fs/cachefiles/security.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* CacheFiles security management
   3  *
   4  * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
   5  * Written by David Howells (dhowells@redhat.com)
   6  */
   7
   8 #include <linux/fs.h>
   9 #include <linux/cred.h>
  10 #include "internal.h"
  11
  12 /*
  13  * determine the security context within which we access the cache from within
  14  * the kernel
  15  */
  16 int cachefiles_get_security_ID(struct cachefiles_cache *cache)
  17 {
  18         struct cred *new;
  19         int ret;
  20
  21         _enter("{%s}", cache->secctx);
  22
  23         new = prepare_kernel_cred(current);
  24         if (!new) {
  25                 ret = -ENOMEM;
  26                 goto error;
  27         }
  28
  29         if (cache->secctx) {
  30                 ret = set_security_override_from_ctx(new, cache->secctx);
  31                 if (ret < 0) {
  32                         put_cred(new);
  33                         pr_err("Security denies permission to nominate security context: error %d\n",
  34                                ret);
  35                         goto error;
  36                 }
  37         }
  38
  39         cache->cache_cred = new;
  40         ret = 0;
  41 error:
  42         _leave(" = %d", ret);
  43         return ret;
  44 }
  45
  46 /*
  47  * see if mkdir and create can be performed in the root directory
  48  */
  49 static int cachefiles_check_cache_dir(struct cachefiles_cache *cache,
  50                                       struct dentry *root)
  51 {
  52         int ret;
  53
  54         ret = security_inode_mkdir(d_backing_inode(root), root, 0);
  55         if (ret < 0) {
  56                 pr_err("Security denies permission to make dirs: error %d",
  57                        ret);
  58                 return ret;
  59         }
  60
  61         ret = security_inode_create(d_backing_inode(root), root, 0);
  62         if (ret < 0)
  63                 pr_err("Security denies permission to create files: error %d",
  64                        ret);
  65
  66         return ret;
  67 }
  68
  69 /*
  70  * check the security details of the on-disk cache
  71  * - must be called with security override in force
  72  * - must return with a security override in force - even in the case of an
  73  *   error
  74  */
  75 int cachefiles_determine_cache_security(struct cachefiles_cache *cache,
  76                                         struct dentry *root,
  77                                         const struct cred **_saved_cred)
  78 {
  79         struct cred *new;
  80         int ret;
  81
  82         _enter("");
  83
  84         /* duplicate the cache creds for COW (the override is currently in
  85          * force, so we can use prepare_creds() to do this) */
  86         new = prepare_creds();
  87         if (!new)
  88                 return -ENOMEM;
  89
  90         cachefiles_end_secure(cache, *_saved_cred);
  91
  92         /* use the cache root dir's security context as the basis with
  93          * which create files */
  94         ret = set_create_files_as(new, d_backing_inode(root));
  95         if (ret < 0) {
  96                 abort_creds(new);
  97                 cachefiles_begin_secure(cache, _saved_cred);
  98                 _leave(" = %d [cfa]", ret);
  99                 return ret;
 100         }
 101
 102         put_cred(cache->cache_cred);
 103         cache->cache_cred = new;
 104
 105         cachefiles_begin_secure(cache, _saved_cred);
 106         ret = cachefiles_check_cache_dir(cache, root);
 107
 108         if (ret == -EOPNOTSUPP)
 109                 ret = 0;
 110         _leave(" = %d", ret);
 111         return ret;
 112 }