security/keys/permission.c

   1 /* Key permission checking
   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  * key_task_permission - Check a key can be used
  18  * @key_ref: The key to check.
  19  * @cred: The credentials to use.
  20  * @perm: The permissions to check for.
  21  *
  22  * Check to see whether permission is granted to use a key in the desired way,
  23  * but permit the security modules to override.
  24  *
  25  * The caller must hold either a ref on cred or must hold the RCU readlock.
  26  *
  27  * Returns 0 if successful, -EACCES if access is denied based on the
  28  * permissions bits or the LSM check.
  29  */
  30 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
  31                         key_perm_t perm)
  32 {
  33         struct key *key;
  34         key_perm_t kperm;
  35         int ret;
  36
  37         key = key_ref_to_ptr(key_ref);
  38
  39         if (key->user->user_ns != cred->user_ns)
  40                 goto use_other_perms;
  41
  42         /* use the second 8-bits of permissions for keys the caller owns */
  43         if (key->uid == cred->fsuid) {
  44                 kperm = key->perm >> 16;
  45                 goto use_these_perms;
  46         }
  47
  48         /* use the third 8-bits of permissions for keys the caller has a group
  49          * membership in common with */
  50         if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
  51                 if (key->gid == cred->fsgid) {
  52                         kperm = key->perm >> 8;
  53                         goto use_these_perms;
  54                 }
  55
  56                 ret = groups_search(cred->group_info,
  57                                     make_kgid(current_user_ns(), key->gid));
  58                 if (ret) {
  59                         kperm = key->perm >> 8;
  60                         goto use_these_perms;
  61                 }
  62         }
  63
  64 use_other_perms:
  65
  66         /* otherwise use the least-significant 8-bits */
  67         kperm = key->perm;
  68
  69 use_these_perms:
  70
  71         /* use the top 8-bits of permissions for keys the caller possesses
  72          * - possessor permissions are additive with other permissions
  73          */
  74         if (is_key_possessed(key_ref))
  75                 kperm |= key->perm >> 24;
  76
  77         kperm = kperm & perm & KEY_ALL;
  78
  79         if (kperm != perm)
  80                 return -EACCES;
  81
  82         /* let LSM be the final arbiter */
  83         return security_key_permission(key_ref, cred, perm);
  84 }
  85 EXPORT_SYMBOL(key_task_permission);
  86
  87 /**
  88  * key_validate - Validate a key.
  89  * @key: The key to be validated.
  90  *
  91  * Check that a key is valid, returning 0 if the key is okay, -EKEYREVOKED if
  92  * the key's type has been removed or if the key has been revoked or
  93  * -EKEYEXPIRED if the key has expired.
  94  */
  95 int key_validate(struct key *key)
  96 {
  97         struct timespec now;
  98         int ret = 0;
  99
 100         if (key) {
 101                 /* check it's still accessible */
 102                 ret = -EKEYREVOKED;
 103                 if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
 104                     test_bit(KEY_FLAG_DEAD, &key->flags))
 105                         goto error;
 106
 107                 /* check it hasn't expired */
 108                 ret = 0;
 109                 if (key->expiry) {
 110                         now = current_kernel_time();
 111                         if (now.tv_sec >= key->expiry)
 112                                 ret = -EKEYEXPIRED;
 113                 }
 114         }
 115
 116 error:
 117         return ret;
 118 }
 119 EXPORT_SYMBOL(key_validate);