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/cdefs.h>
39 __FBSDID("$FreeBSD$");
40
41 #include <sys/param.h>
42 #include <sys/wait.h>
43
44 #include <errno.h>
45 #include <fcntl.h>
46 #include <paths.h>
47 #include <pwd.h>
48 #include <signal.h>
49 #include <stdio.h>
50 #include <string.h>
51 #include <unistd.h>
52
53 #define PAM_SM_AUTH
54 #define PAM_SM_SESSION
55
56 #include <security/pam_appl.h>
57 #include <security/pam_modules.h>
58 #include <security/openpam.h>
59
60 #include <openssl/evp.h>
61
62 #define __bounded__(x, y, z)
63 #include "authfd.h"
64 #include "authfile.h"
65 #include "sshkey.h"
66
67 #define ssh_add_identity(auth, key, comment) \
68 ssh_add_identity_constrained(auth, key, comment, 0, 0, 0, NULL)
69
70 extern char **environ;
71
72 struct pam_ssh_key {
73 struct sshkey *key;
74 char *comment;
75 };
76
77 static const char *pam_ssh_prompt = "SSH passphrase: ";
78 static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
79
80 static const char *pam_ssh_keyfiles[] = {
81 ".ssh/id_rsa", /* SSH2 RSA key */
82 ".ssh/id_dsa", /* SSH2 DSA key */
83 ".ssh/id_ecdsa", /* SSH2 ECDSA key */
84 ".ssh/id_ed25519", /* SSH2 Ed25519 key */
85 NULL
86 };
87
88 static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
89 static char str_ssh_agent[] = "ssh-agent";
90 static char str_dash_s[] = "-s";
91 static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL };
92 static char *const pam_ssh_agent_envp[] = { NULL };
93
94 /*
95 * Attempts to load a private key from the specified file in the specified
96 * directory, using the specified passphrase. If successful, returns a
97 * struct pam_ssh_key containing the key and its comment.
98 */
99 static struct pam_ssh_key *
pam_ssh_load_key(const char * dir,const char * kfn,const char * passphrase,int nullok)100 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase,
101 int nullok)
102 {
103 char fn[PATH_MAX];
104 struct pam_ssh_key *psk;
105 struct sshkey *key;
106 char *comment;
107 int ret;
108
109 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
110 return (NULL);
111 /*
112 * If the key is unencrypted, OpenSSL ignores the passphrase, so
113 * it will seem like the user typed in the right one. This allows
114 * a user to circumvent nullok by providing a dummy passphrase.
115 * Verify that the key really *is* encrypted by trying to load it
116 * with an empty passphrase, and if the key is not encrypted,
117 * accept only an empty passphrase.
118 */
119 ret = sshkey_load_private(fn, "", &key, &comment);
120 if (ret == 0 && !(*passphrase == '\0' && nullok)) {
121 sshkey_free(key);
122 return (NULL);
123 }
124 if (ret != 0)
125 ret = sshkey_load_private(fn, passphrase, &key, &comment);
126 if (ret != 0) {
127 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn);
128 return (NULL);
129 }
130
131 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn);
132 if ((psk = malloc(sizeof(*psk))) == NULL) {
133 sshkey_free(key);
134 free(comment);
135 return (NULL);
136 }
137 psk->key = key;
138 psk->comment = comment;
139 return (psk);
140 }
141
142 /*
143 * Wipes a private key and frees the associated resources.
144 */
145 static void
pam_ssh_free_key(pam_handle_t * pamh __unused,void * data,int pam_err __unused)146 pam_ssh_free_key(pam_handle_t *pamh __unused,
147 void *data, int pam_err __unused)
148 {
149 struct pam_ssh_key *psk;
150
151 psk = data;
152 sshkey_free(psk->key);
153 free(psk->comment);
154 free(psk);
155 }
156
157 PAM_EXTERN int
pam_sm_authenticate(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)158 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
159 int argc __unused, const char *argv[] __unused)
160 {
161 const char **kfn, *passphrase, *user;
162 const void *item;
163 struct passwd *pwd;
164 struct pam_ssh_key *psk;
165 int nkeys, nullok, pam_err, pass;
166
167 nullok = (openpam_get_option(pamh, "nullok") != NULL);
168
169 /* PEM is not loaded by default */
170 OpenSSL_add_all_algorithms();
171
172 /* get user name and home directory */
173 pam_err = pam_get_user(pamh, &user, NULL);
174 if (pam_err != PAM_SUCCESS)
175 return (pam_err);
176 pwd = getpwnam(user);
177 if (pwd == NULL)
178 return (PAM_USER_UNKNOWN);
179 if (pwd->pw_dir == NULL)
180 return (PAM_AUTH_ERR);
181
182 nkeys = 0;
183 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS &&
184 item != NULL);
185 load_keys:
186 /* get passphrase */
187 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
188 &passphrase, pam_ssh_prompt);
189 if (pam_err != PAM_SUCCESS)
190 return (pam_err);
191
192 /* switch to user credentials */
193 pam_err = openpam_borrow_cred(pamh, pwd);
194 if (pam_err != PAM_SUCCESS)
195 return (pam_err);
196
197 /* try to load keys from all keyfiles we know of */
198 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
199 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok);
200 if (psk != NULL) {
201 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
202 ++nkeys;
203 }
204 }
205
206 /* switch back to arbitrator credentials */
207 openpam_restore_cred(pamh);
208
209 /*
210 * If we tried an old token and didn't get anything, and
211 * try_first_pass was specified, try again after prompting the
212 * user for a new passphrase.
213 */
214 if (nkeys == 0 && pass == 1 &&
215 openpam_get_option(pamh, "try_first_pass") != NULL) {
216 pam_set_item(pamh, PAM_AUTHTOK, NULL);
217 pass = 0;
218 goto load_keys;
219 }
220
221 /* no keys? */
222 if (nkeys == 0)
223 return (PAM_AUTH_ERR);
224
225 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
226 return (PAM_SUCCESS);
227 }
228
229 PAM_EXTERN int
pam_sm_setcred(pam_handle_t * pamh __unused,int flags __unused,int argc __unused,const char * argv[]__unused)230 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
231 int argc __unused, const char *argv[] __unused)
232 {
233
234 return (PAM_SUCCESS);
235 }
236
237 /*
238 * Parses a line from ssh-agent's output.
239 */
240 static void
pam_ssh_process_agent_output(pam_handle_t * pamh,FILE * f)241 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
242 {
243 char *line, *p, *key, *val;
244 size_t len;
245
246 while ((line = fgetln(f, &len)) != NULL) {
247 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
248 continue;
249
250 /* find equal sign at end of key */
251 for (p = key = line; p < line + len; ++p)
252 if (*p == '=')
253 break;
254 if (p == line + len || *p != '=')
255 continue;
256 *p = '\0';
257
258 /* find semicolon at end of value */
259 for (val = ++p; p < line + len; ++p)
260 if (*p == ';')
261 break;
262 if (p == line + len || *p != ';')
263 continue;
264 *p = '\0';
265
266 /* store key-value pair in environment */
267 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
268 pam_setenv(pamh, key, val, 1);
269 }
270 }
271
272 /*
273 * Starts an ssh agent and stores the environment variables derived from
274 * its output.
275 */
276 static int
pam_ssh_start_agent(pam_handle_t * pamh)277 pam_ssh_start_agent(pam_handle_t *pamh)
278 {
279 int agent_pipe[2];
280 pid_t pid;
281 FILE *f;
282
283 /* get a pipe which we will use to read the agent's output */
284 if (pipe(agent_pipe) == -1)
285 return (PAM_SYSTEM_ERR);
286
287 /* start the agent */
288 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
289 pid = fork();
290 if (pid == (pid_t)-1) {
291 /* failed */
292 close(agent_pipe[0]);
293 close(agent_pipe[1]);
294 return (PAM_SYSTEM_ERR);
295 }
296 if (pid == 0) {
297 int fd;
298
299 /* child: drop privs, close fds and start agent */
300 setgid(getegid());
301 setuid(geteuid());
302 close(STDIN_FILENO);
303 open(_PATH_DEVNULL, O_RDONLY);
304 dup2(agent_pipe[1], STDOUT_FILENO);
305 dup2(agent_pipe[1], STDERR_FILENO);
306 for (fd = 3; fd < getdtablesize(); ++fd)
307 close(fd);
308 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp);
309 _exit(127);
310 }
311
312 /* parent */
313 close(agent_pipe[1]);
314 if ((f = fdopen(agent_pipe[0], "r")) == NULL)
315 return (PAM_SYSTEM_ERR);
316 pam_ssh_process_agent_output(pamh, f);
317 fclose(f);
318
319 return (PAM_SUCCESS);
320 }
321
322 /*
323 * Adds previously stored keys to a running agent.
324 */
325 static int
pam_ssh_add_keys_to_agent(pam_handle_t * pamh)326 pam_ssh_add_keys_to_agent(pam_handle_t *pamh)
327 {
328 const struct pam_ssh_key *psk;
329 const char **kfn;
330 const void *item;
331 char **envlist, **env;
332 int fd, pam_err;
333
334 /* switch to PAM environment */
335 envlist = environ;
336 if ((environ = pam_getenvlist(pamh)) == NULL) {
337 environ = envlist;
338 return (PAM_SYSTEM_ERR);
339 }
340
341 /* get a connection to the agent */
342 if (ssh_get_authentication_socket(&fd) != 0) {
343 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent");
344 pam_err = PAM_SYSTEM_ERR;
345 goto end;
346 }
347
348 /* look for keys to add to it */
349 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
350 pam_err = pam_get_data(pamh, *kfn, &item);
351 if (pam_err == PAM_SUCCESS && item != NULL) {
352 psk = item;
353 if (ssh_add_identity(fd, psk->key, psk->comment) == 0)
354 openpam_log(PAM_LOG_DEBUG,
355 "added %s to ssh agent", psk->comment);
356 else
357 openpam_log(PAM_LOG_DEBUG, "failed "
358 "to add %s to ssh agent", psk->comment);
359 /* we won't need the key again, so wipe it */
360 pam_set_data(pamh, *kfn, NULL, NULL);
361 }
362 }
363 pam_err = PAM_SUCCESS;
364
365 /* disconnect from agent */
366 ssh_close_authentication_socket(fd);
367
368 end:
369 /* switch back to original environment */
370 for (env = environ; *env != NULL; ++env)
371 free(*env);
372 free(environ);
373 environ = envlist;
374
375 return (pam_err);
376 }
377
378 PAM_EXTERN int
pam_sm_open_session(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)379 pam_sm_open_session(pam_handle_t *pamh, int flags __unused,
380 int argc __unused, const char *argv[] __unused)
381 {
382 struct passwd *pwd;
383 const char *user;
384 const void *data;
385 int pam_err;
386
387 /* no keys, no work */
388 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS &&
389 openpam_get_option(pamh, "want_agent") == NULL)
390 return (PAM_SUCCESS);
391
392 /* switch to user credentials */
393 pam_err = pam_get_user(pamh, &user, NULL);
394 if (pam_err != PAM_SUCCESS)
395 return (pam_err);
396 pwd = getpwnam(user);
397 if (pwd == NULL)
398 return (PAM_USER_UNKNOWN);
399 pam_err = openpam_borrow_cred(pamh, pwd);
400 if (pam_err != PAM_SUCCESS)
401 return (pam_err);
402
403 /* start the agent */
404 pam_err = pam_ssh_start_agent(pamh);
405 if (pam_err != PAM_SUCCESS) {
406 openpam_restore_cred(pamh);
407 return (pam_err);
408 }
409
410 /* we have an agent, see if we can add any keys to it */
411 pam_err = pam_ssh_add_keys_to_agent(pamh);
412 if (pam_err != PAM_SUCCESS) {
413 /* XXX ignore failures */
414 }
415
416 openpam_restore_cred(pamh);
417 return (PAM_SUCCESS);
418 }
419
420 PAM_EXTERN int
pam_sm_close_session(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)421 pam_sm_close_session(pam_handle_t *pamh, int flags __unused,
422 int argc __unused, const char *argv[] __unused)
423 {
424 const char *ssh_agent_pid;
425 char *end;
426 int status;
427 pid_t pid;
428
429 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) {
430 openpam_log(PAM_LOG_DEBUG, "no ssh agent");
431 return (PAM_SUCCESS);
432 }
433 pid = (pid_t)strtol(ssh_agent_pid, &end, 10);
434 if (*ssh_agent_pid == '\0' || *end != '\0') {
435 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid");
436 return (PAM_SESSION_ERR);
437 }
438 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid);
439 if (kill(pid, SIGTERM) == -1 ||
440 (waitpid(pid, &status, 0) == -1 && errno != ECHILD))
441 return (PAM_SYSTEM_ERR);
442 return (PAM_SUCCESS);
443 }
444
445 PAM_MODULE_ENTRY("pam_ssh");
446