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  * @need_perm: The permission required.
  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                         enum key_need_perm need_perm)
  28 {
  29         struct key *key;
  30         key_perm_t kperm, mask;
  31         int ret;
  32
  33         switch (need_perm) {
  34         default:
  35                 WARN_ON(1);
  36                 return -EACCES;
  37         case KEY_NEED_UNLINK:
  38         case KEY_SYSADMIN_OVERRIDE:
  39         case KEY_AUTHTOKEN_OVERRIDE:
  40         case KEY_DEFER_PERM_CHECK:
  41                 goto lsm;
  42
  43         case KEY_NEED_VIEW:     mask = KEY_OTH_VIEW;    break;
  44         case KEY_NEED_READ:     mask = KEY_OTH_READ;    break;
  45         case KEY_NEED_WRITE:    mask = KEY_OTH_WRITE;   break;
  46         case KEY_NEED_SEARCH:   mask = KEY_OTH_SEARCH;  break;
  47         case KEY_NEED_LINK:     mask = KEY_OTH_LINK;    break;
  48         case KEY_NEED_SETATTR:  mask = KEY_OTH_SETATTR; break;
  49         }
  50
  51         key = key_ref_to_ptr(key_ref);
  52
  53         /* use the second 8-bits of permissions for keys the caller owns */
  54         if (uid_eq(key->uid, cred->fsuid)) {
  55                 kperm = key->perm >> 16;
  56                 goto use_these_perms;
  57         }
  58
  59         /* use the third 8-bits of permissions for keys the caller has a group
  60          * membership in common with */
  61         if (gid_valid(key->gid) && key->perm & KEY_GRP_ALL) {
  62                 if (gid_eq(key->gid, cred->fsgid)) {
  63                         kperm = key->perm >> 8;
  64                         goto use_these_perms;
  65                 }
  66
  67                 ret = groups_search(cred->group_info, key->gid);
  68                 if (ret) {
  69                         kperm = key->perm >> 8;
  70                         goto use_these_perms;
  71                 }
  72         }
  73
  74         /* otherwise use the least-significant 8-bits */
  75         kperm = key->perm;
  76
  77 use_these_perms:
  78
  79         /* use the top 8-bits of permissions for keys the caller possesses
  80          * - possessor permissions are additive with other permissions
  81          */
  82         if (is_key_possessed(key_ref))
  83                 kperm |= key->perm >> 24;
  84
  85         if ((kperm & mask) != mask)
  86                 return -EACCES;
  87
  88         /* let LSM be the final arbiter */
  89 lsm:
  90         return security_key_permission(key_ref, cred, need_perm);
  91 }
  92 EXPORT_SYMBOL(key_task_permission);
  93
  94 /**
  95  * key_validate - Validate a key.
  96  * @key: The key to be validated.
  97  *
  98  * Check that a key is valid, returning 0 if the key is okay, -ENOKEY if the
  99  * key is invalidated, -EKEYREVOKED if the key's type has been removed or if
 100  * the key has been revoked or -EKEYEXPIRED if the key has expired.
 101  */
 102 int key_validate(const struct key *key)
 103 {
 104         unsigned long flags = READ_ONCE(key->flags);
 105         time64_t expiry = READ_ONCE(key->expiry);
 106
 107         if (flags & (1 << KEY_FLAG_INVALIDATED))
 108                 return -ENOKEY;
 109
 110         /* check it's still accessible */
 111         if (flags & ((1 << KEY_FLAG_REVOKED) |
 112                      (1 << KEY_FLAG_DEAD)))
 113                 return -EKEYREVOKED;
 114
 115         /* check it hasn't expired */
 116         if (expiry) {
 117                 if (ktime_get_real_seconds() >= expiry)
 118                         return -EKEYEXPIRED;
 119         }
 120
 121         return 0;
 122 }
 123 EXPORT_SYMBOL(key_validate);