Fix #91: Add support for tty nologin, to start /bin/sh immediately

This patch adds a `nologin` flag to the `tty` configuration directive,
making it possible to set up really simple embedded systems with no
login.

Example, put the following line in `/etc/finit.d/getty.conf` to get
a "Please press Enter to ..." prompt before being presented with a
root shell prompt.

    tty [12345] @console noclear nologin

Needless to say, this is not very secure, but can be really useful
for developer setups, during board bringup, or similar.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/exec.c

@@ -423,6 +423,20 @@ pid_t run_getty2(char *tty, char *cmd, char *args[], int noclear, int nowait, st
 	return pid;
 }
 
+pid_t run_sh(char *tty, int noclear, int nowait, struct rlimit rlimit[])
+{
+	pid_t pid;
+
+	pid = fork();
+	if (!pid) {
+		prepare_tty(tty, B0, "finit-sh", rlimit);
+		if (activate_console(noclear, nowait))
+			_exit(sh(tty));
+	}
+
+	return pid;
+}
+
 int run_parts(char *dir, char *cmd)
 {
 	struct dirent **e;

src/getty.c

@@ -243,6 +243,48 @@ int getty(char *tty, speed_t speed, char *term, char *user)
 	return do_login(name);
 }
 
+int sh(char *tty)
+{
+	int fd;
+	char *arg0;
+	char *args[2] = {
+		NULL,
+		NULL
+	};
+	size_t len;
+
+	/* Detach from initial controlling TTY */
+	vhangup();
+
+	fd = open(tty, O_RDWR);
+	if (fd < 0)
+		err(1, "Failed opening %s", tty);
+
+	dup2(fd, STDIN_FILENO);
+	dup2(fd, STDOUT_FILENO);
+	dup2(fd, STDERR_FILENO);
+
+	if (ioctl(STDIN_FILENO, TIOCSCTTY, 1) < 0)
+		warn("Failed TIOCSCTTY");
+
+	/* The getty process is usually responsible for the UTMP login record */
+	utmp_set_login(tty, NULL);
+
+	/* Set up TTY, re-enabling ISIG et al. */
+	stty(fd, B0);
+	close(fd);
+
+	/* Start /bin/sh as a login shell, i.e. with a prefix '-' */
+	len = strlen(_PATH_BSHELL) + 2;
+	arg0 = malloc(len);
+	if (!arg0)
+		err(1, "Failed allocating memory");
+	snprintf(arg0, len, "-%s", _PATH_BSHELL);
+	args[0] = arg0;
+
+	return execv(_PATH_BSHELL, args);
+}
+
 /**
  * Local Variables:
  *  indent-tabs-mode: t

src/helpers.h

@@ -52,6 +52,7 @@ struct fstab *getfsent  (void);
 char   *strip_line      (char *line);
 
 int     getty           (char *tty, speed_t speed, char *term, char *user);
+int     sh              (char *tty);
 
 int     stty            (int fd, speed_t speed);
 speed_t stty_parse_speed(char *baud);
@@ -74,6 +75,7 @@ int     run_interactive (char *cmd, char *fmt, ...);
 int     exec_runtask    (char *cmd, char *args[]);
 pid_t   run_getty       (char *tty, char *baud, char *term,  int noclear, int nowait, struct rlimit rlimit[]);
 pid_t   run_getty2      (char *tty, char *cmd, char *args[], int noclear, int nowait, struct rlimit rlimit[]);
+pid_t   run_sh          (char *tty, int noclear, int nowait, struct rlimit rlimit[]);
 int     run_parts       (char *dir, char *cmd);
 
 static inline void create(char *path, mode_t mode, uid_t uid, gid_t gid)

src/tty.c

@@ -137,7 +137,7 @@ void tty_sweep(void)
 int tty_register(char *line, struct rlimit rlimit[], char *file)
 {
 	tty_node_t *entry;
-	int         insert = 0, noclear = 0, nowait = 0;
+	int         insert = 0, noclear = 0, nowait = 0, nologin = 0;
 	size_t      i, num = 0;
 	char       *tok, *cmd = NULL, *args[TTY_MAX_ARGS];
 	char             *dev = NULL, *baud = NULL;
@@ -159,6 +159,8 @@ int tty_register(char *line, struct rlimit rlimit[], char *file)
 			noclear = 1;
 		else if (!strcmp(tok, "nowait"))
 			nowait = 1;
+		else if (!strcmp(tok, "nologin"))
+			nologin = 1;
 		else
 			args[num++] = tok;
 
@@ -241,6 +243,7 @@ int tty_register(char *line, struct rlimit rlimit[], char *file)
 	entry->data.term = term ? strdup(term) : NULL;
 	entry->data.noclear = noclear;
 	entry->data.nowait  = nowait;
+	entry->data.nologin = nologin;
 	entry->data.runlevels = conf_parse_runlevels(runlevels);
 
 	/* External getty */
@@ -392,6 +395,11 @@ void tty_start(finit_tty_t *tty)
 		return;
 	}
 
+	if (tty->nologin) {
+		tty->pid = run_sh(dev, tty->noclear, tty->nowait, tty->rlimit);
+		return;
+	}
+
 	if (!tty->cmd)
 		tty->pid = run_getty(dev, tty->baud, tty->term, tty->noclear, tty->nowait, tty->rlimit);
 	else

src/tty.h

@@ -38,6 +38,7 @@ typedef struct {
 	char  *term;
 	int    noclear;
 	int    nowait;
+	int    nologin;
 	int    runlevels;
 
 	char  *cmd;		/* NULL when running built-in getty */