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
 }