loginutils/getty.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Based on agetty - another getty program for Linux. By W. Z. Venema 1989
   4  * Ported to Linux by Peter Orbaek <poe@daimi.aau.dk>
   5  * This program is freely distributable.
   6  *
   7  * option added by Eric Rasmussen <ear@usfirst.org> - 12/28/95
   8  *
   9  * 1999-02-22 Arkadiusz Mickiewicz <misiek@misiek.eu.org>
  10  * - Added Native Language Support
  11  *
  12  * 1999-05-05 Thorsten Kranzkowski <dl8bcu@gmx.net>
  13  * - Enabled hardware flow control before displaying /etc/issue
  14  *
  15  * 2011-01 Venys Vlasenko
  16  * - Removed parity detection code. It can't work reliably:
  17  * if all chars received have bit 7 cleared and odd (or even) parity,
  18  * it is impossible to determine whether other side is 8-bit,no-parity
  19  * or 7-bit,odd(even)-parity. It also interferes with non-ASCII usernames.
  20  * - From now on, we assume that parity is correctly set.
  21  *
  22  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  23  */
  24 //config:config GETTY
  25 //config:       bool "getty (11 kb)"
  26 //config:       default y
  27 //config:       select FEATURE_SYSLOG
  28 //config:       help
  29 //config:       getty lets you log in on a tty. It is normally invoked by init.
  30 //config:
  31 //config:       Note that you can save a few bytes by disabling it and
  32 //config:       using login applet directly.
  33 //config:       If you need to reset tty attributes before calling login,
  34 //config:       this script approximates getty:
  35 //config:
  36 //config:       exec </dev/$1 >/dev/$1 2>&1 || exit 1
  37 //config:       reset
  38 //config:       stty sane; stty ispeed 38400; stty ospeed 38400
  39 //config:       printf "%s login: " "`hostname`"
  40 //config:       read -r login
  41 //config:       exec /bin/login "$login"
  42
  43 //applet:IF_GETTY(APPLET(getty, BB_DIR_SBIN, BB_SUID_DROP))
  44
  45 //kbuild:lib-$(CONFIG_GETTY) += getty.o
  46
  47 #include "libbb.h"
  48 #include <syslog.h>
  49 #ifndef IUCLC
  50 # define IUCLC 0
  51 #endif
  52
  53 #ifndef LOGIN_PROCESS
  54 # undef ENABLE_FEATURE_UTMP
  55 # undef ENABLE_FEATURE_WTMP
  56 # define ENABLE_FEATURE_UTMP 0
  57 # define ENABLE_FEATURE_WTMP 0
  58 #endif
  59
  60
  61 /* The following is used for understandable diagnostics */
  62 #ifdef DEBUGGING
  63 static FILE *dbf;
  64 # define DEBUGTERM "/dev/ttyp0"
  65 # define debug(...) do { fprintf(dbf, __VA_ARGS__); fflush(dbf); } while (0)
  66 #else
  67 # define debug(...) ((void)0)
  68 #endif
  69
  70
  71 /*
  72  * Things you may want to modify.
  73  *
  74  * You may disagree with the default line-editing etc. characters defined
  75  * below. Note, however, that DEL cannot be used for interrupt generation
  76  * and for line editing at the same time.
  77  */
  78 #undef  _PATH_LOGIN
  79 #define _PATH_LOGIN "/bin/login"
  80
  81 /* Displayed before the login prompt.
  82  * If ISSUE is not defined, getty will never display the contents of the
  83  * /etc/issue file. You will not want to spit out large "issue" files at the
  84  * wrong baud rate.
  85  */
  86 #define ISSUE "/etc/issue"
  87
  88 /* Macro to build Ctrl-LETTER. Assumes ASCII dialect */
  89 #define CTL(x)          ((x) ^ 0100)
  90
  91 /*
  92  * When multiple baud rates are specified on the command line,
  93  * the first one we will try is the first one specified.
  94  */
  95 #define MAX_SPEED       10              /* max. nr. of baud rates */
  96
  97 struct globals {
  98         unsigned timeout;
  99         const char *login;              /* login program */
 100         const char *fakehost;
 101         const char *tty_name;
 102         char *initstring;               /* modem init string */
 103         const char *issue;              /* alternative issue file */
 104         int numspeed;                   /* number of baud rates to try */
 105         int speeds[MAX_SPEED];          /* baud rates to be tried */
 106         unsigned char eol;              /* end-of-line char seen (CR or NL) */
 107         struct termios tty_attrs;
 108         char line_buf[128];
 109 };
 110
 111 #define G (*ptr_to_globals)
 112 #define INIT_G() do { \
 113         SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
 114 } while (0)
 115
 116 //usage:#define getty_trivial_usage
 117 //usage:       "[OPTIONS] BAUD_RATE[,BAUD_RATE]... TTY [TERMTYPE]"
 118 //usage:#define getty_full_usage "\n\n"
 119 //usage:       "Open TTY, prompt for login name, then invoke /bin/login\n"
 120 //usage:     "\n        -h              Enable hardware RTS/CTS flow control"
 121 //usage:     "\n        -L              Set CLOCAL (ignore Carrier Detect state)"
 122 //usage:     "\n        -m              Get baud rate from modem's CONNECT status message"
 123 //usage:     "\n        -n              Don't prompt for login name"
 124 //usage:     "\n        -w              Wait for CR or LF before sending /etc/issue"
 125 //usage:     "\n        -i              Don't display /etc/issue"
 126 //usage:     "\n        -f ISSUE_FILE   Display ISSUE_FILE instead of /etc/issue"
 127 //usage:     "\n        -l LOGIN        Invoke LOGIN instead of /bin/login"
 128 //usage:     "\n        -t SEC          Terminate after SEC if no login name is read"
 129 //usage:     "\n        -I INITSTR      Send INITSTR before anything else"
 130 //usage:     "\n        -H HOST         Log HOST into the utmp file as the hostname"
 131 //usage:     "\n"
 132 //usage:     "\nBAUD_RATE of 0 leaves it unchanged"
 133
 134 #define OPT_STR "I:LH:f:hil:mt:+wn"
 135 #define F_INITSTRING    (1 << 0)   /* -I */
 136 #define F_LOCAL         (1 << 1)   /* -L */
 137 #define F_FAKEHOST      (1 << 2)   /* -H */
 138 #define F_CUSTISSUE     (1 << 3)   /* -f */
 139 #define F_RTSCTS        (1 << 4)   /* -h */
 140 #define F_NOISSUE       (1 << 5)   /* -i */
 141 #define F_LOGIN         (1 << 6)   /* -l */
 142 #define F_PARSE         (1 << 7)   /* -m */
 143 #define F_TIMEOUT       (1 << 8)   /* -t */
 144 #define F_WAITCRLF      (1 << 9)   /* -w */
 145 #define F_NOPROMPT      (1 << 10)  /* -n */
 146
 147
 148 /* convert speed string to speed code; return <= 0 on failure */
 149 static int bcode(const char *s)
 150 {
 151         int value = bb_strtou(s, NULL, 10); /* yes, int is intended! */
 152         if (value < 0) /* bad terminating char, overflow, etc */
 153                 return value;
 154         return tty_value_to_baud(value);
 155 }
 156
 157 /* parse alternate baud rates */
 158 static void parse_speeds(char *arg)
 159 {
 160         char *cp;
 161
 162         /* NB: at least one iteration is always done */
 163         debug("entered parse_speeds\n");
 164         while ((cp = strsep(&arg, ",")) != NULL) {
 165                 G.speeds[G.numspeed] = bcode(cp);
 166                 if (G.speeds[G.numspeed] < 0)
 167                         bb_error_msg_and_die("bad speed: %s", cp);
 168                 /* note: arg "0" turns into speed B0 */
 169                 G.numspeed++;
 170                 if (G.numspeed > MAX_SPEED)
 171                         bb_simple_error_msg_and_die("too many alternate speeds");
 172         }
 173         debug("exiting parse_speeds\n");
 174 }
 175
 176 /* parse command-line arguments */
 177 static void parse_args(char **argv)
 178 {
 179         char *ts;
 180         int flags;
 181
 182         flags = getopt32(argv, "^" OPT_STR "\0" "-2"/* at least 2 args*/,
 183                 &G.initstring, &G.fakehost, &G.issue,
 184                 &G.login, &G.timeout
 185         );
 186         if (flags & F_INITSTRING) {
 187                 G.initstring = xstrdup(G.initstring);
 188                 /* decode \ddd octal codes into chars */
 189                 strcpy_and_process_escape_sequences(G.initstring, G.initstring);
 190         }
 191         argv += optind;
 192         debug("after getopt\n");
 193
 194         /* We loosen up a bit and accept both "baudrate tty" and "tty baudrate" */
 195         G.tty_name = argv[0];
 196         ts = argv[1];            /* baud rate(s) */
 197         if (isdigit(argv[0][0])) {
 198                 /* A number first, assume it's a speed (BSD style) */
 199                 G.tty_name = ts; /* tty name is in argv[1] */
 200                 ts = argv[0];    /* baud rate(s) */
 201         }
 202         parse_speeds(ts);
 203
 204         if (argv[2])
 205                 xsetenv("TERM", argv[2]);
 206
 207         debug("exiting parse_args\n");
 208 }
 209
 210 /* set up tty as standard input, output, error */
 211 static void open_tty(void)
 212 {
 213         /* Set up new standard input, unless we are given an already opened port */
 214         if (NOT_LONE_DASH(G.tty_name)) {
 215                 if (G.tty_name[0] != '/')
 216                         G.tty_name = xasprintf("/dev/%s", G.tty_name); /* will leak it */
 217
 218                 /* Open the tty as standard input */
 219                 debug("open(2)\n");
 220                 close(0);
 221                 xopen(G.tty_name, O_RDWR | O_NONBLOCK); /* uses fd 0 */
 222
 223                 /* Set proper protections and ownership */
 224                 fchown(0, 0, 0);        /* 0:0 */
 225                 fchmod(0, 0620);        /* crw--w---- */
 226         } else {
 227                 char *n;
 228                 /*
 229                  * Standard input should already be connected to an open port.
 230                  * Make sure it is open for read/write.
 231                  */
 232                 if ((fcntl(0, F_GETFL) & (O_RDWR|O_RDONLY|O_WRONLY)) != O_RDWR)
 233                         bb_simple_error_msg_and_die("stdin is not open for read/write");
 234
 235                 /* Try to get real tty name instead of "-" */
 236                 n = xmalloc_ttyname(0);
 237                 if (n)
 238                         G.tty_name = n;
 239         }
 240         applet_name = xasprintf("getty: %s", skip_dev_pfx(G.tty_name));
 241 }
 242
 243 static void set_tty_attrs(void)
 244 {
 245         if (tcsetattr_stdin_TCSANOW(&G.tty_attrs) < 0)
 246                 bb_simple_perror_msg_and_die("tcsetattr");
 247 }
 248
 249 /* We manipulate tty_attrs this way:
 250  * - first, we read existing tty_attrs
 251  * - init_tty_attrs modifies some parts and sets it
 252  * - auto_baud and/or BREAK processing can set different speed and set tty attrs
 253  * - finalize_tty_attrs again modifies some parts and sets tty attrs before
 254  *   execing login
 255  */
 256 static void init_tty_attrs(int speed)
 257 {
 258         /* Try to drain output buffer, with 5 sec timeout.
 259          * Added on request from users of ~600 baud serial interface
 260          * with biggish buffer on a 90MHz CPU.
 261          * They were losing hundreds of bytes of buffered output
 262          * on tcflush.
 263          */
 264         signal_no_SA_RESTART_empty_mask(SIGALRM, record_signo);
 265         alarm(5);
 266         tcdrain(STDIN_FILENO);
 267         alarm(0);
 268
 269         /* Flush input and output queues, important for modems! */
 270         tcflush(STDIN_FILENO, TCIOFLUSH);
 271
 272         /* Set speed if it wasn't specified as "0" on command line */
 273         if (speed != B0)
 274                 cfsetspeed(&G.tty_attrs, speed);
 275
 276         /* Initial settings: 8-bit characters, raw mode, blocking i/o.
 277          * Special characters are set after we have read the login name; all
 278          * reads will be done in raw mode anyway.
 279          */
 280         /* Clear all bits except: */
 281         G.tty_attrs.c_cflag &= (0
 282                 /* 2 stop bits (1 otherwise)
 283                  * Enable parity bit (both on input and output)
 284                  * Odd parity (else even)
 285                  */
 286                 | CSTOPB | PARENB | PARODD
 287 #ifdef CMSPAR
 288                 | CMSPAR  /* mark or space parity */
 289 #endif
 290 #ifdef CBAUD
 291                 | CBAUD   /* (output) baud rate */
 292 #endif
 293 #ifdef CBAUDEX
 294                 | CBAUDEX /* (output) baud rate */
 295 #endif
 296 #ifdef CIBAUD
 297                 | CIBAUD   /* input baud rate */
 298 #endif
 299         );
 300         /* Set: 8 bits; hang up (drop DTR) on last close; enable receive */
 301         G.tty_attrs.c_cflag |= CS8 | HUPCL | CREAD;
 302         if (option_mask32 & F_LOCAL) {
 303                 /* ignore Carrier Detect pin:
 304                  * opens don't block when CD is low,
 305                  * losing CD doesn't hang up processes whose ctty is this tty
 306                  */
 307                 G.tty_attrs.c_cflag |= CLOCAL;
 308         }
 309 #ifdef CRTSCTS
 310         if (option_mask32 & F_RTSCTS)
 311                 G.tty_attrs.c_cflag |= CRTSCTS; /* flow control using RTS/CTS pins */
 312 #endif
 313         G.tty_attrs.c_iflag = 0;
 314         G.tty_attrs.c_lflag = 0;
 315         /* non-raw output; add CR to each NL */
 316         G.tty_attrs.c_oflag = OPOST | ONLCR;
 317
 318         /* reads will block only if < 1 char is available */
 319         G.tty_attrs.c_cc[VMIN] = 1;
 320         /* no timeout (reads block forever) */
 321         G.tty_attrs.c_cc[VTIME] = 0;
 322 #ifdef __linux__
 323         G.tty_attrs.c_line = 0;
 324 #endif
 325
 326         set_tty_attrs();
 327
 328         debug("term_io 2\n");
 329 }
 330
 331 static void finalize_tty_attrs(void)
 332 {
 333         /* software flow control on output (stop sending if XOFF is recvd);
 334          * and on input (send XOFF when buffer is full)
 335          */
 336         G.tty_attrs.c_iflag |= IXON | IXOFF;
 337         if (G.eol == '\r') {
 338                 G.tty_attrs.c_iflag |= ICRNL; /* map CR on input to NL */
 339         }
 340         /* Other bits in c_iflag:
 341          * IXANY   Any recvd char enables output (any char is also a XON)
 342          * INPCK   Enable parity check
 343          * IGNPAR  Ignore parity errors (drop bad bytes)
 344          * PARMRK  Mark parity errors with 0xff, 0x00 prefix
 345          *         (else bad byte is received as 0x00)
 346          * ISTRIP  Strip parity bit
 347          * IGNBRK  Ignore break condition
 348          * BRKINT  Send SIGINT on break - maybe set this?
 349          * INLCR   Map NL to CR
 350          * IGNCR   Ignore CR
 351          * ICRNL   Map CR to NL
 352          * IUCLC   Map uppercase to lowercase
 353          * IMAXBEL Echo BEL on input line too long
 354          * IUTF8   Appears to affect tty's idea of char widths,
 355          *         observed to improve backspacing through Unicode chars
 356          */
 357
 358         /* ICANON  line buffered input (NL or EOL or EOF chars end a line);
 359          * ISIG    recognize INT/QUIT/SUSP chars;
 360          * ECHO    echo input chars;
 361          * ECHOE   echo BS-SP-BS on erase character;
 362          * ECHOK   echo kill char specially, not as ^c (ECHOKE controls how exactly);
 363          * ECHOKE  erase all input via BS-SP-BS on kill char (else go to next line)
 364          * ECHOCTL Echo ctrl chars as ^c (else echo verbatim:
 365          *         e.g. up arrow emits "ESC-something" and thus moves cursor up!)
 366          */
 367         G.tty_attrs.c_lflag |= ICANON | ISIG | ECHO | ECHOE | ECHOK | ECHOKE | ECHOCTL;
 368         /* Other bits in c_lflag:
 369          * XCASE   Map uppercase to \lowercase [tried, doesn't work]
 370          * ECHONL  Echo NL even if ECHO is not set
 371          * ECHOPRT On erase, echo erased chars
 372          *         [qwe<BS><BS><BS> input looks like "qwe\ewq/" on screen]
 373          * NOFLSH  Don't flush input buffer after interrupt or quit chars
 374          * IEXTEN  Enable extended functions (??)
 375          *         [glibc says it enables c_cc[LNEXT] "enter literal char"
 376          *         and c_cc[VDISCARD] "toggle discard buffered output" chars]
 377          * FLUSHO  Output being flushed (c_cc[VDISCARD] is in effect)
 378          * PENDIN  Retype pending input at next read or input char
 379          *         (c_cc[VREPRINT] is being processed)
 380          * TOSTOP  Send SIGTTOU for background output
 381          *         (why "stty sane" unsets this bit?)
 382          */
 383
 384         G.tty_attrs.c_cc[VINTR] = CTL('C');
 385         G.tty_attrs.c_cc[VQUIT] = CTL('\\');
 386         G.tty_attrs.c_cc[VEOF] = CTL('D');
 387         G.tty_attrs.c_cc[VEOL] = '\n';
 388 #ifdef VSWTC
 389         G.tty_attrs.c_cc[VSWTC] = 0;
 390 #endif
 391 #ifdef VSWTCH
 392         G.tty_attrs.c_cc[VSWTCH] = 0;
 393 #endif
 394         G.tty_attrs.c_cc[VKILL] = CTL('U');
 395         /* Other control chars:
 396          * VEOL2
 397          * VERASE, VWERASE - (word) erase. we may set VERASE in get_logname
 398          * VREPRINT - reprint current input buffer
 399          * VLNEXT, VDISCARD, VSTATUS
 400          * VSUSP, VDSUSP - send (delayed) SIGTSTP
 401          * VSTART, VSTOP - chars used for IXON/IXOFF
 402          */
 403
 404         set_tty_attrs();
 405
 406         /* Now the newline character should be properly written */
 407         full_write1_str("\n");
 408 }
 409
 410 /* extract baud rate from modem status message */
 411 static void auto_baud(void)
 412 {
 413         int nread;
 414
 415         /*
 416          * This works only if the modem produces its status code AFTER raising
 417          * the DCD line, and if the computer is fast enough to set the proper
 418          * baud rate before the message has gone by. We expect a message of the
 419          * following format:
 420          *
 421          * <junk><number><junk>
 422          *
 423          * The number is interpreted as the baud rate of the incoming call. If the
 424          * modem does not tell us the baud rate within one second, we will keep
 425          * using the current baud rate. It is advisable to enable BREAK
 426          * processing (comma-separated list of baud rates) if the processing of
 427          * modem status messages is enabled.
 428          */
 429
 430         G.tty_attrs.c_cc[VMIN] = 0; /* don't block reads (min read is 0 chars) */
 431         set_tty_attrs();
 432
 433         /*
 434          * Wait for a while, then read everything the modem has said so far and
 435          * try to extract the speed of the dial-in call.
 436          */
 437         sleep1();
 438         nread = safe_read(STDIN_FILENO, G.line_buf, sizeof(G.line_buf) - 1);
 439         if (nread > 0) {
 440                 int speed;
 441                 char *bp;
 442                 G.line_buf[nread] = '\0';
 443                 for (bp = G.line_buf; bp < G.line_buf + nread; bp++) {
 444                         if (isdigit(*bp)) {
 445                                 speed = bcode(bp);
 446                                 if (speed > 0)
 447                                         cfsetspeed(&G.tty_attrs, speed);
 448                                 break;
 449                         }
 450                 }
 451         }
 452
 453         /* Restore terminal settings */
 454         G.tty_attrs.c_cc[VMIN] = 1; /* restore to value set by init_tty_attrs */
 455         set_tty_attrs();
 456 }
 457
 458 /* get user name, establish parity, speed, erase, kill, eol;
 459  * return NULL on BREAK, logname on success
 460  */
 461 static char *get_logname(void)
 462 {
 463         char *bp;
 464         char c;
 465
 466         /* Flush pending input (esp. after parsing or switching the baud rate) */
 467         usleep(100*1000); /* 0.1 sec */
 468         tcflush(STDIN_FILENO, TCIFLUSH);
 469
 470         /* Prompt for and read a login name */
 471         do {
 472                 /* Write issue file and prompt */
 473 #ifdef ISSUE
 474                 if (!(option_mask32 & F_NOISSUE))
 475                         print_login_issue(G.issue, G.tty_name);
 476 #endif
 477                 print_login_prompt();
 478
 479                 /* Read name, watch for break, erase, kill, end-of-line */
 480                 bp = G.line_buf;
 481                 while (1) {
 482                         /* Do not report trivial EINTR/EIO errors */
 483                         errno = EINTR; /* make read of 0 bytes be silent too */
 484                         if (read(STDIN_FILENO, &c, 1) < 1) {
 485                                 finalize_tty_attrs();
 486                                 if (errno == EINTR || errno == EIO)
 487                                         exit_SUCCESS();
 488                                 bb_simple_perror_msg_and_die(bb_msg_read_error);
 489                         }
 490
 491                         switch (c) {
 492                         case '\r':
 493                         case '\n':
 494                                 *bp = '\0';
 495                                 G.eol = c;
 496                                 goto got_logname;
 497                         case CTL('H'):
 498                         case 0x7f:
 499                                 G.tty_attrs.c_cc[VERASE] = c;
 500                                 if (bp > G.line_buf) {
 501                                         full_write1_str("\010 \010");
 502                                         bp--;
 503                                 }
 504                                 break;
 505                         case CTL('U'):
 506                                 while (bp > G.line_buf) {
 507                                         full_write1_str("\010 \010");
 508                                         bp--;
 509                                 }
 510                                 break;
 511                         case CTL('C'):
 512                         case CTL('D'):
 513                                 finalize_tty_attrs();
 514                                 exit_SUCCESS();
 515                         case '\0':
 516                                 /* BREAK. If we have speeds to try,
 517                                  * return NULL (will switch speeds and return here) */
 518                                 if (G.numspeed > 1)
 519                                         return NULL;
 520                                 /* fall through and ignore it */
 521                         default:
 522                                 if ((unsigned char)c < ' ') {
 523                                         /* ignore garbage characters */
 524                                 } else if ((int)(bp - G.line_buf) < sizeof(G.line_buf) - 1) {
 525                                         /* echo and store the character */
 526                                         full_write(STDOUT_FILENO, &c, 1);
 527                                         *bp++ = c;
 528                                 }
 529                                 break;
 530                         }
 531                 } /* end of get char loop */
 532  got_logname: ;
 533         } while (G.line_buf[0] == '\0');  /* while logname is empty */
 534
 535         return G.line_buf;
 536 }
 537
 538 static void alarm_handler(int sig UNUSED_PARAM)
 539 {
 540         finalize_tty_attrs();
 541         _exit_SUCCESS();
 542 }
 543
 544 static void sleep10(void)
 545 {
 546         sleep(10);
 547 }
 548
 549 int getty_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 550 int getty_main(int argc UNUSED_PARAM, char **argv)
 551 {
 552         int n;
 553         pid_t pid, tsid;
 554         char *logname;
 555
 556         INIT_G();
 557         G.login = _PATH_LOGIN;    /* default login program */
 558 #ifdef ISSUE
 559         G.issue = ISSUE;          /* default issue file */
 560 #endif
 561         G.eol = '\r';
 562
 563         /* Parse command-line arguments */
 564         parse_args(argv);
 565
 566         /* Create new session and pgrp, lose controlling tty */
 567         pid = setsid();  /* this also gives us our pid :) */
 568         if (pid < 0) {
 569                 int fd;
 570                 /* :(
 571                  * docs/ctty.htm says:
 572                  * "This is allowed only when the current process
 573                  *  is not a process group leader".
 574                  * Thus, setsid() will fail if we _already_ are
 575                  * a session leader - which is quite possible for getty!
 576                  */
 577                 pid = getpid();
 578                 if (getsid(0) != pid) {
 579                         //for debugging:
 580                         //bb_perror_msg_and_die("setsid failed:"
 581                         //      " pid %d ppid %d"
 582                         //      " sid %d pgid %d",
 583                         //      pid, getppid(),
 584                         //      getsid(0), getpgid(0));
 585                         bb_simple_perror_msg_and_die("setsid");
 586                         /*
 587                          * When we can end up here?
 588                          * Example: setsid() fails when run alone in interactive shell:
 589                          *  # getty 115200 /dev/tty2
 590                          * because shell's child (getty) is put in a new process group.
 591                          * But doesn't fail if shell is not interactive
 592                          * (and therefore doesn't create process groups for pipes),
 593                          * or if getty is not the first process in the process group:
 594                          *  # true | getty 115200 /dev/tty2
 595                          */
 596                 }
 597                 /* Looks like we are already a session leader.
 598                  * In this case (setsid failed) we may still have ctty,
 599                  * and it may be different from tty we need to control!
 600                  * If we still have ctty, on Linux ioctl(TIOCSCTTY)
 601                  * (which we are going to use a bit later) always fails -
 602                  * even if we try to take ctty which is already ours!
 603                  * Try to drop old ctty now to prevent that.
 604                  * Use O_NONBLOCK: old ctty may be a serial line.
 605                  */
 606                 fd = open("/dev/tty", O_RDWR | O_NONBLOCK);
 607                 if (fd >= 0) {
 608                         /* TIOCNOTTY sends SIGHUP to the foreground
 609                          * process group - which may include us!
 610                          * Make sure to not die on it:
 611                          */
 612                         sighandler_t old = signal(SIGHUP, SIG_IGN);
 613                         ioctl(fd, TIOCNOTTY);
 614                         close(fd);
 615                         signal(SIGHUP, old);
 616                 }
 617         }
 618
 619         /* Close stdio, and stray descriptors, just in case */
 620         n = xopen(bb_dev_null, O_RDWR);
 621         /* dup2(n, 0); - no, we need to handle "getty - 9600" too */
 622         xdup2(n, 1);
 623         xdup2(n, 2);
 624         while (n > 2)
 625                 close(n--);
 626
 627         /* Logging. We want special flavor of error_msg_and_die */
 628         die_func = sleep10;
 629         msg_eol = "\r\n";
 630         /* most likely will internally use fd #3 in CLOEXEC mode: */
 631         openlog(applet_name, LOG_PID, LOG_AUTH);
 632         logmode = LOGMODE_BOTH;
 633
 634 #ifdef DEBUGGING
 635         dbf = xfopen_for_write(DEBUGTERM);
 636         for (n = 1; argv[n]; n++) {
 637                 debug(argv[n]);
 638                 debug("\n");
 639         }
 640 #endif
 641
 642         /* Open the tty as standard input, if it is not "-" */
 643         debug("calling open_tty\n");
 644         open_tty();
 645         ndelay_off(STDIN_FILENO);
 646         debug("duping\n");
 647         xdup2(STDIN_FILENO, 1);
 648         xdup2(STDIN_FILENO, 2);
 649
 650         /* Steal ctty if we don't have it yet */
 651         tsid = tcgetsid(STDIN_FILENO);
 652         if (tsid < 0 || pid != tsid) {
 653                 if (ioctl(STDIN_FILENO, TIOCSCTTY, /*force:*/ (long)1) < 0)
 654                         bb_simple_perror_msg_and_die("TIOCSCTTY");
 655         }
 656
 657 #ifdef __linux__
 658         /* Make ourself a foreground process group within our session */
 659         if (tcsetpgrp(STDIN_FILENO, pid) < 0)
 660                 bb_simple_perror_msg_and_die("tcsetpgrp");
 661 #endif
 662
 663         /*
 664          * The following ioctl will fail if stdin is not a tty, but also when
 665          * there is noise on the modem control lines. In the latter case, the
 666          * common course of action is (1) fix your cables (2) give the modem more
 667          * time to properly reset after hanging up. SunOS users can achieve (2)
 668          * by patching the SunOS kernel variable "zsadtrlow" to a larger value;
 669          * 5 seconds seems to be a good value.
 670          */
 671         if (tcgetattr(STDIN_FILENO, &G.tty_attrs) < 0)
 672                 bb_simple_perror_msg_and_die("tcgetattr");
 673
 674         /* Update the utmp file. This tty is ours now! */
 675         update_utmp(pid, LOGIN_PROCESS, G.tty_name, "LOGIN", G.fakehost);
 676
 677         /* Initialize tty attrs (raw mode, eight-bit, blocking i/o) */
 678         debug("calling init_tty_attrs\n");
 679         init_tty_attrs(G.speeds[0]);
 680
 681         /* Write the modem init string and DON'T flush the buffers */
 682         if (option_mask32 & F_INITSTRING) {
 683                 debug("writing init string\n");
 684                 full_write1_str(G.initstring);
 685         }
 686
 687         /* Optionally detect the baud rate from the modem status message */
 688         debug("before autobaud\n");
 689         if (option_mask32 & F_PARSE)
 690                 auto_baud();
 691
 692         /* Set the optional timer */
 693         signal(SIGALRM, alarm_handler);
 694         alarm(G.timeout); /* if 0, alarm is not set */
 695
 696         /* Optionally wait for CR or LF before writing /etc/issue */
 697         if (option_mask32 & F_WAITCRLF) {
 698                 char ch;
 699                 debug("waiting for cr-lf\n");
 700                 while (safe_read(STDIN_FILENO, &ch, 1) == 1) {
 701                         debug("read %x\n", (unsigned char)ch);
 702                         if (ch == '\n' || ch == '\r')
 703                                 break;
 704                 }
 705         }
 706
 707         logname = NULL;
 708         if (!(option_mask32 & F_NOPROMPT)) {
 709                 /* NB: init_tty_attrs already set line speed
 710                  * to G.speeds[0] */
 711                 int baud_index = 0;
 712
 713                 while (1) {
 714                         /* Read the login name */
 715                         debug("reading login name\n");
 716                         logname = get_logname();
 717                         if (logname)
 718                                 break;
 719                         /* We are here only if G.numspeed > 1 */
 720                         baud_index = (baud_index + 1) % G.numspeed;
 721                         cfsetspeed(&G.tty_attrs, G.speeds[baud_index]);
 722                         set_tty_attrs();
 723                 }
 724         }
 725
 726         /* Disable timer */
 727         alarm(0);
 728
 729         finalize_tty_attrs();
 730
 731         /* Let the login program take care of password validation */
 732         /* We use PATH because we trust that root doesn't set "bad" PATH,
 733          * and getty is not suid-root applet */
 734         /* With -n, logname == NULL, and login will ask for username instead */
 735         BB_EXECLP(G.login, G.login, "--", logname, (char *)0);
 736         bb_error_msg_and_die("can't execute '%s'", G.login);
 737 }