linux/security/keys/permission.c
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   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 */
  30int 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->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, key->gid);
  57                if (ret) {
  58                        kperm = key->perm >> 8;
  59                        goto use_these_perms;
  60                }
  61        }
  62
  63use_other_perms:
  64
  65        /* otherwise use the least-significant 8-bits */
  66        kperm = key->perm;
  67
  68use_these_perms:
  69
  70        /* use the top 8-bits of permissions for keys the caller possesses
  71         * - possessor permissions are additive with other permissions
  72         */
  73        if (is_key_possessed(key_ref))
  74                kperm |= key->perm >> 24;
  75
  76        kperm = kperm & perm & KEY_ALL;
  77
  78        if (kperm != perm)
  79                return -EACCES;
  80
  81        /* let LSM be the final arbiter */
  82        return security_key_permission(key_ref, cred, perm);
  83}
  84EXPORT_SYMBOL(key_task_permission);
  85
  86/**
  87 * key_validate - Validate a key.
  88 * @key: The key to be validated.
  89 *
  90 * Check that a key is valid, returning 0 if the key is okay, -EKEYREVOKED if
  91 * the key's type has been removed or if the key has been revoked or
  92 * -EKEYEXPIRED if the key has expired.
  93 */
  94int key_validate(struct key *key)
  95{
  96        struct timespec now;
  97        int ret = 0;
  98
  99        if (key) {
 100                /* check it's still accessible */
 101                ret = -EKEYREVOKED;
 102                if (test_bit(KEY_FLAG_REVOKED, &key->flags) ||
 103                    test_bit(KEY_FLAG_DEAD, &key->flags))
 104                        goto error;
 105
 106                /* check it hasn't expired */
 107                ret = 0;
 108                if (key->expiry) {
 109                        now = current_kernel_time();
 110                        if (now.tv_sec >= key->expiry)
 111                                ret = -EKEYEXPIRED;
 112                }
 113        }
 114
 115error:
 116        return ret;
 117}
 118EXPORT_SYMBOL(key_validate);
 119