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8efc0c15 | 1 | /* |
6ae2364d | 2 | * |
5260325f | 3 | * auth-rsa.c |
6ae2364d | 4 | * |
5260325f | 5 | * Author: Tatu Ylonen <ylo@cs.hut.fi> |
6ae2364d | 6 | * |
5260325f | 7 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
8 | * All rights reserved | |
6ae2364d | 9 | * |
5260325f | 10 | * Created: Mon Mar 27 01:46:52 1995 ylo |
6ae2364d | 11 | * |
5260325f | 12 | * RSA-based authentication. This code determines whether to admit a login |
13 | * based on RSA authentication. This file also contains functions to check | |
14 | * validity of the host key. | |
6ae2364d | 15 | * |
5260325f | 16 | */ |
8efc0c15 | 17 | |
18 | #include "includes.h" | |
19 | RCSID("$Id$"); | |
20 | ||
21 | #include "rsa.h" | |
22 | #include "packet.h" | |
23 | #include "xmalloc.h" | |
24 | #include "ssh.h" | |
25 | #include "mpaux.h" | |
26 | #include "uidswap.h" | |
4fe2af09 | 27 | #include "match.h" |
6fa724bc | 28 | #include "servconf.h" |
8efc0c15 | 29 | |
30 | #include <openssl/rsa.h> | |
31 | #include <openssl/md5.h> | |
32 | ||
33 | /* Flags that may be set in authorized_keys options. */ | |
34 | extern int no_port_forwarding_flag; | |
35 | extern int no_agent_forwarding_flag; | |
36 | extern int no_x11_forwarding_flag; | |
37 | extern int no_pty_flag; | |
38 | extern char *forced_command; | |
39 | extern struct envstring *custom_environment; | |
40 | ||
aa3378df | 41 | /* |
42 | * Session identifier that is used to bind key exchange and authentication | |
43 | * responses to a particular session. | |
44 | */ | |
8efc0c15 | 45 | extern unsigned char session_id[16]; |
46 | ||
aa3378df | 47 | /* |
48 | * The .ssh/authorized_keys file contains public keys, one per line, in the | |
49 | * following format: | |
50 | * options bits e n comment | |
51 | * where bits, e and n are decimal numbers, | |
52 | * and comment is any string of characters up to newline. The maximum | |
53 | * length of a line is 8000 characters. See the documentation for a | |
54 | * description of the options. | |
55 | */ | |
8efc0c15 | 56 | |
aa3378df | 57 | /* |
58 | * Performs the RSA authentication challenge-response dialog with the client, | |
59 | * and returns true (non-zero) if the client gave the correct answer to | |
60 | * our challenge; returns zero if the client gives a wrong answer. | |
61 | */ | |
8efc0c15 | 62 | |
63 | int | |
4fe2af09 | 64 | auth_rsa_challenge_dialog(RSA *pk) |
8efc0c15 | 65 | { |
c8d54615 | 66 | BIGNUM *challenge, *encrypted_challenge; |
c8d54615 | 67 | BN_CTX *ctx; |
5260325f | 68 | unsigned char buf[32], mdbuf[16], response[16]; |
69 | MD5_CTX md; | |
70 | unsigned int i; | |
71 | int plen, len; | |
72 | ||
73 | encrypted_challenge = BN_new(); | |
74 | challenge = BN_new(); | |
5260325f | 75 | |
76 | /* Generate a random challenge. */ | |
77 | BN_rand(challenge, 256, 0, 0); | |
c8d54615 | 78 | ctx = BN_CTX_new(); |
4fe2af09 | 79 | BN_mod(challenge, challenge, pk->n, ctx); |
c8d54615 | 80 | BN_CTX_free(ctx); |
5260325f | 81 | |
5260325f | 82 | /* Encrypt the challenge with the public key. */ |
83 | rsa_public_encrypt(encrypted_challenge, challenge, pk); | |
5260325f | 84 | |
85 | /* Send the encrypted challenge to the client. */ | |
86 | packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); | |
87 | packet_put_bignum(encrypted_challenge); | |
88 | packet_send(); | |
c8d54615 | 89 | BN_clear_free(encrypted_challenge); |
5260325f | 90 | packet_write_wait(); |
91 | ||
c8d54615 | 92 | /* Wait for a response. */ |
93 | packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE); | |
94 | packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE); | |
95 | for (i = 0; i < 16; i++) | |
96 | response[i] = packet_get_char(); | |
97 | ||
5260325f | 98 | /* The response is MD5 of decrypted challenge plus session id. */ |
99 | len = BN_num_bytes(challenge); | |
100 | if (len <= 0 || len > 32) | |
101 | fatal("auth_rsa_challenge_dialog: bad challenge length %d", len); | |
102 | memset(buf, 0, 32); | |
103 | BN_bn2bin(challenge, buf + 32 - len); | |
104 | MD5_Init(&md); | |
105 | MD5_Update(&md, buf, 32); | |
106 | MD5_Update(&md, session_id, 16); | |
107 | MD5_Final(mdbuf, &md); | |
5260325f | 108 | BN_clear_free(challenge); |
5260325f | 109 | |
110 | /* Verify that the response is the original challenge. */ | |
111 | if (memcmp(response, mdbuf, 16) != 0) { | |
112 | /* Wrong answer. */ | |
113 | return 0; | |
114 | } | |
115 | /* Correct answer. */ | |
116 | return 1; | |
8efc0c15 | 117 | } |
118 | ||
aa3378df | 119 | /* |
120 | * Performs the RSA authentication dialog with the client. This returns | |
121 | * 0 if the client could not be authenticated, and 1 if authentication was | |
122 | * successful. This may exit if there is a serious protocol violation. | |
123 | */ | |
8efc0c15 | 124 | |
125 | int | |
6fa724bc | 126 | auth_rsa(struct passwd *pw, BIGNUM *client_n) |
8efc0c15 | 127 | { |
5260325f | 128 | extern ServerOptions options; |
129 | char line[8192], file[1024]; | |
130 | int authenticated; | |
131 | unsigned int bits; | |
132 | FILE *f; | |
133 | unsigned long linenum = 0; | |
134 | struct stat st; | |
4fe2af09 | 135 | RSA *pk; |
5260325f | 136 | |
137 | /* Temporarily use the user's uid. */ | |
138 | temporarily_use_uid(pw->pw_uid); | |
139 | ||
140 | /* The authorized keys. */ | |
141 | snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir, | |
142 | SSH_USER_PERMITTED_KEYS); | |
143 | ||
144 | /* Fail quietly if file does not exist */ | |
145 | if (stat(file, &st) < 0) { | |
146 | /* Restore the privileged uid. */ | |
147 | restore_uid(); | |
148 | return 0; | |
8efc0c15 | 149 | } |
5260325f | 150 | /* Open the file containing the authorized keys. */ |
151 | f = fopen(file, "r"); | |
152 | if (!f) { | |
153 | /* Restore the privileged uid. */ | |
154 | restore_uid(); | |
155 | packet_send_debug("Could not open %.900s for reading.", file); | |
156 | packet_send_debug("If your home is on an NFS volume, it may need to be world-readable."); | |
157 | return 0; | |
8efc0c15 | 158 | } |
5260325f | 159 | if (options.strict_modes) { |
160 | int fail = 0; | |
161 | char buf[1024]; | |
162 | /* Check open file in order to avoid open/stat races */ | |
163 | if (fstat(fileno(f), &st) < 0 || | |
164 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
165 | (st.st_mode & 022) != 0) { | |
166 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " | |
167 | "bad ownership or modes for '%s'.", pw->pw_name, file); | |
168 | fail = 1; | |
169 | } else { | |
170 | /* Check path to SSH_USER_PERMITTED_KEYS */ | |
171 | int i; | |
172 | static const char *check[] = { | |
173 | "", SSH_USER_DIR, NULL | |
174 | }; | |
175 | for (i = 0; check[i]; i++) { | |
176 | snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]); | |
177 | if (stat(line, &st) < 0 || | |
178 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
179 | (st.st_mode & 022) != 0) { | |
180 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " | |
181 | "bad ownership or modes for '%s'.", pw->pw_name, line); | |
182 | fail = 1; | |
183 | break; | |
184 | } | |
185 | } | |
8efc0c15 | 186 | } |
5260325f | 187 | if (fail) { |
188 | log(buf); | |
189 | packet_send_debug(buf); | |
190 | restore_uid(); | |
191 | return 0; | |
8efc0c15 | 192 | } |
5260325f | 193 | } |
194 | /* Flag indicating whether authentication has succeeded. */ | |
195 | authenticated = 0; | |
196 | ||
4fe2af09 | 197 | pk = RSA_new(); |
198 | pk->e = BN_new(); | |
199 | pk->n = BN_new(); | |
5260325f | 200 | |
aa3378df | 201 | /* |
202 | * Go though the accepted keys, looking for the current key. If | |
203 | * found, perform a challenge-response dialog to verify that the | |
204 | * user really has the corresponding private key. | |
205 | */ | |
5260325f | 206 | while (fgets(line, sizeof(line), f)) { |
207 | char *cp; | |
208 | char *options; | |
209 | ||
210 | linenum++; | |
211 | ||
aa3378df | 212 | /* Skip leading whitespace, empty and comment lines. */ |
213 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) | |
214 | ; | |
5260325f | 215 | if (!*cp || *cp == '\n' || *cp == '#') |
216 | continue; | |
217 | ||
aa3378df | 218 | /* |
219 | * Check if there are options for this key, and if so, | |
220 | * save their starting address and skip the option part | |
221 | * for now. If there are no options, set the starting | |
222 | * address to NULL. | |
223 | */ | |
5260325f | 224 | if (*cp < '0' || *cp > '9') { |
225 | int quoted = 0; | |
226 | options = cp; | |
227 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { | |
228 | if (*cp == '\\' && cp[1] == '"') | |
229 | cp++; /* Skip both */ | |
230 | else if (*cp == '"') | |
231 | quoted = !quoted; | |
8efc0c15 | 232 | } |
5260325f | 233 | } else |
234 | options = NULL; | |
235 | ||
236 | /* Parse the key from the line. */ | |
4fe2af09 | 237 | if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) { |
5260325f | 238 | debug("%.100s, line %lu: bad key syntax", |
239 | SSH_USER_PERMITTED_KEYS, linenum); | |
240 | packet_send_debug("%.100s, line %lu: bad key syntax", | |
6ae2364d | 241 | SSH_USER_PERMITTED_KEYS, linenum); |
5260325f | 242 | continue; |
8efc0c15 | 243 | } |
5260325f | 244 | /* cp now points to the comment part. */ |
245 | ||
5260325f | 246 | /* Check if the we have found the desired key (identified by its modulus). */ |
4fe2af09 | 247 | if (BN_cmp(pk->n, client_n) != 0) |
aa3378df | 248 | continue; |
5260325f | 249 | |
57112b5a | 250 | /* check the real bits */ |
4fe2af09 | 251 | if (bits != BN_num_bits(pk->n)) |
57112b5a | 252 | log("Warning: %s, line %ld: keysize mismatch: " |
253 | "actual %d vs. announced %d.", | |
4fe2af09 | 254 | file, linenum, BN_num_bits(pk->n), bits); |
57112b5a | 255 | |
5260325f | 256 | /* We have found the desired key. */ |
257 | ||
4fe2af09 | 258 | |
5260325f | 259 | /* Perform the challenge-response dialog for this key. */ |
4fe2af09 | 260 | if (!auth_rsa_challenge_dialog(pk)) { |
5260325f | 261 | /* Wrong response. */ |
262 | verbose("Wrong response to RSA authentication challenge."); | |
263 | packet_send_debug("Wrong response to RSA authentication challenge."); | |
264 | continue; | |
8efc0c15 | 265 | } |
aa3378df | 266 | /* |
267 | * Correct response. The client has been successfully | |
268 | * authenticated. Note that we have not yet processed the | |
269 | * options; this will be reset if the options cause the | |
270 | * authentication to be rejected. | |
271 | */ | |
5260325f | 272 | authenticated = 1; |
273 | ||
274 | /* RSA part of authentication was accepted. Now process the options. */ | |
275 | if (options) { | |
276 | while (*options && *options != ' ' && *options != '\t') { | |
277 | cp = "no-port-forwarding"; | |
278 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
279 | packet_send_debug("Port forwarding disabled."); | |
280 | no_port_forwarding_flag = 1; | |
281 | options += strlen(cp); | |
282 | goto next_option; | |
283 | } | |
284 | cp = "no-agent-forwarding"; | |
285 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
286 | packet_send_debug("Agent forwarding disabled."); | |
287 | no_agent_forwarding_flag = 1; | |
288 | options += strlen(cp); | |
289 | goto next_option; | |
290 | } | |
291 | cp = "no-X11-forwarding"; | |
292 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
293 | packet_send_debug("X11 forwarding disabled."); | |
294 | no_x11_forwarding_flag = 1; | |
295 | options += strlen(cp); | |
296 | goto next_option; | |
297 | } | |
298 | cp = "no-pty"; | |
299 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
300 | packet_send_debug("Pty allocation disabled."); | |
301 | no_pty_flag = 1; | |
302 | options += strlen(cp); | |
303 | goto next_option; | |
304 | } | |
305 | cp = "command=\""; | |
306 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
307 | int i; | |
308 | options += strlen(cp); | |
309 | forced_command = xmalloc(strlen(options) + 1); | |
310 | i = 0; | |
311 | while (*options) { | |
312 | if (*options == '"') | |
313 | break; | |
314 | if (*options == '\\' && options[1] == '"') { | |
315 | options += 2; | |
316 | forced_command[i++] = '"'; | |
317 | continue; | |
318 | } | |
319 | forced_command[i++] = *options++; | |
320 | } | |
321 | if (!*options) { | |
322 | debug("%.100s, line %lu: missing end quote", | |
323 | SSH_USER_PERMITTED_KEYS, linenum); | |
324 | packet_send_debug("%.100s, line %lu: missing end quote", | |
325 | SSH_USER_PERMITTED_KEYS, linenum); | |
326 | continue; | |
327 | } | |
328 | forced_command[i] = 0; | |
329 | packet_send_debug("Forced command: %.900s", forced_command); | |
330 | options++; | |
331 | goto next_option; | |
332 | } | |
333 | cp = "environment=\""; | |
334 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
335 | int i; | |
336 | char *s; | |
337 | struct envstring *new_envstring; | |
338 | options += strlen(cp); | |
339 | s = xmalloc(strlen(options) + 1); | |
340 | i = 0; | |
341 | while (*options) { | |
342 | if (*options == '"') | |
343 | break; | |
344 | if (*options == '\\' && options[1] == '"') { | |
345 | options += 2; | |
346 | s[i++] = '"'; | |
347 | continue; | |
348 | } | |
349 | s[i++] = *options++; | |
350 | } | |
351 | if (!*options) { | |
352 | debug("%.100s, line %lu: missing end quote", | |
353 | SSH_USER_PERMITTED_KEYS, linenum); | |
354 | packet_send_debug("%.100s, line %lu: missing end quote", | |
355 | SSH_USER_PERMITTED_KEYS, linenum); | |
356 | continue; | |
357 | } | |
358 | s[i] = 0; | |
359 | packet_send_debug("Adding to environment: %.900s", s); | |
360 | debug("Adding to environment: %.900s", s); | |
361 | options++; | |
362 | new_envstring = xmalloc(sizeof(struct envstring)); | |
363 | new_envstring->s = s; | |
364 | new_envstring->next = custom_environment; | |
365 | custom_environment = new_envstring; | |
366 | goto next_option; | |
367 | } | |
368 | cp = "from=\""; | |
369 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
370 | char *patterns = xmalloc(strlen(options) + 1); | |
371 | int i; | |
372 | options += strlen(cp); | |
373 | i = 0; | |
374 | while (*options) { | |
375 | if (*options == '"') | |
376 | break; | |
377 | if (*options == '\\' && options[1] == '"') { | |
378 | options += 2; | |
379 | patterns[i++] = '"'; | |
380 | continue; | |
381 | } | |
382 | patterns[i++] = *options++; | |
383 | } | |
384 | if (!*options) { | |
385 | debug("%.100s, line %lu: missing end quote", | |
386 | SSH_USER_PERMITTED_KEYS, linenum); | |
387 | packet_send_debug("%.100s, line %lu: missing end quote", | |
388 | SSH_USER_PERMITTED_KEYS, linenum); | |
389 | continue; | |
390 | } | |
391 | patterns[i] = 0; | |
392 | options++; | |
393 | if (!match_hostname(get_canonical_hostname(), patterns, | |
394 | strlen(patterns)) && | |
395 | !match_hostname(get_remote_ipaddr(), patterns, | |
396 | strlen(patterns))) { | |
397 | log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).", | |
398 | pw->pw_name, get_canonical_hostname(), | |
399 | get_remote_ipaddr()); | |
400 | packet_send_debug("Your host '%.200s' is not permitted to use this key for login.", | |
401 | get_canonical_hostname()); | |
402 | xfree(patterns); | |
7b2ea3a1 | 403 | /* key invalid for this host, reset flags */ |
5260325f | 404 | authenticated = 0; |
7b2ea3a1 | 405 | no_agent_forwarding_flag = 0; |
406 | no_port_forwarding_flag = 0; | |
407 | no_pty_flag = 0; | |
408 | no_x11_forwarding_flag = 0; | |
409 | while (custom_environment) { | |
410 | struct envstring *ce = custom_environment; | |
411 | custom_environment = ce->next; | |
412 | xfree(ce->s); | |
413 | xfree(ce); | |
414 | } | |
415 | if (forced_command) { | |
416 | xfree(forced_command); | |
417 | forced_command = NULL; | |
418 | } | |
5260325f | 419 | break; |
420 | } | |
421 | xfree(patterns); | |
422 | /* Host name matches. */ | |
423 | goto next_option; | |
424 | } | |
425 | bad_option: | |
5260325f | 426 | log("Bad options in %.100s file, line %lu: %.50s", |
427 | SSH_USER_PERMITTED_KEYS, linenum, options); | |
428 | packet_send_debug("Bad options in %.100s file, line %lu: %.50s", | |
429 | SSH_USER_PERMITTED_KEYS, linenum, options); | |
430 | authenticated = 0; | |
431 | break; | |
432 | ||
433 | next_option: | |
aa3378df | 434 | /* |
435 | * Skip the comma, and move to the next option | |
436 | * (or break out if there are no more). | |
437 | */ | |
5260325f | 438 | if (!*options) |
439 | fatal("Bugs in auth-rsa.c option processing."); | |
440 | if (*options == ' ' || *options == '\t') | |
aa3378df | 441 | break; /* End of options. */ |
5260325f | 442 | if (*options != ',') |
443 | goto bad_option; | |
444 | options++; | |
445 | /* Process the next option. */ | |
446 | continue; | |
8efc0c15 | 447 | } |
8efc0c15 | 448 | } |
aa3378df | 449 | /* |
450 | * Break out of the loop if authentication was successful; | |
451 | * otherwise continue searching. | |
452 | */ | |
5260325f | 453 | if (authenticated) |
454 | break; | |
8efc0c15 | 455 | } |
456 | ||
5260325f | 457 | /* Restore the privileged uid. */ |
458 | restore_uid(); | |
8efc0c15 | 459 | |
5260325f | 460 | /* Close the file. */ |
461 | fclose(f); | |
8efc0c15 | 462 | |
4fe2af09 | 463 | RSA_free(pk); |
8efc0c15 | 464 | |
5260325f | 465 | if (authenticated) |
466 | packet_send_debug("RSA authentication accepted."); | |
8efc0c15 | 467 | |
5260325f | 468 | /* Return authentication result. */ |
469 | return authenticated; | |
8efc0c15 | 470 | } |