1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 2003 Networks Associates Technology, Inc.
5 * Copyright (c) 2004-2011 Dag-Erling Sm��rgrav
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)
69
70extern char **environ;
71
72struct pam_ssh_key {
73	struct sshkey	*key;
74	char		*comment;
75};
76
77static const char *pam_ssh_prompt = "SSH passphrase: ";
78static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
79
80static 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
88static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
89static char str_ssh_agent[] = "ssh-agent";
90static char str_dash_s[] = "-s";
91static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL };
92static 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 */
99static struct pam_ssh_key *
100pam_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 */
145static void
146pam_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
157PAM_EXTERN int
158pam_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
229PAM_EXTERN int
230pam_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 */
240static void
241pam_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 */
276static int
277pam_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 */
325static int
326pam_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
378PAM_EXTERN int
379pam_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
420PAM_EXTERN int
421pam_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
445PAM_MODULE_ENTRY("pam_ssh");
446