security/keys/permission.c

   1 /* permission.c: key permission determination
   2  *
   3  * Copyright (C) 2005 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/security.h>
  14 #include "internal.h"
  15
  16 /*****************************************************************************/
  17 /**
  18  * key_task_permission - Check a key can be used
  19  * @key_ref: The key to check
  20  * @cred: The credentials to use
  21  * @perm: The permissions to check for
  22  *
  23  * Check to see whether permission is granted to use a key in the desired way,
  24  * but permit the security modules to override.
  25  *
  26  * The caller must hold either a ref on cred or must hold the RCU readlock or a
  27  * spinlock.
  28  */
  29 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
  30                         key_perm_t perm)
  31 {
  32         struct key *key;
  33         key_perm_t kperm;
  34         int ret;
  35
  36         key = key_ref_to_ptr(key_ref);
  37
  38         /* use the second 8-bits of permissions for keys the caller owns */
  39         if (key->uid == cred->fsuid) {
  40                 kperm = key->perm >> 16;
  41                 goto use_these_perms;
  42         }
  43
  44         /* use the third 8-bits of permissions for keys the caller has a group
  45          * membership in common with */
  46         if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
  47                 if (key->gid == cred->fsgid) {
  48                         kperm = key->perm >> 8;
  49                         goto use_these_perms;
  50                 }
  51
  52                 ret = groups_search(cred->group_info, key->gid);
  53                 if (ret) {
  54                         kperm = key->perm >> 8;
  55                         goto use_these_perms;
  56                 }
  57         }
  58
  59         /* otherwise use the least-significant 8-bits */
  60         kperm = key->perm;
  61
  62 use_these_perms:
  63
  64         /* use the top 8-bits of permissions for keys the caller possesses
  65          * - possessor permissions are additive with other permissions
  66          */
  67         if (is_key_possessed(key_ref))
  68                 kperm |= key->perm >> 24;
  69
  70         kperm = kperm & perm & KEY_ALL;
  71
  72         if (kperm != perm)
  73                 return -EACCES;
  74
  75         /* let LSM be the final arbiter */
  76         return security_key_permission(key_ref, cred, perm);
  77
  78 } /* end key_task_permission() */
  79
  80 EXPORT_SYMBOL(key_task_permission);
  81
  82 /*****************************************************************************/
  83 /*
  84  * validate a key
  85  */
  86 int key_validate(struct key *key)
  87 {
  88         struct timespec now;
  89         int ret = 0;
  90
  91         if (key) {
  92                 /* check it's still accessible */
  93                 ret = -EKEYREVOKED;
  94                 if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
  95                     test_bit(KEY_FLAG_DEAD, &key->flags))
  96                         goto error;
  97
  98                 /* check it hasn't expired */
  99                 ret = 0;
 100                 if (key->expiry) {
 101                         now = current_kernel_time();
 102                         if (now.tv_sec >= key->expiry)
 103                                 ret = -EKEYEXPIRED;
 104                 }
 105         }
 106
 107  error:
 108         return ret;
 109
 110 } /* end key_validate() */
 111
 112 EXPORT_SYMBOL(key_validate);