blob: ba6c784a39dad84b65082b7f6d0f547269b6ff45 [file] [log] [blame]
/* vi: set sw=4 ts=4: */
/*
* Based on agetty - another getty program for Linux. By W. Z. Venema 1989
* Ported to Linux by Peter Orbaek <poe@daimi.aau.dk>
* This program is freely distributable.
*
* option added by Eric Rasmussen <ear@usfirst.org> - 12/28/95
*
* 1999-02-22 Arkadiusz Mickiewicz <misiek@misiek.eu.org>
* - Added Native Language Support
*
* 1999-05-05 Thorsten Kranzkowski <dl8bcu@gmx.net>
* - Enabled hardware flow control before displaying /etc/issue
*
* 2011-01 Venys Vlasenko
* - Removed parity detection code. It can't work reliably:
* if all chars received have bit 7 cleared and odd (or even) parity,
* it is impossible to determine whether other side is 8-bit,no-parity
* or 7-bit,odd(even)-parity. It also interferes with non-ASCII usernames.
* - From now on, we assume that parity is correctly set.
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
//config:config GETTY
//config: bool "getty"
//config: default y
//config: select FEATURE_SYSLOG
//config: help
//config: getty lets you log in on a tty. It is normally invoked by init.
//config:
//config: Note that you can save a few bytes by disabling it and
//config: using login applet directly.
//config: If you need to reset tty attributes before calling login,
//config: this script approximates getty:
//config:
//config: exec </dev/$1 >/dev/$1 2>&1 || exit 1
//config: reset
//config: stty sane; stty ispeed 38400; stty ospeed 38400
//config: printf "%s login: " "`hostname`"
//config: read -r login
//config: exec /bin/login "$login"
//applet:IF_GETTY(APPLET(getty, BB_DIR_SBIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_GETTY) += getty.o
#include "libbb.h"
#include <syslog.h>
#ifndef IUCLC
# define IUCLC 0
#endif
#ifndef LOGIN_PROCESS
# undef ENABLE_FEATURE_UTMP
# undef ENABLE_FEATURE_WTMP
# define ENABLE_FEATURE_UTMP 0
# define ENABLE_FEATURE_WTMP 0
#endif
/* The following is used for understandable diagnostics */
#ifdef DEBUGGING
static FILE *dbf;
# define DEBUGTERM "/dev/ttyp0"
# define debug(...) do { fprintf(dbf, __VA_ARGS__); fflush(dbf); } while (0)
#else
# define debug(...) ((void)0)
#endif
/*
* Things you may want to modify.
*
* You may disagree with the default line-editing etc. characters defined
* below. Note, however, that DEL cannot be used for interrupt generation
* and for line editing at the same time.
*/
#undef _PATH_LOGIN
#define _PATH_LOGIN "/bin/login"
/* Displayed before the login prompt.
* If ISSUE is not defined, getty will never display the contents of the
* /etc/issue file. You will not want to spit out large "issue" files at the
* wrong baud rate.
*/
#define ISSUE "/etc/issue"
/* Macro to build Ctrl-LETTER. Assumes ASCII dialect */
#define CTL(x) ((x) ^ 0100)
/*
* When multiple baud rates are specified on the command line,
* the first one we will try is the first one specified.
*/
#define MAX_SPEED 10 /* max. nr. of baud rates */
struct globals {
unsigned timeout;
const char *login; /* login program */
const char *fakehost;
const char *tty_name;
char *initstring; /* modem init string */
const char *issue; /* alternative issue file */
int numspeed; /* number of baud rates to try */
int speeds[MAX_SPEED]; /* baud rates to be tried */
unsigned char eol; /* end-of-line char seen (CR or NL) */
struct termios tty_attrs;
char line_buf[128];
};
#define G (*ptr_to_globals)
#define INIT_G() do { \
SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
} while (0)
//usage:#define getty_trivial_usage
//usage: "[OPTIONS] BAUD_RATE[,BAUD_RATE]... TTY [TERMTYPE]"
//usage:#define getty_full_usage "\n\n"
//usage: "Open TTY, prompt for login name, then invoke /bin/login\n"
//usage: "\n -h Enable hardware RTS/CTS flow control"
//usage: "\n -L Set CLOCAL (ignore Carrier Detect state)"
//usage: "\n -m Get baud rate from modem's CONNECT status message"
//usage: "\n -n Don't prompt for login name"
//usage: "\n -w Wait for CR or LF before sending /etc/issue"
//usage: "\n -i Don't display /etc/issue"
//usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue"
//usage: "\n -l LOGIN Invoke LOGIN instead of /bin/login"
//usage: "\n -t SEC Terminate after SEC if no login name is read"
//usage: "\n -I INITSTR Send INITSTR before anything else"
//usage: "\n -H HOST Log HOST into the utmp file as the hostname"
//usage: "\n"
//usage: "\nBAUD_RATE of 0 leaves it unchanged"
static const char opt_string[] ALIGN1 = "I:LH:f:hil:mt:+wn";
#define F_INITSTRING (1 << 0) /* -I */
#define F_LOCAL (1 << 1) /* -L */
#define F_FAKEHOST (1 << 2) /* -H */
#define F_CUSTISSUE (1 << 3) /* -f */
#define F_RTSCTS (1 << 4) /* -h */
#define F_NOISSUE (1 << 5) /* -i */
#define F_LOGIN (1 << 6) /* -l */
#define F_PARSE (1 << 7) /* -m */
#define F_TIMEOUT (1 << 8) /* -t */
#define F_WAITCRLF (1 << 9) /* -w */
#define F_NOPROMPT (1 << 10) /* -n */
/* convert speed string to speed code; return <= 0 on failure */
static int bcode(const char *s)
{
int value = bb_strtou(s, NULL, 10); /* yes, int is intended! */
if (value < 0) /* bad terminating char, overflow, etc */
return value;
return tty_value_to_baud(value);
}
/* parse alternate baud rates */
static void parse_speeds(char *arg)
{
char *cp;
/* NB: at least one iteration is always done */
debug("entered parse_speeds\n");
while ((cp = strsep(&arg, ",")) != NULL) {
G.speeds[G.numspeed] = bcode(cp);
if (G.speeds[G.numspeed] < 0)
bb_error_msg_and_die("bad speed: %s", cp);
/* note: arg "0" turns into speed B0 */
G.numspeed++;
if (G.numspeed > MAX_SPEED)
bb_error_msg_and_die("too many alternate speeds");
}
debug("exiting parse_speeds\n");
}
/* parse command-line arguments */
static void parse_args(char **argv)
{
char *ts;
int flags;
opt_complementary = "-2"; /* at least 2 args; -t N */
flags = getopt32(argv, opt_string,
&G.initstring, &G.fakehost, &G.issue,
&G.login, &G.timeout
);
if (flags & F_INITSTRING) {
G.initstring = xstrdup(G.initstring);
/* decode \ddd octal codes into chars */
strcpy_and_process_escape_sequences(G.initstring, G.initstring);
}
argv += optind;
debug("after getopt\n");
/* We loosen up a bit and accept both "baudrate tty" and "tty baudrate" */
G.tty_name = argv[0];
ts = argv[1]; /* baud rate(s) */
if (isdigit(argv[0][0])) {
/* A number first, assume it's a speed (BSD style) */
G.tty_name = ts; /* tty name is in argv[1] */
ts = argv[0]; /* baud rate(s) */
}
parse_speeds(ts);
if (argv[2])
xsetenv("TERM", argv[2]);
debug("exiting parse_args\n");
}
/* set up tty as standard input, output, error */
static void open_tty(void)
{
/* Set up new standard input, unless we are given an already opened port */
if (NOT_LONE_DASH(G.tty_name)) {
if (G.tty_name[0] != '/')
G.tty_name = xasprintf("/dev/%s", G.tty_name); /* will leak it */
/* Open the tty as standard input */
debug("open(2)\n");
close(0);
xopen(G.tty_name, O_RDWR | O_NONBLOCK); /* uses fd 0 */
/* Set proper protections and ownership */
fchown(0, 0, 0); /* 0:0 */
fchmod(0, 0620); /* crw--w---- */
} else {
char *n;
/*
* Standard input should already be connected to an open port.
* Make sure it is open for read/write.
*/
if ((fcntl(0, F_GETFL) & (O_RDWR|O_RDONLY|O_WRONLY)) != O_RDWR)
bb_error_msg_and_die("stdin is not open for read/write");
/* Try to get real tty name instead of "-" */
n = xmalloc_ttyname(0);
if (n)
G.tty_name = n;
}
applet_name = xasprintf("getty: %s", skip_dev_pfx(G.tty_name));
}
static void set_tty_attrs(void)
{
if (tcsetattr_stdin_TCSANOW(&G.tty_attrs) < 0)
bb_perror_msg_and_die("tcsetattr");
}
/* We manipulate tty_attrs this way:
* - first, we read existing tty_attrs
* - init_tty_attrs modifies some parts and sets it
* - auto_baud and/or BREAK processing can set different speed and set tty attrs
* - finalize_tty_attrs again modifies some parts and sets tty attrs before
* execing login
*/
static void init_tty_attrs(int speed)
{
/* Try to drain output buffer, with 5 sec timeout.
* Added on request from users of ~600 baud serial interface
* with biggish buffer on a 90MHz CPU.
* They were losing hundreds of bytes of buffered output
* on tcflush.
*/
signal_no_SA_RESTART_empty_mask(SIGALRM, record_signo);
alarm(5);
tcdrain(STDIN_FILENO);
alarm(0);
/* Flush input and output queues, important for modems! */
tcflush(STDIN_FILENO, TCIOFLUSH);
/* Set speed if it wasn't specified as "0" on command line */
if (speed != B0)
cfsetspeed(&G.tty_attrs, speed);
/* Initial settings: 8-bit characters, raw mode, blocking i/o.
* Special characters are set after we have read the login name; all
* reads will be done in raw mode anyway.
*/
/* Clear all bits except: */
G.tty_attrs.c_cflag &= (0
/* 2 stop bits (1 otherwise)
* Enable parity bit (both on input and output)
* Odd parity (else even)
*/
| CSTOPB | PARENB | PARODD
#ifdef CMSPAR
| CMSPAR /* mark or space parity */
#endif
#ifdef CBAUD
| CBAUD /* (output) baud rate */
#endif
#ifdef CBAUDEX
| CBAUDEX /* (output) baud rate */
#endif
#ifdef CIBAUD
| CIBAUD /* input baud rate */
#endif
);
/* Set: 8 bits; hang up (drop DTR) on last close; enable receive */
G.tty_attrs.c_cflag |= CS8 | HUPCL | CREAD;
if (option_mask32 & F_LOCAL) {
/* ignore Carrier Detect pin:
* opens don't block when CD is low,
* losing CD doesn't hang up processes whose ctty is this tty
*/
G.tty_attrs.c_cflag |= CLOCAL;
}
#ifdef CRTSCTS
if (option_mask32 & F_RTSCTS)
G.tty_attrs.c_cflag |= CRTSCTS; /* flow control using RTS/CTS pins */
#endif
G.tty_attrs.c_iflag = 0;
G.tty_attrs.c_lflag = 0;
/* non-raw output; add CR to each NL */
G.tty_attrs.c_oflag = OPOST | ONLCR;
/* reads will block only if < 1 char is available */
G.tty_attrs.c_cc[VMIN] = 1;
/* no timeout (reads block forever) */
G.tty_attrs.c_cc[VTIME] = 0;
#ifdef __linux__
G.tty_attrs.c_line = 0;
#endif
set_tty_attrs();
debug("term_io 2\n");
}
static void finalize_tty_attrs(void)
{
/* software flow control on output (stop sending if XOFF is recvd);
* and on input (send XOFF when buffer is full)
*/
G.tty_attrs.c_iflag |= IXON | IXOFF;
if (G.eol == '\r') {
G.tty_attrs.c_iflag |= ICRNL; /* map CR on input to NL */
}
/* Other bits in c_iflag:
* IXANY Any recvd char enables output (any char is also a XON)
* INPCK Enable parity check
* IGNPAR Ignore parity errors (drop bad bytes)
* PARMRK Mark parity errors with 0xff, 0x00 prefix
* (else bad byte is received as 0x00)
* ISTRIP Strip parity bit
* IGNBRK Ignore break condition
* BRKINT Send SIGINT on break - maybe set this?
* INLCR Map NL to CR
* IGNCR Ignore CR
* ICRNL Map CR to NL
* IUCLC Map uppercase to lowercase
* IMAXBEL Echo BEL on input line too long
* IUTF8 Appears to affect tty's idea of char widths,
* observed to improve backspacing through Unicode chars
*/
/* ICANON line buffered input (NL or EOL or EOF chars end a line);
* ISIG recognize INT/QUIT/SUSP chars;
* ECHO echo input chars;
* ECHOE echo BS-SP-BS on erase character;
* ECHOK echo kill char specially, not as ^c (ECHOKE controls how exactly);
* ECHOKE erase all input via BS-SP-BS on kill char (else go to next line)
* ECHOCTL Echo ctrl chars as ^c (else echo verbatim:
* e.g. up arrow emits "ESC-something" and thus moves cursor up!)
*/
G.tty_attrs.c_lflag |= ICANON | ISIG | ECHO | ECHOE | ECHOK | ECHOKE | ECHOCTL;
/* Other bits in c_lflag:
* XCASE Map uppercase to \lowercase [tried, doesn't work]
* ECHONL Echo NL even if ECHO is not set
* ECHOPRT On erase, echo erased chars
* [qwe<BS><BS><BS> input looks like "qwe\ewq/" on screen]
* NOFLSH Don't flush input buffer after interrupt or quit chars
* IEXTEN Enable extended functions (??)
* [glibc says it enables c_cc[LNEXT] "enter literal char"
* and c_cc[VDISCARD] "toggle discard buffered output" chars]
* FLUSHO Output being flushed (c_cc[VDISCARD] is in effect)
* PENDIN Retype pending input at next read or input char
* (c_cc[VREPRINT] is being processed)
* TOSTOP Send SIGTTOU for background output
* (why "stty sane" unsets this bit?)
*/
G.tty_attrs.c_cc[VINTR] = CTL('C');
G.tty_attrs.c_cc[VQUIT] = CTL('\\');
G.tty_attrs.c_cc[VEOF] = CTL('D');
G.tty_attrs.c_cc[VEOL] = '\n';
#ifdef VSWTC
G.tty_attrs.c_cc[VSWTC] = 0;
#endif
#ifdef VSWTCH
G.tty_attrs.c_cc[VSWTCH] = 0;
#endif
G.tty_attrs.c_cc[VKILL] = CTL('U');
/* Other control chars:
* VEOL2
* VERASE, VWERASE - (word) erase. we may set VERASE in get_logname
* VREPRINT - reprint current input buffer
* VLNEXT, VDISCARD, VSTATUS
* VSUSP, VDSUSP - send (delayed) SIGTSTP
* VSTART, VSTOP - chars used for IXON/IXOFF
*/
set_tty_attrs();
/* Now the newline character should be properly written */
full_write(STDOUT_FILENO, "\n", 1);
}
/* extract baud rate from modem status message */
static void auto_baud(void)
{
int nread;
/*
* This works only if the modem produces its status code AFTER raising
* the DCD line, and if the computer is fast enough to set the proper
* baud rate before the message has gone by. We expect a message of the
* following format:
*
* <junk><number><junk>
*
* The number is interpreted as the baud rate of the incoming call. If the
* modem does not tell us the baud rate within one second, we will keep
* using the current baud rate. It is advisable to enable BREAK
* processing (comma-separated list of baud rates) if the processing of
* modem status messages is enabled.
*/
G.tty_attrs.c_cc[VMIN] = 0; /* don't block reads (min read is 0 chars) */
set_tty_attrs();
/*
* Wait for a while, then read everything the modem has said so far and
* try to extract the speed of the dial-in call.
*/
sleep(1);
nread = safe_read(STDIN_FILENO, G.line_buf, sizeof(G.line_buf) - 1);
if (nread > 0) {
int speed;
char *bp;
G.line_buf[nread] = '\0';
for (bp = G.line_buf; bp < G.line_buf + nread; bp++) {
if (isdigit(*bp)) {
speed = bcode(bp);
if (speed > 0)
cfsetspeed(&G.tty_attrs, speed);
break;
}
}
}
/* Restore terminal settings */
G.tty_attrs.c_cc[VMIN] = 1; /* restore to value set by init_tty_attrs */
set_tty_attrs();
}
/* get user name, establish parity, speed, erase, kill, eol;
* return NULL on BREAK, logname on success
*/
static char *get_logname(void)
{
char *bp;
char c;
/* Flush pending input (esp. after parsing or switching the baud rate) */
usleep(100*1000); /* 0.1 sec */
tcflush(STDIN_FILENO, TCIFLUSH);
/* Prompt for and read a login name */
do {
/* Write issue file and prompt */
#ifdef ISSUE
if (!(option_mask32 & F_NOISSUE))
print_login_issue(G.issue, G.tty_name);
#endif
print_login_prompt();
/* Read name, watch for break, erase, kill, end-of-line */
bp = G.line_buf;
while (1) {
/* Do not report trivial EINTR/EIO errors */
errno = EINTR; /* make read of 0 bytes be silent too */
if (read(STDIN_FILENO, &c, 1) < 1) {
finalize_tty_attrs();
if (errno == EINTR || errno == EIO)
exit(EXIT_SUCCESS);
bb_perror_msg_and_die(bb_msg_read_error);
}
switch (c) {
case '\r':
case '\n':
*bp = '\0';
G.eol = c;
goto got_logname;
case CTL('H'):
case 0x7f:
G.tty_attrs.c_cc[VERASE] = c;
if (bp > G.line_buf) {
full_write(STDOUT_FILENO, "\010 \010", 3);
bp--;
}
break;
case CTL('U'):
while (bp > G.line_buf) {
full_write(STDOUT_FILENO, "\010 \010", 3);
bp--;
}
break;
case CTL('C'):
case CTL('D'):
finalize_tty_attrs();
exit(EXIT_SUCCESS);
case '\0':
/* BREAK. If we have speeds to try,
* return NULL (will switch speeds and return here) */
if (G.numspeed > 1)
return NULL;
/* fall through and ignore it */
default:
if ((unsigned char)c < ' ') {
/* ignore garbage characters */
} else if ((int)(bp - G.line_buf) < sizeof(G.line_buf) - 1) {
/* echo and store the character */
full_write(STDOUT_FILENO, &c, 1);
*bp++ = c;
}
break;
}
} /* end of get char loop */
got_logname: ;
} while (G.line_buf[0] == '\0'); /* while logname is empty */
return G.line_buf;
}
static void alarm_handler(int sig UNUSED_PARAM)
{
finalize_tty_attrs();
_exit(EXIT_SUCCESS);
}
static void sleep10(void)
{
sleep(10);
}
int getty_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int getty_main(int argc UNUSED_PARAM, char **argv)
{
int n;
pid_t pid, tsid;
char *logname;
INIT_G();
G.login = _PATH_LOGIN; /* default login program */
#ifdef ISSUE
G.issue = ISSUE; /* default issue file */
#endif
G.eol = '\r';
/* Parse command-line arguments */
parse_args(argv);
/* Create new session and pgrp, lose controlling tty */
pid = setsid(); /* this also gives us our pid :) */
if (pid < 0) {
int fd;
/* :(
* docs/ctty.htm says:
* "This is allowed only when the current process
* is not a process group leader".
* Thus, setsid() will fail if we _already_ are
* a session leader - which is quite possible for getty!
*/
pid = getpid();
if (getsid(0) != pid) {
//for debugging:
//bb_perror_msg_and_die("setsid failed:"
// " pid %d ppid %d"
// " sid %d pgid %d",
// pid, getppid(),
// getsid(0), getpgid(0));
bb_perror_msg_and_die("setsid");
/*
* When we can end up here?
* Example: setsid() fails when run alone in interactive shell:
* # getty 115200 /dev/tty2
* because shell's child (getty) is put in a new process group.
* But doesn't fail if shell is not interactive
* (and therefore doesn't create process groups for pipes),
* or if getty is not the first process in the process group:
* # true | getty 115200 /dev/tty2
*/
}
/* Looks like we are already a session leader.
* In this case (setsid failed) we may still have ctty,
* and it may be different from tty we need to control!
* If we still have ctty, on Linux ioctl(TIOCSCTTY)
* (which we are going to use a bit later) always fails -
* even if we try to take ctty which is already ours!
* Try to drop old ctty now to prevent that.
* Use O_NONBLOCK: old ctty may be a serial line.
*/
fd = open("/dev/tty", O_RDWR | O_NONBLOCK);
if (fd >= 0) {
/* TIOCNOTTY sends SIGHUP to the foreground
* process group - which may include us!
* Make sure to not die on it:
*/
sighandler_t old = signal(SIGHUP, SIG_IGN);
ioctl(fd, TIOCNOTTY);
close(fd);
signal(SIGHUP, old);
}
}
/* Close stdio, and stray descriptors, just in case */
n = xopen(bb_dev_null, O_RDWR);
/* dup2(n, 0); - no, we need to handle "getty - 9600" too */
xdup2(n, 1);
xdup2(n, 2);
while (n > 2)
close(n--);
/* Logging. We want special flavor of error_msg_and_die */
die_func = sleep10;
msg_eol = "\r\n";
/* most likely will internally use fd #3 in CLOEXEC mode: */
openlog(applet_name, LOG_PID, LOG_AUTH);
logmode = LOGMODE_BOTH;
#ifdef DEBUGGING
dbf = xfopen_for_write(DEBUGTERM);
for (n = 1; argv[n]; n++) {
debug(argv[n]);
debug("\n");
}
#endif
/* Open the tty as standard input, if it is not "-" */
debug("calling open_tty\n");
open_tty();
ndelay_off(STDIN_FILENO);
debug("duping\n");
xdup2(STDIN_FILENO, 1);
xdup2(STDIN_FILENO, 2);
/* Steal ctty if we don't have it yet */
tsid = tcgetsid(STDIN_FILENO);
if (tsid < 0 || pid != tsid) {
if (ioctl(STDIN_FILENO, TIOCSCTTY, /*force:*/ (long)1) < 0)
bb_perror_msg_and_die("TIOCSCTTY");
}
#ifdef __linux__
/* Make ourself a foreground process group within our session */
if (tcsetpgrp(STDIN_FILENO, pid) < 0)
bb_perror_msg_and_die("tcsetpgrp");
#endif
/*
* The following ioctl will fail if stdin is not a tty, but also when
* there is noise on the modem control lines. In the latter case, the
* common course of action is (1) fix your cables (2) give the modem more
* time to properly reset after hanging up. SunOS users can achieve (2)
* by patching the SunOS kernel variable "zsadtrlow" to a larger value;
* 5 seconds seems to be a good value.
*/
if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0)
bb_perror_msg_and_die("tcgetattr");
/* Update the utmp file. This tty is ours now! */
update_utmp(pid, LOGIN_PROCESS, G.tty_name, "LOGIN", G.fakehost);
/* Initialize tty attrs (raw mode, eight-bit, blocking i/o) */
debug("calling init_tty_attrs\n");
init_tty_attrs(G.speeds[0]);
/* Write the modem init string and DON'T flush the buffers */
if (option_mask32 & F_INITSTRING) {
debug("writing init string\n");
full_write1_str(G.initstring);
}
/* Optionally detect the baud rate from the modem status message */
debug("before autobaud\n");
if (option_mask32 & F_PARSE)
auto_baud();
/* Set the optional timer */
signal(SIGALRM, alarm_handler);
alarm(G.timeout); /* if 0, alarm is not set */
/* Optionally wait for CR or LF before writing /etc/issue */
if (option_mask32 & F_WAITCRLF) {
char ch;
debug("waiting for cr-lf\n");
while (safe_read(STDIN_FILENO, &ch, 1) == 1) {
debug("read %x\n", (unsigned char)ch);
if (ch == '\n' || ch == '\r')
break;
}
}
logname = NULL;
if (!(option_mask32 & F_NOPROMPT)) {
/* NB: init_tty_attrs already set line speed
* to G.speeds[0] */
int baud_index = 0;
while (1) {
/* Read the login name */
debug("reading login name\n");
logname = get_logname();
if (logname)
break;
/* We are here only if G.numspeed > 1 */
baud_index = (baud_index + 1) % G.numspeed;
cfsetspeed(&G.tty_attrs, G.speeds[baud_index]);
set_tty_attrs();
}
}
/* Disable timer */
alarm(0);
finalize_tty_attrs();
/* Let the login program take care of password validation */
/* We use PATH because we trust that root doesn't set "bad" PATH,
* and getty is not suid-root applet */
/* With -n, logname == NULL, and login will ask for username instead */
BB_EXECLP(G.login, G.login, "--", logname, (char *)0);
bb_error_msg_and_die("can't execute '%s'", G.login);
}