security/keys/request_key.c

   1 /* request_key.c: request a key from userspace
   2  *
   3  * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
   4  * Written by David Howells (dhowells@redhat.com)
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the License, or (at your option) any later version.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/sched.h>
  14 #include <linux/kmod.h>
  15 #include <linux/err.h>
  16 #include "internal.h"
  17
  18 struct key_construction {
  19         struct list_head        link;   /* link in construction queue */
  20         struct key              *key;   /* key being constructed */
  21 };
  22
  23 /* when waiting for someone else's keys, you get added to this */
  24 DECLARE_WAIT_QUEUE_HEAD(request_key_conswq);
  25
  26 /*****************************************************************************/
  27 /*
  28  * request userspace finish the construction of a key
  29  * - execute "/sbin/request-key <op> <key> <uid> <gid> <keyring> <keyring> <keyring> <info>"
  30  * - if callout_info is an empty string, it'll be rendered as a "-" instead
  31  */
  32 static int call_request_key(struct key *key,
  33                             const char *op,
  34                             const char *callout_info)
  35 {
  36         struct task_struct *tsk = current;
  37         unsigned long flags;
  38         key_serial_t prkey, sskey;
  39         char *argv[10], *envp[3], uid_str[12], gid_str[12];
  40         char key_str[12], keyring_str[3][12];
  41         int i;
  42
  43         /* record the UID and GID */
  44         sprintf(uid_str, "%d", current->fsuid);
  45         sprintf(gid_str, "%d", current->fsgid);
  46
  47         /* we say which key is under construction */
  48         sprintf(key_str, "%d", key->serial);
  49
  50         /* we specify the process's default keyrings */
  51         sprintf(keyring_str[0], "%d",
  52                 tsk->thread_keyring ? tsk->thread_keyring->serial : 0);
  53
  54         prkey = 0;
  55         if (tsk->signal->process_keyring)
  56                 prkey = tsk->signal->process_keyring->serial;
  57
  58         sskey = 0;
  59         spin_lock_irqsave(&tsk->sighand->siglock, flags);
  60         if (tsk->signal->session_keyring)
  61                 sskey = tsk->signal->session_keyring->serial;
  62         spin_unlock_irqrestore(&tsk->sighand->siglock, flags);
  63
  64
  65         if (!sskey)
  66                 sskey = tsk->user->session_keyring->serial;
  67
  68         sprintf(keyring_str[1], "%d", prkey);
  69         sprintf(keyring_str[2], "%d", sskey);
  70
  71         /* set up a minimal environment */
  72         i = 0;
  73         envp[i++] = "HOME=/";
  74         envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
  75         envp[i] = NULL;
  76
  77         /* set up the argument list */
  78         i = 0;
  79         argv[i++] = "/sbin/request-key";
  80         argv[i++] = (char *) op;
  81         argv[i++] = key_str;
  82         argv[i++] = uid_str;
  83         argv[i++] = gid_str;
  84         argv[i++] = keyring_str[0];
  85         argv[i++] = keyring_str[1];
  86         argv[i++] = keyring_str[2];
  87         argv[i++] = callout_info[0] ? (char *) callout_info : "-";
  88         argv[i] = NULL;
  89
  90         /* do it */
  91         return call_usermodehelper_keys(argv[0], argv, envp, NULL, 1);
  92
  93 } /* end call_request_key() */
  94
  95 /*****************************************************************************/
  96 /*
  97  * call out to userspace for the key
  98  * - called with the construction sem held, but the sem is dropped here
  99  * - we ignore program failure and go on key status instead
 100  */
 101 static struct key *__request_key_construction(struct key_type *type,
 102                                               const char *description,
 103                                               const char *callout_info)
 104 {
 105         struct key_construction cons;
 106         struct timespec now;
 107         struct key *key;
 108         int ret, negated;
 109
 110         /* create a key and add it to the queue */
 111         key = key_alloc(type, description,
 112                         current->fsuid, current->fsgid, KEY_USR_ALL, 0);
 113         if (IS_ERR(key))
 114                 goto alloc_failed;
 115
 116         set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
 117
 118         cons.key = key;
 119         list_add_tail(&cons.link, &key->user->consq);
 120
 121         /* we drop the construction sem here on behalf of the caller */
 122         up_write(&key_construction_sem);
 123
 124         /* make the call */
 125         ret = call_request_key(key, "create", callout_info);
 126         if (ret < 0)
 127                 goto request_failed;
 128
 129         /* if the key wasn't instantiated, then we want to give an error */
 130         ret = -ENOKEY;
 131         if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags))
 132                 goto request_failed;
 133
 134         down_write(&key_construction_sem);
 135         list_del(&cons.link);
 136         up_write(&key_construction_sem);
 137
 138         /* also give an error if the key was negatively instantiated */
 139  check_not_negative:
 140         if (test_bit(KEY_FLAG_NEGATIVE, &key->flags)) {
 141                 key_put(key);
 142                 key = ERR_PTR(-ENOKEY);
 143         }
 144
 145  out:
 146         return key;
 147
 148  request_failed:
 149         /* it wasn't instantiated
 150          * - remove from construction queue
 151          * - mark the key as dead
 152          */
 153         negated = 0;
 154         down_write(&key_construction_sem);
 155
 156         list_del(&cons.link);
 157
 158         /* check it didn't get instantiated between the check and the down */
 159         if (!test_bit(KEY_FLAG_INSTANTIATED, &key->flags)) {
 160                 set_bit(KEY_FLAG_NEGATIVE, &key->flags);
 161                 set_bit(KEY_FLAG_INSTANTIATED, &key->flags);
 162                 negated = 1;
 163         }
 164
 165         clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
 166
 167         up_write(&key_construction_sem);
 168
 169         if (!negated)
 170                 goto check_not_negative; /* surprisingly, the key got
 171                                           * instantiated */
 172
 173         /* set the timeout and store in the session keyring if we can */
 174         now = current_kernel_time();
 175         key->expiry = now.tv_sec + key_negative_timeout;
 176
 177         if (current->signal->session_keyring) {
 178                 struct key *keyring;
 179
 180                 rcu_read_lock();
 181                 keyring = rcu_dereference(current->signal->session_keyring);
 182                 atomic_inc(&keyring->usage);
 183                 rcu_read_unlock();
 184
 185                 key_link(keyring, key);
 186                 key_put(keyring);
 187         }
 188
 189         key_put(key);
 190
 191         /* notify anyone who was waiting */
 192         wake_up_all(&request_key_conswq);
 193
 194         key = ERR_PTR(ret);
 195         goto out;
 196
 197  alloc_failed:
 198         up_write(&key_construction_sem);
 199         goto out;
 200
 201 } /* end __request_key_construction() */
 202
 203 /*****************************************************************************/
 204 /*
 205  * call out to userspace to request the key
 206  * - we check the construction queue first to see if an appropriate key is
 207  *   already being constructed by userspace
 208  */
 209 static struct key *request_key_construction(struct key_type *type,
 210                                             const char *description,
 211                                             struct key_user *user,
 212                                             const char *callout_info)
 213 {
 214         struct key_construction *pcons;
 215         struct key *key, *ckey;
 216
 217         DECLARE_WAITQUEUE(myself, current);
 218
 219         /* see if there's such a key under construction already */
 220         down_write(&key_construction_sem);
 221
 222         list_for_each_entry(pcons, &user->consq, link) {
 223                 ckey = pcons->key;
 224
 225                 if (ckey->type != type)
 226                         continue;
 227
 228                 if (type->match(ckey, description))
 229                         goto found_key_under_construction;
 230         }
 231
 232         /* see about getting userspace to construct the key */
 233         key = __request_key_construction(type, description, callout_info);
 234  error:
 235         return key;
 236
 237         /* someone else has the same key under construction
 238          * - we want to keep an eye on their key
 239          */
 240  found_key_under_construction:
 241         atomic_inc(&ckey->usage);
 242         up_write(&key_construction_sem);
 243
 244         /* wait for the key to be completed one way or another */
 245         add_wait_queue(&request_key_conswq, &myself);
 246
 247         for (;;) {
 248                 set_current_state(TASK_UNINTERRUPTIBLE);
 249                 if (!test_bit(KEY_FLAG_USER_CONSTRUCT, &ckey->flags))
 250                         break;
 251                 schedule();
 252         }
 253
 254         set_current_state(TASK_RUNNING);
 255         remove_wait_queue(&request_key_conswq, &myself);
 256
 257         /* we'll need to search this process's keyrings to see if the key is
 258          * now there since we can't automatically assume it's also available
 259          * there */
 260         key_put(ckey);
 261         ckey = NULL;
 262
 263         key = NULL; /* request a retry */
 264         goto error;
 265
 266 } /* end request_key_construction() */
 267
 268 /*****************************************************************************/
 269 /*
 270  * request a key
 271  * - search the process's keyrings
 272  * - check the list of keys being created or updated
 273  * - call out to userspace for a key if requested (supplementary info can be
 274  *   passed)
 275  */
 276 struct key *request_key(struct key_type *type,
 277                         const char *description,
 278                         const char *callout_info)
 279 {
 280         struct key_user *user;
 281         struct key *key;
 282
 283         /* search all the process keyrings for a key */
 284         key = search_process_keyrings_aux(type, description, type->match);
 285
 286         if (PTR_ERR(key) == -EAGAIN) {
 287                 /* the search failed, but the keyrings were searchable, so we
 288                  * should consult userspace if we can */
 289                 key = ERR_PTR(-ENOKEY);
 290                 if (!callout_info)
 291                         goto error;
 292
 293                 /* - get hold of the user's construction queue */
 294                 user = key_user_lookup(current->fsuid);
 295                 if (!user) {
 296                         key = ERR_PTR(-ENOMEM);
 297                         goto error;
 298                 }
 299
 300                 for (;;) {
 301                         /* ask userspace (returns NULL if it waited on a key
 302                          * being constructed) */
 303                         key = request_key_construction(type, description,
 304                                                        user, callout_info);
 305                         if (key)
 306                                 break;
 307
 308                         /* someone else made the key we want, so we need to
 309                          * search again as it might now be available to us */
 310                         key = search_process_keyrings_aux(type, description,
 311                                                           type->match);
 312                         if (PTR_ERR(key) != -EAGAIN)
 313                                 break;
 314                 }
 315
 316                 key_user_put(user);
 317         }
 318
 319  error:
 320         return key;
 321
 322 } /* end request_key() */
 323
 324 EXPORT_SYMBOL(request_key);
 325
 326 /*****************************************************************************/
 327 /*
 328  * validate a key
 329  */
 330 int key_validate(struct key *key)
 331 {
 332         struct timespec now;
 333         int ret = 0;
 334
 335         if (key) {
 336                 /* check it's still accessible */
 337                 ret = -EKEYREVOKED;
 338                 if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
 339                     test_bit(KEY_FLAG_DEAD, &key->flags))
 340                         goto error;
 341
 342                 /* check it hasn't expired */
 343                 ret = 0;
 344                 if (key->expiry) {
 345                         now = current_kernel_time();
 346                         if (now.tv_sec >= key->expiry)
 347                                 ret = -EKEYEXPIRED;
 348                 }
 349         }
 350
 351  error:
 352         return ret;
 353
 354 } /* end key_validate() */
 355
 356 EXPORT_SYMBOL(key_validate);