src/components/policy/core/common/cloud/resource_cache.cc

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "components/policy/core/common/cloud/resource_cache.h"
   6
   7 #include "base/base64.h"
   8 #include "base/callback.h"
   9 #include "base/files/file_enumerator.h"
  10 #include "base/files/file_util.h"
  11 #include "base/logging.h"
  12 #include "base/numerics/safe_conversions.h"
  13 #include "base/sequenced_task_runner.h"
  14 #include "base/strings/string_util.h"
  15
  16 namespace policy {
  17
  18 namespace {
  19
  20 // Verifies that |value| is not empty and encodes it into base64url format,
  21 // which is safe to use as a file name on all platforms.
  22 bool Base64UrlEncode(const std::string& value, std::string* encoded) {
  23   DCHECK(!value.empty());
  24   if (value.empty())
  25     return false;
  26   base::Base64Encode(value, encoded);
  27   base::ReplaceChars(*encoded, "+", "-", encoded);
  28   base::ReplaceChars(*encoded, "/", "_", encoded);
  29   // Note: this encoding keeps the padding chars, though the "Baset64 with safe
  30   // URL alphabet" encoding trims them. See Base64UrlDecode below.
  31   return true;
  32 }
  33
  34 // Decodes all elements of |input| from base64url format and stores the decoded
  35 // elements in |output|.
  36 bool Base64UrlEncode(const std::set<std::string>& input,
  37                      std::set<std::string>* output) {
  38   output->clear();
  39   for (std::set<std::string>::const_iterator it = input.begin();
  40        it != input.end(); ++it) {
  41     std::string encoded;
  42     if (!Base64UrlEncode(*it, &encoded)) {
  43       output->clear();
  44       return false;
  45     }
  46     output->insert(encoded);
  47   }
  48   return true;
  49 }
  50
  51 // Decodes |encoded| from base64url format and verifies that the result is not
  52 // emtpy.
  53 bool Base64UrlDecode(const std::string& encoded, std::string* value) {
  54   std::string buffer;
  55   base::ReplaceChars(encoded, "-", "+", &buffer);
  56   base::ReplaceChars(buffer, "_", "/", &buffer);
  57   return base::Base64Decode(buffer, value) && !value->empty();
  58 }
  59
  60 }  // namespace
  61
  62 ResourceCache::ResourceCache(
  63     const base::FilePath& cache_dir,
  64     scoped_refptr<base::SequencedTaskRunner> task_runner)
  65     : cache_dir_(cache_dir),
  66       task_runner_(task_runner) {
  67 }
  68
  69 ResourceCache::~ResourceCache() {
  70   DCHECK(task_runner_->RunsTasksOnCurrentThread());
  71 }
  72
  73 bool ResourceCache::Store(const std::string& key,
  74                           const std::string& subkey,
  75                           const std::string& data) {
  76   DCHECK(task_runner_->RunsTasksOnCurrentThread());
  77   base::FilePath subkey_path;
  78   // Delete the file before writing to it. This ensures that the write does not
  79   // follow a symlink planted at |subkey_path|, clobbering a file outside the
  80   // cache directory. The mechanism is meant to foil file-system-level attacks
  81   // where a symlink is planted in the cache directory before Chrome has
  82   // started. An attacker controlling a process running concurrently with Chrome
  83   // would be able to race against the protection by re-creating the symlink
  84   // between these two calls. There is nothing in file_util that could be used
  85   // to protect against such races, especially as the cache is cross-platform
  86   // and therefore cannot use any POSIX-only tricks.
  87   int size = base::checked_cast<int>(data.size());
  88   return VerifyKeyPathAndGetSubkeyPath(key, true, subkey, &subkey_path) &&
  89          base::DeleteFile(subkey_path, false) &&
  90          (base::WriteFile(subkey_path, data.data(), size) == size);
  91 }
  92
  93 bool ResourceCache::Load(const std::string& key,
  94                          const std::string& subkey,
  95                          std::string* data) {
  96   DCHECK(task_runner_->RunsTasksOnCurrentThread());
  97   base::FilePath subkey_path;
  98   // Only read from |subkey_path| if it is not a symlink.
  99   if (!VerifyKeyPathAndGetSubkeyPath(key, false, subkey, &subkey_path) ||
 100       base::IsLink(subkey_path)) {
 101     return false;
 102   }
 103   data->clear();
 104   return base::ReadFileToString(subkey_path, data);
 105 }
 106
 107 void ResourceCache::LoadAllSubkeys(
 108     const std::string& key,
 109     std::map<std::string, std::string>* contents) {
 110   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 111   contents->clear();
 112   base::FilePath key_path;
 113   if (!VerifyKeyPath(key, false, &key_path))
 114     return;
 115
 116   base::FileEnumerator enumerator(key_path, false, base::FileEnumerator::FILES);
 117   for (base::FilePath path = enumerator.Next(); !path.empty();
 118        path = enumerator.Next()) {
 119     const std::string encoded_subkey = path.BaseName().MaybeAsASCII();
 120     std::string subkey;
 121     std::string data;
 122     // Only read from |subkey_path| if it is not a symlink and its name is
 123     // a base64-encoded string.
 124     if (!base::IsLink(path) &&
 125         Base64UrlDecode(encoded_subkey, &subkey) &&
 126         base::ReadFileToString(path, &data)) {
 127       (*contents)[subkey].swap(data);
 128     }
 129   }
 130 }
 131
 132 void ResourceCache::Delete(const std::string& key, const std::string& subkey) {
 133   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 134   base::FilePath subkey_path;
 135   if (VerifyKeyPathAndGetSubkeyPath(key, false, subkey, &subkey_path))
 136     base::DeleteFile(subkey_path, false);
 137   // Delete() does nothing if the directory given to it is not empty. Hence, the
 138   // call below deletes the directory representing |key| if its last subkey was
 139   // just removed and does nothing otherwise.
 140   base::DeleteFile(subkey_path.DirName(), false);
 141 }
 142
 143 void ResourceCache::Clear(const std::string& key) {
 144   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 145   base::FilePath key_path;
 146   if (VerifyKeyPath(key, false, &key_path))
 147     base::DeleteFile(key_path, true);
 148 }
 149
 150 void ResourceCache::FilterSubkeys(const std::string& key,
 151                                   const SubkeyFilter& test) {
 152   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 153
 154   base::FilePath key_path;
 155   if (!VerifyKeyPath(key, false, &key_path))
 156     return;
 157
 158   base::FileEnumerator enumerator(key_path, false, base::FileEnumerator::FILES);
 159   for (base::FilePath subkey_path = enumerator.Next();
 160        !subkey_path.empty(); subkey_path = enumerator.Next()) {
 161     std::string subkey;
 162     // Delete files with invalid names, and files whose subkey doesn't pass the
 163     // filter.
 164     if (!Base64UrlDecode(subkey_path.BaseName().MaybeAsASCII(), &subkey) ||
 165         test.Run(subkey)) {
 166       base::DeleteFile(subkey_path, true);
 167     }
 168   }
 169
 170   // Delete() does nothing if the directory given to it is not empty. Hence, the
 171   // call below deletes the directory representing |key| if all of its subkeys
 172   // were just removed and does nothing otherwise.
 173   base::DeleteFile(key_path, false);
 174 }
 175
 176 void ResourceCache::PurgeOtherKeys(const std::set<std::string>& keys_to_keep) {
 177   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 178   std::set<std::string> encoded_keys_to_keep;
 179   if (!Base64UrlEncode(keys_to_keep, &encoded_keys_to_keep))
 180     return;
 181
 182   base::FileEnumerator enumerator(
 183       cache_dir_, false, base::FileEnumerator::DIRECTORIES);
 184   for (base::FilePath path = enumerator.Next(); !path.empty();
 185        path = enumerator.Next()) {
 186     const std::string name(path.BaseName().MaybeAsASCII());
 187     if (encoded_keys_to_keep.find(name) == encoded_keys_to_keep.end())
 188       base::DeleteFile(path, true);
 189   }
 190 }
 191
 192 void ResourceCache::PurgeOtherSubkeys(
 193     const std::string& key,
 194     const std::set<std::string>& subkeys_to_keep) {
 195   DCHECK(task_runner_->RunsTasksOnCurrentThread());
 196   base::FilePath key_path;
 197   if (!VerifyKeyPath(key, false, &key_path))
 198     return;
 199
 200   std::set<std::string> encoded_subkeys_to_keep;
 201   if (!Base64UrlEncode(subkeys_to_keep, &encoded_subkeys_to_keep))
 202     return;
 203
 204   base::FileEnumerator enumerator(key_path, false, base::FileEnumerator::FILES);
 205   for (base::FilePath path = enumerator.Next(); !path.empty();
 206        path = enumerator.Next()) {
 207     const std::string name(path.BaseName().MaybeAsASCII());
 208     if (encoded_subkeys_to_keep.find(name) == encoded_subkeys_to_keep.end())
 209       base::DeleteFile(path, false);
 210   }
 211   // Delete() does nothing if the directory given to it is not empty. Hence, the
 212   // call below deletes the directory representing |key| if all of its subkeys
 213   // were just removed and does nothing otherwise.
 214   base::DeleteFile(key_path, false);
 215 }
 216
 217 bool ResourceCache::VerifyKeyPath(const std::string& key,
 218                                   bool allow_create,
 219                                   base::FilePath* path) {
 220   std::string encoded;
 221   if (!Base64UrlEncode(key, &encoded))
 222     return false;
 223   *path = cache_dir_.AppendASCII(encoded);
 224   return allow_create ? base::CreateDirectory(*path) :
 225                         base::DirectoryExists(*path);
 226 }
 227
 228 bool ResourceCache::VerifyKeyPathAndGetSubkeyPath(const std::string& key,
 229                                                   bool allow_create_key,
 230                                                   const std::string& subkey,
 231                                                   base::FilePath* path) {
 232   base::FilePath key_path;
 233   std::string encoded;
 234   if (!VerifyKeyPath(key, allow_create_key, &key_path) ||
 235       !Base64UrlEncode(subkey, &encoded)) {
 236     return false;
 237   }
 238   *path = key_path.AppendASCII(encoded);
 239   return true;
 240 }
 241
 242
 243 }  // namespace policy