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                         printk(KERN_ERR "CacheFiles:"
  38                                " Security denies permission to nominate"
  39                                " security context: error %d\n",
  40                                ret);
  41                         goto error;
  42                 }
  43         }
  44
  45         cache->cache_cred = new;
  46         ret = 0;
  47 error:
  48         _leave(" = %d", ret);
  49         return ret;
  50 }
  51
  52 /*
  53  * see if mkdir and create can be performed in the root directory
  54  */
  55 static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
  56                                       struct dentry *root)
  57 {
  58         int ret;
  59
  60         ret = security_inode_mkdir(root->d_inode, root, 0);
  61         if (ret < 0) {
  62                 printk(KERN_ERR "CacheFiles:"
  63                        " Security denies permission to make dirs: error %d",
  64                        ret);
  65                 return ret;
  66         }
  67
  68         ret = security_inode_create(root->d_inode, root, 0);
  69         if (ret < 0)
  70                 printk(KERN_ERR "CacheFiles:"
  71                        " Security denies permission to create files: error %d",
  72                        ret);
  73
  74         return ret;
  75 }
  76
  77 /*
  78  * check the security details of the on-disk cache
  79  * - must be called with security override in force
  80  * - must return with a security override in force - even in the case of an
  81  *   error
  82  */
  83 int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
  84                                         struct dentry *root,
  85                                         const struct cred **_saved_cred)
  86 {
  87         struct cred *new;
  88         int ret;
  89
  90         _enter("");
  91
  92         /* duplicate the cache creds for COW (the override is currently in
  93          * force, so we can use prepare_creds() to do this) */
  94         new = prepare_creds();
  95         if (!new)
  96                 return -ENOMEM;
  97
  98         cachefiles_end_secure(cache, *_saved_cred);
  99
 100         /* use the cache root dir's security context as the basis with
 101          * which create files */
 102         ret = set_create_files_as(new, root->d_inode);
 103         if (ret < 0) {
 104                 abort_creds(new);
 105                 cachefiles_begin_secure(cache, _saved_cred);
 106                 _leave(" = %d [cfa]", ret);
 107                 return ret;
 108         }
 109
 110         put_cred(cache->cache_cred);
 111         cache->cache_cred = new;
 112
 113         cachefiles_begin_secure(cache, _saved_cred);
 114         ret = cachefiles_check_cache_dir(cache, root);
 115
 116         if (ret == -EOPNOTSUPP)
 117                 ret = 0;
 118         _leave(" = %d", ret);
 119         return ret;
 120 }