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         if (key->user->user_ns != cred->user->user_ns)
  39                 goto use_other_perms;
  40
  41         /* use the second 8-bits of permissions for keys the caller owns */
  42         if (key->uid == cred->fsuid) {
  43                 kperm = key->perm >> 16;
  44                 goto use_these_perms;
  45         }
  46
  47         /* use the third 8-bits of permissions for keys the caller has a group
  48          * membership in common with */
  49         if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
  50                 if (key->gid == cred->fsgid) {
  51                         kperm = key->perm >> 8;
  52                         goto use_these_perms;
  53                 }
  54
  55                 ret = groups_search(cred->group_info, key->gid);
  56                 if (ret) {
  57                         kperm = key->perm >> 8;
  58                         goto use_these_perms;
  59                 }
  60         }
  61
  62 use_other_perms:
  63
  64         /* otherwise use the least-significant 8-bits */
  65         kperm = key->perm;
  66
  67 use_these_perms:
  68
  69         /* use the top 8-bits of permissions for keys the caller possesses
  70          * - possessor permissions are additive with other permissions
  71          */
  72         if (is_key_possessed(key_ref))
  73                 kperm |= key->perm >> 24;
  74
  75         kperm = kperm & perm & KEY_ALL;
  76
  77         if (kperm != perm)
  78                 return -EACCES;
  79
  80         /* let LSM be the final arbiter */
  81         return security_key_permission(key_ref, cred, perm);
  82
  83 } /* end key_task_permission() */
  84
  85 EXPORT_SYMBOL(key_task_permission);
  86
  87 /*****************************************************************************/
  88 /*
  89  * validate a key
  90  */
  91 int key_validate(struct key *key)
  92 {
  93         struct timespec now;
  94         int ret = 0;
  95
  96         if (key) {
  97                 /* check it's still accessible */
  98                 ret = -EKEYREVOKED;
  99                 if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
 100                     test_bit(KEY_FLAG_DEAD, &key->flags))
 101                         goto error;
 102
 103                 /* check it hasn't expired */
 104                 ret = 0;
 105                 if (key->expiry) {
 106                         now = current_kernel_time();
 107                         if (now.tv_sec >= key->expiry)
 108                                 ret = -EKEYEXPIRED;
 109                 }
 110         }
 111
 112  error:
 113         return ret;
 114
 115 } /* end key_validate() */
 116
 117 EXPORT_SYMBOL(key_validate);