fs/cachefiles/security.c

   1 /* CacheFiles security management
   2  *
   3  * Copyright (C) 2007 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 Licence
   8  * as published by the Free Software Foundation; either version
   9  * 2 of the Licence, or (at your option) any later version.
  10  */
  11
  12 #include <linux/fs.h>
  13 #include <linux/cred.h>
  14 #include "internal.h"
  15
  16 /*
  17  * determine the security context within which we access the cache from within
  18  * the kernel
  19  */
  20 int cachefiles_get_security_ID(struct cachefiles_cache *cache)
  21 {
  22         struct cred *new;
  23         int ret;
  24
  25         _enter("{%s}", cache->secctx);
  26
  27         new = prepare_kernel_cred(current);
  28         if (!new) {
  29                 ret = -ENOMEM;
  30                 goto error;
  31         }
  32
  33         if (cache->secctx) {
  34                 ret = set_security_override_from_ctx(new, cache->secctx);
  35                 if (ret < 0) {
  36                         put_cred(new);
  37                         pr_err("Security denies permission to nominate security context: error %d\n",
  38                                ret);
  39                         goto error;
  40                 }
  41         }
  42
  43         cache->cache_cred = new;
  44         ret = 0;
  45 error:
  46         _leave(" = %d", ret);
  47         return ret;
  48 }
  49
  50 /*
  51  * see if mkdir and create can be performed in the root directory
  52  */
  53 static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
  54                                       struct dentry *root)
  55 {
  56         int ret;
  57
  58         ret = security_inode_mkdir(d_backing_inode(root), root, 0);
  59         if (ret < 0) {
  60                 pr_err("Security denies permission to make dirs: error %d",
  61                        ret);
  62                 return ret;
  63         }
  64
  65         ret = security_inode_create(d_backing_inode(root), root, 0);
  66         if (ret < 0)
  67                 pr_err("Security denies permission to create files: error %d",
  68                        ret);
  69
  70         return ret;
  71 }
  72
  73 /*
  74  * check the security details of the on-disk cache
  75  * - must be called with security override in force
  76  * - must return with a security override in force - even in the case of an
  77  *   error
  78  */
  79 int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
  80                                         struct dentry *root,
  81                                         const struct cred **_saved_cred)
  82 {
  83         struct cred *new;
  84         int ret;
  85
  86         _enter("");
  87
  88         /* duplicate the cache creds for COW (the override is currently in
  89          * force, so we can use prepare_creds() to do this) */
  90         new = prepare_creds();
  91         if (!new)
  92                 return -ENOMEM;
  93
  94         cachefiles_end_secure(cache, *_saved_cred);
  95
  96         /* use the cache root dir's security context as the basis with
  97          * which create files */
  98         ret = set_create_files_as(new, d_backing_inode(root));
  99         if (ret < 0) {
 100                 abort_creds(new);
 101                 cachefiles_begin_secure(cache, _saved_cred);
 102                 _leave(" = %d [cfa]", ret);
 103                 return ret;
 104         }
 105
 106         put_cred(cache->cache_cred);
 107         cache->cache_cred = new;
 108
 109         cachefiles_begin_secure(cache, _saved_cred);
 110         ret = cachefiles_check_cache_dir(cache, root);
 111
 112         if (ret == -EOPNOTSUPP)
 113                 ret = 0;
 114         _leave(" = %d", ret);
 115         return ret;
 116 }