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1 | /* $OpenBSD: auth2-pubkey.c,v 1.16 2008/06/13 04:40:22 djm Exp $ */ | |
2 | /* | |
3 | * Copyright (c) 2000 Markus Friedl. All rights reserved. | |
4 | * | |
5 | * Redistribution and use in source and binary forms, with or without | |
6 | * modification, are permitted provided that the following conditions | |
7 | * are met: | |
8 | * 1. Redistributions of source code must retain the above copyright | |
9 | * notice, this list of conditions and the following disclaimer. | |
10 | * 2. Redistributions in binary form must reproduce the above copyright | |
11 | * notice, this list of conditions and the following disclaimer in the | |
12 | * documentation and/or other materials provided with the distribution. | |
13 | * | |
14 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |
15 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
16 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
17 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
18 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
19 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
20 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
21 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
22 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
23 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
24 | */ | |
25 | ||
26 | #include "includes.h" | |
27 | ||
28 | #include <sys/types.h> | |
29 | #include <sys/stat.h> | |
30 | ||
31 | #include <fcntl.h> | |
32 | #include <pwd.h> | |
33 | #include <stdio.h> | |
34 | #include <stdarg.h> | |
35 | ||
36 | #include "xmalloc.h" | |
37 | #include "ssh.h" | |
38 | #include "ssh2.h" | |
39 | #include "packet.h" | |
40 | #include "buffer.h" | |
41 | #include "log.h" | |
42 | #include "servconf.h" | |
43 | #include "compat.h" | |
44 | #include "key.h" | |
45 | #include "hostfile.h" | |
46 | #include "auth.h" | |
47 | #include "pathnames.h" | |
48 | #include "uidswap.h" | |
49 | #include "auth-options.h" | |
50 | #include "canohost.h" | |
51 | #ifdef GSSAPI | |
52 | #include "ssh-gss.h" | |
53 | #endif | |
54 | #include "monitor_wrap.h" | |
55 | #include "misc.h" | |
56 | ||
57 | /* import */ | |
58 | extern ServerOptions options; | |
59 | extern u_char *session_id2; | |
60 | extern u_int session_id2_len; | |
61 | ||
62 | static int | |
63 | userauth_pubkey(Authctxt *authctxt) | |
64 | { | |
65 | Buffer b; | |
66 | Key *key = NULL; | |
67 | char *pkalg; | |
68 | u_char *pkblob, *sig; | |
69 | u_int alen, blen, slen; | |
70 | int have_sig, pktype; | |
71 | int authenticated = 0; | |
72 | ||
73 | if (!authctxt->valid) { | |
74 | debug2("userauth_pubkey: disabled because of invalid user"); | |
75 | return 0; | |
76 | } | |
77 | have_sig = packet_get_char(); | |
78 | if (datafellows & SSH_BUG_PKAUTH) { | |
79 | debug2("userauth_pubkey: SSH_BUG_PKAUTH"); | |
80 | /* no explicit pkalg given */ | |
81 | pkblob = packet_get_string(&blen); | |
82 | buffer_init(&b); | |
83 | buffer_append(&b, pkblob, blen); | |
84 | /* so we have to extract the pkalg from the pkblob */ | |
85 | pkalg = buffer_get_string(&b, &alen); | |
86 | buffer_free(&b); | |
87 | } else { | |
88 | pkalg = packet_get_string(&alen); | |
89 | pkblob = packet_get_string(&blen); | |
90 | } | |
91 | pktype = key_type_from_name(pkalg); | |
92 | if (pktype == KEY_UNSPEC) { | |
93 | /* this is perfectly legal */ | |
94 | logit("userauth_pubkey: unsupported public key algorithm: %s", | |
95 | pkalg); | |
96 | goto done; | |
97 | } | |
98 | key = key_from_blob(pkblob, blen); | |
99 | if (key == NULL) { | |
100 | error("userauth_pubkey: cannot decode key: %s", pkalg); | |
101 | goto done; | |
102 | } | |
103 | if (key->type != pktype) { | |
104 | error("userauth_pubkey: type mismatch for decoded key " | |
105 | "(received %d, expected %d)", key->type, pktype); | |
106 | goto done; | |
107 | } | |
108 | if (have_sig) { | |
109 | sig = packet_get_string(&slen); | |
110 | packet_check_eom(); | |
111 | buffer_init(&b); | |
112 | if (datafellows & SSH_OLD_SESSIONID) { | |
113 | buffer_append(&b, session_id2, session_id2_len); | |
114 | } else { | |
115 | buffer_put_string(&b, session_id2, session_id2_len); | |
116 | } | |
117 | /* reconstruct packet */ | |
118 | buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); | |
119 | buffer_put_cstring(&b, authctxt->user); | |
120 | buffer_put_cstring(&b, | |
121 | datafellows & SSH_BUG_PKSERVICE ? | |
122 | "ssh-userauth" : | |
123 | authctxt->service); | |
124 | if (datafellows & SSH_BUG_PKAUTH) { | |
125 | buffer_put_char(&b, have_sig); | |
126 | } else { | |
127 | buffer_put_cstring(&b, "publickey"); | |
128 | buffer_put_char(&b, have_sig); | |
129 | buffer_put_cstring(&b, pkalg); | |
130 | } | |
131 | buffer_put_string(&b, pkblob, blen); | |
132 | #ifdef DEBUG_PK | |
133 | buffer_dump(&b); | |
134 | #endif | |
135 | /* test for correct signature */ | |
136 | authenticated = 0; | |
137 | if (PRIVSEP(user_key_allowed(authctxt->pw, key)) && | |
138 | PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), | |
139 | buffer_len(&b))) == 1) | |
140 | authenticated = 1; | |
141 | buffer_free(&b); | |
142 | xfree(sig); | |
143 | } else { | |
144 | debug("test whether pkalg/pkblob are acceptable"); | |
145 | packet_check_eom(); | |
146 | ||
147 | /* XXX fake reply and always send PK_OK ? */ | |
148 | /* | |
149 | * XXX this allows testing whether a user is allowed | |
150 | * to login: if you happen to have a valid pubkey this | |
151 | * message is sent. the message is NEVER sent at all | |
152 | * if a user is not allowed to login. is this an | |
153 | * issue? -markus | |
154 | */ | |
155 | if (PRIVSEP(user_key_allowed(authctxt->pw, key))) { | |
156 | packet_start(SSH2_MSG_USERAUTH_PK_OK); | |
157 | packet_put_string(pkalg, alen); | |
158 | packet_put_string(pkblob, blen); | |
159 | packet_send(); | |
160 | packet_write_wait(); | |
161 | authctxt->postponed = 1; | |
162 | } | |
163 | } | |
164 | if (authenticated != 1) | |
165 | auth_clear_options(); | |
166 | done: | |
167 | debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg); | |
168 | if (key != NULL) | |
169 | key_free(key); | |
170 | xfree(pkalg); | |
171 | xfree(pkblob); | |
172 | #ifdef HAVE_CYGWIN | |
173 | if (check_nt_auth(0, authctxt->pw) == 0) | |
174 | authenticated = 0; | |
175 | #endif | |
176 | return authenticated; | |
177 | } | |
178 | ||
179 | /* return 1 if user allows given key */ | |
180 | static int | |
181 | user_key_allowed2(struct passwd *pw, Key *key, char *file) | |
182 | { | |
183 | char line[SSH_MAX_PUBKEY_BYTES]; | |
184 | int found_key = 0, fd; | |
185 | FILE *f; | |
186 | u_long linenum = 0; | |
187 | struct stat st; | |
188 | Key *found; | |
189 | char *fp; | |
190 | ||
191 | /* Temporarily use the user's uid. */ | |
192 | temporarily_use_uid(pw); | |
193 | ||
194 | debug("trying public key file %s", file); | |
195 | ||
196 | /* | |
197 | * Open the file containing the authorized keys | |
198 | * Fail quietly if file does not exist | |
199 | */ | |
200 | if ((fd = open(file, O_RDONLY|O_NONBLOCK)) == -1) { | |
201 | restore_uid(); | |
202 | return 0; | |
203 | } | |
204 | if (fstat(fd, &st) < 0) { | |
205 | close(fd); | |
206 | restore_uid(); | |
207 | return 0; | |
208 | } | |
209 | if (!S_ISREG(st.st_mode)) { | |
210 | logit("User %s authorized keys %s is not a regular file", | |
211 | pw->pw_name, file); | |
212 | close(fd); | |
213 | restore_uid(); | |
214 | return 0; | |
215 | } | |
216 | unset_nonblock(fd); | |
217 | if ((f = fdopen(fd, "r")) == NULL) { | |
218 | close(fd); | |
219 | restore_uid(); | |
220 | return 0; | |
221 | } | |
222 | if (options.strict_modes && | |
223 | secure_filename(f, file, pw, line, sizeof(line)) != 0) { | |
224 | fclose(f); | |
225 | logit("Authentication refused: %s", line); | |
226 | restore_uid(); | |
227 | return 0; | |
228 | } | |
229 | ||
230 | found_key = 0; | |
231 | found = key_new(key->type); | |
232 | ||
233 | while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { | |
234 | char *cp, *key_options = NULL; | |
235 | ||
236 | /* Skip leading whitespace, empty and comment lines. */ | |
237 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) | |
238 | ; | |
239 | if (!*cp || *cp == '\n' || *cp == '#') | |
240 | continue; | |
241 | ||
242 | if (key_read(found, &cp) != 1) { | |
243 | /* no key? check if there are options for this key */ | |
244 | int quoted = 0; | |
245 | debug2("user_key_allowed: check options: '%s'", cp); | |
246 | key_options = cp; | |
247 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { | |
248 | if (*cp == '\\' && cp[1] == '"') | |
249 | cp++; /* Skip both */ | |
250 | else if (*cp == '"') | |
251 | quoted = !quoted; | |
252 | } | |
253 | /* Skip remaining whitespace. */ | |
254 | for (; *cp == ' ' || *cp == '\t'; cp++) | |
255 | ; | |
256 | if (key_read(found, &cp) != 1) { | |
257 | debug2("user_key_allowed: advance: '%s'", cp); | |
258 | /* still no key? advance to next line*/ | |
259 | continue; | |
260 | } | |
261 | } | |
262 | if (key_equal(found, key) && | |
263 | auth_parse_options(pw, key_options, file, linenum) == 1) { | |
264 | found_key = 1; | |
265 | debug("matching key found: file %s, line %lu", | |
266 | file, linenum); | |
267 | fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX); | |
268 | verbose("Found matching %s key: %s", | |
269 | key_type(found), fp); | |
270 | xfree(fp); | |
271 | break; | |
272 | } | |
273 | } | |
274 | restore_uid(); | |
275 | fclose(f); | |
276 | key_free(found); | |
277 | if (!found_key) | |
278 | debug2("key not found"); | |
279 | return found_key; | |
280 | } | |
281 | ||
282 | /* check whether given key is in .ssh/authorized_keys* */ | |
283 | int | |
284 | user_key_allowed(struct passwd *pw, Key *key) | |
285 | { | |
286 | int success; | |
287 | char *file; | |
288 | ||
289 | file = authorized_keys_file(pw); | |
290 | success = user_key_allowed2(pw, key, file); | |
291 | xfree(file); | |
292 | if (success) | |
293 | return success; | |
294 | ||
295 | /* try suffix "2" for backward compat, too */ | |
296 | file = authorized_keys_file2(pw); | |
297 | success = user_key_allowed2(pw, key, file); | |
298 | xfree(file); | |
299 | return success; | |
300 | } | |
301 | ||
302 | Authmethod method_pubkey = { | |
303 | "publickey", | |
304 | userauth_pubkey, | |
305 | &options.pubkey_authentication | |
306 | }; |