security/keys/permission.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* Key permission checking
   3  *
   4  * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/export.h>
   9 #include <linux/security.h>
  10 #include "internal.h"
  11
  12 /**
  13  * key_task_permission - Check a key can be used
  14  * @key_ref: The key to check.
  15  * @cred: The credentials to use.
  16  * @perm: The permissions to check for.
  17  *
  18  * Check to see whether permission is granted to use a key in the desired way,
  19  * but permit the security modules to override.
  20  *
  21  * The caller must hold either a ref on cred or must hold the RCU readlock.
  22  *
  23  * Returns 0 if successful, -EACCES if access is denied based on the
  24  * permissions bits or the LSM check.
  25  */
  26 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
  27                         unsigned perm)
  28 {
  29         struct key *key;
  30         key_perm_t kperm;
  31         int ret;
  32
  33         key = key_ref_to_ptr(key_ref);
  34
  35         /* use the second 8-bits of permissions for keys the caller owns */
  36         if (uid_eq(key->uid, cred->fsuid)) {
  37                 kperm = key->perm >> 16;
  38                 goto use_these_perms;
  39         }
  40
  41         /* use the third 8-bits of permissions for keys the caller has a group
  42          * membership in common with */
  43         if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
  44                 if (gid_eq(key->gid, cred->fsgid)) {
  45                         kperm = key->perm >> 8;
  46                         goto use_these_perms;
  47                 }
  48
  49                 ret = groups_search(cred->group_info, key->gid);
  50                 if (ret) {
  51                         kperm = key->perm >> 8;
  52                         goto use_these_perms;
  53                 }
  54         }
  55
  56         /* otherwise use the least-significant 8-bits */
  57         kperm = key->perm;
  58
  59 use_these_perms:
  60
  61         /* use the top 8-bits of permissions for keys the caller possesses
  62          * - possessor permissions are additive with other permissions
  63          */
  64         if (is_key_possessed(key_ref))
  65                 kperm |= key->perm >> 24;
  66
  67         kperm = kperm & perm & KEY_NEED_ALL;
  68
  69         if (kperm != perm)
  70                 return -EACCES;
  71
  72         /* let LSM be the final arbiter */
  73         return security_key_permission(key_ref, cred, perm);
  74 }
  75 EXPORT_SYMBOL(key_task_permission);
  76
  77 /**
  78  * key_validate - Validate a key.
  79  * @key: The key to be validated.
  80  *
  81  * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
  82  * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
  83  * the key has been revoked or -EKEYEXPIRED if the key has expired.
  84  */
  85 int key_validate(const struct key *key)
  86 {
  87         unsigned long flags = READ_ONCE(key->flags);
  88         time64_t expiry = READ_ONCE(key->expiry);
  89
  90         if (flags & (1 << KEY_FLAG_INVALIDATED))
  91                 return -ENOKEY;
  92
  93         /* check it's still accessible */
  94         if (flags & ((1 << KEY_FLAG_REVOKED) |
  95                      (1 << KEY_FLAG_DEAD)))
  96                 return -EKEYREVOKED;
  97
  98         /* check it hasn't expired */
  99         if (expiry) {
 100                 if (ktime_get_real_seconds() >= expiry)
 101                         return -EKEYEXPIRED;
 102         }
 103
 104         return 0;
 105 }
 106 EXPORT_SYMBOL(key_validate);