1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2002 Jacques A. Vidrine <nectar@FreeBSD.org>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29 #include <sys/param.h>
30 #include <errno.h>
31 #include <stdio.h>
32 #include <stdlib.h>
33 #include <string.h>
34 #include <unistd.h>
35
36 #include <krb5.h>
37
38 #define PAM_SM_AUTH
39 #define PAM_SM_CRED
40 #include <security/pam_appl.h>
41 #include <security/pam_modules.h>
42 #include <security/pam_mod_misc.h>
43
44 static const char superuser[] = "root";
45
46 static long get_su_principal(krb5_context, const char *, const char *,
47 char **, krb5_principal *);
48 static int auth_krb5(pam_handle_t *, krb5_context, const char *,
49 krb5_principal);
50
51 PAM_EXTERN int
pam_sm_authenticate(pam_handle_t * pamh,int flags __unused,int argc __unused,const char * argv[]__unused)52 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
53 int argc __unused, const char *argv[] __unused)
54 {
55 krb5_context context;
56 krb5_principal su_principal;
57 const char *user;
58 const void *ruser;
59 char *su_principal_name;
60 long rv;
61 int pamret;
62
63 pamret = pam_get_user(pamh, &user, NULL);
64 if (pamret != PAM_SUCCESS)
65 return (pamret);
66 PAM_LOG("Got user: %s", user);
67 pamret = pam_get_item(pamh, PAM_RUSER, &ruser);
68 if (pamret != PAM_SUCCESS)
69 return (pamret);
70 PAM_LOG("Got ruser: %s", (const char *)ruser);
71 rv = krb5_init_context(&context);
72 if (rv != 0) {
73 const char *msg = krb5_get_error_message(context, rv);
74 PAM_LOG("krb5_init_context failed: %s", msg);
75 krb5_free_error_message(context, msg);
76 return (PAM_SERVICE_ERR);
77 }
78 rv = get_su_principal(context, user, ruser, &su_principal_name, &su_principal);
79 if (rv != 0)
80 return (PAM_AUTH_ERR);
81 PAM_LOG("kuserok: %s -> %s", su_principal_name, user);
82 rv = krb5_kuserok(context, su_principal, user);
83 pamret = rv ? auth_krb5(pamh, context, su_principal_name, su_principal) : PAM_AUTH_ERR;
84 free(su_principal_name);
85 krb5_free_principal(context, su_principal);
86 krb5_free_context(context);
87 return (pamret);
88 }
89
90 PAM_EXTERN int
pam_sm_setcred(pam_handle_t * pamh __unused,int flags __unused,int ac __unused,const char * av[]__unused)91 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
92 int ac __unused, const char *av[] __unused)
93 {
94
95 return (PAM_SUCCESS);
96 }
97
98 /* Authenticate using Kerberos 5.
99 * pamh -- The PAM handle.
100 * context -- An initialized krb5_context.
101 * su_principal_name -- The target principal name, used only for password prompts.
102 * If NULL, the password prompts will not include a principal
103 * name.
104 * su_principal -- The target krb5_principal.
105 * Note that a valid keytab in the default location with a host entry
106 * must be available, and that the PAM application must have sufficient
107 * privileges to access it.
108 * Returns PAM_SUCCESS if authentication was successful, or an appropriate
109 * PAM error code if it was not.
110 */
111 static int
auth_krb5(pam_handle_t * pamh,krb5_context context,const char * su_principal_name,krb5_principal su_principal)112 auth_krb5(pam_handle_t *pamh, krb5_context context, const char *su_principal_name,
113 krb5_principal su_principal)
114 {
115 krb5_creds creds;
116 krb5_get_init_creds_opt *gic_opt;
117 krb5_verify_init_creds_opt vic_opt;
118 const char *pass;
119 char *prompt;
120 long rv;
121 int pamret;
122
123 prompt = NULL;
124 krb5_verify_init_creds_opt_init(&vic_opt);
125 if (su_principal_name != NULL)
126 (void)asprintf(&prompt, "Password for %s:", su_principal_name);
127 else
128 (void)asprintf(&prompt, "Password:");
129 if (prompt == NULL)
130 return (PAM_BUF_ERR);
131 pass = NULL;
132 pamret = pam_get_authtok(pamh, PAM_AUTHTOK, &pass, prompt);
133 free(prompt);
134 if (pamret != PAM_SUCCESS)
135 return (pamret);
136 rv = krb5_get_init_creds_opt_alloc(context, &gic_opt);
137 if (rv != 0) {
138 const char *msg = krb5_get_error_message(context, rv);
139 PAM_LOG("krb5_get_init_creds_opt_alloc: %s", msg);
140 krb5_free_error_message(context, msg);
141 return (PAM_AUTH_ERR);
142 }
143 rv = krb5_get_init_creds_password(context, &creds, su_principal,
144 pass, NULL, NULL, 0, NULL, gic_opt);
145 krb5_get_init_creds_opt_free(context, gic_opt);
146 if (rv != 0) {
147 const char *msg = krb5_get_error_message(context, rv);
148 PAM_LOG("krb5_get_init_creds_password: %s", msg);
149 krb5_free_error_message(context, msg);
150 return (PAM_AUTH_ERR);
151 }
152 krb5_verify_init_creds_opt_set_ap_req_nofail(&vic_opt, 1);
153 rv = krb5_verify_init_creds(context, &creds, NULL, NULL, NULL,
154 &vic_opt);
155 krb5_free_cred_contents(context, &creds);
156 if (rv != 0) {
157 const char *msg = krb5_get_error_message(context, rv);
158 PAM_LOG("krb5_verify_init_creds: %s", msg);
159 krb5_free_error_message(context, msg);
160 return (PAM_AUTH_ERR);
161 }
162 return (PAM_SUCCESS);
163 }
164
165 /* Determine the target principal given the current user and the target user.
166 * context -- An initialized krb5_context.
167 * target_user -- The target username.
168 * current_user -- The current username.
169 * su_principal_name -- (out) The target principal name.
170 * su_principal -- (out) The target krb5_principal.
171 * When the target user is `root', the target principal will be a `root
172 * instance', e.g. `luser/root@REA.LM'. Otherwise, the target principal
173 * will simply be the current user's default principal name. Note that
174 * in any case, if KRB5CCNAME is set and a credentials cache exists, the
175 * principal name found there will be the `starting point', rather than
176 * the ruser parameter.
177 *
178 * Returns 0 for success, or a com_err error code on failure.
179 */
180 static long
get_su_principal(krb5_context context,const char * target_user,const char * current_user,char ** su_principal_name,krb5_principal * su_principal)181 get_su_principal(krb5_context context, const char *target_user, const char *current_user,
182 char **su_principal_name, krb5_principal *su_principal)
183 {
184 krb5_principal default_principal;
185 krb5_ccache ccache;
186 char *principal_name, *ccname, *p;
187 long rv;
188 uid_t euid, ruid;
189
190 *su_principal = NULL;
191 default_principal = NULL;
192 /* Unless KRB5CCNAME was explicitly set, we won't really be able
193 * to look at the credentials cache since krb5_cc_default will
194 * look at getuid().
195 */
196 ruid = getuid();
197 euid = geteuid();
198 rv = seteuid(ruid);
199 if (rv != 0)
200 return (errno);
201 p = getenv("KRB5CCNAME");
202 if (p != NULL)
203 ccname = strdup(p);
204 else
205 (void)asprintf(&ccname, "%s%lu", KRB5_DEFAULT_CCROOT, (unsigned long)ruid);
206 if (ccname == NULL)
207 return (errno);
208 rv = krb5_cc_resolve(context, ccname, &ccache);
209 free(ccname);
210 if (rv == 0) {
211 rv = krb5_cc_get_principal(context, ccache, &default_principal);
212 krb5_cc_close(context, ccache);
213 if (rv != 0)
214 default_principal = NULL; /* just to be safe */
215 }
216 rv = seteuid(euid);
217 if (rv != 0)
218 return (errno);
219 if (default_principal == NULL) {
220 rv = krb5_make_principal(context, &default_principal, NULL, current_user, NULL);
221 if (rv != 0) {
222 PAM_LOG("Could not determine default principal name.");
223 return (rv);
224 }
225 }
226 /* Now that we have some principal, if the target account is
227 * `root', then transform it into a `root' instance, e.g.
228 * `user@REA.LM' -> `user/root@REA.LM'.
229 */
230 rv = krb5_unparse_name(context, default_principal, &principal_name);
231 krb5_free_principal(context, default_principal);
232 if (rv != 0) {
233 const char *msg = krb5_get_error_message(context, rv);
234 PAM_LOG("krb5_unparse_name: %s", msg);
235 krb5_free_error_message(context, msg);
236 return (rv);
237 }
238 PAM_LOG("Default principal name: %s", principal_name);
239 if (strcmp(target_user, superuser) == 0) {
240 p = strrchr(principal_name, '@');
241 if (p == NULL) {
242 PAM_LOG("malformed principal name `%s'", principal_name);
243 free(principal_name);
244 return (rv);
245 }
246 *p++ = '\0';
247 *su_principal_name = NULL;
248 (void)asprintf(su_principal_name, "%s/%s@%s", principal_name, superuser, p);
249 free(principal_name);
250 } else
251 *su_principal_name = principal_name;
252
253 if (*su_principal_name == NULL)
254 return (errno);
255 rv = krb5_parse_name(context, *su_principal_name, &default_principal);
256 if (rv != 0) {
257 const char *msg = krb5_get_error_message(context, rv);
258 PAM_LOG("krb5_parse_name `%s': %s", *su_principal_name, msg);
259 krb5_free_error_message(context, msg);
260 free(*su_principal_name);
261 return (rv);
262 }
263 PAM_LOG("Target principal name: %s", *su_principal_name);
264 *su_principal = default_principal;
265 return (0);
266 }
267
268 PAM_MODULE_ENTRY("pam_ksu");
269