1 /* telnetd.c - Telnet Server
2 *
3 * Copyright 2013 Sandeep Sharma <sandeep.jack2756@gmail.com>
4 * Copyright 2013 Kyungwan Han <asura321@gmail.com>
5 *
6 USE_TELNETD(NEWTOY(telnetd, "w#<0b:p#<0>65535=23f:l:FSKi[!wi]", TOYFLAG_USR|TOYFLAG_BIN))
7
8 config TELNETD
9 bool "telnetd"
10 default n
11 help
12 Handle incoming telnet connections
13
14 -l LOGIN Exec LOGIN on connect
15 -f ISSUE_FILE Display ISSUE_FILE instead of /etc/issue
16 -K Close connection as soon as login exits
17 -p PORT Port to listen on
18 -b ADDR[:PORT] Address to bind to
19 -F Run in foreground
20 -i Inetd mode
21 -w SEC Inetd 'wait' mode, linger time SEC
22 -S Log to syslog (implied by -i or without -F and -w)
23 */
24
25 #define FOR_telnetd
26 #include "toys.h"
27 #include <utmp.h>
28 GLOBALS(
29 char *login_path;
30 char *issue_path;
31 int port;
32 char *host_addr;
33 long w_sec;
34
35 int gmax_fd;
36 pid_t fork_pid;
37 )
38
39
40 # define IAC 255 /* interpret as command: */
41 # define DONT 254 /* you are not to use option */
42 # define DO 253 /* please, you use option */
43 # define WONT 252 /* I won't use option */
44 # define WILL 251 /* I will use option */
45 # define SB 250 /* interpret as subnegotiation */
46 # define SE 240 /* end sub negotiation */
47 # define NOP 241 /* No Operation */
48 # define TELOPT_ECHO 1 /* echo */
49 # define TELOPT_SGA 3 /* suppress go ahead */
50 # define TELOPT_TTYPE 24 /* terminal type */
51 # define TELOPT_NAWS 31 /* window size */
52
53 #define BUFSIZE 4*1024
54 struct term_session {
55 int new_fd, pty_fd;
56 pid_t child_pid;
57 int buff1_avail, buff2_avail;
58 int buff1_written, buff2_written;
59 int rem; //unprocessed data from socket
60 char buff1[BUFSIZE], buff2[BUFSIZE];
61 struct term_session *next;
62 };
63
64 struct term_session *session_list = NULL;
65
get_sockaddr(char * host,void * buf)66 static void get_sockaddr(char *host, void *buf)
67 {
68 in_port_t port_num = htons(TT.port);
69 struct addrinfo hints, *result;
70 int status, af = AF_UNSPEC;
71 char *s;
72
73 // [ipv6]:port or exactly one :
74 if (*host == '[') {
75 host++;
76 s = strchr(host, ']');
77 if (s) *s++ = 0;
78 else error_exit("bad address '%s'", host-1);
79 af = AF_INET6;
80 } else {
81 s = strrchr(host, ':');
82 if (s && strchr(host, ':') == s) {
83 *s = 0;
84 af = AF_INET;
85 } else if (s && strchr(host, ':') != s) {
86 af = AF_INET6;
87 s = 0;
88 }
89 }
90
91 if (s++) {
92 char *ss;
93 unsigned long p = strtoul(s, &ss, 0);
94 if (!*s || *ss || p > 65535) error_exit("bad port '%s'", s);
95 port_num = htons(p);
96 }
97
98 memset(&hints, 0 , sizeof(struct addrinfo));
99 hints.ai_family = af;
100 hints.ai_socktype = SOCK_STREAM;
101
102 status = getaddrinfo(host, NULL, &hints, &result);
103 if (status) error_exit("bad address '%s' : %s", host, gai_strerror(status));
104
105 memcpy(buf, result->ai_addr, result->ai_addrlen);
106 freeaddrinfo(result);
107
108 if (af == AF_INET) ((struct sockaddr_in*)buf)->sin_port = port_num;
109 else ((struct sockaddr_in6*)buf)->sin6_port = port_num;
110 }
111
utmp_entry(void)112 static void utmp_entry(void)
113 {
114 struct utmp entry;
115 struct utmp *utp_ptr;
116 pid_t pid = getpid();
117
118 utmpname(_PATH_UTMP);
119 setutent(); //start from start
120 while ((utp_ptr = getutent()) != NULL) {
121 if (utp_ptr->ut_pid == pid && utp_ptr->ut_type >= INIT_PROCESS) break;
122 }
123 if (!utp_ptr) entry.ut_type = DEAD_PROCESS;
124 time(&entry.ut_time);
125 setutent();
126 pututline(&entry);
127 }
128
listen_socket(void)129 static int listen_socket(void)
130 {
131 int s, af = AF_INET, yes = 1;
132 char buf[sizeof(struct sockaddr_storage)];
133
134 memset(buf, 0, sizeof(buf));
135 if (toys.optflags & FLAG_b) {
136 get_sockaddr(TT.host_addr, buf);
137 af = ((struct sockaddr *)buf)->sa_family;
138 } else {
139 ((struct sockaddr_in*)buf)->sin_port = htons(TT.port);
140 ((struct sockaddr_in*)buf)->sin_family = af;
141 }
142 s = xsocket(af, SOCK_STREAM, 0);
143 if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&yes, sizeof(yes)) == -1)
144 perror_exit("setsockopt");
145
146 if (bind(s, (struct sockaddr *)buf, ((af == AF_INET)?
147 (sizeof(struct sockaddr_in)):(sizeof(struct sockaddr_in6)))) == -1) {
148 close(s);
149 perror_exit("bind");
150 }
151
152 if (listen(s, 1) < 0) perror_exit("listen");
153 return s;
154 }
155
write_issue(char * tty)156 static void write_issue(char *tty)
157 {
158 int size;
159 char ch = 0;
160 struct utsname u;
161 int fd = open(TT.issue_path, O_RDONLY);
162
163 if (fd < 0) return ;
164 uname(&u);
165 while ((size = readall(fd, &ch, 1)) > 0) {
166 if (ch == '\\' || ch == '%') {
167 if (readall(fd, &ch, 1) <= 0) perror_exit("readall!");
168 if (ch == 's') fputs(u.sysname, stdout);
169 if (ch == 'n'|| ch == 'h') fputs(u.nodename, stdout);
170 if (ch == 'r') fputs(u.release, stdout);
171 if (ch == 'm') fputs(u.machine, stdout);
172 if (ch == 'l') fputs(tty, stdout);
173 }
174 else if (ch == '\n') {
175 fputs("\n\r\0", stdout);
176 } else fputc(ch, stdout);
177 }
178 fflush(NULL);
179 close(fd);
180 }
181
new_session(int sockfd)182 static int new_session(int sockfd)
183 {
184 char *argv_login[2]; //arguments for execvp cmd, NULL
185 char tty_name[30]; //tty name length.
186 int fd, flags, i = 1;
187 char intial_iacs[] = {IAC, DO, TELOPT_ECHO, IAC, DO, TELOPT_NAWS,
188 IAC, WILL, TELOPT_ECHO, IAC, WILL, TELOPT_SGA };
189
190 setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &i, sizeof(i));
191 flags = fcntl(sockfd, F_GETFL);
192 fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
193 if (toys.optflags & FLAG_i) fcntl((sockfd + 1), F_SETFL, flags | O_NONBLOCK);
194
195 writeall((toys.optflags & FLAG_i)?1:sockfd, intial_iacs, sizeof(intial_iacs));
196 if ((TT.fork_pid = forkpty(&fd, tty_name, NULL, NULL)) > 0) {
197 flags = fcntl(fd, F_GETFL);
198 fcntl(fd, F_SETFL, flags | O_NONBLOCK);
199 return fd;
200 }
201 if (TT.fork_pid < 0) perror_exit("fork");
202 write_issue(tty_name);
203 argv_login[0] = strdup(TT.login_path);
204 argv_login[1] = NULL;
205 execvp(argv_login[0], argv_login);
206 exit(EXIT_FAILURE);
207 }
208
handle_iacs(struct term_session * tm,int c,int fd)209 static int handle_iacs(struct term_session *tm, int c, int fd)
210 {
211 char *curr ,*start,*end;
212 int i = 0;
213
214 curr = start = tm->buff2+tm->buff2_avail;
215 end = tm->buff2 + c -1;
216 tm->rem = 0;
217 while (curr <= end) {
218 if (*curr != IAC){
219
220 if (*curr != '\r') {
221 toybuf[i++] = *curr++;
222 continue;
223 } else {
224 toybuf[i++] = *curr++;
225 curr++;
226 if (curr < end && (*curr == '\n' || *curr == '\0'))
227 curr++;
228 continue;
229 }
230 }
231
232 if ((curr + 1) > end) {
233 tm->rem = 1;
234 break;
235 }
236 if (*(curr+1) == IAC) { //IAC as data --> IAC IAC
237 toybuf[i++] = *(curr+1);
238 curr += 2; //IAC IAC --> 2 bytes
239 continue;
240 }
241 if (*(curr + 1) == NOP || *(curr + 1) == SE) {
242 curr += 2;
243 continue;
244 }
245
246 if (*(curr + 1) == SB ) {
247 if (*(curr+2) == TELOPT_NAWS) {
248 struct winsize ws;
249 if ((curr+8) >= end) { //ensure we have data to process.
250 tm->rem = end - curr;
251 break;
252 }
253 ws.ws_col = (curr[3] << 8) | curr[4];
254 ws.ws_row = (curr[5] << 8) | curr[6];
255 ioctl(fd, TIOCSWINSZ, (char *)&ws);
256 curr += 9;
257 continue;
258 } else { //eat non-supported sub neg. options.
259 curr++, tm->rem++;
260 while (*curr != IAC && curr <= end) {
261 curr++;
262 tm->rem++;
263 }
264 if (*curr == IAC) {
265 tm->rem = 0;
266 continue;
267 } else break;
268 }
269 }
270 curr += 3; //skip non-supported 3 bytes.
271 }
272 memcpy(start, toybuf, i);
273 memcpy(start + i, end - tm->rem, tm->rem); //put remaining if we break;
274 return i;
275 }
276
dup_iacs(char * start,int fd,int len)277 static int dup_iacs(char *start, int fd, int len)
278 {
279 char arr[] = {IAC, IAC};
280 char *needle = NULL;
281 int ret = 0, c, count = 0;
282
283 while (len) {
284 if (*start == IAC) {
285 count = writeall(fd, arr, sizeof(arr));
286 if (count != 2) break; //short write
287 start++;
288 ret++;
289 len--;
290 continue;
291 }
292 needle = memchr(start, IAC, len);
293 if (needle) c = needle - start;
294 else c = len;
295 count = writeall(fd, start, c);
296 if (count < 0) break;
297 len -= count;
298 ret += count;
299 start += count;
300 }
301 return ret;
302 }
303
telnetd_main(void)304 void telnetd_main(void)
305 {
306 errno = 0;
307 fd_set rd, wr;
308 struct term_session *tm = NULL;
309 struct timeval tv, *tv_ptr = NULL;
310 int pty_fd, new_fd, c = 0, w, master_fd = 0;
311 int inetd_m = toys.optflags & FLAG_i;
312
313 if (!(toys.optflags & FLAG_l)) TT.login_path = "/bin/login";
314 if (!(toys.optflags & FLAG_f)) TT.issue_path = "/etc/issue.net";
315 if (toys.optflags & FLAG_w) toys.optflags |= FLAG_F;
316 if (!inetd_m) {
317 master_fd = listen_socket();
318 fcntl(master_fd, F_SETFD, FD_CLOEXEC);
319 if (master_fd > TT.gmax_fd) TT.gmax_fd = master_fd;
320 if (!(toys.optflags & FLAG_F)) daemon(0, 0);
321 } else {
322 pty_fd = new_session(master_fd); //master_fd = 0
323 if (pty_fd > TT.gmax_fd) TT.gmax_fd = pty_fd;
324 tm = xzalloc(sizeof(struct term_session));
325 tm->child_pid = TT.fork_pid;
326 tm->new_fd = 0;
327 tm->pty_fd = pty_fd;
328 if (session_list) {
329 tm->next = session_list;
330 session_list = tm;
331 } else session_list = tm;
332 }
333
334 if ((toys.optflags & FLAG_w) && !session_list) {
335 tv.tv_sec = TT.w_sec;
336 tv.tv_usec = 0;
337 tv_ptr = &tv;
338 }
339 signal(SIGCHLD, generic_signal);
340
341 for (;;) {
342 FD_ZERO(&rd);
343 FD_ZERO(&wr);
344 if (!inetd_m) FD_SET(master_fd, &rd);
345
346 tm = session_list;
347 while (tm) {
348
349 if (tm->pty_fd > 0 && tm->buff1_avail < BUFSIZE) FD_SET(tm->pty_fd, &rd);
350 if (tm->new_fd >= 0 && tm->buff2_avail < BUFSIZE) FD_SET(tm->new_fd, &rd);
351 if (tm->pty_fd > 0 && (tm->buff2_avail - tm->buff2_written) > 0)
352 FD_SET(tm->pty_fd, &wr);
353 if (tm->new_fd >= 0 && (tm->buff1_avail - tm->buff1_written) > 0)
354 FD_SET(tm->new_fd, &wr);
355 tm = tm->next;
356 }
357
358
359 int r = select(TT.gmax_fd + 1, &rd, &wr, NULL, tv_ptr);
360 if (!r) return; //timeout
361 if (r < -1) continue;
362
363 if (!inetd_m && FD_ISSET(master_fd, &rd)) { //accept new connection
364 new_fd = accept(master_fd, NULL, NULL);
365 if (new_fd < 0) continue;
366 tv_ptr = NULL;
367 fcntl(new_fd, F_SETFD, FD_CLOEXEC);
368 if (new_fd > TT.gmax_fd) TT.gmax_fd = new_fd;
369 pty_fd = new_session(new_fd);
370 if (pty_fd > TT.gmax_fd) TT.gmax_fd = pty_fd;
371
372 tm = xzalloc(sizeof(struct term_session));
373 tm->child_pid = TT.fork_pid;
374 tm->new_fd = new_fd;
375 tm->pty_fd = pty_fd;
376 if (session_list) {
377 tm->next = session_list;
378 session_list = tm;
379 } else session_list = tm;
380 }
381
382 tm = session_list;
383 for (;tm;tm=tm->next) {
384 if (FD_ISSET(tm->pty_fd, &rd)) {
385 if ((c = read(tm->pty_fd, tm->buff1 + tm->buff1_avail,
386 BUFSIZE-tm->buff1_avail)) <= 0) break;
387 tm->buff1_avail += c;
388 if ((w = dup_iacs(tm->buff1 + tm->buff1_written, tm->new_fd + inetd_m,
389 tm->buff1_avail - tm->buff1_written)) < 0) break;
390 tm->buff1_written += w;
391 }
392 if (FD_ISSET(tm->new_fd, &rd)) {
393 if ((c = read(tm->new_fd, tm->buff2+tm->buff2_avail,
394 BUFSIZE-tm->buff2_avail)) <= 0) break;
395 c = handle_iacs(tm, c, tm->pty_fd);
396 tm->buff2_avail += c;
397 if ((w = write(tm->pty_fd, tm->buff2+ tm->buff2_written,
398 tm->buff2_avail - tm->buff2_written)) < 0) break;
399 tm->buff2_written += w;
400 }
401 if (FD_ISSET(tm->pty_fd, &wr)) {
402 if ((w = write(tm->pty_fd, tm->buff2 + tm->buff2_written,
403 tm->buff2_avail - tm->buff2_written)) < 0) break;
404 tm->buff2_written += w;
405 }
406 if (FD_ISSET(tm->new_fd, &wr)) {
407 if ((w = dup_iacs(tm->buff1 + tm->buff1_written, tm->new_fd + inetd_m,
408 tm->buff1_avail - tm->buff1_written)) < 0) break;
409 tm->buff1_written += w;
410 }
411 if (tm->buff1_written == tm->buff1_avail)
412 tm->buff1_written = tm->buff1_avail = 0;
413 if (tm->buff2_written == tm->buff2_avail)
414 tm->buff2_written = tm->buff2_avail = 0;
415 fflush(NULL);
416 }
417
418 // Loop to handle (unknown number of) SIGCHLD notifications
419 while (toys.signal) {
420 int status;
421 struct term_session *prev = NULL;
422 pid_t pid;
423
424 // funny little dance to avoid race conditions.
425 toys.signal = 0;
426 pid = waitpid(-1, &status, WNOHANG);
427 if (pid < 0) break;
428 toys.signal++;
429
430
431 for (tm = session_list; tm; tm = tm->next) {
432 if (tm->child_pid == pid) break;
433 prev = tm;
434 }
435 if (!tm) return; // reparented child we don't care about
436
437 if (toys.optflags & FLAG_i) exit(EXIT_SUCCESS);
438 if (!prev) session_list = session_list->next;
439 else prev->next = tm->next;
440 utmp_entry();
441 xclose(tm->pty_fd);
442 xclose(tm->new_fd);
443 free(tm);
444 }
445 }
446 }
447