blob: d00d87deab2812b54767595d5ea7d554dee5bcd7
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * Simple telnet server |
4 | * Bjorn Wesen, Axis Communications AB (bjornw@axis.com) |
5 | * |
6 | * Licensed under GPLv2 or later, see file LICENSE in this source tree. |
7 | * |
8 | * --------------------------------------------------------------------------- |
9 | * (C) Copyright 2000, Axis Communications AB, LUND, SWEDEN |
10 | **************************************************************************** |
11 | * |
12 | * The telnetd manpage says it all: |
13 | * |
14 | * Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for |
15 | * a client, then creating a login process which has the slave side of the |
16 | * pseudo-terminal as stdin, stdout, and stderr. Telnetd manipulates the |
17 | * master side of the pseudo-terminal, implementing the telnet protocol and |
18 | * passing characters between the remote client and the login process. |
19 | * |
20 | * Vladimir Oleynik <dzo@simtreas.ru> 2001 |
21 | * Set process group corrections, initial busybox port |
22 | */ |
23 | |
24 | //usage:#define telnetd_trivial_usage |
25 | //usage: "[OPTIONS]" |
26 | //usage:#define telnetd_full_usage "\n\n" |
27 | //usage: "Handle incoming telnet connections" |
28 | //usage: IF_NOT_FEATURE_TELNETD_STANDALONE(" via inetd") "\n" |
29 | //usage: "\n -l LOGIN Exec LOGIN on connect" |
30 | //usage: "\n -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue" |
31 | //usage: "\n -K Close connection as soon as login exits" |
32 | //usage: "\n (normally wait until all programs close slave pty)" |
33 | //usage: IF_FEATURE_TELNETD_STANDALONE( |
34 | //usage: "\n -p PORT Port to listen on" |
35 | //usage: "\n -b ADDR[:PORT] Address to bind to" |
36 | //usage: "\n -F Run in foreground" |
37 | //usage: "\n -i Inetd mode" |
38 | //usage: IF_FEATURE_TELNETD_INETD_WAIT( |
39 | //usage: "\n -w SEC Inetd 'wait' mode, linger time SEC" |
40 | //usage: "\n -S Log to syslog (implied by -i or without -F and -w)" |
41 | //usage: ) |
42 | //usage: ) |
43 | |
44 | #define DEBUG 0 |
45 | |
46 | #include "libbb.h" |
47 | #include <syslog.h> |
48 | |
49 | #if DEBUG |
50 | # define TELCMDS |
51 | # define TELOPTS |
52 | #endif |
53 | #include <arpa/telnet.h> |
54 | |
55 | |
56 | struct tsession { |
57 | struct tsession *next; |
58 | pid_t shell_pid; |
59 | int sockfd_read; |
60 | int sockfd_write; |
61 | int ptyfd; |
62 | |
63 | /* two circular buffers */ |
64 | /*char *buf1, *buf2;*/ |
65 | /*#define TS_BUF1(ts) ts->buf1*/ |
66 | /*#define TS_BUF2(ts) TS_BUF2(ts)*/ |
67 | #define TS_BUF1(ts) ((unsigned char*)(ts + 1)) |
68 | #define TS_BUF2(ts) (((unsigned char*)(ts + 1)) + BUFSIZE) |
69 | int rdidx1, wridx1, size1; |
70 | int rdidx2, wridx2, size2; |
71 | }; |
72 | |
73 | /* Two buffers are directly after tsession in malloced memory. |
74 | * Make whole thing fit in 4k */ |
75 | enum { BUFSIZE = (4 * 1024 - sizeof(struct tsession)) / 2 }; |
76 | |
77 | |
78 | /* Globals */ |
79 | struct globals { |
80 | struct tsession *sessions; |
81 | const char *loginpath; |
82 | const char *issuefile; |
83 | int maxfd; |
84 | } FIX_ALIASING; |
85 | #define G (*(struct globals*)&bb_common_bufsiz1) |
86 | #define INIT_G() do { \ |
87 | G.loginpath = "/system/xbin/login"; \ |
88 | G.issuefile = "/etc/issue.net"; \ |
89 | } while (0) |
90 | |
91 | |
92 | /* |
93 | Remove all IAC's from buf1 (received IACs are ignored and must be removed |
94 | so as to not be interpreted by the terminal). Make an uninterrupted |
95 | string of characters fit for the terminal. Do this by packing |
96 | all characters meant for the terminal sequentially towards the end of buf. |
97 | |
98 | Return a pointer to the beginning of the characters meant for the terminal |
99 | and make *num_totty the number of characters that should be sent to |
100 | the terminal. |
101 | |
102 | Note - if an IAC (3 byte quantity) starts before (bf + len) but extends |
103 | past (bf + len) then that IAC will be left unprocessed and *processed |
104 | will be less than len. |
105 | |
106 | CR-LF ->'s CR mapping is also done here, for convenience. |
107 | |
108 | NB: may fail to remove iacs which wrap around buffer! |
109 | */ |
110 | static unsigned char * |
111 | remove_iacs(struct tsession *ts, int *pnum_totty) |
112 | { |
113 | unsigned char *ptr0 = TS_BUF1(ts) + ts->wridx1; |
114 | unsigned char *ptr = ptr0; |
115 | unsigned char *totty = ptr; |
116 | unsigned char *end = ptr + MIN(BUFSIZE - ts->wridx1, ts->size1); |
117 | int num_totty; |
118 | |
119 | while (ptr < end) { |
120 | if (*ptr != IAC) { |
121 | char c = *ptr; |
122 | |
123 | *totty++ = c; |
124 | ptr++; |
125 | /* We map \r\n ==> \r for pragmatic reasons. |
126 | * Many client implementations send \r\n when |
127 | * the user hits the CarriageReturn key. |
128 | * See RFC 1123 3.3.1 Telnet End-of-Line Convention. |
129 | */ |
130 | if (c == '\r' && ptr < end && (*ptr == '\n' || *ptr == '\0')) |
131 | ptr++; |
132 | continue; |
133 | } |
134 | |
135 | if ((ptr+1) >= end) |
136 | break; |
137 | if (ptr[1] == NOP) { /* Ignore? (putty keepalive, etc.) */ |
138 | ptr += 2; |
139 | continue; |
140 | } |
141 | if (ptr[1] == IAC) { /* Literal IAC? (emacs M-DEL) */ |
142 | *totty++ = ptr[1]; |
143 | ptr += 2; |
144 | continue; |
145 | } |
146 | |
147 | /* |
148 | * TELOPT_NAWS support! |
149 | */ |
150 | if ((ptr+2) >= end) { |
151 | /* Only the beginning of the IAC is in the |
152 | buffer we were asked to process, we can't |
153 | process this char */ |
154 | break; |
155 | } |
156 | /* |
157 | * IAC -> SB -> TELOPT_NAWS -> 4-byte -> IAC -> SE |
158 | */ |
159 | if (ptr[1] == SB && ptr[2] == TELOPT_NAWS) { |
160 | struct winsize ws; |
161 | if ((ptr+8) >= end) |
162 | break; /* incomplete, can't process */ |
163 | ws.ws_col = (ptr[3] << 8) | ptr[4]; |
164 | ws.ws_row = (ptr[5] << 8) | ptr[6]; |
165 | ioctl(ts->ptyfd, TIOCSWINSZ, (char *)&ws); |
166 | ptr += 9; |
167 | continue; |
168 | } |
169 | /* skip 3-byte IAC non-SB cmd */ |
170 | #if DEBUG |
171 | fprintf(stderr, "Ignoring IAC %s,%s\n", |
172 | TELCMD(ptr[1]), TELOPT(ptr[2])); |
173 | #endif |
174 | ptr += 3; |
175 | } |
176 | |
177 | num_totty = totty - ptr0; |
178 | *pnum_totty = num_totty; |
179 | /* The difference between ptr and totty is number of iacs |
180 | we removed from the stream. Adjust buf1 accordingly */ |
181 | if ((ptr - totty) == 0) /* 99.999% of cases */ |
182 | return ptr0; |
183 | ts->wridx1 += ptr - totty; |
184 | ts->size1 -= ptr - totty; |
185 | /* Move chars meant for the terminal towards the end of the buffer */ |
186 | return memmove(ptr - num_totty, ptr0, num_totty); |
187 | } |
188 | |
189 | /* |
190 | * Converting single IAC into double on output |
191 | */ |
192 | static size_t iac_safe_write(int fd, const char *buf, size_t count) |
193 | { |
194 | const char *IACptr; |
195 | size_t wr, rc, total; |
196 | |
197 | total = 0; |
198 | while (1) { |
199 | if (count == 0) |
200 | return total; |
201 | if (*buf == (char)IAC) { |
202 | static const char IACIAC[] ALIGN1 = { IAC, IAC }; |
203 | rc = safe_write(fd, IACIAC, 2); |
204 | if (rc != 2) |
205 | break; |
206 | buf++; |
207 | total++; |
208 | count--; |
209 | continue; |
210 | } |
211 | /* count != 0, *buf != IAC */ |
212 | IACptr = memchr(buf, IAC, count); |
213 | wr = count; |
214 | if (IACptr) |
215 | wr = IACptr - buf; |
216 | rc = safe_write(fd, buf, wr); |
217 | if (rc != wr) |
218 | break; |
219 | buf += rc; |
220 | total += rc; |
221 | count -= rc; |
222 | } |
223 | /* here: rc - result of last short write */ |
224 | if ((ssize_t)rc < 0) { /* error? */ |
225 | if (total == 0) |
226 | return rc; |
227 | rc = 0; |
228 | } |
229 | return total + rc; |
230 | } |
231 | |
232 | /* Must match getopt32 string */ |
233 | enum { |
234 | OPT_WATCHCHILD = (1 << 2), /* -K */ |
235 | OPT_INETD = (1 << 3) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -i */ |
236 | OPT_PORT = (1 << 4) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -p PORT */ |
237 | OPT_FOREGROUND = (1 << 6) * ENABLE_FEATURE_TELNETD_STANDALONE, /* -F */ |
238 | OPT_SYSLOG = (1 << 7) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -S */ |
239 | OPT_WAIT = (1 << 8) * ENABLE_FEATURE_TELNETD_INETD_WAIT, /* -w SEC */ |
240 | }; |
241 | |
242 | static struct tsession * |
243 | make_new_session( |
244 | IF_FEATURE_TELNETD_STANDALONE(int sock) |
245 | IF_NOT_FEATURE_TELNETD_STANDALONE(void) |
246 | ) { |
247 | #if !ENABLE_FEATURE_TELNETD_STANDALONE |
248 | enum { sock = 0 }; |
249 | #endif |
250 | const char *login_argv[2]; |
251 | struct termios termbuf; |
252 | int fd, pid; |
253 | char tty_name[GETPTY_BUFSIZE]; |
254 | struct tsession *ts = xzalloc(sizeof(struct tsession) + BUFSIZE * 2); |
255 | |
256 | /*ts->buf1 = (char *)(ts + 1);*/ |
257 | /*ts->buf2 = ts->buf1 + BUFSIZE;*/ |
258 | |
259 | /* Got a new connection, set up a tty */ |
260 | fd = xgetpty(tty_name); |
261 | if (fd > G.maxfd) |
262 | G.maxfd = fd; |
263 | ts->ptyfd = fd; |
264 | ndelay_on(fd); |
265 | close_on_exec_on(fd); |
266 | |
267 | /* SO_KEEPALIVE by popular demand */ |
268 | setsockopt(sock, SOL_SOCKET, SO_KEEPALIVE, &const_int_1, sizeof(const_int_1)); |
269 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
270 | ts->sockfd_read = sock; |
271 | ndelay_on(sock); |
272 | if (sock == 0) { /* We are called with fd 0 - we are in inetd mode */ |
273 | sock++; /* so use fd 1 for output */ |
274 | ndelay_on(sock); |
275 | } |
276 | ts->sockfd_write = sock; |
277 | if (sock > G.maxfd) |
278 | G.maxfd = sock; |
279 | #else |
280 | /* ts->sockfd_read = 0; - done by xzalloc */ |
281 | ts->sockfd_write = 1; |
282 | ndelay_on(0); |
283 | ndelay_on(1); |
284 | #endif |
285 | |
286 | /* Make the telnet client understand we will echo characters so it |
287 | * should not do it locally. We don't tell the client to run linemode, |
288 | * because we want to handle line editing and tab completion and other |
289 | * stuff that requires char-by-char support. */ |
290 | { |
291 | static const char iacs_to_send[] ALIGN1 = { |
292 | IAC, DO, TELOPT_ECHO, |
293 | IAC, DO, TELOPT_NAWS, |
294 | /* This requires telnetd.ctrlSQ.patch (incomplete) */ |
295 | /*IAC, DO, TELOPT_LFLOW,*/ |
296 | IAC, WILL, TELOPT_ECHO, |
297 | IAC, WILL, TELOPT_SGA |
298 | }; |
299 | /* This confuses iac_safe_write(), it will try to duplicate |
300 | * each IAC... */ |
301 | //memcpy(TS_BUF2(ts), iacs_to_send, sizeof(iacs_to_send)); |
302 | //ts->rdidx2 = sizeof(iacs_to_send); |
303 | //ts->size2 = sizeof(iacs_to_send); |
304 | /* So just stuff it into TCP stream! (no error check...) */ |
305 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
306 | safe_write(sock, iacs_to_send, sizeof(iacs_to_send)); |
307 | #else |
308 | safe_write(1, iacs_to_send, sizeof(iacs_to_send)); |
309 | #endif |
310 | /*ts->rdidx2 = 0; - xzalloc did it */ |
311 | /*ts->size2 = 0;*/ |
312 | } |
313 | |
314 | fflush_all(); |
315 | pid = vfork(); /* NOMMU-friendly */ |
316 | if (pid < 0) { |
317 | free(ts); |
318 | close(fd); |
319 | /* sock will be closed by caller */ |
320 | bb_perror_msg("vfork"); |
321 | return NULL; |
322 | } |
323 | if (pid > 0) { |
324 | /* Parent */ |
325 | ts->shell_pid = pid; |
326 | return ts; |
327 | } |
328 | |
329 | /* Child */ |
330 | /* Careful - we are after vfork! */ |
331 | |
332 | /* Restore default signal handling ASAP */ |
333 | bb_signals((1 << SIGCHLD) + (1 << SIGPIPE), SIG_DFL); |
334 | |
335 | pid = getpid(); |
336 | |
337 | if (ENABLE_FEATURE_UTMP) { |
338 | len_and_sockaddr *lsa = get_peer_lsa(sock); |
339 | char *hostname = NULL; |
340 | if (lsa) { |
341 | hostname = xmalloc_sockaddr2dotted(&lsa->u.sa); |
342 | free(lsa); |
343 | } |
344 | write_new_utmp(pid, LOGIN_PROCESS, tty_name, /*username:*/ "LOGIN", hostname); |
345 | free(hostname); |
346 | } |
347 | |
348 | /* Make new session and process group */ |
349 | setsid(); |
350 | |
351 | /* Open the child's side of the tty */ |
352 | /* NB: setsid() disconnects from any previous ctty's. Therefore |
353 | * we must open child's side of the tty AFTER setsid! */ |
354 | close(0); |
355 | xopen(tty_name, O_RDWR); /* becomes our ctty */ |
356 | xdup2(0, 1); |
357 | xdup2(0, 2); |
358 | tcsetpgrp(0, pid); /* switch this tty's process group to us */ |
359 | |
360 | /* The pseudo-terminal allocated to the client is configured to operate |
361 | * in cooked mode, and with XTABS CRMOD enabled (see tty(4)) */ |
362 | tcgetattr(0, &termbuf); |
363 | termbuf.c_lflag |= ECHO; /* if we use readline we dont want this */ |
364 | termbuf.c_oflag |= ONLCR | XTABS; |
365 | termbuf.c_iflag |= ICRNL; |
366 | termbuf.c_iflag &= ~IXOFF; |
367 | /*termbuf.c_lflag &= ~ICANON;*/ |
368 | tcsetattr_stdin_TCSANOW(&termbuf); |
369 | |
370 | /* Uses FILE-based I/O to stdout, but does fflush_all(), |
371 | * so should be safe with vfork. |
372 | * I fear, though, that some users will have ridiculously big |
373 | * issue files, and they may block writing to fd 1, |
374 | * (parent is supposed to read it, but parent waits |
375 | * for vforked child to exec!) */ |
376 | print_login_issue(G.issuefile, tty_name); |
377 | |
378 | /* Exec shell / login / whatever */ |
379 | login_argv[0] = G.loginpath; |
380 | login_argv[1] = NULL; |
381 | /* exec busybox applet (if PREFER_APPLETS=y), if that fails, |
382 | * exec external program. |
383 | * NB: sock is either 0 or has CLOEXEC set on it. |
384 | * fd has CLOEXEC set on it too. These two fds will be closed here. |
385 | */ |
386 | BB_EXECVP(G.loginpath, (char **)login_argv); |
387 | /* _exit is safer with vfork, and we shouldn't send message |
388 | * to remote clients anyway */ |
389 | _exit(EXIT_FAILURE); /*bb_perror_msg_and_die("execv %s", G.loginpath);*/ |
390 | } |
391 | |
392 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
393 | |
394 | static void |
395 | free_session(struct tsession *ts) |
396 | { |
397 | struct tsession *t; |
398 | |
399 | if (option_mask32 & OPT_INETD) |
400 | exit(EXIT_SUCCESS); |
401 | |
402 | /* Unlink this telnet session from the session list */ |
403 | t = G.sessions; |
404 | if (t == ts) |
405 | G.sessions = ts->next; |
406 | else { |
407 | while (t->next != ts) |
408 | t = t->next; |
409 | t->next = ts->next; |
410 | } |
411 | |
412 | #if 0 |
413 | /* It was said that "normal" telnetd just closes ptyfd, |
414 | * doesn't send SIGKILL. When we close ptyfd, |
415 | * kernel sends SIGHUP to processes having slave side opened. */ |
416 | kill(ts->shell_pid, SIGKILL); |
417 | waitpid(ts->shell_pid, NULL, 0); |
418 | #endif |
419 | close(ts->ptyfd); |
420 | close(ts->sockfd_read); |
421 | /* We do not need to close(ts->sockfd_write), it's the same |
422 | * as sockfd_read unless we are in inetd mode. But in inetd mode |
423 | * we do not reach this */ |
424 | free(ts); |
425 | |
426 | /* Scan all sessions and find new maxfd */ |
427 | G.maxfd = 0; |
428 | ts = G.sessions; |
429 | while (ts) { |
430 | if (G.maxfd < ts->ptyfd) |
431 | G.maxfd = ts->ptyfd; |
432 | if (G.maxfd < ts->sockfd_read) |
433 | G.maxfd = ts->sockfd_read; |
434 | #if 0 |
435 | /* Again, sockfd_write == sockfd_read here */ |
436 | if (G.maxfd < ts->sockfd_write) |
437 | G.maxfd = ts->sockfd_write; |
438 | #endif |
439 | ts = ts->next; |
440 | } |
441 | } |
442 | |
443 | #else /* !FEATURE_TELNETD_STANDALONE */ |
444 | |
445 | /* Used in main() only, thus "return 0" actually is exit(EXIT_SUCCESS). */ |
446 | #define free_session(ts) return 0 |
447 | |
448 | #endif |
449 | |
450 | static void handle_sigchld(int sig UNUSED_PARAM) |
451 | { |
452 | pid_t pid; |
453 | struct tsession *ts; |
454 | int save_errno = errno; |
455 | |
456 | /* Looping: more than one child may have exited */ |
457 | while (1) { |
458 | pid = wait_any_nohang(NULL); |
459 | if (pid <= 0) |
460 | break; |
461 | ts = G.sessions; |
462 | while (ts) { |
463 | if (ts->shell_pid == pid) { |
464 | ts->shell_pid = -1; |
465 | // man utmp: |
466 | // When init(8) finds that a process has exited, it locates its utmp entry |
467 | // by ut_pid, sets ut_type to DEAD_PROCESS, and clears ut_user, ut_host |
468 | // and ut_time with null bytes. |
469 | // [same applies to other processes which maintain utmp entries, like telnetd] |
470 | // |
471 | // We do not bother actually clearing fields: |
472 | // it might be interesting to know who was logged in and from where |
473 | update_utmp(pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL); |
474 | break; |
475 | } |
476 | ts = ts->next; |
477 | } |
478 | } |
479 | |
480 | errno = save_errno; |
481 | } |
482 | |
483 | int telnetd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
484 | int telnetd_main(int argc UNUSED_PARAM, char **argv) |
485 | { |
486 | fd_set rdfdset, wrfdset; |
487 | unsigned opt; |
488 | int count; |
489 | struct tsession *ts; |
490 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
491 | #define IS_INETD (opt & OPT_INETD) |
492 | int master_fd = 0; |
493 | int sec_linger = 0; |
494 | char *opt_bindaddr = NULL; |
495 | char *opt_portnbr; |
496 | #else |
497 | enum { |
498 | IS_INETD = 1, |
499 | master_fd = -1, |
500 | }; |
501 | #endif |
502 | INIT_G(); |
503 | |
504 | /* -w NUM, and implies -F. -w and -i don't mix */ |
505 | IF_FEATURE_TELNETD_INETD_WAIT(opt_complementary = "wF:w+:i--w:w--i";) |
506 | /* Even if !STANDALONE, we accept (and ignore) -i, thus people |
507 | * don't need to guess whether it's ok to pass -i to us */ |
508 | opt = getopt32(argv, "f:l:Ki" |
509 | IF_FEATURE_TELNETD_STANDALONE("p:b:F") |
510 | IF_FEATURE_TELNETD_INETD_WAIT("Sw:"), |
511 | &G.issuefile, &G.loginpath |
512 | IF_FEATURE_TELNETD_STANDALONE(, &opt_portnbr, &opt_bindaddr) |
513 | IF_FEATURE_TELNETD_INETD_WAIT(, &sec_linger) |
514 | ); |
515 | if (!IS_INETD /*&& !re_execed*/) { |
516 | /* inform that we start in standalone mode? |
517 | * May be useful when people forget to give -i */ |
518 | /*bb_error_msg("listening for connections");*/ |
519 | if (!(opt & OPT_FOREGROUND)) { |
520 | /* DAEMON_CHDIR_ROOT was giving inconsistent |
521 | * behavior with/without -F, -i */ |
522 | bb_daemonize_or_rexec(0 /*was DAEMON_CHDIR_ROOT*/, argv); |
523 | } |
524 | } |
525 | /* Redirect log to syslog early, if needed */ |
526 | if (IS_INETD || (opt & OPT_SYSLOG) || !(opt & OPT_FOREGROUND)) { |
527 | openlog(applet_name, LOG_PID, LOG_DAEMON); |
528 | logmode = LOGMODE_SYSLOG; |
529 | } |
530 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
531 | if (IS_INETD) { |
532 | G.sessions = make_new_session(0); |
533 | if (!G.sessions) /* pty opening or vfork problem, exit */ |
534 | return 1; /* make_new_session printed error message */ |
535 | } else { |
536 | master_fd = 0; |
537 | if (!(opt & OPT_WAIT)) { |
538 | unsigned portnbr = 23; |
539 | if (opt & OPT_PORT) |
540 | portnbr = xatou16(opt_portnbr); |
541 | master_fd = create_and_bind_stream_or_die(opt_bindaddr, portnbr); |
542 | xlisten(master_fd, 1); |
543 | } |
544 | close_on_exec_on(master_fd); |
545 | } |
546 | #else |
547 | G.sessions = make_new_session(); |
548 | if (!G.sessions) /* pty opening or vfork problem, exit */ |
549 | return 1; /* make_new_session printed error message */ |
550 | #endif |
551 | |
552 | /* We don't want to die if just one session is broken */ |
553 | signal(SIGPIPE, SIG_IGN); |
554 | |
555 | if (opt & OPT_WATCHCHILD) |
556 | signal(SIGCHLD, handle_sigchld); |
557 | else /* prevent dead children from becoming zombies */ |
558 | signal(SIGCHLD, SIG_IGN); |
559 | |
560 | /* |
561 | This is how the buffers are used. The arrows indicate data flow. |
562 | |
563 | +-------+ wridx1++ +------+ rdidx1++ +----------+ |
564 | | | <-------------- | buf1 | <-------------- | | |
565 | | | size1-- +------+ size1++ | | |
566 | | pty | | socket | |
567 | | | rdidx2++ +------+ wridx2++ | | |
568 | | | --------------> | buf2 | --------------> | | |
569 | +-------+ size2++ +------+ size2-- +----------+ |
570 | |
571 | size1: "how many bytes are buffered for pty between rdidx1 and wridx1?" |
572 | size2: "how many bytes are buffered for socket between rdidx2 and wridx2?" |
573 | |
574 | Each session has got two buffers. Buffers are circular. If sizeN == 0, |
575 | buffer is empty. If sizeN == BUFSIZE, buffer is full. In both these cases |
576 | rdidxN == wridxN. |
577 | */ |
578 | again: |
579 | FD_ZERO(&rdfdset); |
580 | FD_ZERO(&wrfdset); |
581 | |
582 | /* Select on the master socket, all telnet sockets and their |
583 | * ptys if there is room in their session buffers. |
584 | * NB: scalability problem: we recalculate entire bitmap |
585 | * before each select. Can be a problem with 500+ connections. */ |
586 | ts = G.sessions; |
587 | while (ts) { |
588 | struct tsession *next = ts->next; /* in case we free ts */ |
589 | if (ts->shell_pid == -1) { |
590 | /* Child died and we detected that */ |
591 | free_session(ts); |
592 | } else { |
593 | if (ts->size1 > 0) /* can write to pty */ |
594 | FD_SET(ts->ptyfd, &wrfdset); |
595 | if (ts->size1 < BUFSIZE) /* can read from socket */ |
596 | FD_SET(ts->sockfd_read, &rdfdset); |
597 | if (ts->size2 > 0) /* can write to socket */ |
598 | FD_SET(ts->sockfd_write, &wrfdset); |
599 | if (ts->size2 < BUFSIZE) /* can read from pty */ |
600 | FD_SET(ts->ptyfd, &rdfdset); |
601 | } |
602 | ts = next; |
603 | } |
604 | if (!IS_INETD) { |
605 | FD_SET(master_fd, &rdfdset); |
606 | /* This is needed because free_session() does not |
607 | * take master_fd into account when it finds new |
608 | * maxfd among remaining fd's */ |
609 | if (master_fd > G.maxfd) |
610 | G.maxfd = master_fd; |
611 | } |
612 | |
613 | { |
614 | struct timeval *tv_ptr = NULL; |
615 | #if ENABLE_FEATURE_TELNETD_INETD_WAIT |
616 | struct timeval tv; |
617 | if ((opt & OPT_WAIT) && !G.sessions) { |
618 | tv.tv_sec = sec_linger; |
619 | tv.tv_usec = 0; |
620 | tv_ptr = &tv; |
621 | } |
622 | #endif |
623 | count = select(G.maxfd + 1, &rdfdset, &wrfdset, NULL, tv_ptr); |
624 | } |
625 | if (count == 0) /* "telnetd -w SEC" timed out */ |
626 | return 0; |
627 | if (count < 0) |
628 | goto again; /* EINTR or ENOMEM */ |
629 | |
630 | #if ENABLE_FEATURE_TELNETD_STANDALONE |
631 | /* Check for and accept new sessions */ |
632 | if (!IS_INETD && FD_ISSET(master_fd, &rdfdset)) { |
633 | int fd; |
634 | struct tsession *new_ts; |
635 | |
636 | fd = accept(master_fd, NULL, NULL); |
637 | if (fd < 0) |
638 | goto again; |
639 | close_on_exec_on(fd); |
640 | |
641 | /* Create a new session and link it into active list */ |
642 | new_ts = make_new_session(fd); |
643 | if (new_ts) { |
644 | new_ts->next = G.sessions; |
645 | G.sessions = new_ts; |
646 | } else { |
647 | close(fd); |
648 | } |
649 | } |
650 | #endif |
651 | |
652 | /* Then check for data tunneling */ |
653 | ts = G.sessions; |
654 | while (ts) { /* For all sessions... */ |
655 | struct tsession *next = ts->next; /* in case we free ts */ |
656 | |
657 | if (/*ts->size1 &&*/ FD_ISSET(ts->ptyfd, &wrfdset)) { |
658 | int num_totty; |
659 | unsigned char *ptr; |
660 | /* Write to pty from buffer 1 */ |
661 | ptr = remove_iacs(ts, &num_totty); |
662 | count = safe_write(ts->ptyfd, ptr, num_totty); |
663 | if (count < 0) { |
664 | if (errno == EAGAIN) |
665 | goto skip1; |
666 | goto kill_session; |
667 | } |
668 | ts->size1 -= count; |
669 | ts->wridx1 += count; |
670 | if (ts->wridx1 >= BUFSIZE) /* actually == BUFSIZE */ |
671 | ts->wridx1 = 0; |
672 | } |
673 | skip1: |
674 | if (/*ts->size2 &&*/ FD_ISSET(ts->sockfd_write, &wrfdset)) { |
675 | /* Write to socket from buffer 2 */ |
676 | count = MIN(BUFSIZE - ts->wridx2, ts->size2); |
677 | count = iac_safe_write(ts->sockfd_write, (void*)(TS_BUF2(ts) + ts->wridx2), count); |
678 | if (count < 0) { |
679 | if (errno == EAGAIN) |
680 | goto skip2; |
681 | goto kill_session; |
682 | } |
683 | ts->size2 -= count; |
684 | ts->wridx2 += count; |
685 | if (ts->wridx2 >= BUFSIZE) /* actually == BUFSIZE */ |
686 | ts->wridx2 = 0; |
687 | } |
688 | skip2: |
689 | /* Should not be needed, but... remove_iacs is actually buggy |
690 | * (it cannot process iacs which wrap around buffer's end)! |
691 | * Since properly fixing it requires writing bigger code, |
692 | * we rely instead on this code making it virtually impossible |
693 | * to have wrapped iac (people don't type at 2k/second). |
694 | * It also allows for bigger reads in common case. */ |
695 | if (ts->size1 == 0) { |
696 | ts->rdidx1 = 0; |
697 | ts->wridx1 = 0; |
698 | } |
699 | if (ts->size2 == 0) { |
700 | ts->rdidx2 = 0; |
701 | ts->wridx2 = 0; |
702 | } |
703 | |
704 | if (/*ts->size1 < BUFSIZE &&*/ FD_ISSET(ts->sockfd_read, &rdfdset)) { |
705 | /* Read from socket to buffer 1 */ |
706 | count = MIN(BUFSIZE - ts->rdidx1, BUFSIZE - ts->size1); |
707 | count = safe_read(ts->sockfd_read, TS_BUF1(ts) + ts->rdidx1, count); |
708 | if (count <= 0) { |
709 | if (count < 0 && errno == EAGAIN) |
710 | goto skip3; |
711 | goto kill_session; |
712 | } |
713 | /* Ignore trailing NUL if it is there */ |
714 | if (!TS_BUF1(ts)[ts->rdidx1 + count - 1]) { |
715 | --count; |
716 | } |
717 | ts->size1 += count; |
718 | ts->rdidx1 += count; |
719 | if (ts->rdidx1 >= BUFSIZE) /* actually == BUFSIZE */ |
720 | ts->rdidx1 = 0; |
721 | } |
722 | skip3: |
723 | if (/*ts->size2 < BUFSIZE &&*/ FD_ISSET(ts->ptyfd, &rdfdset)) { |
724 | /* Read from pty to buffer 2 */ |
725 | count = MIN(BUFSIZE - ts->rdidx2, BUFSIZE - ts->size2); |
726 | count = safe_read(ts->ptyfd, TS_BUF2(ts) + ts->rdidx2, count); |
727 | if (count <= 0) { |
728 | if (count < 0 && errno == EAGAIN) |
729 | goto skip4; |
730 | goto kill_session; |
731 | } |
732 | ts->size2 += count; |
733 | ts->rdidx2 += count; |
734 | if (ts->rdidx2 >= BUFSIZE) /* actually == BUFSIZE */ |
735 | ts->rdidx2 = 0; |
736 | } |
737 | skip4: |
738 | ts = next; |
739 | continue; |
740 | kill_session: |
741 | if (ts->shell_pid > 0) |
742 | update_utmp(ts->shell_pid, DEAD_PROCESS, /*tty_name:*/ NULL, /*username:*/ NULL, /*hostname:*/ NULL); |
743 | free_session(ts); |
744 | ts = next; |
745 | } |
746 | |
747 | goto again; |
748 | } |
749 |