Changeset 2725 in MondoRescue for branches/2.2.9/mindi-busybox/networking/telnetd.c

Timestamp:

Feb 25, 2011, 9:26:54 PM (13 years ago)

Author:

Bruno Cornec

Message:

• Update mindi-busybox to 1.18.3 to avoid problems with the tar command which is now failing on recent versions with busybox 1.7.3

File:

• branches/2.2.9/mindi-busybox/networking/telnetd.c (modified) (6 diffs)

branches/2.2.9/mindi-busybox/networking/telnetd.c

@@ -4 +4 @@
  * 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.
  *
  * ---------------------------------------------------------------------------
@@ -12 +12 @@
  * 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
- *     Set process group corrections, initial busybox port
+ * Set process group corrections, initial busybox port
  */
-
 #define DEBUG 0
 
 #include "libbb.h"
+#include <syslog.h>
 
 #if DEBUG
-#define TELCMDS
-#define TELOPTS
+# define TELCMDS
+# define TELOPTS
 #endif
 #include <arpa/telnet.h>
-#include <sys/syslog.h>
-
-
-#if ENABLE_LOGIN
-static const char *loginpath = "/bin/login";
-#else
-static const char *loginpath = DEFAULT_SHELL;
-#endif
-
-static const char *issuefile = "/etc/issue.net";
-
-/* structure that describes a session */
+
+#if ENABLE_FEATURE_UTMP
+# include <utmp.h> /* LOGIN_PROCESS */
+#endif
+
 
 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;
+    /*char *buf1, *buf2;*/
+/*#define TS_BUF1(ts) ts->buf1*/
+/*#define TS_BUF2(ts) TS_BUF2(ts)*/
+#define TS_BUF1(ts) ((unsigned char*)(ts + 1))
+#define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE)
     int rdidx1, wridx1, size1;
     int rdidx2, wridx2, size2;
@@ -56 +56 @@
 /* Two buffers are directly after tsession in malloced memory.
  * Make whole thing fit in 4k */
-enum { BUFSIZE = (4*1024 - sizeof(struct tsession)) / 2 };
+enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 };
+
+
+/* Globals */
+struct globals {
+    struct tsession *sessions;
+    const char *loginpath;
+    const char *issuefile;
+    int maxfd;
+} FIX_ALIASING;
+#define G (*(struct globals*)&bb_common_bufsiz1)
+#define INIT_G() do { \
+    G.loginpath = "/bin/login"; \
+    G.issuefile = "/etc/issue.net"; \
+} while (0)
+
 
 /*
-   This is how the buffers are used. The arrows indicate the movement
-   of data.
+   Remove all IAC's from buf1 (received IACs are ignored and must be removed
+   so as to not be interpreted by the terminal).  Make an uninterrupted
+   string of characters fit for the terminal.  Do this by packing
+   all characters meant for the terminal sequentially towards the end of buf.
+
+   Return a pointer to the beginning of the characters meant for the terminal
+   and make *num_totty the number of characters that should be sent to
+   the terminal.
+
+   Note - if an IAC (3 byte quantity) starts before (bf + len) but extends
+   past (bf + len) then that IAC will be left unprocessed and *processed
+   will be less than len.
+
+   CR-LF ->'s CR mapping is also done here, for convenience.
+
+   NB: may fail to remove iacs which wrap around buffer!
+ */
+static unsigned char *
+remove_iacs(struct tsession *ts, int *pnum_totty)
+{
+    unsigned char *ptr0 = TS_BUF1(ts) + ts->wridx1;
+    unsigned char *ptr = ptr0;
+    unsigned char *totty = ptr;
+    unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
+    int num_totty;
+
+    while (ptr < end) {
+        if (*ptr != IAC) {
+            char c = *ptr;
+
+            *totty++ = c;
+            ptr++;
+            /* We map \r\n ==> \r for pragmatic reasons.
+             * Many client implementations send \r\n when
+             * the user hits the CarriageReturn key.
+             */
+            if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0'))
+                ptr++;
+            continue;
+        }
+
+        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
+        fprintf(stderr, "Ignoring IAC %s,%s\n",
+                TELCMD(ptr[1]), TELOPT(ptr[2]));
+#endif
+        ptr += 3;
+    }
+
+    num_totty = totty - ptr0;
+    *pnum_totty = num_totty;
+    /* The difference between ptr and totty is number of iacs
+       we removed from the stream. Adjust buf1 accordingly */
+    if ((ptr - totty) == 0) /* 99.999% of cases */
+        return ptr0;
+    ts->wridx1 += ptr - totty;
+    ts->size1 -= ptr - totty;
+    /* Move chars meant for the terminal towards the end of the buffer */
+    return memmove(ptr - num_totty, ptr0, num_totty);
+}
+
+/*
+ * 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(
+        IF_FEATURE_TELNETD_STANDALONE(int sock)
+        IF_NOT_FEATURE_TELNETD_STANDALONE(void)
+) {
+#if !ENABLE_FEATURE_TELNETD_STANDALONE
+    enum { sock = 0 };
+#endif
+    const char *login_argv[2];
+    struct termios termbuf;
+    int fd, pid;
+    char tty_name[GETPTY_BUFSIZE];
+    struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2);
+
+    /*ts->buf1 = (char *)(ts + 1);*/
+    /*ts->buf2 = ts->buf1 + BUFSIZE;*/
+
+    /* Got a new connection, set up a tty */
+    fd = xgetpty(tty_name);
+    if (fd > G.maxfd)
+        G.maxfd = fd;
+    ts->ptyfd = fd;
+    ndelay_on(fd);
+    close_on_exec_on(fd);
+
+    /* SO_KEEPALIVE by popular demand */
+    setsockopt(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 (sock == 0) { /* We are called with fd 0 - we are in inetd mode */
+        sock++; /* so use fd 1 for output */
+        ndelay_on(sock);
+    }
+    ts->sockfd_write = sock;
+    if (sock > G.maxfd)
+        G.maxfd = sock;
+#else
+    /* ts->sockfd_read = 0; - done by xzalloc */
+    ts->sockfd_write = 1;
+    ndelay_on(0);
+    ndelay_on(1);
+#endif
+
+    /* Make the telnet client understand we will echo characters so it
+     * should not do it locally. We don't tell the client to run linemode,
+     * because we want to handle line editing and tab completion and other
+     * stuff that requires char-by-char support. */
+    {
+        static const char iacs_to_send[] ALIGN1 = {
+            IAC, DO, TELOPT_ECHO,
+            IAC, DO, TELOPT_NAWS,
+            /* This requires telnetd.ctrlSQ.patch (incomplete) */
+            /*IAC, DO, TELOPT_LFLOW,*/
+            IAC, WILL, TELOPT_ECHO,
+            IAC, WILL, TELOPT_SGA
+        };
+        /* This confuses 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_all();
+    pid = vfork(); /* NOMMU-friendly */
+    if (pid < 0) {
+        free(ts);
+        close(fd);
+        /* sock will be closed by caller */
+        bb_perror_msg("vfork");
+        return NULL;
+    }
+    if (pid > 0) {
+        /* Parent */
+        ts->shell_pid = pid;
+        return ts;
+    }
+
+    /* Child */
+    /* Careful - we are after vfork! */
+
+    /* Restore default signal handling ASAP */
+    bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL);
+
+    if (ENABLE_FEATURE_UTMP) {
+        len_and_sockaddr *lsa = get_peer_lsa(sock);
+        char *hostname = NULL;
+        if (lsa) {
+            hostname = xmalloc_sockaddr2dotted(&lsa->u.sa);
+            free(lsa);
+        }
+        write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname);
+        free(hostname);
+    }
+
+    /* Make new session and process group */
+    setsid();
+
+    /* Open the child's side of the tty */
+    /* NB: setsid() disconnects from any previous ctty's. Therefore
+     * we must open child's side of the tty AFTER setsid! */
+    close(0);
+    xopen(tty_name, O_RDWR); /* becomes our ctty */
+    xdup2(0, 1);
+    xdup2(0, 2);
+    pid = getpid();
+    tcsetpgrp(0, pid); /* switch this tty's process group to us */
+
+    /* The pseudo-terminal allocated to the client is configured to operate
+     * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */
+    tcgetattr(0, &termbuf);
+    termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */
+    termbuf.c_oflag |= ONLCR | XTABS;
+    termbuf.c_iflag |= ICRNL;
+    termbuf.c_iflag &= ~IXOFF;
+    /*termbuf.c_lflag &= ~ICANON;*/
+    tcsetattr_stdin_TCSANOW(&termbuf);
+
+    /* Uses FILE-based I/O to stdout, but does fflush_all(),
+     * so should be safe with vfork.
+     * I fear, though, that some users will have ridiculously big
+     * issue files, and they may block writing to fd 1,
+     * (parent is supposed to read it, but parent waits
+     * for vforked child to exec!) */
+    print_login_issue(G.issuefile, tty_name);
+
+    /* Exec shell / login / whatever */
+    login_argv[0] = G.loginpath;
+    login_argv[1] = NULL;
+    /* exec busybox applet (if PREFER_APPLETS=y), if that fails,
+     * exec external program.
+     * NB: sock is either 0 or has CLOEXEC set on it.
+     * fd has CLOEXEC set on it too. These two fds will be closed here.
+     */
+    BB_EXECVP(G.loginpath, (char **)login_argv);
+    /* _exit is safer with vfork, and we shouldn't send message
+     * to remote clients anyway */
+    _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/
+}
+
+#if ENABLE_FEATURE_TELNETD_STANDALONE
+
+static void
+free_session(struct tsession *ts)
+{
+    struct tsession *t;
+
+    if (option_mask32 & OPT_INETD)
+        exit(EXIT_SUCCESS);
+
+    /* Unlink this telnet session from the session list */
+    t = G.sessions;
+    if (t == ts)
+        G.sessions = ts->next;
+    else {
+        while (t->next != ts)
+            t = t->next;
+        t->next = ts->next;
+    }
+
+#if 0
+    /* It was said that "normal" telnetd just closes ptyfd,
+     * doesn't send SIGKILL. When we close ptyfd,
+     * kernel sends SIGHUP to processes having slave side opened. */
+    kill(ts->shell_pid, SIGKILL);
+    waitpid(ts->shell_pid, NULL, 0);
+#endif
+    close(ts->ptyfd);
+    close(ts->sockfd_read);
+    /* We do not need to close(ts->sockfd_write), it's the same
+     * as sockfd_read unless we are in inetd mode. But in inetd mode
+     * we do not reach this */
+    free(ts);
+
+    /* Scan all sessions and find new maxfd */
+    G.maxfd = 0;
+    ts = G.sessions;
+    while (ts) {
+        if (G.maxfd < ts->ptyfd)
+            G.maxfd = ts->ptyfd;
+        if (G.maxfd < ts->sockfd_read)
+            G.maxfd = ts->sockfd_read;
+#if 0
+        /* Again, sockfd_write == sockfd_read here */
+        if (G.maxfd < ts->sockfd_write)
+            G.maxfd = ts->sockfd_write;
+#endif
+        ts = ts->next;
+    }
+}
+
+#else /* !FEATURE_TELNETD_STANDALONE */
+
+/* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */
+#define free_session(ts) return 0
+
+#endif
+
+static void handle_sigchld(int sig UNUSED_PARAM)
+{
+    pid_t pid;
+    struct tsession *ts;
+    int save_errno = errno;
+
+    /* Looping: more than one child may have exited */
+    while (1) {
+        pid = wait_any_nohang(NULL);
+        if (pid <= 0)
+            break;
+        ts = G.sessions;
+        while (ts) {
+            if (ts->shell_pid == pid) {
+                ts->shell_pid = -1;
+// 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;
+        }
+    }
+
+    errno = save_errno;
+}
+
+int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int telnetd_main(int argc UNUSED_PARAM, char **argv)
+{
+    fd_set rdfdset, wrfdset;
+    unsigned opt;
+    int count;
+    struct tsession *ts;
+#if ENABLE_FEATURE_TELNETD_STANDALONE
+#define IS_INETD (opt & OPT_INETD)
+    int master_fd = master_fd; /* for compiler */
+    int sec_linger = sec_linger;
+    char *opt_bindaddr = NULL;
+    char *opt_portnbr;
+#else
+    enum {
+        IS_INETD = 1,
+        master_fd = -1,
+    };
+#endif
+    INIT_G();
+
+    /* -w NUM, and implies -F. -w and -i don't mix */
+    IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:w+:i--w:w--i";)
+    /* Even if !STANDALONE, we accept (and ignore) -i, thus people
+     * don't need to guess whether it's ok to pass -i to us */
+    opt = getopt32(argv, "f:l:Ki"
+            IF_FEATURE_TELNETD_STANDALONE("p:b:F")
+            IF_FEATURE_TELNETD_INETD_WAIT("Sw:"),
+            &G.issuefile, &G.loginpath
+            IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr)
+            IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger)
+    );
+    if (!IS_INETD /*&& !re_execed*/) {
+        /* inform that we start in standalone mode?
+         * May be useful when people forget to give -i */
+        /*bb_error_msg("listening for connections");*/
+        if (!(opt & OPT_FOREGROUND)) {
+            /* DAEMON_CHDIR_ROOT was giving inconsistent
+             * behavior with/without -F, -i */
+            bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv);
+        }
+    }
+    /* Redirect log to syslog early, if needed */
+    if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) {
+        openlog(applet_name, LOG_PID, LOG_DAEMON);
+        logmode = LOGMODE_SYSLOG;
+    }
+#if ENABLE_FEATURE_TELNETD_STANDALONE
+    if (IS_INETD) {
+        G.sessions = make_new_session(0);
+        if (!G.sessions) /* pty opening or vfork problem, exit */
+            return 1; /* make_new_session printed error message */
+    } else {
+        master_fd = 0;
+        if (!(opt & OPT_WAIT)) {
+            unsigned portnbr = 23;
+            if (opt & OPT_PORT)
+                portnbr = xatou16(opt_portnbr);
+            master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
+            xlisten(master_fd, 1);
+        }
+        close_on_exec_on(master_fd);
+    }
+#else
+    G.sessions = make_new_session();
+    if (!G.sessions) /* pty opening or vfork problem, exit */
+        return 1; /* make_new_session printed error message */
+#endif
+
+    /* We don't want to die if just one session is broken */
+    signal(SIGPIPE, SIG_IGN);
+
+    if (opt & OPT_WATCHCHILD)
+        signal(SIGCHLD, handle_sigchld);
+    else /* prevent dead children from becoming zombies */
+        signal(SIGCHLD, SIG_IGN);
+
+/*
+   This is how the buffers are used. The arrows indicate data flow.
 
    +-------+     wridx1++     +------+     rdidx1++     +----------+
@@ -70 +550 @@
    +-------+     size2++      +------+     size2--      +----------+
 
-   Each session has got two buffers.
+   size1: "how many bytes are buffered for pty between rdidx1 and wridx1?"
+   size2: "how many bytes are buffered for socket between rdidx2 and wridx2?"
+
+   Each session has got two buffers. Buffers are circular. If sizeN == 0,
+   buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases
+   rdidxN == wridxN.
 */
-
-static int maxfd;
-
-static struct tsession *sessions;
-
-
-/*
-   Remove all IAC's from the buffer pointed to by bf (received IACs are ignored
-   and must be removed so as to not be interpreted by the terminal).  Make an
-   uninterrupted string of characters fit for the terminal.  Do this by packing
-   all characters meant for the terminal sequentially towards the end of bf.
-
-   Return a pointer to the beginning of the characters meant for the terminal.
-   and make *num_totty the number of characters that should be sent to
-   the terminal.
-
-   Note - If an IAC (3 byte quantity) starts before (bf + len) but extends
-   past (bf + len) then that IAC will be left unprocessed and *processed will be
-   less than len.
-
-   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
- */
-static char *
-remove_iacs(struct tsession *ts, int *pnum_totty)
-{
-    unsigned char *ptr0 = (unsigned char *)ts->buf1 + ts->wridx1;
-    unsigned char *ptr = ptr0;
-    unsigned char *totty = ptr;
-    unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1);
-    int processed;
-    int num_totty;
-
-    while (ptr < end) {
-        if (*ptr != IAC) {
-            int c = *ptr;
-            *totty++ = *ptr++;
-            /* We now map \r\n ==> \r for pragmatic reasons.
-             * Many client implementations send \r\n when
-             * the user hits the CarriageReturn key.
-             */
-            if (c == '\r' && (*ptr == '\n' || *ptr == 0) && ptr < end)
-                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;
-            }
-
-            /*
-             * 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 DEBUG
-                fprintf(stderr, "Ignoring IAC %s,%s\n",
-                    TELCMD(ptr[1]), TELOPT(ptr[2]));
-#endif
-                ptr += 3;
-            }
-        }
-    }
-
-    processed = ptr - ptr0;
-    num_totty = totty - ptr0;
-    /* the difference between processed and num_to tty
-       is all the iacs we removed from the stream.
-       Adjust buf1 accordingly. */
-    ts->wridx1 += processed - num_totty;
-    ts->size1 -= processed - num_totty;
-    *pnum_totty = num_totty;
-    /* move the chars meant for the terminal towards the end of the
-    buffer. */
-    return memmove(ptr - num_totty, ptr0, num_totty);
-}
-
-
-static int
-getpty(char *line, int size)
-{
-    int p;
-#if ENABLE_FEATURE_DEVPTS
-    p = open("/dev/ptmx", O_RDWR);
-    if (p > 0) {
-        const char *name;
-        grantpt(p);
-        unlockpt(p);
-        name = ptsname(p);
-        if (!name) {
-            bb_perror_msg("ptsname error (is /dev/pts mounted?)");
-            return -1;
-        }
-        safe_strncpy(line, name, size);
-        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] = j < 10 ? j + '0' : j - 10 + 'a';
-            if (DEBUG)
-                fprintf(stderr, "Trying to open device: %s\n", line);
-            p = open(line, O_RDWR | O_NOCTTY);
-            if (p >= 0) {
-                line[5] = 't';
-                return p;
-            }
-        }
-    }
-#endif /* FEATURE_DEVPTS */
-    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(
-        USE_FEATURE_TELNETD_STANDALONE(int sock_r, int sock_w)
-        SKIP_FEATURE_TELNETD_STANDALONE(void)
-) {
-    const char *login_argv[2];
-    struct termios termbuf;
-    int fd, pid;
-    char tty_name[32];
-    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("all terminals in use");
-        return NULL;
-    }
-    if (fd > maxfd) maxfd = fd;
-    ndelay_on(ts->ptyfd = fd);
-#if ENABLE_FEATURE_TELNETD_STANDALONE
-    if (sock_w > maxfd) maxfd = sock_w;
-    if (sock_r > maxfd) maxfd = sock_r;
-    ndelay_on(ts->sockfd_write = sock_w);
-    ndelay_on(ts->sockfd_read = sock_r);
-#else
-    ts->sockfd_write = 1;
-    /* xzalloc: ts->sockfd_read = 0; */
-    ndelay_on(0);
-    ndelay_on(1);
-#endif
-    /* Make the telnet client understand we will echo characters so it
-     * should not do it locally. We don't tell the client to run linemode,
-     * because we want to handle line editing and tab completion and other
-     * stuff that requires char-by-char support. */
-    send_iac(ts, DO, TELOPT_ECHO);
-    send_iac(ts, DO, TELOPT_NAWS);
-    send_iac(ts, DO, TELOPT_LFLOW);
-    send_iac(ts, WILL, TELOPT_ECHO);
-    send_iac(ts, WILL, TELOPT_SGA);
-
-    pid = fork();
-    if (pid < 0) {
-        free(ts);
-        close(fd);
-        bb_perror_msg("fork");
-        return NULL;
-    }
-    if (pid > 0) {
-        /* parent */
-        ts->shell_pid = pid;
-        return ts;
-    }
-
-    /* child */
-
-    /* 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! */
-    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)). */
-    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);
-
-    print_login_issue(issuefile, NULL);
-
-    /* exec shell / login /whatever */
-    login_argv[0] = loginpath;
-    login_argv[1] = NULL;
-    execv(loginpath, (char **)login_argv);
-    /* Hmmm... this gets sent to the client thru fd#2! Is it ok?? */
-    bb_perror_msg_and_die("execv %s", loginpath);
-}
-
-#if ENABLE_FEATURE_TELNETD_STANDALONE
-
-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;
-    }
-
-    kill(ts->shell_pid, SIGKILL);
-    wait4(ts->shell_pid, NULL, 0, NULL);
-    close(ts->ptyfd);
-    close(ts->sockfd_read);
-    /* error if ts->sockfd_read == ts->sockfd_write. So what? ;) */
-    close(ts->sockfd_write);
-    free(ts);
-
-    /* scan all sessions and find new maxfd */
-    ts = sessions;
-    maxfd = 0;
-    while (ts) {
-        if (maxfd < ts->ptyfd)
-            maxfd = ts->ptyfd;
-        if (maxfd < ts->sockfd_read)
-            maxfd = ts->sockfd_read;
-        if (maxfd < ts->sockfd_write)
-            maxfd = ts->sockfd_write;
-        ts = ts->next;
-    }
-}
-
-#else /* !FEATURE_TELNETD_STANDALONE */
-
-/* Never actually called */
-void free_session(struct tsession *ts);
-
-#endif
-
-
-int telnetd_main(int argc, char **argv);
-int telnetd_main(int argc, char **argv)
-{
-    fd_set rdfdset, wrfdset;
-    unsigned opt;
-    int selret, maxlen, w, r;
-    struct tsession *ts;
-#if ENABLE_FEATURE_TELNETD_STANDALONE
-#define IS_INETD (opt & OPT_INETD)
-    int master_fd = -1; /* be happy, gcc */
-    unsigned portnbr = 23;
-    char *opt_bindaddr = NULL;
-    char *opt_portnbr;
-#else
-    enum {
-        IS_INETD = 1,
-        master_fd = -1,
-        portnbr = 23,
-    };
-#endif
-    enum {
-        OPT_PORT = 4 * ENABLE_FEATURE_TELNETD_STANDALONE,
-        OPT_FOREGROUND = 0x10 * ENABLE_FEATURE_TELNETD_STANDALONE,
-        OPT_INETD = 0x20 * ENABLE_FEATURE_TELNETD_STANDALONE,
-    };
-
-    opt = getopt32(argv, "f:l:" USE_FEATURE_TELNETD_STANDALONE("p:b:Fi"),
-            &issuefile, &loginpath
-            USE_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr));
-    /* Redirect log to syslog early, if needed */
-    if (IS_INETD || !(opt & OPT_FOREGROUND)) {
-        openlog(applet_name, 0, LOG_USER);
-        logmode = LOGMODE_SYSLOG;
-    }
-    //if (opt & 1) // -f
-    //if (opt & 2) // -l
-    USE_FEATURE_TELNETD_STANDALONE(
-        if (opt & OPT_PORT) // -p
-            portnbr = xatou16(opt_portnbr);
-        //if (opt & 8) // -b
-        //if (opt & 0x10) // -F
-        //if (opt & 0x20) // -i
-    );
-
-    /* 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) {
-        sessions = make_new_session(0, 1);
-    } else {
-        master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr);
-        xlisten(master_fd, 1);
-        if (!(opt & OPT_FOREGROUND))
-            bb_daemonize(DAEMON_CHDIR_ROOT);
-    }
-#else
-    sessions = make_new_session();
-#endif
-
-    /* We don't want to die if just one session is broken */
-    signal(SIGPIPE, SIG_IGN);
-
  again:
     FD_ZERO(&rdfdset);
     FD_ZERO(&wrfdset);
+
+    /* Select on the master socket, all telnet sockets and their
+     * ptys if there is room in their session buffers.
+     * NB: scalability problem: we recalculate entire bitmap
+     * before each select. Can be a problem with 500+ connections. */
+    ts = G.sessions;
+    while (ts) {
+        struct tsession *next = ts->next; /* in case we free ts */
+        if (ts->shell_pid == -1) {
+            /* Child died and we detected that */
+            free_session(ts);
+        } else {
+            if (ts->size1 > 0)       /* can write to pty */
+                FD_SET(ts->ptyfd, &wrfdset);
+            if (ts->size1 < BUFSIZE) /* can read from socket */
+                FD_SET(ts->sockfd_read, &rdfdset);
+            if (ts->size2 > 0)       /* can write to socket */
+                FD_SET(ts->sockfd_write, &wrfdset);
+            if (ts->size2 < BUFSIZE) /* can read from pty */
+                FD_SET(ts->ptyfd, &rdfdset);
+        }
+        ts = next;
+    }
     if (!IS_INETD) {
         FD_SET(master_fd, &rdfdset);
         /* This is needed because free_session() does not
-         * take into account master_fd when it finds new
-         * maxfd among remaining fd's: */
-        if (master_fd > maxfd)
-            maxfd = master_fd;
-    }
-
-    /* select on the master socket, all telnet sockets and their
-     * ptys if there is room in their session buffers. */
-    ts = sessions;
-    while (ts) {
-        /* buf1 is used from socket to pty
-         * buf2 is used from pty to socket */
-        if (ts->size1 > 0)       /* can write to pty */
-            FD_SET(ts->ptyfd, &wrfdset);
-        if (ts->size1 < BUFSIZE) /* can read from socket */
-            FD_SET(ts->sockfd_read, &rdfdset);
-        if (ts->size2 > 0)       /* can write to socket */
-            FD_SET(ts->sockfd_write, &wrfdset);
-        if (ts->size2 < BUFSIZE) /* can read from pty */
-            FD_SET(ts->ptyfd, &rdfdset);
-        ts = ts->next;
-    }
-
-    selret = select(maxfd + 1, &rdfdset, &wrfdset, 0, 0);
-    if (!selret)
+         * take master_fd into account when it finds new
+         * maxfd among remaining fd's */
+        if (master_fd > G.maxfd)
+            G.maxfd = master_fd;
+    }
+
+    {
+        struct timeval *tv_ptr = NULL;
+#if ENABLE_FEATURE_TELNETD_INETD_WAIT
+        struct timeval tv;
+        if ((opt & OPT_WAIT) && !G.sessions) {
+            tv.tv_sec = sec_linger;
+            tv.tv_usec = 0;
+            tv_ptr = &tv;
+        }
+#endif
+        count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr);
+    }
+    if (count == 0) /* "telnetd -w SEC" timed out */
         return 0;
+    if (count < 0)
+        goto again; /* EINTR or ENOMEM */
 
 #if ENABLE_FEATURE_TELNETD_STANDALONE
-    /* 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;
 
-        fd = accept(master_fd, NULL, 0);
+        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, fd);
+        close_on_exec_on(fd);
+
+        /* Create a new session and link it into active list */
+        new_ts = make_new_session(fd);
         if (new_ts) {
-            new_ts->next = sessions;
-            sessions = new_ts;
+            new_ts->next = G.sessions;
+            G.sessions = new_ts;
         } else {
             close(fd);
@@ -477 +631 @@
 #endif
 
-    /* Then check for data tunneling. */
-    ts = sessions;
+    /* Then check for data tunneling */
+    ts = G.sessions;
     while (ts) { /* For all sessions... */
-        struct tsession *next = ts->next; /* in case we free ts. */
-
-        if (ts->size1 && FD_ISSET(ts->ptyfd, &wrfdset)) {
+        struct tsession *next = ts->next; /* in case we free ts */
+
+        if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) {
             int num_totty;
-            char *ptr;
-            /* Write to pty from buffer 1. */
+            unsigned char *ptr;
+            /* Write to pty from buffer 1 */
             ptr = remove_iacs(ts, &num_totty);
-            w = safe_write(ts->ptyfd, ptr, num_totty);
-            /* needed? if (w < 0 && errno == EAGAIN) continue; */
-            if (w < 0) {
-                if (IS_INETD)
-                    return 0;
-                free_session(ts);
-                ts = next;
-                continue;
+            count = safe_write(ts->ptyfd, ptr, num_totty);
+            if (count < 0) {
+                if (errno == EAGAIN)
+                    goto skip1;
+                goto kill_session;
             }
-            ts->wridx1 += w;
-            ts->size1 -= w;
-            if (ts->wridx1 == BUFSIZE)
+            ts->size1 -= count;
+            ts->wridx1 += count;
+            if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */
                 ts->wridx1 = 0;
         }
-
-        if (ts->size2 && FD_ISSET(ts->sockfd_write, &wrfdset)) {
-            /* Write to socket from buffer 2. */
-            maxlen = MIN(BUFSIZE - ts->wridx2, ts->size2);
-            w = safe_write(ts->sockfd_write, ts->buf2 + ts->wridx2, maxlen);
-            /* needed? if (w < 0 && errno == EAGAIN) continue; */
-            if (w < 0) {
-                if (IS_INETD)
-                    return 0;
-                free_session(ts);
-                ts = next;
-                continue;
+ skip1:
+        if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) {
+            /* Write to socket from buffer 2 */
+            count = MIN(BUFSIZE - ts->wridx2, ts->size2);
+            count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count);
+            if (count < 0) {
+                if (errno == EAGAIN)
+                    goto skip2;
+                goto kill_session;
             }
-            ts->wridx2 += w;
-            ts->size2 -= w;
-            if (ts->wridx2 == BUFSIZE)
+            ts->size2 -= count;
+            ts->wridx2 += count;
+            if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */
                 ts->wridx2 = 0;
         }
-
-        if (ts->size1 < BUFSIZE && FD_ISSET(ts->sockfd_read, &rdfdset)) {
-            /* Read from socket to buffer 1. */
-            maxlen = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1);
-            r = safe_read(ts->sockfd_read, ts->buf1 + ts->rdidx1, maxlen);
-            if (r < 0 && errno == EAGAIN) continue;
-            if (r <= 0) {
-                if (IS_INETD)
-                    return 0;
-                free_session(ts);
-                ts = next;
-                continue;
-            }
-            if (!ts->buf1[ts->rdidx1 + r - 1])
-                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 = safe_read(ts->ptyfd, ts->buf2 + ts->rdidx2, maxlen);
-            if (r < 0 && errno == EAGAIN) continue;
-            if (r <= 0) {
-                if (IS_INETD)
-                    return 0;
-                free_session(ts);
-                ts = next;
-                continue;
-            }
-            ts->rdidx2 += r;
-            ts->size2 += r;
-            if (ts->rdidx2 == BUFSIZE)
-                ts->rdidx2 = 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;
@@ -567 +682 @@
             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) + ts->rdidx1, count);
+            if (count <= 0) {
+                if (count < 0 && errno == EAGAIN)
+                    goto skip3;
+                goto kill_session;
+            }
+            /* Ignore trailing NUL if it is there */
+            if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) {
+                --count;
+            }
+            ts->size1 += count;
+            ts->rdidx1 += count;
+            if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */
+                ts->rdidx1 = 0;
+        }
+ skip3:
+        if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) {
+            /* Read from pty to buffer 2 */
+            count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2);
+            count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count);
+            if (count <= 0) {
+                if (count < 0 && errno == EAGAIN)
+                    goto skip4;
+                goto kill_session;
+            }
+            ts->size2 += count;
+            ts->rdidx2 += count;
+            if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */
+                ts->rdidx2 = 0;
+        }
+ skip4:
         ts = next;
-    }
+        continue;
+ kill_session:
+        if (ts->shell_pid > 0)
+            update_utmp(ts->shell_pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL);
+        free_session(ts);
+        ts = next;
+    }
+
     goto again;
 }