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/export.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                         unsigned 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         /* use the second 8-bits of permissions for keys the caller owns */
  40         if (uid_eq(key->uid, cred->fsuid)) {
  41                 kperm = key->perm >> 16;
  42                 goto use_these_perms;
  43         }
  44
  45         /* use the third 8-bits of permissions for keys the caller has a group
  46          * membership in common with */
  47         if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
  48                 if (gid_eq(key->gid, cred->fsgid)) {
  49                         kperm = key->perm >> 8;
  50                         goto use_these_perms;
  51                 }
  52
  53                 ret = groups_search(cred->group_info, key->gid);
  54                 if (ret) {
  55                         kperm = key->perm >> 8;
  56                         goto use_these_perms;
  57                 }
  58         }
  59
  60         /* otherwise use the least-significant 8-bits */
  61         kperm = key->perm;
  62
  63 use_these_perms:
  64
  65         /* use the top 8-bits of permissions for keys the caller possesses
  66          * - possessor permissions are additive with other permissions
  67          */
  68         if (is_key_possessed(key_ref))
  69                 kperm |= key->perm >> 24;
  70
  71         kperm = kperm & perm & KEY_NEED_ALL;
  72
  73         if (kperm != perm)
  74                 return -EACCES;
  75
  76         /* let LSM be the final arbiter */
  77         return security_key_permission(key_ref, cred, perm);
  78 }
  79 EXPORT_SYMBOL(key_task_permission);
  80
  81 /**
  82  * key_validate - Validate a key.
  83  * @key: The key to be validated.
  84  *
  85  * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
  86  * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
  87  * the key has been revoked or -EKEYEXPIRED if the key has expired.
  88  */
  89 int key_validate(const struct key *key)
  90 {
  91         unsigned long flags = READ_ONCE(key->flags);
  92         time64_t expiry = READ_ONCE(key->expiry);
  93
  94         if (flags & (1 << KEY_FLAG_INVALIDATED))
  95                 return -ENOKEY;
  96
  97         /* check it's still accessible */
  98         if (flags & ((1 << KEY_FLAG_REVOKED) |
  99                      (1 << KEY_FLAG_DEAD)))
 100                 return -EKEYREVOKED;
 101
 102         /* check it hasn't expired */
 103         if (expiry) {
 104                 if (ktime_get_real_seconds() >= expiry)
 105                         return -EKEYEXPIRED;
 106         }
 107
 108         return 0;
 109 }
 110 EXPORT_SYMBOL(key_validate);