Annotation of src/usr.bin/ssh/auth2.c, Revision 1.8
1.1 markus 1: /*
2: * Copyright (c) 2000 Markus Friedl. All rights reserved.
3: *
4: * Redistribution and use in source and binary forms, with or without
5: * modification, are permitted provided that the following conditions
6: * are met:
7: * 1. Redistributions of source code must retain the above copyright
8: * notice, this list of conditions and the following disclaimer.
9: * 2. Redistributions in binary form must reproduce the above copyright
10: * notice, this list of conditions and the following disclaimer in the
11: * documentation and/or other materials provided with the distribution.
12: * 3. All advertising materials mentioning features or use of this software
13: * must display the following acknowledgement:
14: * This product includes software developed by Markus Friedl.
15: * 4. The name of the author may not be used to endorse or promote products
16: * derived from this software without specific prior written permission.
17: *
18: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28: */
29: #include "includes.h"
1.8 ! markus 30: RCSID("$OpenBSD: auth2.c,v 1.7 2000/05/06 17:45:36 markus Exp $");
1.1 markus 31:
32: #include <openssl/dsa.h>
33: #include <openssl/rsa.h>
34: #include <openssl/evp.h>
35:
36: #include "xmalloc.h"
37: #include "rsa.h"
38: #include "ssh.h"
39: #include "pty.h"
40: #include "packet.h"
41: #include "buffer.h"
42: #include "cipher.h"
43: #include "servconf.h"
44: #include "compat.h"
45: #include "channels.h"
46: #include "bufaux.h"
47: #include "ssh2.h"
48: #include "auth.h"
49: #include "session.h"
50: #include "dispatch.h"
51: #include "auth.h"
52: #include "key.h"
53: #include "kex.h"
54:
55: #include "dsa.h"
56: #include "uidswap.h"
57:
58: /* import */
59: extern ServerOptions options;
60: extern unsigned char *session_id2;
61: extern int session_id2_len;
62:
63: /* protocol */
64:
65: void input_service_request(int type, int plen);
66: void input_userauth_request(int type, int plen);
67: void protocol_error(int type, int plen);
68:
69: /* auth */
70: int ssh2_auth_none(struct passwd *pw);
71: int ssh2_auth_password(struct passwd *pw);
72: int ssh2_auth_pubkey(struct passwd *pw, unsigned char *raw, unsigned int rlen);
73:
74: /* helper */
75: struct passwd* auth_set_user(char *u, char *s);
76: int user_dsa_key_allowed(struct passwd *pw, Key *key);
77:
78: typedef struct Authctxt Authctxt;
79: struct Authctxt {
80: char *user;
81: char *service;
82: struct passwd pw;
83: int valid;
84: };
85: static Authctxt *authctxt = NULL;
86: static int userauth_success = 0;
87:
88: /*
89: * loop until userauth_success == TRUE
90: */
91:
92: void
93: do_authentication2()
94: {
1.4 markus 95: /* turn off skey/kerberos, not supported by SSH2 */
1.5 djm 96: #ifdef SKEY
1.4 markus 97: options.skey_authentication = 0;
1.5 djm 98: #endif
99: #ifdef KRB4
1.4 markus 100: options.kerberos_authentication = 0;
1.5 djm 101: #endif
1.4 markus 102:
1.1 markus 103: dispatch_init(&protocol_error);
104: dispatch_set(SSH2_MSG_SERVICE_REQUEST, &input_service_request);
105: dispatch_run(DISPATCH_BLOCK, &userauth_success);
106: do_authenticated2();
107: }
108:
109: void
110: protocol_error(int type, int plen)
111: {
112: log("auth: protocol error: type %d plen %d", type, plen);
113: packet_start(SSH2_MSG_UNIMPLEMENTED);
114: packet_put_int(0);
115: packet_send();
116: packet_write_wait();
117: }
118:
119: void
120: input_service_request(int type, int plen)
121: {
122: unsigned int len;
123: int accept = 0;
124: char *service = packet_get_string(&len);
125: packet_done();
126:
127: if (strcmp(service, "ssh-userauth") == 0) {
128: if (!userauth_success) {
129: accept = 1;
130: /* now we can handle user-auth requests */
131: dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &input_userauth_request);
132: }
133: }
134: /* XXX all other service requests are denied */
135:
136: if (accept) {
137: packet_start(SSH2_MSG_SERVICE_ACCEPT);
138: packet_put_cstring(service);
139: packet_send();
140: packet_write_wait();
141: } else {
142: debug("bad service request %s", service);
143: packet_disconnect("bad service request %s", service);
144: }
145: xfree(service);
146: }
147:
148: void
149: input_userauth_request(int type, int plen)
150: {
1.3 markus 151: static void (*authlog) (const char *fmt,...) = verbose;
152: static int attempt = 0;
1.1 markus 153: unsigned int len, rlen;
154: int authenticated = 0;
1.3 markus 155: char *raw, *user, *service, *method, *authmsg = NULL;
1.1 markus 156: struct passwd *pw;
157:
1.3 markus 158: if (++attempt == AUTH_FAIL_MAX)
1.1 markus 159: packet_disconnect("too many failed userauth_requests");
160:
161: raw = packet_get_raw(&rlen);
162: if (plen != rlen)
163: fatal("plen != rlen");
164: user = packet_get_string(&len);
165: service = packet_get_string(&len);
166: method = packet_get_string(&len);
167: debug("userauth-request for user %s service %s method %s", user, service, method);
168:
169: /* XXX we only allow the ssh-connection service */
170: pw = auth_set_user(user, service);
171: if (pw && strcmp(service, "ssh-connection")==0) {
172: if (strcmp(method, "none") == 0) {
173: authenticated = ssh2_auth_none(pw);
174: } else if (strcmp(method, "password") == 0) {
175: authenticated = ssh2_auth_password(pw);
176: } else if (strcmp(method, "publickey") == 0) {
177: authenticated = ssh2_auth_pubkey(pw, raw, rlen);
178: }
179: }
1.3 markus 180: if (authenticated && pw && pw->pw_uid == 0 && !options.permit_root_login) {
181: authenticated = 0;
182: log("ROOT LOGIN REFUSED FROM %.200s",
183: get_canonical_hostname());
184: }
185:
1.6 markus 186: /* Raise logging level */
187: if (authenticated == 1 ||
188: attempt == AUTH_FAIL_LOG ||
189: strcmp(method, "password") == 0)
190: authlog = log;
191:
192: /* Log before sending the reply */
193: if (authenticated == 1) {
194: authmsg = "Accepted";
195: } else if (authenticated == 0) {
196: authmsg = "Failed";
197: } else {
198: authmsg = "Postponed";
199: }
200: authlog("%s %s for %.200s from %.200s port %d ssh2",
201: authmsg,
202: method,
203: pw && pw->pw_uid == 0 ? "ROOT" : user,
204: get_remote_ipaddr(),
205: get_remote_port());
206:
1.3 markus 207: /* XXX todo: check if multiple auth methods are needed */
1.1 markus 208: if (authenticated == 1) {
209: /* turn off userauth */
210: dispatch_set(SSH2_MSG_USERAUTH_REQUEST, &protocol_error);
211: packet_start(SSH2_MSG_USERAUTH_SUCCESS);
212: packet_send();
213: packet_write_wait();
214: /* now we can break out */
215: userauth_success = 1;
216: } else if (authenticated == 0) {
217: packet_start(SSH2_MSG_USERAUTH_FAILURE);
218: packet_put_cstring("publickey,password"); /* XXX dynamic */
219: packet_put_char(0); /* XXX partial success, unused */
220: packet_send();
221: packet_write_wait();
222: }
1.3 markus 223:
1.1 markus 224: xfree(service);
225: xfree(user);
226: xfree(method);
227: }
228:
229: int
230: ssh2_auth_none(struct passwd *pw)
231: {
232: packet_done();
233: return auth_password(pw, "");
234: }
235: int
236: ssh2_auth_password(struct passwd *pw)
237: {
238: char *password;
239: int authenticated = 0;
240: int change;
241: unsigned int len;
242: change = packet_get_char();
243: if (change)
244: log("password change not supported");
245: password = packet_get_string(&len);
246: packet_done();
1.3 markus 247: if (options.password_authentication &&
248: auth_password(pw, password) == 1)
1.1 markus 249: authenticated = 1;
250: memset(password, 0, len);
251: xfree(password);
252: return authenticated;
253: }
254: int
255: ssh2_auth_pubkey(struct passwd *pw, unsigned char *raw, unsigned int rlen)
256: {
257: Buffer b;
258: Key *key;
259: char *pkalg, *pkblob, *sig;
260: unsigned int alen, blen, slen;
261: int have_sig;
262: int authenticated = 0;
263:
1.7 markus 264: if (options.dsa_authentication == 0) {
1.3 markus 265: debug("pubkey auth disabled");
1.8 ! markus 266: return 0;
! 267: }
! 268: if (datafellows & SSH_BUG_PUBKEYAUTH) {
! 269: log("bug compatibility with ssh-2.0.13 pubkey not implemented");
1.3 markus 270: return 0;
271: }
1.1 markus 272: have_sig = packet_get_char();
273: pkalg = packet_get_string(&alen);
274: if (strcmp(pkalg, KEX_DSS) != 0) {
275: xfree(pkalg);
276: log("bad pkalg %s", pkalg); /*XXX*/
277: return 0;
278: }
279: pkblob = packet_get_string(&blen);
280: key = dsa_key_from_blob(pkblob, blen);
1.2 markus 281: if (key != NULL) {
282: if (have_sig) {
283: sig = packet_get_string(&slen);
284: packet_done();
285: buffer_init(&b);
286: buffer_append(&b, session_id2, session_id2_len);
287: buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
288: if (slen + 4 > rlen)
289: fatal("bad rlen/slen");
290: buffer_append(&b, raw, rlen - slen - 4);
1.1 markus 291: #ifdef DEBUG_DSS
1.2 markus 292: buffer_dump(&b);
1.1 markus 293: #endif
1.2 markus 294: /* test for correct signature */
295: if (user_dsa_key_allowed(pw, key) &&
296: dsa_verify(key, sig, slen, buffer_ptr(&b), buffer_len(&b)) == 1)
297: authenticated = 1;
298: buffer_clear(&b);
299: xfree(sig);
300: } else {
301: packet_done();
302: debug("test key...");
303: /* test whether pkalg/pkblob are acceptable */
304: /* XXX fake reply and always send PK_OK ? */
1.6 markus 305: /*
306: * XXX this allows testing whether a user is allowed
307: * to login: if you happen to have a valid pubkey this
308: * message is sent. the message is NEVER sent at all
309: * if a user is not allowed to login. is this an
310: * issue? -markus
311: */
1.2 markus 312: if (user_dsa_key_allowed(pw, key)) {
313: packet_start(SSH2_MSG_USERAUTH_PK_OK);
314: packet_put_string(pkalg, alen);
315: packet_put_string(pkblob, blen);
316: packet_send();
317: packet_write_wait();
318: authenticated = -1;
319: }
1.1 markus 320: }
1.2 markus 321: key_free(key);
1.1 markus 322: }
323: xfree(pkalg);
324: xfree(pkblob);
325: return authenticated;
326: }
327:
328: /* set and get current user */
329:
330: struct passwd*
331: auth_get_user(void)
332: {
333: return (authctxt != NULL && authctxt->valid) ? &authctxt->pw : NULL;
334: }
335:
336: struct passwd*
337: auth_set_user(char *u, char *s)
338: {
339: struct passwd *pw, *copy;
340:
341: if (authctxt == NULL) {
342: authctxt = xmalloc(sizeof(*authctxt));
343: authctxt->valid = 0;
344: authctxt->user = xstrdup(u);
345: authctxt->service = xstrdup(s);
346: setproctitle("%s", u);
347: pw = getpwnam(u);
348: if (!pw || !allowed_user(pw)) {
1.3 markus 349: log("auth_set_user: illegal user %s", u);
1.1 markus 350: return NULL;
351: }
352: copy = &authctxt->pw;
353: memset(copy, 0, sizeof(*copy));
354: copy->pw_name = xstrdup(pw->pw_name);
355: copy->pw_passwd = xstrdup(pw->pw_passwd);
356: copy->pw_uid = pw->pw_uid;
357: copy->pw_gid = pw->pw_gid;
358: copy->pw_dir = xstrdup(pw->pw_dir);
359: copy->pw_shell = xstrdup(pw->pw_shell);
360: authctxt->valid = 1;
361: } else {
362: if (strcmp(u, authctxt->user) != 0 ||
363: strcmp(s, authctxt->service) != 0) {
364: log("auth_set_user: missmatch: (%s,%s)!=(%s,%s)",
365: u, s, authctxt->user, authctxt->service);
366: return NULL;
367: }
368: }
369: return auth_get_user();
370: }
371:
372: /* return 1 if user allows given key */
373: int
374: user_dsa_key_allowed(struct passwd *pw, Key *key)
375: {
376: char line[8192], file[1024];
377: int found_key = 0;
378: unsigned int bits = -1;
379: FILE *f;
380: unsigned long linenum = 0;
381: struct stat st;
382: Key *found;
383:
384: /* Temporarily use the user's uid. */
385: temporarily_use_uid(pw->pw_uid);
386:
387: /* The authorized keys. */
388: snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir,
389: SSH_USER_PERMITTED_KEYS2);
390:
391: /* Fail quietly if file does not exist */
392: if (stat(file, &st) < 0) {
393: /* Restore the privileged uid. */
394: restore_uid();
395: return 0;
396: }
397: /* Open the file containing the authorized keys. */
398: f = fopen(file, "r");
399: if (!f) {
400: /* Restore the privileged uid. */
401: restore_uid();
402: return 0;
403: }
404: if (options.strict_modes) {
405: int fail = 0;
406: char buf[1024];
407: /* Check open file in order to avoid open/stat races */
408: if (fstat(fileno(f), &st) < 0 ||
409: (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
410: (st.st_mode & 022) != 0) {
411: snprintf(buf, sizeof buf, "DSA authentication refused for %.100s: "
412: "bad ownership or modes for '%s'.", pw->pw_name, file);
413: fail = 1;
414: } else {
415: /* Check path to SSH_USER_PERMITTED_KEYS */
416: int i;
417: static const char *check[] = {
418: "", SSH_USER_DIR, NULL
419: };
420: for (i = 0; check[i]; i++) {
421: snprintf(line, sizeof line, "%.500s/%.100s",
422: pw->pw_dir, check[i]);
423: if (stat(line, &st) < 0 ||
424: (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
425: (st.st_mode & 022) != 0) {
426: snprintf(buf, sizeof buf,
427: "DSA authentication refused for %.100s: "
428: "bad ownership or modes for '%s'.",
429: pw->pw_name, line);
430: fail = 1;
431: break;
432: }
433: }
434: }
435: if (fail) {
436: log(buf);
437: fclose(f);
438: restore_uid();
439: return 0;
440: }
441: }
442: found_key = 0;
443: found = key_new(KEY_DSA);
444:
445: while (fgets(line, sizeof(line), f)) {
446: char *cp;
447: linenum++;
448: /* Skip leading whitespace, empty and comment lines. */
449: for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
450: ;
451: if (!*cp || *cp == '\n' || *cp == '#')
452: continue;
453: bits = key_read(found, &cp);
454: if (bits == 0)
455: continue;
456: if (key_equal(found, key)) {
457: found_key = 1;
458: debug("matching key found: file %s, line %ld",
459: file, linenum);
460: break;
461: }
462: }
463: restore_uid();
464: fclose(f);
465: key_free(found);
466: return found_key;
467: }
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