1 /*
2 * Dropbear - a SSH2 server
3 *
4 * Copyright (c) 2002,2003 Matt Johnston
5 * All rights reserved.
6 *
7 * Permission is hereby granted, free of charge, to any person obtaining a copy
8 * of this software and associated documentation files (the "Software"), to deal
9 * in the Software without restriction, including without limitation the rights
10 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
11 * copies of the Software, and to permit persons to whom the Software is
12 * furnished to do so, subject to the following conditions:
13 *
14 * The above copyright notice and this permission notice shall be included in
15 * all copies or substantial portions of the Software.
16 *
17 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
18 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
19 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
20 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
21 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
22 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
23 * SOFTWARE. */
24
25 #include "includes.h"
26 #include "session.h"
27 #include "dbutil.h"
28 #include "packet.h"
29 #include "algo.h"
30 #include "buffer.h"
31 #include "dss.h"
32 #include "ssh.h"
33 #include "random.h"
34 #include "kex.h"
35 #include "channel.h"
36 #include "atomicio.h"
37
38 static void checktimeouts();
39 static int ident_readln(int fd, char* buf, int count);
40
41 struct sshsession ses; /* GLOBAL */
42
43 /* need to know if the session struct has been initialised, this way isn't the
44 * cleanest, but works OK */
45 int sessinitdone = 0; /* GLOBAL */
46
47 /* this is set when we get SIGINT or SIGTERM, the handler is in main.c */
48 int exitflag = 0; /* GLOBAL */
49
50
51
52 /* called only at the start of a session, set up initial state */
common_session_init(int sock,char * remotehost)53 void common_session_init(int sock, char* remotehost) {
54
55 TRACE(("enter session_init"))
56
57 ses.remotehost = remotehost;
58
59 ses.sock = sock;
60 ses.maxfd = sock;
61
62 ses.connecttimeout = 0;
63
64 if (pipe(ses.signal_pipe) < 0) {
65 dropbear_exit("signal pipe failed");
66 }
67 setnonblocking(ses.signal_pipe[0]);
68 setnonblocking(ses.signal_pipe[1]);
69
70 kexfirstinitialise(); /* initialise the kex state */
71
72 ses.writepayload = buf_new(MAX_TRANS_PAYLOAD_LEN);
73 ses.transseq = 0;
74
75 ses.readbuf = NULL;
76 ses.decryptreadbuf = NULL;
77 ses.payload = NULL;
78 ses.recvseq = 0;
79
80 initqueue(&ses.writequeue);
81
82 ses.requirenext = SSH_MSG_KEXINIT;
83 ses.dataallowed = 0; /* don't send data yet, we'll wait until after kex */
84 ses.ignorenext = 0;
85 ses.lastpacket = 0;
86
87 /* set all the algos to none */
88 ses.keys = (struct key_context*)m_malloc(sizeof(struct key_context));
89 ses.newkeys = NULL;
90 ses.keys->recv_algo_crypt = &dropbear_nocipher;
91 ses.keys->trans_algo_crypt = &dropbear_nocipher;
92
93 ses.keys->recv_algo_mac = &dropbear_nohash;
94 ses.keys->trans_algo_mac = &dropbear_nohash;
95
96 ses.keys->algo_kex = -1;
97 ses.keys->algo_hostkey = -1;
98 ses.keys->recv_algo_comp = DROPBEAR_COMP_NONE;
99 ses.keys->trans_algo_comp = DROPBEAR_COMP_NONE;
100
101 #ifndef DISABLE_ZLIB
102 ses.keys->recv_zstream = NULL;
103 ses.keys->trans_zstream = NULL;
104 #endif
105
106 /* key exchange buffers */
107 ses.session_id = NULL;
108 ses.kexhashbuf = NULL;
109 ses.transkexinit = NULL;
110 ses.dh_K = NULL;
111 ses.remoteident = NULL;
112
113 ses.chantypes = NULL;
114
115 ses.allowprivport = 0;
116
117 TRACE(("leave session_init"))
118 }
119
session_loop(void (* loophandler)())120 void session_loop(void(*loophandler)()) {
121
122 fd_set readfd, writefd;
123 struct timeval timeout;
124 int val;
125
126 /* main loop, select()s for all sockets in use */
127 for(;;) {
128
129 timeout.tv_sec = SELECT_TIMEOUT;
130 timeout.tv_usec = 0;
131 FD_ZERO(&writefd);
132 FD_ZERO(&readfd);
133 dropbear_assert(ses.payload == NULL);
134 if (ses.sock != -1) {
135 FD_SET(ses.sock, &readfd);
136 if (!isempty(&ses.writequeue)) {
137 FD_SET(ses.sock, &writefd);
138 }
139 }
140
141 /* We get woken up when signal handlers write to this pipe.
142 SIGCHLD in svr-chansession is the only one currently. */
143 FD_SET(ses.signal_pipe[0], &readfd);
144
145 /* set up for channels which require reading/writing */
146 if (ses.dataallowed) {
147 setchannelfds(&readfd, &writefd);
148 }
149 val = select(ses.maxfd+1, &readfd, &writefd, NULL, &timeout);
150
151 if (exitflag) {
152 dropbear_exit("Terminated by signal");
153 }
154
155 if (val < 0 && errno != EINTR) {
156 dropbear_exit("Error in select");
157 }
158
159 if (val <= 0) {
160 /* If we were interrupted or the select timed out, we still
161 * want to iterate over channels etc for reading, to handle
162 * server processes exiting etc.
163 * We don't want to read/write FDs. */
164 FD_ZERO(&writefd);
165 FD_ZERO(&readfd);
166 }
167
168 /* We'll just empty out the pipe if required. We don't do
169 any thing with the data, since the pipe's purpose is purely to
170 wake up the select() above. */
171 if (FD_ISSET(ses.signal_pipe[0], &readfd)) {
172 char x;
173 while (read(ses.signal_pipe[0], &x, 1) > 0) {}
174 }
175
176 /* check for auth timeout, rekeying required etc */
177 checktimeouts();
178
179 /* process session socket's incoming/outgoing data */
180 if (ses.sock != -1) {
181 if (FD_ISSET(ses.sock, &writefd) && !isempty(&ses.writequeue)) {
182 write_packet();
183 }
184
185 if (FD_ISSET(ses.sock, &readfd)) {
186 read_packet();
187 }
188
189 /* Process the decrypted packet. After this, the read buffer
190 * will be ready for a new packet */
191 if (ses.payload != NULL) {
192 process_packet();
193 }
194 }
195
196 /* process pipes etc for the channels, ses.dataallowed == 0
197 * during rekeying ) */
198 if (ses.dataallowed) {
199 channelio(&readfd, &writefd);
200 }
201
202 if (loophandler) {
203 loophandler();
204 }
205
206 } /* for(;;) */
207
208 /* Not reached */
209 }
210
211 /* clean up a session on exit */
common_session_cleanup()212 void common_session_cleanup() {
213
214 TRACE(("enter session_cleanup"))
215
216 /* we can't cleanup if we don't know the session state */
217 if (!sessinitdone) {
218 TRACE(("leave session_cleanup: !sessinitdone"))
219 return;
220 }
221
222 m_free(ses.session_id);
223 m_burn(ses.keys, sizeof(struct key_context));
224 m_free(ses.keys);
225
226 chancleanup();
227
228 TRACE(("leave session_cleanup"))
229 }
230
231
session_identification()232 void session_identification() {
233
234 /* max length of 255 chars */
235 char linebuf[256];
236 int len = 0;
237 char done = 0;
238 int i;
239
240 /* write our version string, this blocks */
241 if (atomicio(write, ses.sock, LOCAL_IDENT "\r\n",
242 strlen(LOCAL_IDENT "\r\n")) == DROPBEAR_FAILURE) {
243 ses.remoteclosed();
244 }
245
246 /* If they send more than 50 lines, something is wrong */
247 for (i = 0; i < 50; i++) {
248 len = ident_readln(ses.sock, linebuf, sizeof(linebuf));
249
250 if (len < 0 && errno != EINTR) {
251 /* It failed */
252 break;
253 }
254
255 if (len >= 4 && memcmp(linebuf, "SSH-", 4) == 0) {
256 /* start of line matches */
257 done = 1;
258 break;
259 }
260 }
261
262 if (!done) {
263 TRACE(("err: %s for '%s'\n", strerror(errno), linebuf))
264 ses.remoteclosed();
265 } else {
266 /* linebuf is already null terminated */
267 ses.remoteident = m_malloc(len);
268 memcpy(ses.remoteident, linebuf, len);
269 }
270
271 /* Shall assume that 2.x will be backwards compatible. */
272 if (strncmp(ses.remoteident, "SSH-2.", 6) != 0
273 && strncmp(ses.remoteident, "SSH-1.99-", 9) != 0) {
274 dropbear_exit("Incompatible remote version '%s'", ses.remoteident);
275 }
276
277 TRACE(("remoteident: %s", ses.remoteident))
278
279 }
280
281 /* returns the length including null-terminating zero on success,
282 * or -1 on failure */
ident_readln(int fd,char * buf,int count)283 static int ident_readln(int fd, char* buf, int count) {
284
285 char in;
286 int pos = 0;
287 int num = 0;
288 fd_set fds;
289 struct timeval timeout;
290
291 TRACE(("enter ident_readln"))
292
293 if (count < 1) {
294 return -1;
295 }
296
297 FD_ZERO(&fds);
298
299 /* select since it's a non-blocking fd */
300
301 /* leave space to null-terminate */
302 while (pos < count-1) {
303
304 FD_SET(fd, &fds);
305
306 timeout.tv_sec = 1;
307 timeout.tv_usec = 0;
308 if (select(fd+1, &fds, NULL, NULL, &timeout) < 0) {
309 if (errno == EINTR) {
310 continue;
311 }
312 TRACE(("leave ident_readln: select error"))
313 return -1;
314 }
315
316 checktimeouts();
317
318 /* Have to go one byte at a time, since we don't want to read past
319 * the end, and have to somehow shove bytes back into the normal
320 * packet reader */
321 if (FD_ISSET(fd, &fds)) {
322 num = read(fd, &in, 1);
323 /* a "\n" is a newline, "\r" we want to read in and keep going
324 * so that it won't be read as part of the next line */
325 if (num < 0) {
326 /* error */
327 if (errno == EINTR) {
328 continue; /* not a real error */
329 }
330 TRACE(("leave ident_readln: read error"))
331 return -1;
332 }
333 if (num == 0) {
334 /* EOF */
335 TRACE(("leave ident_readln: EOF"))
336 return -1;
337 }
338 if (in == '\n') {
339 /* end of ident string */
340 break;
341 }
342 /* we don't want to include '\r's */
343 if (in != '\r') {
344 buf[pos] = in;
345 pos++;
346 }
347 }
348 }
349
350 buf[pos] = '\0';
351 TRACE(("leave ident_readln: return %d", pos+1))
352 return pos+1;
353 }
354
355 /* Check all timeouts which are required. Currently these are the time for
356 * user authentication, and the automatic rekeying. */
checktimeouts()357 static void checktimeouts() {
358
359 struct timeval tv;
360 long secs;
361
362 if (gettimeofday(&tv, 0) < 0) {
363 dropbear_exit("Error getting time");
364 }
365
366 secs = tv.tv_sec;
367
368 if (ses.connecttimeout != 0 && secs > ses.connecttimeout) {
369 dropbear_close("Timeout before auth");
370 }
371
372 /* we can't rekey if we haven't done remote ident exchange yet */
373 if (ses.remoteident == NULL) {
374 return;
375 }
376
377 if (!ses.kexstate.sentkexinit
378 && (secs - ses.kexstate.lastkextime >= KEX_REKEY_TIMEOUT
379 || ses.kexstate.datarecv+ses.kexstate.datatrans >= KEX_REKEY_DATA)){
380 TRACE(("rekeying after timeout or max data reached"))
381 send_msg_kexinit();
382 }
383 }
384
385