security/keys/permission.c

   1 /* permission.c: key permission determination
   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 "internal.h"
  14
  15 /*****************************************************************************/
  16 /*
  17  * check to see whether permission is granted to use a key in the desired way,
  18  * but permit the security modules to override
  19  */
  20 int key_task_permission(const key_ref_t key_ref,
  21                         struct task_struct *context,
  22                         key_perm_t perm)
  23 {
  24         struct key *key;
  25         key_perm_t kperm;
  26         int ret;
  27
  28         key = key_ref_to_ptr(key_ref);
  29
  30         /* use the second 8-bits of permissions for keys the caller owns */
  31         if (key->uid == context->fsuid) {
  32                 kperm = key->perm >> 16;
  33                 goto use_these_perms;
  34         }
  35
  36         /* use the third 8-bits of permissions for keys the caller has a group
  37          * membership in common with */
  38         if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
  39                 if (key->gid == context->fsgid) {
  40                         kperm = key->perm >> 8;
  41                         goto use_these_perms;
  42                 }
  43
  44                 task_lock(context);
  45                 ret = groups_search(context->group_info, key->gid);
  46                 task_unlock(context);
  47
  48                 if (ret) {
  49                         kperm = key->perm >> 8;
  50                         goto use_these_perms;
  51                 }
  52         }
  53
  54         /* otherwise use the least-significant 8-bits */
  55         kperm = key->perm;
  56
  57 use_these_perms:
  58         /* use the top 8-bits of permissions for keys the caller possesses
  59          * - possessor permissions are additive with other permissions
  60          */
  61         if (is_key_possessed(key_ref))
  62                 kperm |= key->perm >> 24;
  63
  64         kperm = kperm & perm & KEY_ALL;
  65
  66         return kperm == perm;
  67
  68 } /* end key_task_permission() */
  69
  70 EXPORT_SYMBOL(key_task_permission);