lib/pam_module/pam_ksu/pam_ksu.c

   1 /*-
   2  * Copyright (c) 2002 Jacques A. Vidrine <nectar@FreeBSD.org>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  *
  26  * $FreeBSD: src/lib/libpam/modules/pam_ksu/pam_ksu.c,v 1.5 2004/02/10 10:13:21 des Exp $
  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
  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                 PAM_LOG("krb5_init_context failed: %s",
  74                         krb5_get_err_text(context, rv));
  75                 return (PAM_SERVICE_ERR);
  76         }
  77         rv = get_su_principal(context, user, ruser, &su_principal_name, &su_principal);
  78         if (rv != 0)
  79                 return (PAM_AUTH_ERR);
  80         PAM_LOG("kuserok: %s -> %s", su_principal_name, user);
  81         rv = krb5_kuserok(context, su_principal, user);
  82         pamret = rv ? auth_krb5(pamh, context, su_principal_name, su_principal) : PAM_AUTH_ERR;
  83         free(su_principal_name);
  84         krb5_free_principal(context, su_principal);
  85         krb5_free_context(context);
  86         return (pamret);
  87 }
  88
  89 PAM_EXTERN int
  90 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
  91                int ac __unused, const char *av[] __unused)
  92 {
  93
  94         return (PAM_SUCCESS);
  95 }
  96
  97 /* Authenticate using Kerberos 5.
  98  *   pamh              -- The PAM handle.
  99  *   context           -- An initialized krb5_context.
 100  *   su_principal_name -- The target principal name, used only for password prompts.
 101  *              If NULL, the password prompts will not include a principal
 102  *              name.
 103  *   su_principal      -- The target krb5_principal.
 104  * Note that a valid keytab in the default location with a host entry
 105  * must be available, and that the PAM application must have sufficient
 106  * privileges to access it.
 107  * Returns PAM_SUCCESS if authentication was successful, or an appropriate
 108  * PAM error code if it was not.
 109  */
 110 static int
 111 auth_krb5(pam_handle_t *pamh, krb5_context context, const char *su_principal_name,
 112           krb5_principal su_principal)
 113 {
 114         krb5_creds       creds;
 115         krb5_get_init_creds_opt gic_opt;
 116         krb5_verify_init_creds_opt vic_opt;
 117         const char      *pass;
 118         char            *prompt;
 119         long             rv;
 120         int              pamret;
 121
 122         prompt = NULL;
 123         krb5_get_init_creds_opt_init(&gic_opt);
 124         krb5_verify_init_creds_opt_init(&vic_opt);
 125         if (su_principal_name != NULL)
 126                 asprintf(&prompt, "Password for %s:", su_principal_name);
 127         else
 128                 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_password(context, &creds, su_principal,
 137             pass, NULL, NULL, 0, NULL, &gic_opt);
 138         if (rv != 0) {
 139                 PAM_LOG("krb5_get_init_creds_password: %s",
 140                         krb5_get_err_text(context, rv));
 141                 return (PAM_AUTH_ERR);
 142         }
 143         krb5_verify_init_creds_opt_set_ap_req_nofail(&vic_opt, 1);
 144         rv = krb5_verify_init_creds(context, &creds, NULL, NULL, NULL,
 145             &vic_opt);
 146         krb5_free_cred_contents(context, &creds);
 147         if (rv != 0) {
 148                 PAM_LOG("krb5_verify_init_creds: %s",
 149                        krb5_get_err_text(context, rv));
 150                 return (PAM_AUTH_ERR);
 151         }
 152         return (PAM_SUCCESS);
 153 }
 154
 155 /* Determine the target principal given the current user and the target user.
 156  *   context           -- An initialized krb5_context.
 157  *   target_user       -- The target username.
 158  *   current_user      -- The current username.
 159  *   su_principal_name -- (out) The target principal name.
 160  *   su_principal      -- (out) The target krb5_principal.
 161  * When the target user is `root', the target principal will be a `root
 162  * instance', e.g. `luser/root@REA.LM'.  Otherwise, the target principal
 163  * will simply be the current user's default principal name.  Note that
 164  * in any case, if KRB5CCNAME is set and a credentials cache exists, the
 165  * principal name found there will be the `starting point', rather than
 166  * the ruser parameter.
 167  *
 168  * Returns 0 for success, or a com_err error code on failure.
 169  */
 170 static long
 171 get_su_principal(krb5_context context, const char *target_user,
 172                  const char *current_user, char **su_principal_name,
 173                  krb5_principal *su_principal)
 174 {
 175         krb5_principal   default_principal;
 176         krb5_ccache      ccache;
 177         char            *principal_name, *ccname, *p;
 178         long             rv;
 179         uid_t            euid, ruid;
 180
 181         *su_principal = NULL;
 182         default_principal = NULL;
 183         /* Unless KRB5CCNAME was explicitly set, we won't really be able
 184          * to look at the credentials cache since krb5_cc_default will
 185          * look at getuid().
 186          */
 187         ruid = getuid();
 188         euid = geteuid();
 189         rv = seteuid(ruid);
 190         if (rv != 0)
 191                 return (errno);
 192         p = getenv("KRB5CCNAME");
 193         if (p != NULL)
 194                 ccname = strdup(p);
 195         else
 196                 asprintf(&ccname, "%s%lu", KRB5_DEFAULT_CCROOT, (unsigned long)ruid);
 197         if (ccname == NULL)
 198                 return (errno);
 199         rv = krb5_cc_resolve(context, ccname, &ccache);
 200         free(ccname);
 201         if (rv == 0) {
 202                 rv = krb5_cc_get_principal(context, ccache, &default_principal);
 203                 krb5_cc_close(context, ccache);
 204                 if (rv != 0)
 205                         default_principal = NULL; /* just to be safe */
 206         }
 207         rv = seteuid(euid);
 208         if (rv != 0)
 209                 return (errno);
 210         if (default_principal == NULL) {
 211                 rv = krb5_make_principal(context, &default_principal, NULL, current_user, NULL);
 212                 if (rv != 0) {
 213                         PAM_LOG("Could not determine default principal name.");
 214                         return (rv);
 215                 }
 216         }
 217         /* Now that we have some principal, if the target account is
 218          * `root', then transform it into a `root' instance, e.g.
 219          * `user@REA.LM' -> `user/root@REA.LM'.
 220          */
 221         rv = krb5_unparse_name(context, default_principal, &principal_name);
 222         krb5_free_principal(context, default_principal);
 223         if (rv != 0) {
 224                 PAM_LOG("krb5_unparse_name: %s",
 225                     krb5_get_err_text(context, rv));
 226                 return (rv);
 227         }
 228         PAM_LOG("Default principal name: %s", principal_name);
 229         if (strcmp(target_user, superuser) == 0) {
 230                 p = strrchr(principal_name, '@');
 231                 if (p == NULL) {
 232                         PAM_LOG("malformed principal name `%s'", principal_name);
 233                         free(principal_name);
 234                         return (rv);
 235                 }
 236                 *p++ = '\0';
 237                 *su_principal_name = NULL;
 238                 asprintf(su_principal_name, "%s/%s@%s", principal_name, superuser, p);
 239                 free(principal_name);
 240         } else
 241                 *su_principal_name = principal_name;
 242
 243         if (*su_principal_name == NULL)
 244                 return (errno);
 245         rv = krb5_parse_name(context, *su_principal_name, &default_principal);
 246         if (rv != 0) {
 247                 PAM_LOG("krb5_parse_name `%s': %s", *su_principal_name,
 248                     krb5_get_err_text(context, rv));
 249                 free(*su_principal_name);
 250                 return (rv);
 251         }
 252         PAM_LOG("Target principal name: %s", *su_principal_name);
 253         *su_principal = default_principal;
 254         return (0);
 255 }
 256
 257 PAM_MODULE_ENTRY("pam_ksu");