nc: show help text on bad parameters

[oweals/busybox.git] / networking / telnetd.c

diff --git a/networking/telnetd.c b/networking/telnetd.c
index cab94f0f7eacc3be75d093d31b1b57b49ac5f5e3..5c011e15d58b45b8af336c5ca80688488211b652 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)
  *
- * 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
@@ -20,18 +20,22 @@
  * Vladimir Oleynik <dzo@simtreas.ru> 2001
  * 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>
 
+#if ENABLE_FEATURE_UTMP
+# include <utmp.h> /* LOGIN_PROCESS */
+#endif
+
+
 struct tsession {
        struct tsession *next;
        pid_t shell_pid;
@@ -222,6 +226,9 @@ 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;
@@ -239,9 +246,9 @@ make_new_session(
        ndelay_on(fd);
        close_on_exec_on(fd);
 
-#if ENABLE_FEATURE_TELNETD_STANDALONE
        /* SO_KEEPALIVE by popular demand */
        setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
+#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 */
@@ -252,8 +259,6 @@ make_new_session(
        if (sock > G.maxfd)
                G.maxfd = sock;
 #else
-       /* SO_KEEPALIVE by popular demand */
-       setsockopt(0, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1));
        /* ts->sockfd_read = 0; - done by xzalloc */
        ts->sockfd_write = 1;
        ndelay_on(0);
@@ -309,6 +314,17 @@ make_new_session(
        /* 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();
 
@@ -319,7 +335,8 @@ make_new_session(
        xopen(tty_name, O_RDWR); /* becomes our ctty */
        xdup2(0, 1);
        xdup2(0, 2);
-       tcsetpgrp(0, getpid()); /* switch this tty's process group to us */
+       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)) */
@@ -358,12 +375,13 @@ make_new_session(
 static void
 free_session(struct tsession *ts)
 {
-       struct tsession *t = G.sessions;
+       struct tsession *t;
 
        if (option_mask32 & OPT_INETD)
                exit(EXIT_SUCCESS);
 
        /* Unlink this telnet session from the session list */
+       t = G.sessions;
        if (t == ts)
                G.sessions = ts->next;
        else {
@@ -414,6 +432,7 @@ 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) {
@@ -424,11 +443,22 @@ static void handle_sigchld(int sig UNUSED_PARAM)
                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;
@@ -689,6 +719,8 @@ int telnetd_main(int argc UNUSED_PARAM, char **argv)
                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;
        }