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Commit | Line | Data |
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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 | |
5881cd60 | 30 | #ifdef HAVE_OPENSSL |
8efc0c15 | 31 | #include <openssl/rsa.h> |
32 | #include <openssl/md5.h> | |
5881cd60 | 33 | #endif |
34 | #ifdef HAVE_SSL | |
35 | #include <ssl/rsa.h> | |
36 | #include <ssl/md5.h> | |
37 | #endif | |
8efc0c15 | 38 | |
39 | /* Flags that may be set in authorized_keys options. */ | |
40 | extern int no_port_forwarding_flag; | |
41 | extern int no_agent_forwarding_flag; | |
42 | extern int no_x11_forwarding_flag; | |
43 | extern int no_pty_flag; | |
44 | extern char *forced_command; | |
45 | extern struct envstring *custom_environment; | |
46 | ||
aa3378df | 47 | /* |
48 | * Session identifier that is used to bind key exchange and authentication | |
49 | * responses to a particular session. | |
50 | */ | |
8efc0c15 | 51 | extern unsigned char session_id[16]; |
52 | ||
aa3378df | 53 | /* |
54 | * The .ssh/authorized_keys file contains public keys, one per line, in the | |
55 | * following format: | |
56 | * options bits e n comment | |
57 | * where bits, e and n are decimal numbers, | |
58 | * and comment is any string of characters up to newline. The maximum | |
59 | * length of a line is 8000 characters. See the documentation for a | |
60 | * description of the options. | |
61 | */ | |
8efc0c15 | 62 | |
aa3378df | 63 | /* |
64 | * Performs the RSA authentication challenge-response dialog with the client, | |
65 | * and returns true (non-zero) if the client gave the correct answer to | |
66 | * our challenge; returns zero if the client gives a wrong answer. | |
67 | */ | |
8efc0c15 | 68 | |
69 | int | |
4fe2af09 | 70 | auth_rsa_challenge_dialog(RSA *pk) |
8efc0c15 | 71 | { |
c8d54615 | 72 | BIGNUM *challenge, *encrypted_challenge; |
c8d54615 | 73 | BN_CTX *ctx; |
5260325f | 74 | unsigned char buf[32], mdbuf[16], response[16]; |
75 | MD5_CTX md; | |
76 | unsigned int i; | |
77 | int plen, len; | |
78 | ||
79 | encrypted_challenge = BN_new(); | |
80 | challenge = BN_new(); | |
5260325f | 81 | |
82 | /* Generate a random challenge. */ | |
83 | BN_rand(challenge, 256, 0, 0); | |
c8d54615 | 84 | ctx = BN_CTX_new(); |
4fe2af09 | 85 | BN_mod(challenge, challenge, pk->n, ctx); |
c8d54615 | 86 | BN_CTX_free(ctx); |
5260325f | 87 | |
5260325f | 88 | /* Encrypt the challenge with the public key. */ |
89 | rsa_public_encrypt(encrypted_challenge, challenge, pk); | |
5260325f | 90 | |
91 | /* Send the encrypted challenge to the client. */ | |
92 | packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); | |
93 | packet_put_bignum(encrypted_challenge); | |
94 | packet_send(); | |
c8d54615 | 95 | BN_clear_free(encrypted_challenge); |
5260325f | 96 | packet_write_wait(); |
97 | ||
c8d54615 | 98 | /* Wait for a response. */ |
99 | packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE); | |
100 | packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE); | |
101 | for (i = 0; i < 16; i++) | |
102 | response[i] = packet_get_char(); | |
103 | ||
5260325f | 104 | /* The response is MD5 of decrypted challenge plus session id. */ |
105 | len = BN_num_bytes(challenge); | |
106 | if (len <= 0 || len > 32) | |
107 | fatal("auth_rsa_challenge_dialog: bad challenge length %d", len); | |
108 | memset(buf, 0, 32); | |
109 | BN_bn2bin(challenge, buf + 32 - len); | |
110 | MD5_Init(&md); | |
111 | MD5_Update(&md, buf, 32); | |
112 | MD5_Update(&md, session_id, 16); | |
113 | MD5_Final(mdbuf, &md); | |
5260325f | 114 | BN_clear_free(challenge); |
5260325f | 115 | |
116 | /* Verify that the response is the original challenge. */ | |
117 | if (memcmp(response, mdbuf, 16) != 0) { | |
118 | /* Wrong answer. */ | |
119 | return 0; | |
120 | } | |
121 | /* Correct answer. */ | |
122 | return 1; | |
8efc0c15 | 123 | } |
124 | ||
aa3378df | 125 | /* |
126 | * Performs the RSA authentication dialog with the client. This returns | |
127 | * 0 if the client could not be authenticated, and 1 if authentication was | |
128 | * successful. This may exit if there is a serious protocol violation. | |
129 | */ | |
8efc0c15 | 130 | |
131 | int | |
6fa724bc | 132 | auth_rsa(struct passwd *pw, BIGNUM *client_n) |
8efc0c15 | 133 | { |
5260325f | 134 | extern ServerOptions options; |
135 | char line[8192], file[1024]; | |
136 | int authenticated; | |
137 | unsigned int bits; | |
138 | FILE *f; | |
139 | unsigned long linenum = 0; | |
140 | struct stat st; | |
4fe2af09 | 141 | RSA *pk; |
5260325f | 142 | |
143 | /* Temporarily use the user's uid. */ | |
144 | temporarily_use_uid(pw->pw_uid); | |
145 | ||
146 | /* The authorized keys. */ | |
147 | snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir, | |
148 | SSH_USER_PERMITTED_KEYS); | |
149 | ||
150 | /* Fail quietly if file does not exist */ | |
151 | if (stat(file, &st) < 0) { | |
152 | /* Restore the privileged uid. */ | |
153 | restore_uid(); | |
154 | return 0; | |
8efc0c15 | 155 | } |
5260325f | 156 | /* Open the file containing the authorized keys. */ |
157 | f = fopen(file, "r"); | |
158 | if (!f) { | |
159 | /* Restore the privileged uid. */ | |
160 | restore_uid(); | |
161 | packet_send_debug("Could not open %.900s for reading.", file); | |
162 | packet_send_debug("If your home is on an NFS volume, it may need to be world-readable."); | |
163 | return 0; | |
8efc0c15 | 164 | } |
5260325f | 165 | if (options.strict_modes) { |
166 | int fail = 0; | |
167 | char buf[1024]; | |
168 | /* Check open file in order to avoid open/stat races */ | |
169 | if (fstat(fileno(f), &st) < 0 || | |
170 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
171 | (st.st_mode & 022) != 0) { | |
172 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " | |
173 | "bad ownership or modes for '%s'.", pw->pw_name, file); | |
174 | fail = 1; | |
175 | } else { | |
176 | /* Check path to SSH_USER_PERMITTED_KEYS */ | |
177 | int i; | |
178 | static const char *check[] = { | |
179 | "", SSH_USER_DIR, NULL | |
180 | }; | |
181 | for (i = 0; check[i]; i++) { | |
182 | snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]); | |
183 | if (stat(line, &st) < 0 || | |
184 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || | |
185 | (st.st_mode & 022) != 0) { | |
186 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " | |
187 | "bad ownership or modes for '%s'.", pw->pw_name, line); | |
188 | fail = 1; | |
189 | break; | |
190 | } | |
191 | } | |
8efc0c15 | 192 | } |
5260325f | 193 | if (fail) { |
194 | log(buf); | |
195 | packet_send_debug(buf); | |
196 | restore_uid(); | |
197 | return 0; | |
8efc0c15 | 198 | } |
5260325f | 199 | } |
200 | /* Flag indicating whether authentication has succeeded. */ | |
201 | authenticated = 0; | |
202 | ||
4fe2af09 | 203 | pk = RSA_new(); |
204 | pk->e = BN_new(); | |
205 | pk->n = BN_new(); | |
5260325f | 206 | |
aa3378df | 207 | /* |
208 | * Go though the accepted keys, looking for the current key. If | |
209 | * found, perform a challenge-response dialog to verify that the | |
210 | * user really has the corresponding private key. | |
211 | */ | |
5260325f | 212 | while (fgets(line, sizeof(line), f)) { |
213 | char *cp; | |
214 | char *options; | |
215 | ||
216 | linenum++; | |
217 | ||
aa3378df | 218 | /* Skip leading whitespace, empty and comment lines. */ |
219 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) | |
220 | ; | |
5260325f | 221 | if (!*cp || *cp == '\n' || *cp == '#') |
222 | continue; | |
223 | ||
aa3378df | 224 | /* |
225 | * Check if there are options for this key, and if so, | |
226 | * save their starting address and skip the option part | |
227 | * for now. If there are no options, set the starting | |
228 | * address to NULL. | |
229 | */ | |
5260325f | 230 | if (*cp < '0' || *cp > '9') { |
231 | int quoted = 0; | |
232 | options = cp; | |
233 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { | |
234 | if (*cp == '\\' && cp[1] == '"') | |
235 | cp++; /* Skip both */ | |
236 | else if (*cp == '"') | |
237 | quoted = !quoted; | |
8efc0c15 | 238 | } |
5260325f | 239 | } else |
240 | options = NULL; | |
241 | ||
242 | /* Parse the key from the line. */ | |
4fe2af09 | 243 | if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) { |
5260325f | 244 | debug("%.100s, line %lu: bad key syntax", |
245 | SSH_USER_PERMITTED_KEYS, linenum); | |
246 | packet_send_debug("%.100s, line %lu: bad key syntax", | |
6ae2364d | 247 | SSH_USER_PERMITTED_KEYS, linenum); |
5260325f | 248 | continue; |
8efc0c15 | 249 | } |
5260325f | 250 | /* cp now points to the comment part. */ |
251 | ||
5260325f | 252 | /* Check if the we have found the desired key (identified by its modulus). */ |
4fe2af09 | 253 | if (BN_cmp(pk->n, client_n) != 0) |
aa3378df | 254 | continue; |
5260325f | 255 | |
57112b5a | 256 | /* check the real bits */ |
4fe2af09 | 257 | if (bits != BN_num_bits(pk->n)) |
57112b5a | 258 | log("Warning: %s, line %ld: keysize mismatch: " |
259 | "actual %d vs. announced %d.", | |
4fe2af09 | 260 | file, linenum, BN_num_bits(pk->n), bits); |
57112b5a | 261 | |
5260325f | 262 | /* We have found the desired key. */ |
263 | ||
4fe2af09 | 264 | |
5260325f | 265 | /* Perform the challenge-response dialog for this key. */ |
4fe2af09 | 266 | if (!auth_rsa_challenge_dialog(pk)) { |
5260325f | 267 | /* Wrong response. */ |
268 | verbose("Wrong response to RSA authentication challenge."); | |
269 | packet_send_debug("Wrong response to RSA authentication challenge."); | |
270 | continue; | |
8efc0c15 | 271 | } |
aa3378df | 272 | /* |
273 | * Correct response. The client has been successfully | |
274 | * authenticated. Note that we have not yet processed the | |
275 | * options; this will be reset if the options cause the | |
276 | * authentication to be rejected. | |
277 | */ | |
5260325f | 278 | authenticated = 1; |
279 | ||
280 | /* RSA part of authentication was accepted. Now process the options. */ | |
281 | if (options) { | |
282 | while (*options && *options != ' ' && *options != '\t') { | |
283 | cp = "no-port-forwarding"; | |
284 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
285 | packet_send_debug("Port forwarding disabled."); | |
286 | no_port_forwarding_flag = 1; | |
287 | options += strlen(cp); | |
288 | goto next_option; | |
289 | } | |
290 | cp = "no-agent-forwarding"; | |
291 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
292 | packet_send_debug("Agent forwarding disabled."); | |
293 | no_agent_forwarding_flag = 1; | |
294 | options += strlen(cp); | |
295 | goto next_option; | |
296 | } | |
297 | cp = "no-X11-forwarding"; | |
298 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
299 | packet_send_debug("X11 forwarding disabled."); | |
300 | no_x11_forwarding_flag = 1; | |
301 | options += strlen(cp); | |
302 | goto next_option; | |
303 | } | |
304 | cp = "no-pty"; | |
305 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
306 | packet_send_debug("Pty allocation disabled."); | |
307 | no_pty_flag = 1; | |
308 | options += strlen(cp); | |
309 | goto next_option; | |
310 | } | |
311 | cp = "command=\""; | |
312 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
313 | int i; | |
314 | options += strlen(cp); | |
315 | forced_command = xmalloc(strlen(options) + 1); | |
316 | i = 0; | |
317 | while (*options) { | |
318 | if (*options == '"') | |
319 | break; | |
320 | if (*options == '\\' && options[1] == '"') { | |
321 | options += 2; | |
322 | forced_command[i++] = '"'; | |
323 | continue; | |
324 | } | |
325 | forced_command[i++] = *options++; | |
326 | } | |
327 | if (!*options) { | |
328 | debug("%.100s, line %lu: missing end quote", | |
329 | SSH_USER_PERMITTED_KEYS, linenum); | |
330 | packet_send_debug("%.100s, line %lu: missing end quote", | |
331 | SSH_USER_PERMITTED_KEYS, linenum); | |
332 | continue; | |
333 | } | |
334 | forced_command[i] = 0; | |
335 | packet_send_debug("Forced command: %.900s", forced_command); | |
336 | options++; | |
337 | goto next_option; | |
338 | } | |
339 | cp = "environment=\""; | |
340 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
341 | int i; | |
342 | char *s; | |
343 | struct envstring *new_envstring; | |
344 | options += strlen(cp); | |
345 | s = xmalloc(strlen(options) + 1); | |
346 | i = 0; | |
347 | while (*options) { | |
348 | if (*options == '"') | |
349 | break; | |
350 | if (*options == '\\' && options[1] == '"') { | |
351 | options += 2; | |
352 | s[i++] = '"'; | |
353 | continue; | |
354 | } | |
355 | s[i++] = *options++; | |
356 | } | |
357 | if (!*options) { | |
358 | debug("%.100s, line %lu: missing end quote", | |
359 | SSH_USER_PERMITTED_KEYS, linenum); | |
360 | packet_send_debug("%.100s, line %lu: missing end quote", | |
361 | SSH_USER_PERMITTED_KEYS, linenum); | |
362 | continue; | |
363 | } | |
364 | s[i] = 0; | |
365 | packet_send_debug("Adding to environment: %.900s", s); | |
366 | debug("Adding to environment: %.900s", s); | |
367 | options++; | |
368 | new_envstring = xmalloc(sizeof(struct envstring)); | |
369 | new_envstring->s = s; | |
370 | new_envstring->next = custom_environment; | |
371 | custom_environment = new_envstring; | |
372 | goto next_option; | |
373 | } | |
374 | cp = "from=\""; | |
375 | if (strncmp(options, cp, strlen(cp)) == 0) { | |
376 | char *patterns = xmalloc(strlen(options) + 1); | |
377 | int i; | |
378 | options += strlen(cp); | |
379 | i = 0; | |
380 | while (*options) { | |
381 | if (*options == '"') | |
382 | break; | |
383 | if (*options == '\\' && options[1] == '"') { | |
384 | options += 2; | |
385 | patterns[i++] = '"'; | |
386 | continue; | |
387 | } | |
388 | patterns[i++] = *options++; | |
389 | } | |
390 | if (!*options) { | |
391 | debug("%.100s, line %lu: missing end quote", | |
392 | SSH_USER_PERMITTED_KEYS, linenum); | |
393 | packet_send_debug("%.100s, line %lu: missing end quote", | |
394 | SSH_USER_PERMITTED_KEYS, linenum); | |
395 | continue; | |
396 | } | |
397 | patterns[i] = 0; | |
398 | options++; | |
399 | if (!match_hostname(get_canonical_hostname(), patterns, | |
400 | strlen(patterns)) && | |
401 | !match_hostname(get_remote_ipaddr(), patterns, | |
402 | strlen(patterns))) { | |
403 | log("RSA authentication tried for %.100s with correct key but not from a permitted host (host=%.200s, ip=%.200s).", | |
404 | pw->pw_name, get_canonical_hostname(), | |
405 | get_remote_ipaddr()); | |
406 | packet_send_debug("Your host '%.200s' is not permitted to use this key for login.", | |
407 | get_canonical_hostname()); | |
408 | xfree(patterns); | |
7b2ea3a1 | 409 | /* key invalid for this host, reset flags */ |
5260325f | 410 | authenticated = 0; |
7b2ea3a1 | 411 | no_agent_forwarding_flag = 0; |
412 | no_port_forwarding_flag = 0; | |
413 | no_pty_flag = 0; | |
414 | no_x11_forwarding_flag = 0; | |
415 | while (custom_environment) { | |
416 | struct envstring *ce = custom_environment; | |
417 | custom_environment = ce->next; | |
418 | xfree(ce->s); | |
419 | xfree(ce); | |
420 | } | |
421 | if (forced_command) { | |
422 | xfree(forced_command); | |
423 | forced_command = NULL; | |
424 | } | |
5260325f | 425 | break; |
426 | } | |
427 | xfree(patterns); | |
428 | /* Host name matches. */ | |
429 | goto next_option; | |
430 | } | |
431 | bad_option: | |
5260325f | 432 | log("Bad options in %.100s file, line %lu: %.50s", |
433 | SSH_USER_PERMITTED_KEYS, linenum, options); | |
434 | packet_send_debug("Bad options in %.100s file, line %lu: %.50s", | |
435 | SSH_USER_PERMITTED_KEYS, linenum, options); | |
436 | authenticated = 0; | |
437 | break; | |
438 | ||
439 | next_option: | |
aa3378df | 440 | /* |
441 | * Skip the comma, and move to the next option | |
442 | * (or break out if there are no more). | |
443 | */ | |
5260325f | 444 | if (!*options) |
445 | fatal("Bugs in auth-rsa.c option processing."); | |
446 | if (*options == ' ' || *options == '\t') | |
aa3378df | 447 | break; /* End of options. */ |
5260325f | 448 | if (*options != ',') |
449 | goto bad_option; | |
450 | options++; | |
451 | /* Process the next option. */ | |
452 | continue; | |
8efc0c15 | 453 | } |
8efc0c15 | 454 | } |
aa3378df | 455 | /* |
456 | * Break out of the loop if authentication was successful; | |
457 | * otherwise continue searching. | |
458 | */ | |
5260325f | 459 | if (authenticated) |
460 | break; | |
8efc0c15 | 461 | } |
462 | ||
5260325f | 463 | /* Restore the privileged uid. */ |
464 | restore_uid(); | |
8efc0c15 | 465 | |
5260325f | 466 | /* Close the file. */ |
467 | fclose(f); | |
8efc0c15 | 468 | |
4fe2af09 | 469 | RSA_free(pk); |
8efc0c15 | 470 | |
5260325f | 471 | if (authenticated) |
472 | packet_send_debug("RSA authentication accepted."); | |
8efc0c15 | 473 | |
5260325f | 474 | /* Return authentication result. */ |
475 | return authenticated; | |
8efc0c15 | 476 | } |