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>

7 files changed, 134 insertions, 56 deletions

diff --git a/include/libbb.h b/include/libbb.h
index ea61701..f3121eb 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -797,9 +797,11 @@ void die_if_bad_username(const char* name) FAST_FUNC;
 #endif
 
 #if ENABLE_FEATURE_UTMP
-void FAST_FUNC update_utmp(int new_type, const char *short_tty, const char *username, const char *opt_host);
+void FAST_FUNC write_new_utmp(pid_t pid, int new_type, const char *tty_name, const char *username, const char *hostname);
+void FAST_FUNC update_utmp(pid_t pid, int new_type, const char *tty_name, const char *username, const char *hostname);
 #else
-# define update_utmp(new_type, short_tty, username, opt_host) ((void)0)
+# define write_new_utmp(pid, new_type, tty_name, username, hostname) ((void)0)
+# define update_utmp(pid, new_type, tty_name, username, hostname) ((void)0)
 #endif
 
 int execable_file(const char *name) FAST_FUNC;
diff --git a/init/halt.c b/init/halt.c
index a3459ee..f1bb2c4 100644
--- a/init/halt.c
+++ b/init/halt.c
@@ -18,17 +18,18 @@ static void write_wtmp(void)
 {
 	struct utmp utmp;
 	struct utsname uts;
-	if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
+	/* "man utmp" says wtmp file should *not* be created automagically */
+	/*if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
 		close(creat(bb_path_wtmp_file, 0664));
-	}
+	}*/
 	memset(&utmp, 0, sizeof(utmp));
 	utmp.ut_tv.tv_sec = time(NULL);
-	safe_strncpy(utmp.ut_user, "shutdown", UT_NAMESIZE);
+	strcpy(utmp.ut_user, "shutdown"); /* it is wide enough */
 	utmp.ut_type = RUN_LVL;
-	safe_strncpy(utmp.ut_id, "~~", sizeof(utmp.ut_id));
-	safe_strncpy(utmp.ut_line, "~~", UT_LINESIZE);
-	if (uname(&uts) == 0)
-		safe_strncpy(utmp.ut_host, uts.release, sizeof(utmp.ut_host));
+	utmp.ut_id[0] = '~'; utmp.ut_id[1] = '~'; /* = strcpy(utmp.ut_id, "~~"); */
+	utmp.ut_line[0] = '~'; utmp.ut_line[1] = '~'; /* = strcpy(utmp.ut_line, "~~"); */
+	uname(&uts);
+	safe_strncpy(utmp.ut_host, uts.release, sizeof(utmp.ut_host));
 	updwtmp(bb_path_wtmp_file, &utmp);
 }
 #else
diff --git a/libbb/utmp.c b/libbb/utmp.c
index 06b939b..d6ba336 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
 }
diff --git a/loginutils/getty.c b/loginutils/getty.c
index 8d1d525..d032357 100644
--- a/loginutils/getty.c
+++ b/loginutils/getty.c
@@ -19,7 +19,7 @@
 #include <syslog.h>
 
 #if ENABLE_FEATURE_UTMP
-#include <utmp.h> /* LOGIN_PROCESS */
+# include <utmp.h> /* LOGIN_PROCESS */
 #endif
 
 #ifndef IUCLC
@@ -579,6 +579,7 @@ int getty_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int getty_main(int argc UNUSED_PARAM, char **argv)
 {
 	int n;
+	pid_t pid;
 	char *fakehost = NULL;          /* Fake hostname for ut_host */
 	char *logname;                  /* login name, given to /bin/login */
 	/* Merging these into "struct local" may _seem_ to reduce
@@ -651,17 +652,18 @@ int getty_main(int argc UNUSED_PARAM, char **argv)
 	/* tcgetattr() + error check */
 	ioctl_or_perror_and_die(0, TCGETS, &termios, "%s: TCGETS", options.tty);
 
+	pid = getpid();
 #ifdef __linux__
 // FIXME: do we need this? Otherwise "-" case seems to be broken...
 	// /* Forcibly make fd 0 our controlling tty, even if another session
 	//  * has it as a ctty. (Another session loses ctty). */
 	// ioctl(0, TIOCSCTTY, (void*)1);
 	/* Make ourself a foreground process group within our session */
-	tcsetpgrp(0, getpid());
+	tcsetpgrp(0, pid);
 #endif
 
 	/* Update the utmp file. This tty is ours now! */
-	update_utmp(LOGIN_PROCESS, options.tty, "LOGIN", fakehost);
+	update_utmp(pid, LOGIN_PROCESS, options.tty, "LOGIN", fakehost);
 
 	/* Initialize the termios settings (raw mode, eight-bit, blocking i/o). */
 	debug("calling termios_init\n");
diff --git a/loginutils/login.c b/loginutils/login.c
index 4a82037..bf21d61 100644
--- a/loginutils/login.c
+++ b/loginutils/login.c
@@ -384,7 +384,7 @@ int login_main(int argc UNUSED_PARAM, char **argv)
 	fchown(0, pw->pw_uid, pw->pw_gid);
 	fchmod(0, 0600);
 
-	update_utmp(USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
+	update_utmp(getpid(), USER_PROCESS, short_tty, username, run_by_root ? opt_host : NULL);
 
 	/* We trust environment only if we run by root */
 	if (ENABLE_LOGIN_SCRIPTS && run_by_root)
diff --git a/miscutils/last.c b/miscutils/last.c
index 6e3ed90..55c03ae 100644
--- a/miscutils/last.c
+++ b/miscutils/last.c
@@ -92,7 +92,8 @@ int last_main(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 				goto next;
 			}
 			if (ut.ut_type != DEAD_PROCESS
-			 && ut.ut_user[0] && ut.ut_line[0]
+			 && ut.ut_user[0]
+			 && ut.ut_line[0]
 			) {
 				ut.ut_type = USER_PROCESS;
 			}
diff --git a/networking/telnetd.c b/networking/telnetd.c
index cab94f0..b3e66eb 100644
--- a/networking/telnetd.c
+++ b/networking/telnetd.c
@@ -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;
@@ -319,7 +323,11 @@ 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 */
+
+//TODO: fetch remote addr via getpeername (see ftpd.c)
+	write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", /*hostname:*/ NULL);
 
 	/* The pseudo-terminal allocated to the client is configured to operate
 	 * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */
@@ -358,12 +366,13 @@ 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 +423,7 @@ 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 +434,22 @@ 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 +710,8 @@ 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;
 	}