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ifupdown: improve compatibility with Debian
[oweals/busybox.git] / networking / telnetd.c
diff --git a/networking/telnetd.c b/networking/telnetd.c
index 20c57925f4d45ec37fd69ab3abb483931130aa25..33020f1b416436d6ad1315459704637401ca4a40 100644 (file)
--- a/networking/telnetd.c
+++ b/networking/telnetd.c
@@ -3,7 +3,7 @@
  * Simple telnet server
  * Bjorn Wesen, Axis Communications AB (bjornw@axis.com)
  *
  * 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
  *
  * ---------------------------------------------------------------------------
  * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN
@@ -11,39 +11,61 @@
  *
  * The telnetd manpage says it all:
  *
  *
  * 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.
+ * 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
  *
  * Vladimir Oleynik <dzo@simtreas.ru> 2001
- *     Set process group corrections, initial busybox port
+ * Set process group corrections, initial busybox port
  */
 
  */
 
+//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 <syslog.h>
 
 #if DEBUG
 #define DEBUG 0
 
 #include "libbb.h"
 #include <syslog.h>
 
 #if DEBUG
-#define TELCMDS
-#define TELOPTS
+# define TELCMDS
+# define TELOPTS
 #endif
 #include <arpa/telnet.h>
 
 #endif
 #include <arpa/telnet.h>
 
-/* Structure that describes a session */
+
 struct tsession {
        struct tsession *next;
 struct tsession {
        struct tsession *next;
-       int sockfd_read, sockfd_write, ptyfd;
-       int shell_pid;
+       pid_t shell_pid;
+       int sockfd_read;
+       int sockfd_write;
+       int ptyfd;
 
        /* two circular buffers */
        /*char *buf1, *buf2;*/
 
        /* two circular buffers */
        /*char *buf1, *buf2;*/
-/*#define TS_BUF1 ts->buf1*/
-/*#define TS_BUF2 TS_BUF2*/
-#define TS_BUF1 ((unsigned char*)(ts + 1))
-#define TS_BUF2 (((unsigned char*)(ts + 1)) + BUFSIZE)
+/*#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;
 };
        int rdidx1, wridx1, size1;
        int rdidx2, wridx2, size2;
 };
@@ -54,14 +76,17 @@ enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
 
 
 /* Globals */
 
 
 /* Globals */
-static int maxfd;
-static struct tsession *sessions;
-#if ENABLE_LOGIN
-static const char *loginpath = "/bin/login";
-#else
-static const char *loginpath = DEFAULT_SHELL;
-#endif
-static const char *issuefile = "/etc/issue.net";
+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 { \
+       G.loginpath = "/bin/login"; \
+       G.issuefile = "/etc/issue.net"; \
+} while (0)
 
 
 /*
 
 
 /*
@@ -70,17 +95,14 @@ static const char *issuefile = "/etc/issue.net";
    string of characters fit for the terminal.  Do this by packing
    all characters meant for the terminal sequentially towards the end of buf.
 
    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.
+   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.
 
    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
+   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.
 
    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.
-
    CR-LF ->'s CR mapping is also done here, for convenience.
 
    NB: may fail to remove iacs which wrap around buffer!
    CR-LF ->'s CR mapping is also done here, for convenience.
 
    NB: may fail to remove iacs which wrap around buffer!
@@ -88,7 +110,7 @@ static const char *issuefile = "/etc/issue.net";
 static unsigned char *
 remove_iacs(struct tsession *ts, int *pnum_totty)
 {
 static unsigned char *
 remove_iacs(struct tsession *ts, int *pnum_totty)
 {
-       unsigned char *ptr0 = TS_BUF1 + ts->wridx1;
+       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);
        unsigned char *ptr = ptr0;
        unsigned char *totty = ptr;
        unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
@@ -100,99 +122,166 @@ remove_iacs(struct tsession *ts, int *pnum_totty)
 
                        *totty++ = c;
                        ptr++;
 
                        *totty++ = c;
                        ptr++;
-                       /* We now map \r\n ==> \r for pragmatic reasons.
+                       /* 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++;
                         * Many client implementations send \r\n when
                         * the user hits the CarriageReturn key.
                         */
                        if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
                                ptr++;
-               } else {
-                       /*
-                        * TELOPT_NAWS support!
-                        */
-                       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;
-                       }
+                       continue;
+               }
 
 
-                       /*
-                        * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
-                        */
-                       else if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
-                               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];
-                               ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
-                               ptr += 9;
-                       } else {
-                               /* skip 3-byte IAC non-SB cmd */
+               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;
+               }
+
+               /*
+                * TELOPT_NAWS support!
+                */
+               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;
+               }
+               /*
+                * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE
+                */
+               if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) {
+                       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];
+                       ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws);
+                       ptr += 9;
+                       continue;
+               }
+               /* skip 3-byte IAC non-SB cmd */
 #if DEBUG
 #if DEBUG
-                               fprintf(stderr, "Ignoring IAC %s,%s\n",
-                                       TELCMD(ptr[1]), TELOPT(ptr[2]));
+               fprintf(stderr, "Ignoring IAC %s,%s\n",
+                               TELCMD(ptr[1]), TELOPT(ptr[2]));
 #endif
 #endif
-                               ptr += 3;
-                       }
-               }
+               ptr += 3;
        }
 
        num_totty = totty - ptr0;
        *pnum_totty = num_totty;
        }
 
        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. */
+       /* 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;
        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 */
+       /* Move chars meant for the terminal towards the end of the buffer */
        return memmove(ptr - num_totty, ptr0, num_totty);
 }
 
        return memmove(ptr - num_totty, ptr0, num_totty);
 }
 
+/*
+ * Converting single IAC into double on output
+ */
+static size_t iac_safe_write(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);
+                       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(
 
 static struct tsession *
 make_new_session(
-               USE_FEATURE_TELNETD_STANDALONE(int sock)
-               SKIP_FEATURE_TELNETD_STANDALONE(void)
+               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;
        const char *login_argv[2];
        struct termios termbuf;
        int fd, pid;
-       char tty_name[32];
+       char tty_name[GETPTY_BUFSIZE];
        struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
 
        /*ts->buf1 = (char *)(ts + 1);*/
        /*ts->buf2 = ts->buf1 + 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 = getpty(tty_name, 32);
-       if (fd < 0) {
-               bb_error_msg("can't create pty");
-               return NULL;
-       }
-       if (fd > maxfd)
-               maxfd = fd;
+       /* 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);
        ts->ptyfd = fd;
        ndelay_on(fd);
+       close_on_exec_on(fd);
+
+       /* SO_KEEPALIVE by popular demand */
+       setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
 #if ENABLE_FEATURE_TELNETD_STANDALONE
        ts->sockfd_read = sock;
        ndelay_on(sock);
 #if ENABLE_FEATURE_TELNETD_STANDALONE
        ts->sockfd_read = sock;
        ndelay_on(sock);
-       if (!sock) { /* We are called with fd 0 - we are in inetd mode */
+       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;
                sock++; /* so use fd 1 for output */
                ndelay_on(sock);
        }
        ts->sockfd_write = sock;
-       if (sock > maxfd)
-               maxfd = 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
 #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
        /* 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
@@ -201,16 +290,27 @@ make_new_session(
                static const char iacs_to_send[] ALIGN1 = {
                        IAC, DO, TELOPT_ECHO,
                        IAC, DO, TELOPT_NAWS,
                static const char iacs_to_send[] ALIGN1 = {
                        IAC, DO, TELOPT_ECHO,
                        IAC, DO, TELOPT_NAWS,
-                       IAC, DO, TELOPT_LFLOW,
+                       /* This requires telnetd.ctrlSQ.patch (incomplete) */
+                       /*IAC, DO, TELOPT_LFLOW,*/
                        IAC, WILL, TELOPT_ECHO,
                        IAC, WILL, TELOPT_SGA
                };
                        IAC, WILL, TELOPT_ECHO,
                        IAC, WILL, TELOPT_SGA
                };
-               memcpy(TS_BUF2, iacs_to_send, sizeof(iacs_to_send));
-               ts->rdidx2 = sizeof(iacs_to_send);
-               ts->size2 = sizeof(iacs_to_send);
+               /* This confuses iac_safe_write(), 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(NULL); /* flush all streams */
+       fflush_all();
        pid = vfork(); /* NOMMU-friendly */
        if (pid < 0) {
                free(ts);
        pid = vfork(); /* NOMMU-friendly */
        if (pid < 0) {
                free(ts);
@@ -228,72 +328,80 @@ make_new_session(
        /* Child */
        /* Careful - we are after vfork! */
 
        /* Child */
        /* Careful - we are after vfork! */
 
-       /* make new session and process group */
-       setsid();
-
-       /* Restore default signal handling */
+       /* Restore default signal handling ASAP */
        bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
 
        bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
 
-       /* open the child's side of the tty. */
+       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! */
        /* NB: setsid() disconnects from any previous ctty's. Therefore
         * we must open child's side of the tty AFTER setsid! */
-       fd = xopen(tty_name, O_RDWR); /* becomes our ctty */
-       dup2(fd, 0);
-       dup2(fd, 1);
-       dup2(fd, 2);
-       while (fd > 2) close(fd--);
-       tcsetpgrp(0, getpid()); /* 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)). */
+       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;*/
        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(0, TCSANOW, &termbuf);
+       tcsetattr_stdin_TCSANOW(&termbuf);
 
 
-       /* Uses FILE-based I/O to stdout, but does fflush(stdout),
+       /* 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!) */
         * 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(issuefile, NULL);
+       print_login_issue(G.issuefile, tty_name);
 
        /* Exec shell / login / whatever */
 
        /* Exec shell / login / whatever */
-       login_argv[0] = loginpath;
+       login_argv[0] = G.loginpath;
        login_argv[1] = NULL;
        /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
        login_argv[1] = NULL;
        /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
-        * exec external program */
-       BB_EXECVP(loginpath, (char **)login_argv);
+        * 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 is safer with vfork, and we shouldn't send message
         * to remote clients anyway */
-       _exit(1); /*bb_perror_msg_and_die("execv %s", loginpath);*/
+       _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
 }
 
 }
 
-/* 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 */
-       OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */
-};
-
 #if ENABLE_FEATURE_TELNETD_STANDALONE
 
 static void
 free_session(struct tsession *ts)
 {
 #if ENABLE_FEATURE_TELNETD_STANDALONE
 
 static void
 free_session(struct tsession *ts)
 {
-       struct tsession *t = sessions;
+       struct tsession *t;
 
        if (option_mask32 & OPT_INETD)
 
        if (option_mask32 & OPT_INETD)
-               exit(0);
+               exit(EXIT_SUCCESS);
 
        /* Unlink this telnet session from the session list */
 
        /* Unlink this telnet session from the session list */
+       t = G.sessions;
        if (t == ts)
        if (t == ts)
-               sessions = ts->next;
+               G.sessions = ts->next;
        else {
                while (t->next != ts)
                        t = t->next;
        else {
                while (t->next != ts)
                        t = t->next;
@@ -305,7 +413,7 @@ free_session(struct tsession *ts)
         * doesn't send SIGKILL. When we close ptyfd,
         * kernel sends SIGHUP to processes having slave side opened. */
        kill(ts->shell_pid, SIGKILL);
         * doesn't send SIGKILL. When we close ptyfd,
         * kernel sends SIGHUP to processes having slave side opened. */
        kill(ts->shell_pid, SIGKILL);
-       wait4(ts->shell_pid, NULL, 0, NULL);
+       waitpid(ts->shell_pid, NULL, 0);
 #endif
        close(ts->ptyfd);
        close(ts->sockfd_read);
 #endif
        close(ts->ptyfd);
        close(ts->sockfd_read);
@@ -315,17 +423,17 @@ free_session(struct tsession *ts)
        free(ts);
 
        /* Scan all sessions and find new maxfd */
        free(ts);
 
        /* Scan all sessions and find new maxfd */
-       maxfd = 0;
-       ts = sessions;
+       G.maxfd = 0;
+       ts = G.sessions;
        while (ts) {
        while (ts) {
-               if (maxfd < ts->ptyfd)
-                       maxfd = ts->ptyfd;
-               if (maxfd < ts->sockfd_read)
-                       maxfd = ts->sockfd_read;
+               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 0
                /* Again, sockfd_write == sockfd_read here */
-               if (maxfd < ts->sockfd_write)
-                       maxfd = ts->sockfd_write;
+               if (G.maxfd < ts->sockfd_write)
+                       G.maxfd = ts->sockfd_write;
 #endif
                ts = ts->next;
        }
 #endif
                ts = ts->next;
        }
@@ -333,34 +441,46 @@ free_session(struct tsession *ts)
 
 #else /* !FEATURE_TELNETD_STANDALONE */
 
 
 #else /* !FEATURE_TELNETD_STANDALONE */
 
-/* Used in main() only, thus "return 0" actually is exit(0). */
+/* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
 #define free_session(ts) return 0
 
 #endif
 
 #define free_session(ts) return 0
 
 #endif
 
-static void handle_sigchld(int sig ATTRIBUTE_UNUSED)
+static void handle_sigchld(int sig UNUSED_PARAM)
 {
        pid_t pid;
        struct tsession *ts;
 {
        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;
 
        /* Looping: more than one child may have exited */
        while (1) {
                pid = wait_any_nohang(NULL);
                if (pid <= 0)
                        break;
-               ts = sessions;
+               ts = G.sessions;
                while (ts) {
                        if (ts->shell_pid == pid) {
                                ts->shell_pid = -1;
                while (ts) {
                        if (ts->shell_pid == pid) {
                                ts->shell_pid = -1;
+// man utmp:
+// When init(8) finds that a process has exited, it locates its utmp entry
+// by ut_pid, sets ut_type to DEAD_PROCESS, and clears ut_user, ut_host
+// and ut_time with null bytes.
+// [same applies to other processes which maintain utmp entries, like telnetd]
+//
+// We do not bother actually clearing fields:
+// it might be interesting to know who was logged in and from where
+                               update_utmp(pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL);
                                break;
                        }
                        ts = ts->next;
                }
        }
                                break;
                        }
                        ts = ts->next;
                }
        }
+
+       errno = save_errno;
 }
 
 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 }
 
 int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
+int telnetd_main(int argc UNUSED_PARAM, char **argv)
 {
        fd_set rdfdset, wrfdset;
        unsigned opt;
 {
        fd_set rdfdset, wrfdset;
        unsigned opt;
@@ -368,22 +488,29 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
        struct tsession *ts;
 #if ENABLE_FEATURE_TELNETD_STANDALONE
 #define IS_INETD (opt & OPT_INETD)
        struct tsession *ts;
 #if ENABLE_FEATURE_TELNETD_STANDALONE
 #define IS_INETD (opt & OPT_INETD)
-       int master_fd = master_fd; /* be happy, gcc */
-       unsigned portnbr = 23;
+       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,
        char *opt_bindaddr = NULL;
        char *opt_portnbr;
 #else
        enum {
                IS_INETD = 1,
                master_fd = -1,
-               portnbr = 23,
        };
 #endif
        };
 #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 */
        /* 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" USE_FEATURE_TELNETD_STANDALONE("p:b:F"),
-                       &issuefile, &loginpath
-                       USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
+       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 */
        if (!IS_INETD /*&& !re_execed*/) {
                /* inform that we start in standalone mode?
                 * May be useful when people forget to give -i */
@@ -395,31 +522,30 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                }
        }
        /* Redirect log to syslog early, if needed */
                }
        }
        /* Redirect log to syslog early, if needed */
-       if (IS_INETD || !(opt & OPT_FOREGROUND)) {
-               openlog(applet_name, 0, LOG_USER);
+       if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
+               openlog(applet_name, LOG_PID, LOG_DAEMON);
                logmode = LOGMODE_SYSLOG;
        }
                logmode = LOGMODE_SYSLOG;
        }
-       USE_FEATURE_TELNETD_STANDALONE(
-               if (opt & OPT_PORT)
-                       portnbr = xatou16(opt_portnbr);
-       );
-
-       /* Used to check access(loginpath, X_OK) here. Pointless.
-        * exec will do this for us for free later. */
-
 #if ENABLE_FEATURE_TELNETD_STANDALONE
        if (IS_INETD) {
 #if ENABLE_FEATURE_TELNETD_STANDALONE
        if (IS_INETD) {
-               sessions = make_new_session(0);
-               if (!sessions) /* pty opening or vfork problem, exit */
-                       return 1; /* make_new_session prints error message */
+               G.sessions = make_new_session(0);
+               if (!G.sessions) /* pty opening or vfork problem, exit */
+                       return 1; /* make_new_session printed error message */
        } else {
        } else {
-               master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
-               xlisten(master_fd, 1);
+               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
        }
 #else
-       sessions = make_new_session();
-       if (!sessions) /* pty opening or vfork problem, exit */
-               return 1; /* make_new_session prints error message */
+       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 */
 #endif
 
        /* We don't want to die if just one session is broken */
@@ -431,8 +557,8 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                signal(SIGCHLD, SIG_IGN);
 
 /*
                signal(SIGCHLD, SIG_IGN);
 
 /*
-   This is how the buffers are used. The arrows indicate the movement
-   of data.
+   This is how the buffers are used. The arrows indicate data flow.
+
    +-------+     wridx1++     +------+     rdidx1++     +----------+
    |       | <--------------  | buf1 | <--------------  |          |
    |       |     size1--      +------+     size1++      |          |
    +-------+     wridx1++     +------+     rdidx1++     +----------+
    |       | <--------------  | buf1 | <--------------  |          |
    |       |     size1--      +------+     size1++      |          |
@@ -456,9 +582,9 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
         * 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. */
         * 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 = sessions;
+       ts = G.sessions;
        while (ts) {
        while (ts) {
-               struct tsession *next = ts->next; /* in case we free 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);
                if (ts->shell_pid == -1) {
                        /* Child died and we detected that */
                        free_session(ts);
@@ -479,16 +605,29 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                /* This is needed because free_session() does not
                 * take master_fd into account when it finds new
                 * maxfd among remaining fd's */
                /* 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 > maxfd)
-                       maxfd = master_fd;
+               if (master_fd > G.maxfd)
+                       G.maxfd = master_fd;
        }
 
        }
 
-       count = select(maxfd + 1, &rdfdset, &wrfdset, NULL, NULL);
+       {
+               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
        if (count < 0)
                goto again; /* EINTR or ENOMEM */
 
 #if ENABLE_FEATURE_TELNETD_STANDALONE
-       /* First check for and accept new sessions. */
+       /* Check for and accept new sessions */
        if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
                int fd;
                struct tsession *new_ts;
        if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) {
                int fd;
                struct tsession *new_ts;
@@ -496,26 +635,28 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                fd = accept(master_fd, NULL, NULL);
                if (fd < 0)
                        goto again;
                fd = accept(master_fd, NULL, NULL);
                if (fd < 0)
                        goto again;
-               /* Create a new session and link it into our active list */
+               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 = make_new_session(fd);
                if (new_ts) {
-                       new_ts->next = sessions;
-                       sessions = new_ts;
+                       new_ts->next = G.sessions;
+                       G.sessions = new_ts;
                } else {
                        close(fd);
                }
        }
 #endif
 
                } else {
                        close(fd);
                }
        }
 #endif
 
-       /* Then check for data tunneling. */
-       ts = sessions;
+       /* Then check for data tunneling */
+       ts = G.sessions;
        while (ts) { /* For all sessions... */
        while (ts) { /* For all sessions... */
-               struct tsession *next = ts->next; /* in case we free ts. */
+               struct tsession *next = ts->next; /* in case we free ts */
 
                if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
                        int num_totty;
                        unsigned char *ptr;
 
                if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
                        int num_totty;
                        unsigned char *ptr;
-                       /* Write to pty from buffer 1. */
+                       /* Write to pty from buffer 1 */
                        ptr = remove_iacs(ts, &num_totty);
                        count = safe_write(ts->ptyfd, ptr, num_totty);
                        if (count < 0) {
                        ptr = remove_iacs(ts, &num_totty);
                        count = safe_write(ts->ptyfd, ptr, num_totty);
                        if (count < 0) {
@@ -530,9 +671,9 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                }
  skip1:
                if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
                }
  skip1:
                if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
-                       /* Write to socket from buffer 2. */
+                       /* Write to socket from buffer 2 */
                        count = MIN(BUFSIZE - ts->wridx2, ts->size2);
                        count = MIN(BUFSIZE - ts->wridx2, ts->size2);
-                       count = safe_write(ts->sockfd_write, TS_BUF2 + ts->wridx2, count);
+                       count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
                        if (count < 0) {
                                if (errno == EAGAIN)
                                        goto skip2;
                        if (count < 0) {
                                if (errno == EAGAIN)
                                        goto skip2;
@@ -560,16 +701,16 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                }
 
                if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
                }
 
                if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) {
-                       /* Read from socket to buffer 1. */
+                       /* Read from socket to buffer 1 */
                        count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
                        count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
-                       count = safe_read(ts->sockfd_read, TS_BUF1 + ts->rdidx1, count);
+                       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 (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]) {
+                       if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
                                --count;
                        }
                        ts->size1 += count;
                                --count;
                        }
                        ts->size1 += count;
@@ -579,9 +720,9 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                }
  skip3:
                if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
                }
  skip3:
                if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
-                       /* Read from pty to buffer 2. */
+                       /* Read from pty to buffer 2 */
                        count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
                        count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
-                       count = safe_read(ts->ptyfd, TS_BUF2 + ts->rdidx2, count);
+                       count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
                        if (count <= 0) {
                                if (count < 0 && errno == EAGAIN)
                                        goto skip4;
                        if (count <= 0) {
                                if (count < 0 && errno == EAGAIN)
                                        goto skip4;
@@ -596,6 +737,8 @@ int telnetd_main(int argc ATTRIBUTE_UNUSED, char **argv)
                ts = next;
                continue;
  kill_session:
                ts = next;
                continue;
  kill_session:
+               if (ts->shell_pid > 0)
+                       update_utmp(ts->shell_pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL);
                free_session(ts);
                ts = next;
        }
                free_session(ts);
                ts = next;
        }
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