1 /*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 2003 Networks Associates Technology, Inc.
5 * Copyright (c) 2004-2011 Dag-Erling Smørgrav
6 * All rights reserved.
7 *
8 * This software was developed for the FreeBSD Project by ThinkSec AS and
9 * NAI Labs, the Security Research Division of Network Associates, Inc.
10 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
11 * DARPA CHATS research program.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 * 3. The name of the author may not be used to endorse or promote
22 * products derived from this software without specific prior written
23 * permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 */
37
38 #include <sys/param.h>
39 #include <sys/wait.h>
40
41 #include <errno.h>
42 #include <fcntl.h>
43 #include <paths.h>
44 #include <pwd.h>
45 #include <signal.h>
46 #include <stdio.h>
47 #include <string.h>
48 #include <unistd.h>
49
50 #define PAM_SM_AUTH
51 #define PAM_SM_SESSION
52
53 #include <security/pam_appl.h>
54 #include <security/pam_modules.h>
55 #include <security/openpam.h>
56
57 #include <openssl/evp.h>
58
59 #define __bounded__(x, y, z)
60 #include "authfd.h"
61 #include "authfile.h"
62 #include "sshkey.h"
63
64 #define ssh_add_identity(auth, key, comment) \
65 ssh_add_identity_constrained(auth, key, comment, 0, 0, 0, NULL, NULL, 0)
66
67 extern char **environ;
68
69 struct pam_ssh_key {
70 struct sshkey *key;
71 char *comment;
72 };
73
74 static const char *pam_ssh_prompt = "SSH passphrase: ";
75 static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
76
77 static const char *pam_ssh_keyfiles[] = {
78 ".ssh/id_rsa", /* SSH2 RSA key */
79 ".ssh/id_dsa", /* SSH2 DSA key */
80 ".ssh/id_ecdsa", /* SSH2 ECDSA key */
81 ".ssh/id_ed25519", /* SSH2 Ed25519 key */
82 NULL
83 };
84
85 static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
86 static char str_ssh_agent[] = "ssh-agent";
87 static char str_dash_s[] = "-s";
88 static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL };
89 static char *const pam_ssh_agent_envp[] = { NULL };
90
91 /*
92 * Attempts to load a private key from the specified file in the specified
93 * directory, using the specified passphrase. If successful, returns a
94 * struct pam_ssh_key containing the key and its comment.
95 */
96 static struct pam_ssh_key *
pam_ssh_load_key(const char * dir,const char * kfn,const char * passphrase,int nullok)97 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase,
98 int nullok)
99 {
100 char fn[PATH_MAX];
101 struct pam_ssh_key *psk;
102 struct sshkey *key;
103 char *comment;
104 int ret;
105
106 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
107 return (NULL);
108 /*
109 * If the key is unencrypted, OpenSSL ignores the passphrase, so
110 * it will seem like the user typed in the right one. This allows
111 * a user to circumvent nullok by providing a dummy passphrase.
112 * Verify that the key really *is* encrypted by trying to load it
113 * with an empty passphrase, and if the key is not encrypted,
114 * accept only an empty passphrase.
115 */
116 ret = sshkey_load_private(fn, "", &key, &comment);
117 if (ret == 0 && !(*passphrase == '\0' && nullok)) {
118 sshkey_free(key);
119 return (NULL);
120 }
121 if (ret != 0)
122 ret = sshkey_load_private(fn, passphrase, &key, &comment);
123 if (ret != 0) {
124 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn);
125 return (NULL);
126 }
127
128 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn);
129 if ((psk = malloc(sizeof(*psk))) == NULL) {
130 sshkey_free(key);
131 free(comment);
132 return (NULL);
133 }
134 psk->key = key;
135 psk->comment = comment;
136 return (psk);
137 }
138
139 /*
140 * Wipes a private key and frees the associated resources.
141 */
142 static void
pam_ssh_free_key(pam_handle_t * pamh __unused,void * data,int pam_err __unused)143 pam_ssh_free_key(pam_handle_t *pamh __unused,
144 void *data, int pam_err __unused)
145 {
146 struct pam_ssh_key *psk;
147
148 psk = data;
149 sshkey_free(psk->key);
150 free(psk->comment);
151 free(psk);
152 }
153
154 PAM_EXTERN int
pam_sm_authenticate(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)155 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
156 int argc __unused, const char *argv[] __unused)
157 {
158 const char **kfn, *passphrase, *user;
159 const void *item;
160 struct passwd *pwd;
161 struct pam_ssh_key *psk;
162 int nkeys, nullok, pam_err, pass;
163
164 nullok = (openpam_get_option(pamh, "nullok") != NULL);
165
166 /* PEM is not loaded by default */
167 OpenSSL_add_all_algorithms();
168
169 /* get user name and home directory */
170 pam_err = pam_get_user(pamh, &user, NULL);
171 if (pam_err != PAM_SUCCESS)
172 return (pam_err);
173 pwd = getpwnam(user);
174 if (pwd == NULL)
175 return (PAM_USER_UNKNOWN);
176 if (pwd->pw_dir == NULL)
177 return (PAM_AUTH_ERR);
178
179 nkeys = 0;
180 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS &&
181 item != NULL);
182 load_keys:
183 /* get passphrase */
184 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
185 &passphrase, pam_ssh_prompt);
186 if (pam_err != PAM_SUCCESS)
187 return (pam_err);
188
189 /* switch to user credentials */
190 pam_err = openpam_borrow_cred(pamh, pwd);
191 if (pam_err != PAM_SUCCESS)
192 return (pam_err);
193
194 /* try to load keys from all keyfiles we know of */
195 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
196 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok);
197 if (psk != NULL) {
198 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
199 ++nkeys;
200 }
201 }
202
203 /* switch back to arbitrator credentials */
204 openpam_restore_cred(pamh);
205
206 /*
207 * If we tried an old token and didn't get anything, and
208 * try_first_pass was specified, try again after prompting the
209 * user for a new passphrase.
210 */
211 if (nkeys == 0 && pass == 1 &&
212 openpam_get_option(pamh, "try_first_pass") != NULL) {
213 pam_set_item(pamh, PAM_AUTHTOK, NULL);
214 pass = 0;
215 goto load_keys;
216 }
217
218 /* no keys? */
219 if (nkeys == 0)
220 return (PAM_AUTH_ERR);
221
222 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
223 return (PAM_SUCCESS);
224 }
225
226 PAM_EXTERN int
pam_sm_setcred(pam_handle_t * pamh __unused,int flags __unused,int argc __unused,const char * argv[]__unused)227 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
228 int argc __unused, const char *argv[] __unused)
229 {
230
231 return (PAM_SUCCESS);
232 }
233
234 /*
235 * Parses a line from ssh-agent's output.
236 */
237 static void
pam_ssh_process_agent_output(pam_handle_t * pamh,FILE * f)238 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
239 {
240 char *line, *p, *key, *val;
241 size_t len;
242
243 while ((line = fgetln(f, &len)) != NULL) {
244 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
245 continue;
246
247 /* find equal sign at end of key */
248 for (p = key = line; p < line + len; ++p)
249 if (*p == '=')
250 break;
251 if (p == line + len || *p != '=')
252 continue;
253 *p = '\0';
254
255 /* find semicolon at end of value */
256 for (val = ++p; p < line + len; ++p)
257 if (*p == ';')
258 break;
259 if (p == line + len || *p != ';')
260 continue;
261 *p = '\0';
262
263 /* store key-value pair in environment */
264 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
265 pam_setenv(pamh, key, val, 1);
266 }
267 }
268
269 /*
270 * Starts an ssh agent and stores the environment variables derived from
271 * its output.
272 */
273 static int
pam_ssh_start_agent(pam_handle_t * pamh)274 pam_ssh_start_agent(pam_handle_t *pamh)
275 {
276 int agent_pipe[2];
277 pid_t pid;
278 FILE *f;
279
280 /* get a pipe which we will use to read the agent's output */
281 if (pipe(agent_pipe) == -1)
282 return (PAM_SYSTEM_ERR);
283
284 /* start the agent */
285 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
286 pid = fork();
287 if (pid == (pid_t)-1) {
288 /* failed */
289 close(agent_pipe[0]);
290 close(agent_pipe[1]);
291 return (PAM_SYSTEM_ERR);
292 }
293 if (pid == 0) {
294 int fd;
295
296 /* child: drop privs, close fds and start agent */
297 setgid(getegid());
298 setuid(geteuid());
299 close(STDIN_FILENO);
300 open(_PATH_DEVNULL, O_RDONLY);
301 dup2(agent_pipe[1], STDOUT_FILENO);
302 dup2(agent_pipe[1], STDERR_FILENO);
303 for (fd = 3; fd < getdtablesize(); ++fd)
304 close(fd);
305 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp);
306 _exit(127);
307 }
308
309 /* parent */
310 close(agent_pipe[1]);
311 if ((f = fdopen(agent_pipe[0], "r")) == NULL)
312 return (PAM_SYSTEM_ERR);
313 pam_ssh_process_agent_output(pamh, f);
314 fclose(f);
315
316 return (PAM_SUCCESS);
317 }
318
319 /*
320 * Adds previously stored keys to a running agent.
321 */
322 static int
pam_ssh_add_keys_to_agent(pam_handle_t * pamh)323 pam_ssh_add_keys_to_agent(pam_handle_t *pamh)
324 {
325 const struct pam_ssh_key *psk;
326 const char **kfn;
327 const void *item;
328 char **envlist, **env;
329 int fd, pam_err;
330
331 /* switch to PAM environment */
332 envlist = environ;
333 if ((environ = pam_getenvlist(pamh)) == NULL) {
334 environ = envlist;
335 return (PAM_SYSTEM_ERR);
336 }
337
338 /* get a connection to the agent */
339 if (ssh_get_authentication_socket(&fd) != 0) {
340 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent");
341 pam_err = PAM_SYSTEM_ERR;
342 goto end;
343 }
344
345 /* look for keys to add to it */
346 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
347 pam_err = pam_get_data(pamh, *kfn, &item);
348 if (pam_err == PAM_SUCCESS && item != NULL) {
349 psk = item;
350 if (ssh_add_identity(fd, psk->key, psk->comment) == 0)
351 openpam_log(PAM_LOG_DEBUG,
352 "added %s to ssh agent", psk->comment);
353 else
354 openpam_log(PAM_LOG_DEBUG, "failed "
355 "to add %s to ssh agent", psk->comment);
356 /* we won't need the key again, so wipe it */
357 pam_set_data(pamh, *kfn, NULL, NULL);
358 }
359 }
360 pam_err = PAM_SUCCESS;
361
362 /* disconnect from agent */
363 ssh_close_authentication_socket(fd);
364
365 end:
366 /* switch back to original environment */
367 for (env = environ; *env != NULL; ++env)
368 free(*env);
369 free(environ);
370 environ = envlist;
371
372 return (pam_err);
373 }
374
375 PAM_EXTERN int
pam_sm_open_session(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)376 pam_sm_open_session(pam_handle_t *pamh, int flags __unused,
377 int argc __unused, const char *argv[] __unused)
378 {
379 struct passwd *pwd;
380 const char *user;
381 const void *data;
382 int pam_err;
383
384 /* no keys, no work */
385 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS &&
386 openpam_get_option(pamh, "want_agent") == NULL)
387 return (PAM_SUCCESS);
388
389 /* switch to user credentials */
390 pam_err = pam_get_user(pamh, &user, NULL);
391 if (pam_err != PAM_SUCCESS)
392 return (pam_err);
393 pwd = getpwnam(user);
394 if (pwd == NULL)
395 return (PAM_USER_UNKNOWN);
396 pam_err = openpam_borrow_cred(pamh, pwd);
397 if (pam_err != PAM_SUCCESS)
398 return (pam_err);
399
400 /* start the agent */
401 pam_err = pam_ssh_start_agent(pamh);
402 if (pam_err != PAM_SUCCESS) {
403 openpam_restore_cred(pamh);
404 return (pam_err);
405 }
406
407 /* we have an agent, see if we can add any keys to it */
408 pam_err = pam_ssh_add_keys_to_agent(pamh);
409 if (pam_err != PAM_SUCCESS) {
410 /* XXX ignore failures */
411 }
412
413 openpam_restore_cred(pamh);
414 return (PAM_SUCCESS);
415 }
416
417 PAM_EXTERN int
pam_sm_close_session(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)418 pam_sm_close_session(pam_handle_t *pamh, int flags __unused,
419 int argc __unused, const char *argv[] __unused)
420 {
421 const char *ssh_agent_pid;
422 char *end;
423 int status;
424 pid_t pid;
425
426 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) {
427 openpam_log(PAM_LOG_DEBUG, "no ssh agent");
428 return (PAM_SUCCESS);
429 }
430 pid = (pid_t)strtol(ssh_agent_pid, &end, 10);
431 if (*ssh_agent_pid == '\0' || *end != '\0') {
432 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid");
433 return (PAM_SESSION_ERR);
434 }
435 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid);
436 if (kill(pid, SIGTERM) == -1 ||
437 (waitpid(pid, &status, 0) == -1 && errno != ECHILD))
438 return (PAM_SYSTEM_ERR);
439 return (PAM_SUCCESS);
440 }
441
442 PAM_MODULE_ENTRY("pam_ssh");
443