telnetd: write LOGIN/DEAD_PROCESS utmp records. Closes bug 1363

function                                             old     new   delta
write_new_utmp                                         -     253    +253
skip_dev_pfx                                           -      30     +30
handle_sigchld                                        42      72     +30
telnetd_main                                        1650    1673     +23
make_new_session                                     415     438     +23
...
login_main                                          1140    1148      +8
update_utmp                                          337     313     -24
write_wtmp                                           220     154     -66
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 11/6 up/down: 406/-115)         Total: ~291 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 86 insertions, 37 deletions

diff --git a/libbb/utmp.c b/libbb/utmp.c
index 06b939b9d..d6ba336e3 100644
--- a/libbb/utmp.c
+++ b/libbb/utmp.c
@@ -15,37 +15,87 @@ static void touch(const char *filename)
                 close(open(filename, O_WRONLY | O_CREAT, 0664));
 }
 
+// TODO: move to libbb
+static const char* skip_dev_pfx(const char *tty_name)
+{
+        if (strncmp(tty_name, "/dev/", 5) == 0)
+                tty_name += 5;
+        return tty_name;
+}
+
+void FAST_FUNC write_new_utmp(pid_t pid, int new_type, const char *tty_name, const char *username, const char *hostname)
+{
+        struct utmp utent;
+        char *id;
+        unsigned width;
+
+        memset(&utent, 0, sizeof(utent));
+        utent.ut_pid = pid;
+        utent.ut_type = new_type;
+        tty_name = skip_dev_pfx(tty_name);
+        safe_strncpy(utent.ut_line, tty_name, sizeof(utent.ut_line));
+        if (username)
+                safe_strncpy(utent.ut_user, username, sizeof(utent.ut_user));
+        if (hostname)
+                safe_strncpy(utent.ut_host, hostname, sizeof(utent.ut_host));
+        utent.ut_tv.tv_sec = time(NULL);
+
+        /* Invent our own ut_id. ut_id is only 4 chars wide.
+         * Try to fit something remotely meaningful... */
+        id = utent.ut_id;
+        width = sizeof(utent.ut_id);
+        if (tty_name[0] == 'p') {
+                /* if "ptyXXX", map to "pXXX" */
+                /* if "pts/XX", map to "p/XX" */
+                *id++ = 'p';
+                width--;
+        } /* else: usually it's "ttyXXXX", map to "XXXX" */
+        if (strlen(tty_name) > 3)
+                tty_name += 3;
+        strncpy(id, tty_name, width);
+
+        touch(_PATH_UTMP);
+        //utmpname(_PATH_UTMP);
+        setutent();
+        /* Append new one (hopefully, unless we collide on ut_id) */
+        pututline(&utent);
+        endutent();
+
+#if ENABLE_FEATURE_WTMP
+        /* "man utmp" says wtmp file should *not* be created automagically */
+        /*touch(bb_path_wtmp_file);*/
+        updwtmp(bb_path_wtmp_file, &utent);
+#endif
+}
+
 /*
  * Read "man utmp" to make sense out of it.
  */
-void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *username, const char *opt_host)
+void FAST_FUNC update_utmp(pid_t pid, int new_type, const char *tty_name, const char *username, const char *hostname)
 {
         struct utmp utent;
-        struct utmp *ut;
-        pid_t pid;
+        struct utmp *utp;
 
         touch(_PATH_UTMP);
-        utmpname(_PATH_UTMP);
+        //utmpname(_PATH_UTMP);
         setutent();
 
-        pid = getpid();
         /* Did init/getty/telnetd/sshd/... create an entry for us?
          * It should be (new_type-1), but we'd also reuse
          * any other potentially stale xxx_PROCESS entry */
-        while ((ut = getutent()) != NULL) {
-                if (ut->ut_pid == pid
+        while ((utp = getutent()) != NULL) {
+                if (utp->ut_pid == pid
                 // && ut->ut_line[0]
-                 && ut->ut_id[0] /* must have nonzero id */
-                 && (  ut->ut_type == INIT_PROCESS
-                    || ut->ut_type == LOGIN_PROCESS
-                    || ut->ut_type == USER_PROCESS
-                    || ut->ut_type == DEAD_PROCESS
+                 && utp->ut_id[0] /* must have nonzero id */
+                 && (  utp->ut_type == INIT_PROCESS
+                    || utp->ut_type == LOGIN_PROCESS
+                    || utp->ut_type == USER_PROCESS
+                    || utp->ut_type == DEAD_PROCESS
                     )
                 ) {
-                        utent = *ut; /* struct copy */
-                        if (ut->ut_type >= new_type) {
+                        if (utp->ut_type >= new_type) {
                                 /* Stale record. Nuke hostname */
-                                memset(utent.ut_host, 0, sizeof(utent.ut_host));
+                                memset(utp->ut_host, 0, sizeof(utp->ut_host));
                         }
                         /* NB: pututline (see later) searches for matching utent
                          * using getutid(utent) - we must not change ut_id
@@ -54,39 +104,38 @@ void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *user
                         break;
                 }
         }
-        endutent();
+        //endutent(); - no need, pututline can deal with (and actually likes)
+        //the situation when utmp file is positioned on found record
 
-        if (!ut) {
-                /* Didn't find anything, create new one */
-                memset(&utent, 0, sizeof(utent));
-                utent.ut_pid = pid;
-                /* Invent our own ut_id. ut_id is only 4 chars wide.
-                 * Try to fit something remotely meaningful... */
-                if (short_tty[0] == 'p') {
-                        /* if "ptyXXX", map to "pXXX" */
-                        /* if "pts/XX", map to "p/XX" */
-                        utent.ut_id[0] = 'p';
-                        strncpy(utent.ut_id + 1, short_tty + 3, sizeof(utent.ut_id)-1);
-                } else {
-                        /* assuming it's "ttyXXXX", map to "XXXX" */
-                        strncpy(utent.ut_id, short_tty + 3, sizeof(utent.ut_id));
-                }
+        if (!utp) {
+                if (new_type != DEAD_PROCESS)
+                        write_new_utmp(pid, new_type, tty_name, username, hostname);
+                else
+                        endutent();
+                return;
         }
 
+        /* Make a copy. We can't use *utp, pututline's internal getutid
+         * will overwrite it before it is used! */
+        utent = *utp;
+
         utent.ut_type = new_type;
-        safe_strncpy(utent.ut_line, short_tty, sizeof(utent.ut_line));
-        safe_strncpy(utent.ut_user, username, sizeof(utent.ut_user));
-        if (opt_host)
-                safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
+        if (tty_name)
+                safe_strncpy(utent.ut_line, skip_dev_pfx(tty_name), sizeof(utent.ut_line));
+        if (username)
+                safe_strncpy(utent.ut_user, username, sizeof(utent.ut_user));
+        if (hostname)
+                safe_strncpy(utent.ut_host, hostname, sizeof(utent.ut_host));
         utent.ut_tv.tv_sec = time(NULL);
 
         /* Update, or append new one */
-        setutent();
+        //setutent();
         pututline(&utent);
         endutent();
 
 #if ENABLE_FEATURE_WTMP
-        touch(bb_path_wtmp_file);
+        /* "man utmp" says wtmp file should *not* be created automagically */
+        /*touch(bb_path_wtmp_file);*/
         updwtmp(bb_path_wtmp_file, &utent);
 #endif
 }