1/*-
2 * Copyright (c) 2003 Networks Associates Technology, Inc.
3 * All rights reserved.
4 *
5 * This software was developed for the FreeBSD Project by ThinkSec AS and
6 * NAI Labs, the Security Research Division of Network Associates, Inc.
7 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
8 * DARPA CHATS research program.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. The name of the author may not be used to endorse or promote
19 * products derived from this software without specific prior written
20 * permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#include <sys/cdefs.h>
36__FBSDID("$FreeBSD: head/lib/libpam/modules/pam_ssh/pam_ssh.c 174837 2007-12-21 12:00:16Z des $");
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#include "key.h"
60#include "buffer.h"
61#include "authfd.h"
62#include "authfile.h"
63
64extern char **environ;
65
66struct pam_ssh_key {
67 Key *key;
68 char *comment;
69};
70
71static const char *pam_ssh_prompt = "SSH passphrase: ";
72static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
73
74static const char *pam_ssh_keyfiles[] = {
75 ".ssh/identity", /* SSH1 RSA key */
76 ".ssh/id_rsa", /* SSH2 RSA key */
77 ".ssh/id_dsa", /* SSH2 DSA key */
78 NULL
79};
80
81static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
82static char *const pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL };
83static char *const pam_ssh_agent_envp[] = { NULL };
84
85/*
86 * Attempts to load a private key from the specified file in the specified
87 * directory, using the specified passphrase. If successful, returns a
88 * struct pam_ssh_key containing the key and its comment.
89 */
90static struct pam_ssh_key *
91pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase)
92{
93 struct pam_ssh_key *psk;
94 char fn[PATH_MAX];
95 char *comment;
96 Key *key;
97
98 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
99 return (NULL);
100 comment = NULL;
101 key = key_load_private(fn, passphrase, &comment);
102 if (key == NULL) {
103 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn);
104 return (NULL);
105 }
106
107 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn);
108 if ((psk = malloc(sizeof(*psk))) == NULL) {
109 key_free(key);
110 free(comment);
111 return (NULL);
112 }
113 psk->key = key;
114 psk->comment = comment;
115 return (psk);
116}
117
118/*
119 * Wipes a private key and frees the associated resources.
120 */
121static void
122pam_ssh_free_key(pam_handle_t *pamh __unused,
123 void *data, int pam_err __unused)
124{
125 struct pam_ssh_key *psk;
126
127 psk = data;
128 key_free(psk->key);
129 free(psk->comment);
130 free(psk);
131}
132
133PAM_EXTERN int
134pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
135 int argc __unused, const char *argv[] __unused)
136{
137 const char **kfn, *passphrase, *user;
138 const void *item;
139 struct passwd *pwd;
140 struct pam_ssh_key *psk;
141 int nkeys, nullok, pam_err, pass;
142
143 nullok = (openpam_get_option(pamh, "nullok") != NULL);
144
145 /* PEM is not loaded by default */
146 OpenSSL_add_all_algorithms();
147
148 /* get user name and home directory */
149 pam_err = pam_get_user(pamh, &user, NULL);
150 if (pam_err != PAM_SUCCESS)
151 return (pam_err);
152 pwd = getpwnam(user);
153 if (pwd == NULL)
154 return (PAM_USER_UNKNOWN);
155 if (pwd->pw_dir == NULL)
156 return (PAM_AUTH_ERR);
157
158 nkeys = 0;
159 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS &&
160 item != NULL);
161 load_keys:
162 /* get passphrase */
163 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
164 &passphrase, pam_ssh_prompt);
165 if (pam_err != PAM_SUCCESS)
166 return (pam_err);
167
168 if (*passphrase == '\0' && !nullok)
169 goto skip_keys;
170
171 /* switch to user credentials */
172 pam_err = openpam_borrow_cred(pamh, pwd);
173 if (pam_err != PAM_SUCCESS)
174 return (pam_err);
175
176 /* try to load keys from all keyfiles we know of */
177 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
178 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase);
179 if (psk != NULL) {
180 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
181 ++nkeys;
182 }
183 }
184
185 /* switch back to arbitrator credentials */
186 openpam_restore_cred(pamh);
187
188 skip_keys:
189 /*
190 * If we tried an old token and didn't get anything, and
191 * try_first_pass was specified, try again after prompting the
192 * user for a new passphrase.
193 */
194 if (nkeys == 0 && pass == 1 &&
195 openpam_get_option(pamh, "try_first_pass") != NULL) {
196 pam_set_item(pamh, PAM_AUTHTOK, NULL);
197 pass = 0;
198 goto load_keys;
199 }
200
201 /* no keys? */
202 if (nkeys == 0)
203 return (PAM_AUTH_ERR);
204
205 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
206 return (PAM_SUCCESS);
207}
208
209PAM_EXTERN int
210pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
211 int argc __unused, const char *argv[] __unused)
212{
213
214 return (PAM_SUCCESS);
215}
216
217/*
218 * Parses a line from ssh-agent's output.
219 */
220static void
221pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
222{
223 char *line, *p, *key, *val;
224 size_t len;
225
226 while ((line = fgetln(f, &len)) != NULL) {
227 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
228 continue;
229
230 /* find equal sign at end of key */
231 for (p = key = line; p < line + len; ++p)
232 if (*p == '=')
233 break;
234 if (p == line + len || *p != '=')
235 continue;
236 *p = '\0';
237
238 /* find semicolon at end of value */
239 for (val = ++p; p < line + len; ++p)
240 if (*p == ';')
241 break;
242 if (p == line + len || *p != ';')
243 continue;
244 *p = '\0';
245
246 /* store key-value pair in environment */
247 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
248 pam_setenv(pamh, key, val, 1);
249 }
250}
251
252/*
253 * Starts an ssh agent and stores the environment variables derived from
254 * its output.
255 */
256static int
257pam_ssh_start_agent(pam_handle_t *pamh)
258{
259 int agent_pipe[2];
260 pid_t pid;
261 FILE *f;
262
263 /* get a pipe which we will use to read the agent's output */
264 if (pipe(agent_pipe) == -1)
265 return (PAM_SYSTEM_ERR);
266
267 /* start the agent */
268 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
269 pid = fork();
270 if (pid == (pid_t)-1) {
271 /* failed */
272 close(agent_pipe[0]);
273 close(agent_pipe[1]);
274 return (PAM_SYSTEM_ERR);
275 }
276 if (pid == 0) {
277 int fd;
278
279 /* child: drop privs, close fds and start agent */
280 setgid(getegid());
281 setuid(geteuid());
282 close(STDIN_FILENO);
283 open(_PATH_DEVNULL, O_RDONLY);
284 dup2(agent_pipe[1], STDOUT_FILENO);
285 dup2(agent_pipe[1], STDERR_FILENO);
286 for (fd = 3; fd < getdtablesize(); ++fd)
287 close(fd);
288 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp);
289 _exit(127);
290 }
291
292 /* parent */
293 close(agent_pipe[1]);
294 if ((f = fdopen(agent_pipe[0], "r")) == NULL)
295 return (PAM_SYSTEM_ERR);
296 pam_ssh_process_agent_output(pamh, f);
297 fclose(f);
298
299 return (PAM_SUCCESS);
300}
301
302/*
303 * Adds previously stored keys to a running agent.
304 */
305static int
306pam_ssh_add_keys_to_agent(pam_handle_t *pamh)
307{
308 AuthenticationConnection *ac;
309 const struct pam_ssh_key *psk;
310 const char **kfn;
311 const void *item;
312 char **envlist, **env;
313 int pam_err;
314
315 /* switch to PAM environment */
316 envlist = environ;
317 if ((environ = pam_getenvlist(pamh)) == NULL) {
318 environ = envlist;
319 return (PAM_SYSTEM_ERR);
320 }
321
322 /* get a connection to the agent */
323 if ((ac = ssh_get_authentication_connection()) == NULL) {
324 pam_err = PAM_SYSTEM_ERR;
325 goto end;
326 }
327
328 /* look for keys to add to it */
329 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
330 pam_err = pam_get_data(pamh, *kfn, &item);
331 if (pam_err == PAM_SUCCESS && item != NULL) {
332 psk = item;
333 if (ssh_add_identity(ac, psk->key, psk->comment))
334 openpam_log(PAM_LOG_DEBUG,
335 "added %s to ssh agent", psk->comment);
336 else
337 openpam_log(PAM_LOG_DEBUG, "failed "
338 "to add %s to ssh agent", psk->comment);
339 /* we won't need the key again, so wipe it */
340 pam_set_data(pamh, *kfn, NULL, NULL);
341 }
342 }
343 pam_err = PAM_SUCCESS;
344 end:
345 /* disconnect from agent */
346 if (ac != NULL)
347 ssh_close_authentication_connection(ac);
348
349 /* switch back to original environment */
350 for (env = environ; *env != NULL; ++env)
351 free(*env);
352 free(environ);
353 environ = envlist;
354
355 return (pam_err);
356}
357
358PAM_EXTERN int
359pam_sm_open_session(pam_handle_t *pamh, int flags __unused,
360 int argc __unused, const char *argv[] __unused)
361{
362 struct passwd *pwd;
363 const char *user;
364 const void *data;
365 int pam_err;
366
367 /* no keys, no work */
368 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS &&
369 openpam_get_option(pamh, "want_agent") == NULL)
370 return (PAM_SUCCESS);
371
372 /* switch to user credentials */
373 pam_err = pam_get_user(pamh, &user, NULL);
374 if (pam_err != PAM_SUCCESS)
375 return (pam_err);
376 pwd = getpwnam(user);
377 if (pwd == NULL)
378 return (PAM_USER_UNKNOWN);
379 pam_err = openpam_borrow_cred(pamh, pwd);
380 if (pam_err != PAM_SUCCESS)
381 return (pam_err);
382
383 /* start the agent */
384 pam_err = pam_ssh_start_agent(pamh);
385 if (pam_err != PAM_SUCCESS) {
386 openpam_restore_cred(pamh);
387 return (pam_err);
388 }
389
390 /* we have an agent, see if we can add any keys to it */
391 pam_err = pam_ssh_add_keys_to_agent(pamh);
392 if (pam_err != PAM_SUCCESS) {
393 /* XXX ignore failures */
394 }
395
396 openpam_restore_cred(pamh);
397 return (PAM_SUCCESS);
398}
399
400PAM_EXTERN int
401pam_sm_close_session(pam_handle_t *pamh, int flags __unused,
402 int argc __unused, const char *argv[] __unused)
403{
404 const char *ssh_agent_pid;
405 char *end;
406 int status;
407 pid_t pid;
408
409 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) {
410 openpam_log(PAM_LOG_DEBUG, "no ssh agent");
411 return (PAM_SUCCESS);
412 }
413 pid = (pid_t)strtol(ssh_agent_pid, &end, 10);
414 if (*ssh_agent_pid == '\0' || *end != '\0') {
415 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid");
416 return (PAM_SESSION_ERR);
417 }
418 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid);
419 if (kill(pid, SIGTERM) == -1 ||
420 (waitpid(pid, &status, 0) == -1 && errno != ECHILD))
421 return (PAM_SYSTEM_ERR);
422 return (PAM_SUCCESS);
423}
424
425PAM_MODULE_ENTRY("pam_ssh");