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 <linux/security.h>
  14 #include "internal.h"
  15
  16 /*****************************************************************************/
  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 int key_task_permission(const key_ref_t key_ref,
  22                         struct task_struct *context,
  23                         key_perm_t perm)
  24 {
  25         struct key *key;
  26         key_perm_t kperm;
  27         int ret;
  28
  29         key = key_ref_to_ptr(key_ref);
  30
  31         /* use the second 8-bits of permissions for keys the caller owns */
  32         if (key->uid == context->fsuid) {
  33                 kperm = key->perm >> 16;
  34                 goto use_these_perms;
  35         }
  36
  37         /* use the third 8-bits of permissions for keys the caller has a group
  38          * membership in common with */
  39         if (key->gid != -1 && key->perm & KEY_GRP_ALL) {
  40                 if (key->gid == context->fsgid) {
  41                         kperm = key->perm >> 8;
  42                         goto use_these_perms;
  43                 }
  44
  45                 task_lock(context);
  46                 ret = groups_search(context->group_info, key->gid);
  47                 task_unlock(context);
  48
  49                 if (ret) {
  50                         kperm = key->perm >> 8;
  51                         goto use_these_perms;
  52                 }
  53         }
  54
  55         /* otherwise use the least-significant 8-bits */
  56         kperm = key->perm;
  57
  58 use_these_perms:
  59         /* use the top 8-bits of permissions for keys the caller possesses
  60          * - possessor permissions are additive with other permissions
  61          */
  62         if (is_key_possessed(key_ref))
  63                 kperm |= key->perm >> 24;
  64
  65         kperm = kperm & perm & KEY_ALL;
  66
  67         if (kperm != perm)
  68                 return -EACCES;
  69
  70         /* let LSM be the final arbiter */
  71         return security_key_permission(key_ref, context, perm);
  72
  73 } /* end key_task_permission() */
  74
  75 EXPORT_SYMBOL(key_task_permission);