summaryrefslogtreecommitdiff
path: root/serverloop.c
blob: 94c2115710dcecb1cc03721aea1c6034c878fd10 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Created: Sun Sep 10 00:30:37 1995 ylo
 * Server main loop for handling the interactive session.
 */

#include "includes.h"
#include "xmalloc.h"
#include "ssh.h"
#include "packet.h"
#include "buffer.h"
#include "servconf.h"
#include "pty.h"

static Buffer stdin_buffer;	/* Buffer for stdin data. */
static Buffer stdout_buffer;	/* Buffer for stdout data. */
static Buffer stderr_buffer;	/* Buffer for stderr data. */
static int fdin;		/* Descriptor for stdin (for writing) */
static int fdout;		/* Descriptor for stdout (for reading);
				   May be same number as fdin. */
static int fderr;		/* Descriptor for stderr.  May be -1. */
static long stdin_bytes = 0;	/* Number of bytes written to stdin. */
static long stdout_bytes = 0;	/* Number of stdout bytes sent to client. */
static long stderr_bytes = 0;	/* Number of stderr bytes sent to client. */
static long fdout_bytes = 0;	/* Number of stdout bytes read from program. */
static int stdin_eof = 0;	/* EOF message received from client. */
static int fdout_eof = 0;	/* EOF encountered reading from fdout. */
static int fderr_eof = 0;	/* EOF encountered readung from fderr. */
static int connection_in;	/* Connection to client (input). */
static int connection_out;	/* Connection to client (output). */
static unsigned int buffer_high;/* "Soft" max buffer size. */
static int max_fd;		/* Max file descriptor number for select(). */

/*
 * This SIGCHLD kludge is used to detect when the child exits.  The server
 * will exit after that, as soon as forwarded connections have terminated.
 */

static int child_pid;			/* Pid of the child. */
static volatile int child_terminated;	/* The child has terminated. */
static volatile int child_wait_status;	/* Status from wait(). */

void 
sigchld_handler(int sig)
{
	int save_errno = errno;
	int wait_pid;
	debug("Received SIGCHLD.");
	wait_pid = wait((int *) &child_wait_status);
	if (wait_pid != -1) {
		if (wait_pid != child_pid)
			error("Strange, got SIGCHLD and wait returned pid %d but child is %d",
			      wait_pid, child_pid);
		if (WIFEXITED(child_wait_status) ||
		    WIFSIGNALED(child_wait_status))
			child_terminated = 1;
	}
	signal(SIGCHLD, sigchld_handler);
	errno = save_errno;
}

/*
 * Process any buffered packets that have been received from the client.
 */
void 
process_buffered_input_packets()
{
	int type;
	char *data;
	unsigned int data_len;
	int row, col, xpixel, ypixel;
	int payload_len;

	/* Process buffered packets from the client. */
	while ((type = packet_read_poll(&payload_len)) != SSH_MSG_NONE) {
		switch (type) {
		case SSH_CMSG_STDIN_DATA:
			/* Stdin data from the client.  Append it to the buffer. */
			/* Ignore any data if the client has closed stdin. */
			if (fdin == -1)
				break;
			data = packet_get_string(&data_len);
			packet_integrity_check(payload_len, (4 + data_len), type);
			buffer_append(&stdin_buffer, data, data_len);
			memset(data, 0, data_len);
			xfree(data);
			break;

		case SSH_CMSG_EOF:
			/*
			 * Eof from the client.  The stdin descriptor to the
			 * program will be closed when all buffered data has
			 * drained.
			 */
			debug("EOF received for stdin.");
			packet_integrity_check(payload_len, 0, type);
			stdin_eof = 1;
			break;

		case SSH_CMSG_WINDOW_SIZE:
			debug("Window change received.");
			packet_integrity_check(payload_len, 4 * 4, type);
			row = packet_get_int();
			col = packet_get_int();
			xpixel = packet_get_int();
			ypixel = packet_get_int();
			if (fdin != -1)
				pty_change_window_size(fdin, row, col, xpixel, ypixel);
			break;

		case SSH_MSG_PORT_OPEN:
			debug("Received port open request.");
			channel_input_port_open(payload_len);
			break;

		case SSH_MSG_CHANNEL_OPEN_CONFIRMATION:
			debug("Received channel open confirmation.");
			packet_integrity_check(payload_len, 4 + 4, type);
			channel_input_open_confirmation();
			break;

		case SSH_MSG_CHANNEL_OPEN_FAILURE:
			debug("Received channel open failure.");
			packet_integrity_check(payload_len, 4, type);
			channel_input_open_failure();
			break;

		case SSH_MSG_CHANNEL_DATA:
			channel_input_data(payload_len);
			break;

		case SSH_MSG_CHANNEL_CLOSE:
			debug("Received channel close.");
			packet_integrity_check(payload_len, 4, type);
			channel_input_close();
			break;

		case SSH_MSG_CHANNEL_CLOSE_CONFIRMATION:
			debug("Received channel close confirmation.");
			packet_integrity_check(payload_len, 4, type);
			channel_input_close_confirmation();
			break;

		default:
			/*
			 * In this phase, any unexpected messages cause a
			 * protocol error.  This is to ease debugging; also,
			 * since no confirmations are sent messages,
			 * unprocessed unknown messages could cause strange
			 * problems.  Any compatible protocol extensions must
			 * be negotiated before entering the interactive
			 * session.
			 */
			packet_disconnect("Protocol error during session: type %d",
					  type);
		}
	}
}

/*
 * Make packets from buffered stderr data, and buffer it for sending
 * to the client.
 */
void 
make_packets_from_stderr_data()
{
	int len;

	/* Send buffered stderr data to the client. */
	while (buffer_len(&stderr_buffer) > 0 &&
	       packet_not_very_much_data_to_write()) {
		len = buffer_len(&stderr_buffer);
		if (packet_is_interactive()) {
			if (len > 512)
				len = 512;
		} else {
			/* Keep the packets at reasonable size. */
			if (len > packet_get_maxsize())
				len = packet_get_maxsize();
		}
		packet_start(SSH_SMSG_STDERR_DATA);
		packet_put_string(buffer_ptr(&stderr_buffer), len);
		packet_send();
		buffer_consume(&stderr_buffer, len);
		stderr_bytes += len;
	}
}

/*
 * Make packets from buffered stdout data, and buffer it for sending to the
 * client.
 */
void 
make_packets_from_stdout_data()
{
	int len;

	/* Send buffered stdout data to the client. */
	while (buffer_len(&stdout_buffer) > 0 &&
	       packet_not_very_much_data_to_write()) {
		len = buffer_len(&stdout_buffer);
		if (packet_is_interactive()) {
			if (len > 512)
				len = 512;
		} else {
			/* Keep the packets at reasonable size. */
			if (len > packet_get_maxsize())
				len = packet_get_maxsize();	
		}
		packet_start(SSH_SMSG_STDOUT_DATA);
		packet_put_string(buffer_ptr(&stdout_buffer), len);
		packet_send();
		buffer_consume(&stdout_buffer, len);
		stdout_bytes += len;
	}
}

/*
 * Sleep in select() until we can do something.  This will initialize the
 * select masks.  Upon return, the masks will indicate which descriptors
 * have data or can accept data.  Optionally, a maximum time can be specified
 * for the duration of the wait (0 = infinite).
 */
void 
wait_until_can_do_something(fd_set * readset, fd_set * writeset,
			    unsigned int max_time_milliseconds)
{
	struct timeval tv, *tvp;
	int ret;

	/* When select fails we restart from here. */
retry_select:

	/* Initialize select() masks. */
	FD_ZERO(readset);

	/*
	 * Read packets from the client unless we have too much buffered
	 * stdin or channel data.
	 */
	if (buffer_len(&stdin_buffer) < 4096 &&
	    channel_not_very_much_buffered_data())
		FD_SET(connection_in, readset);

	/*
	 * If there is not too much data already buffered going to the
	 * client, try to get some more data from the program.
	 */
	if (packet_not_very_much_data_to_write()) {
		if (!fdout_eof)
			FD_SET(fdout, readset);
		if (!fderr_eof)
			FD_SET(fderr, readset);
	}
	FD_ZERO(writeset);

	/* Set masks for channel descriptors. */
	channel_prepare_select(readset, writeset);

	/*
	 * If we have buffered packet data going to the client, mark that
	 * descriptor.
	 */
	if (packet_have_data_to_write())
		FD_SET(connection_out, writeset);

	/* If we have buffered data, try to write some of that data to the
	   program. */
	if (fdin != -1 && buffer_len(&stdin_buffer) > 0)
		FD_SET(fdin, writeset);

	/* Update the maximum descriptor number if appropriate. */
	if (channel_max_fd() > max_fd)
		max_fd = channel_max_fd();

	/*
	 * If child has terminated and there is enough buffer space to read
	 * from it, then read as much as is available and exit.
	 */
	if (child_terminated && packet_not_very_much_data_to_write())
		if (max_time_milliseconds == 0)
			max_time_milliseconds = 100;

	if (max_time_milliseconds == 0)
		tvp = NULL;
	else {
		tv.tv_sec = max_time_milliseconds / 1000;
		tv.tv_usec = 1000 * (max_time_milliseconds % 1000);
		tvp = &tv;
	}

	/* Wait for something to happen, or the timeout to expire. */
	ret = select(max_fd + 1, readset, writeset, NULL, tvp);

	if (ret < 0) {
		if (errno != EINTR)
			error("select: %.100s", strerror(errno));
		else
			goto retry_select;
	}
}

/*
 * Processes input from the client and the program.  Input data is stored
 * in buffers and processed later.
 */
void 
process_input(fd_set * readset)
{
	int len;
	char buf[16384];

	/* Read and buffer any input data from the client. */
	if (FD_ISSET(connection_in, readset)) {
		len = read(connection_in, buf, sizeof(buf));
		if (len == 0) {
			verbose("Connection closed by remote host.");
			fatal_cleanup();
		}
		/*
		 * There is a kernel bug on Solaris that causes select to
		 * sometimes wake up even though there is no data available.
		 */
		if (len < 0 && errno == EAGAIN)
			len = 0;

		if (len < 0) {
			verbose("Read error from remote host: %.100s", strerror(errno));
			fatal_cleanup();
		}
		/* Buffer any received data. */
		packet_process_incoming(buf, len);
	}
	/* Read and buffer any available stdout data from the program. */
	if (!fdout_eof && FD_ISSET(fdout, readset)) {
		len = read(fdout, buf, sizeof(buf));
		if (len <= 0)
			fdout_eof = 1;
		else {
			buffer_append(&stdout_buffer, buf, len);
			fdout_bytes += len;
		}
	}
	/* Read and buffer any available stderr data from the program. */
	if (!fderr_eof && FD_ISSET(fderr, readset)) {
		len = read(fderr, buf, sizeof(buf));
		if (len <= 0)
			fderr_eof = 1;
		else
			buffer_append(&stderr_buffer, buf, len);
	}
}

/*
 * Sends data from internal buffers to client program stdin.
 */
void 
process_output(fd_set * writeset)
{
	int len;

	/* Write buffered data to program stdin. */
	if (fdin != -1 && FD_ISSET(fdin, writeset)) {
		len = write(fdin, buffer_ptr(&stdin_buffer),
			    buffer_len(&stdin_buffer));
		if (len <= 0) {
#ifdef USE_PIPES
			close(fdin);
#else
			if (fdout == -1)
				close(fdin);
			else
				shutdown(fdin, SHUT_WR); /* We will no longer send. */
#endif
			fdin = -1;
		} else {
			/* Successful write.  Consume the data from the buffer. */
			buffer_consume(&stdin_buffer, len);
			/* Update the count of bytes written to the program. */
			stdin_bytes += len;
		}
	}
	/* Send any buffered packet data to the client. */
	if (FD_ISSET(connection_out, writeset))
		packet_write_poll();
}

/*
 * Wait until all buffered output has been sent to the client.
 * This is used when the program terminates.
 */
void 
drain_output()
{
	/* Send any buffered stdout data to the client. */
	if (buffer_len(&stdout_buffer) > 0) {
		packet_start(SSH_SMSG_STDOUT_DATA);
		packet_put_string(buffer_ptr(&stdout_buffer),
				  buffer_len(&stdout_buffer));
		packet_send();
		/* Update the count of sent bytes. */
		stdout_bytes += buffer_len(&stdout_buffer);
	}
	/* Send any buffered stderr data to the client. */
	if (buffer_len(&stderr_buffer) > 0) {
		packet_start(SSH_SMSG_STDERR_DATA);
		packet_put_string(buffer_ptr(&stderr_buffer),
				  buffer_len(&stderr_buffer));
		packet_send();
		/* Update the count of sent bytes. */
		stderr_bytes += buffer_len(&stderr_buffer);
	}
	/* Wait until all buffered data has been written to the client. */
	packet_write_wait();
}

/*
 * Performs the interactive session.  This handles data transmission between
 * the client and the program.  Note that the notion of stdin, stdout, and
 * stderr in this function is sort of reversed: this function writes to
 * stdin (of the child program), and reads from stdout and stderr (of the
 * child program).
 */
void 
server_loop(int pid, int fdin_arg, int fdout_arg, int fderr_arg)
{
	int wait_status, wait_pid;	/* Status and pid returned by wait(). */
	int waiting_termination = 0;	/* Have displayed waiting close message. */
	unsigned int max_time_milliseconds;
	unsigned int previous_stdout_buffer_bytes;
	unsigned int stdout_buffer_bytes;
	int type;

	debug("Entering interactive session.");

	/* Initialize the SIGCHLD kludge. */
	child_pid = pid;
	child_terminated = 0;
	signal(SIGCHLD, sigchld_handler);

	/* Initialize our global variables. */
	fdin = fdin_arg;
	fdout = fdout_arg;
	fderr = fderr_arg;
	connection_in = packet_get_connection_in();
	connection_out = packet_get_connection_out();

	previous_stdout_buffer_bytes = 0;

	/* Set approximate I/O buffer size. */
	if (packet_is_interactive())
		buffer_high = 4096;
	else
		buffer_high = 64 * 1024;

	/* Initialize max_fd to the maximum of the known file descriptors. */
	max_fd = fdin;
	if (fdout > max_fd)
		max_fd = fdout;
	if (fderr != -1 && fderr > max_fd)
		max_fd = fderr;
	if (connection_in > max_fd)
		max_fd = connection_in;
	if (connection_out > max_fd)
		max_fd = connection_out;

	/* Initialize Initialize buffers. */
	buffer_init(&stdin_buffer);
	buffer_init(&stdout_buffer);
	buffer_init(&stderr_buffer);

	/*
	 * If we have no separate fderr (which is the case when we have a pty
	 * - there we cannot make difference between data sent to stdout and
	 * stderr), indicate that we have seen an EOF from stderr.  This way
	 * we don\'t need to check the descriptor everywhere.
	 */
	if (fderr == -1)
		fderr_eof = 1;

	/* Main loop of the server for the interactive session mode. */
	for (;;) {
		fd_set readset, writeset;

		/* Process buffered packets from the client. */
		process_buffered_input_packets();

		/*
		 * If we have received eof, and there is no more pending
		 * input data, cause a real eof by closing fdin.
		 */
		if (stdin_eof && fdin != -1 && buffer_len(&stdin_buffer) == 0) {
#ifdef USE_PIPES
			close(fdin);
#else
			if (fdout == -1)
				close(fdin);
			else
				shutdown(fdin, SHUT_WR); /* We will no longer send. */
#endif
			fdin = -1;
		}
		/* Make packets from buffered stderr data to send to the client. */
		make_packets_from_stderr_data();

		/*
		 * Make packets from buffered stdout data to send to the
		 * client. If there is very little to send, this arranges to
		 * not send them now, but to wait a short while to see if we
		 * are getting more data. This is necessary, as some systems
		 * wake up readers from a pty after each separate character.
		 */
		max_time_milliseconds = 0;
		stdout_buffer_bytes = buffer_len(&stdout_buffer);
		if (stdout_buffer_bytes != 0 && stdout_buffer_bytes < 256 &&
		    stdout_buffer_bytes != previous_stdout_buffer_bytes) {
			/* try again after a while */
			max_time_milliseconds = 10;
		} else {
			/* Send it now. */
			make_packets_from_stdout_data();
		}
		previous_stdout_buffer_bytes = buffer_len(&stdout_buffer);

		/* Send channel data to the client. */
		if (packet_not_very_much_data_to_write())
			channel_output_poll();

		/*
		 * Bail out of the loop if the program has closed its output
		 * descriptors, and we have no more data to send to the
		 * client, and there is no pending buffered data.
		 */
		if (fdout_eof && fderr_eof && !packet_have_data_to_write() &&
		    buffer_len(&stdout_buffer) == 0 && buffer_len(&stderr_buffer) == 0) {
			if (!channel_still_open())
				goto quit;
			if (!waiting_termination) {
				const char *s = "Waiting for forwarded connections to terminate...\r\n";
				char *cp;
				waiting_termination = 1;
				buffer_append(&stderr_buffer, s, strlen(s));

				/* Display list of open channels. */
				cp = channel_open_message();
				buffer_append(&stderr_buffer, cp, strlen(cp));
				xfree(cp);
			}
		}
		/* Sleep in select() until we can do something. */
		wait_until_can_do_something(&readset, &writeset,
					    max_time_milliseconds);

		/* Process any channel events. */
		channel_after_select(&readset, &writeset);

		/* Process input from the client and from program stdout/stderr. */
		process_input(&readset);

		/* Process output to the client and to program stdin. */
		process_output(&writeset);
	}

quit:
	/* Cleanup and termination code. */

	/* Wait until all output has been sent to the client. */
	drain_output();

	debug("End of interactive session; stdin %ld, stdout (read %ld, sent %ld), stderr %ld bytes.",
	      stdin_bytes, fdout_bytes, stdout_bytes, stderr_bytes);

	/* Free and clear the buffers. */
	buffer_free(&stdin_buffer);
	buffer_free(&stdout_buffer);
	buffer_free(&stderr_buffer);

	/* Close the file descriptors. */
	if (fdout != -1)
		close(fdout);
	fdout = -1;
	fdout_eof = 1;
	if (fderr != -1)
		close(fderr);
	fderr = -1;
	fderr_eof = 1;
	if (fdin != -1)
		close(fdin);
	fdin = -1;

	/* Stop listening for channels; this removes unix domain sockets. */
	channel_stop_listening();

	/* Wait for the child to exit.  Get its exit status. */
	wait_pid = wait(&wait_status);
	if (wait_pid < 0) {
		/*
		 * It is possible that the wait was handled by SIGCHLD
		 * handler.  This may result in either: this call
		 * returning with EINTR, or: this call returning ECHILD.
		 */
		if (child_terminated)
			wait_status = child_wait_status;
		else
			packet_disconnect("wait: %.100s", strerror(errno));
	} else {
		/* Check if it matches the process we forked. */
		if (wait_pid != pid)
			error("Strange, wait returned pid %d, expected %d",
			       wait_pid, pid);
	}

	/* We no longer want our SIGCHLD handler to be called. */
	signal(SIGCHLD, SIG_DFL);

	/* Check if it exited normally. */
	if (WIFEXITED(wait_status)) {
		/* Yes, normal exit.  Get exit status and send it to the client. */
		debug("Command exited with status %d.", WEXITSTATUS(wait_status));
		packet_start(SSH_SMSG_EXITSTATUS);
		packet_put_int(WEXITSTATUS(wait_status));
		packet_send();
		packet_write_wait();

		/*
		 * Wait for exit confirmation.  Note that there might be
		 * other packets coming before it; however, the program has
		 * already died so we just ignore them.  The client is
		 * supposed to respond with the confirmation when it receives
		 * the exit status.
		 */
		do {
			int plen;
			type = packet_read(&plen);
		}
		while (type != SSH_CMSG_EXIT_CONFIRMATION);

		debug("Received exit confirmation.");
		return;
	}
	/* Check if the program terminated due to a signal. */
	if (WIFSIGNALED(wait_status))
		packet_disconnect("Command terminated on signal %d.",
				  WTERMSIG(wait_status));

	/* Some weird exit cause.  Just exit. */
	packet_disconnect("wait returned status %04x.", wait_status);
	/* NOTREACHED */
}