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        /* 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
  63use_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_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}
  79EXPORT_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 */
  89int key_validate(const struct key *key)
  90{
  91        unsigned long flags = key->flags;
  92
  93        if (flags & (1 << KEY_FLAG_INVALIDATED))
  94                return -ENOKEY;
  95
  96        /* check it's still accessible */
  97        if (flags & ((1 << KEY_FLAG_REVOKED) |
  98                     (1 << KEY_FLAG_DEAD)))
  99                return -EKEYREVOKED;
 100
 101        /* check it hasn't expired */
 102        if (key->expiry) {
 103                struct timespec now = current_kernel_time();
 104                if (now.tv_sec >= key->expiry)
 105                        return -EKEYEXPIRED;
 106        }
 107
 108        return 0;
 109}
 110EXPORT_SYMBOL(key_validate);
 111
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