
|
ptr = remove_iacs(ts, &num_totty);
|
|
count = safe_write(ts->ptyfd, ptr, num_totty);
|
|
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 = safe_write(ts->sockfd_write, TS_BUF2 + 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;
|
|
}
|
|
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. */
|
|
count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
|
|
count = safe_read(ts->sockfd_read, TS_BUF1 + 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->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->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:
|
|
free_session(ts);
|
|
ts = next;
|
|
}
|
|
|
|
goto again;
|
|
}
|