summaryrefslogtreecommitdiff
path: root/absl/random/internal/seed_material.cc
blob: 1041302b587095baf9c5db646b9819c57d8c905f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/random/internal/seed_material.h"

#include <fcntl.h>

#ifndef _WIN32
#include <unistd.h>
#else
#include <io.h>
#endif

#include <algorithm>
#include <cerrno>
#include <cstdint>
#include <cstdlib>
#include <cstring>

#include "absl/base/dynamic_annotations.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/strings/ascii.h"
#include "absl/strings/escaping.h"
#include "absl/strings/string_view.h"
#include "absl/strings/strip.h"

#if defined(__native_client__)

#include <nacl/nacl_random.h>
#define ABSL_RANDOM_USE_NACL_SECURE_RANDOM 1

#elif defined(_WIN32)

#include <windows.h>
#define ABSL_RANDOM_USE_BCRYPT 1
#pragma comment(lib, "bcrypt.lib")

#elif defined(__Fuchsia__)
#include <zircon/syscalls.h>

#endif

#if defined(__GLIBC__) && \
    (__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 25))
// glibc >= 2.25 has getentropy()
#define ABSL_RANDOM_USE_GET_ENTROPY 1
#endif

#if defined(__EMSCRIPTEN__)
#include <sys/random.h>
// Emscripten has getentropy, but it resides in a different header.
#define ABSL_RANDOM_USE_GET_ENTROPY 1
#endif

#if defined(ABSL_RANDOM_USE_BCRYPT)
#include <bcrypt.h>

#ifndef BCRYPT_SUCCESS
#define BCRYPT_SUCCESS(Status) (((NTSTATUS)(Status)) >= 0)
#endif
// Also link bcrypt; this can be done via linker options or:
// #pragma comment(lib, "bcrypt.lib")
#endif

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace random_internal {
namespace {

// Read OS Entropy for random number seeds.
// TODO(absl-team): Possibly place a cap on how much entropy may be read at a
// time.

#if defined(ABSL_RANDOM_USE_BCRYPT)

// On Windows potentially use the BCRYPT CNG API to read available entropy.
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
  BCRYPT_ALG_HANDLE hProvider;
  NTSTATUS ret;
  ret = BCryptOpenAlgorithmProvider(&hProvider, BCRYPT_RNG_ALGORITHM,
                                    MS_PRIMITIVE_PROVIDER, 0);
  if (!(BCRYPT_SUCCESS(ret))) {
    ABSL_RAW_LOG(ERROR, "Failed to open crypto provider.");
    return false;
  }
  ret = BCryptGenRandom(
      hProvider,                                             // provider
      reinterpret_cast<UCHAR*>(values.data()),               // buffer
      static_cast<ULONG>(sizeof(uint32_t) * values.size()),  // bytes
      0);                                                    // flags
  BCryptCloseAlgorithmProvider(hProvider, 0);
  return BCRYPT_SUCCESS(ret);
}

#elif defined(ABSL_RANDOM_USE_NACL_SECURE_RANDOM)

// On NaCL use nacl_secure_random to acquire bytes.
bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
  auto buffer = reinterpret_cast<uint8_t*>(values.data());
  size_t buffer_size = sizeof(uint32_t) * values.size();

  uint8_t* output_ptr = buffer;
  while (buffer_size > 0) {
    size_t nread = 0;
    const int error = nacl_secure_random(output_ptr, buffer_size, &nread);
    if (error != 0 || nread > buffer_size) {
      ABSL_RAW_LOG(ERROR, "Failed to read secure_random seed data: %d", error);
      return false;
    }
    output_ptr += nread;
    buffer_size -= nread;
  }
  return true;
}

#elif defined(__Fuchsia__)

bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
  auto buffer = reinterpret_cast<uint8_t*>(values.data());
  size_t buffer_size = sizeof(uint32_t) * values.size();
  zx_cprng_draw(buffer, buffer_size);
  return true;
}

#else

#if defined(ABSL_RANDOM_USE_GET_ENTROPY)
// On *nix, use getentropy() if supported. Note that libc may support
// getentropy(), but the kernel may not, in which case this function will return
// false.
bool ReadSeedMaterialFromGetEntropy(absl::Span<uint32_t> values) {
  auto buffer = reinterpret_cast<uint8_t*>(values.data());
  size_t buffer_size = sizeof(uint32_t) * values.size();
  while (buffer_size > 0) {
    // getentropy() has a maximum permitted length of 256.
    size_t to_read = std::min<size_t>(buffer_size, 256);
    int result = getentropy(buffer, to_read);
    if (result < 0) {
      return false;
    }
    // https://github.com/google/sanitizers/issues/1173
    // MemorySanitizer can't see through getentropy().
    ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(buffer, to_read);
    buffer += to_read;
    buffer_size -= to_read;
  }
  return true;
}
#endif  // defined(ABSL_RANDOM_GETENTROPY)

// On *nix, read entropy from /dev/urandom.
bool ReadSeedMaterialFromDevURandom(absl::Span<uint32_t> values) {
  const char kEntropyFile[] = "/dev/urandom";

  auto buffer = reinterpret_cast<uint8_t*>(values.data());
  size_t buffer_size = sizeof(uint32_t) * values.size();

  int dev_urandom = open(kEntropyFile, O_RDONLY);
  bool success = (-1 != dev_urandom);
  if (!success) {
    return false;
  }

  while (success && buffer_size > 0) {
    ssize_t bytes_read = read(dev_urandom, buffer, buffer_size);
    int read_error = errno;
    success = (bytes_read > 0);
    if (success) {
      buffer += bytes_read;
      buffer_size -= static_cast<size_t>(bytes_read);
    } else if (bytes_read == -1 && read_error == EINTR) {
      success = true;  // Need to try again.
    }
  }
  close(dev_urandom);
  return success;
}

bool ReadSeedMaterialFromOSEntropyImpl(absl::Span<uint32_t> values) {
#if defined(ABSL_RANDOM_USE_GET_ENTROPY)
  if (ReadSeedMaterialFromGetEntropy(values)) {
    return true;
  }
#endif
  // Libc may support getentropy, but the kernel may not, so we still have
  // to fallback to ReadSeedMaterialFromDevURandom().
  return ReadSeedMaterialFromDevURandom(values);
}

#endif

}  // namespace

bool ReadSeedMaterialFromOSEntropy(absl::Span<uint32_t> values) {
  assert(values.data() != nullptr);
  if (values.data() == nullptr) {
    return false;
  }
  if (values.empty()) {
    return true;
  }
  return ReadSeedMaterialFromOSEntropyImpl(values);
}

void MixIntoSeedMaterial(absl::Span<const uint32_t> sequence,
                         absl::Span<uint32_t> seed_material) {
  // Algorithm is based on code available at
  // https://gist.github.com/imneme/540829265469e673d045
  constexpr uint32_t kInitVal = 0x43b0d7e5;
  constexpr uint32_t kHashMul = 0x931e8875;
  constexpr uint32_t kMixMulL = 0xca01f9dd;
  constexpr uint32_t kMixMulR = 0x4973f715;
  constexpr uint32_t kShiftSize = sizeof(uint32_t) * 8 / 2;

  uint32_t hash_const = kInitVal;
  auto hash = [&](uint32_t value) {
    value ^= hash_const;
    hash_const *= kHashMul;
    value *= hash_const;
    value ^= value >> kShiftSize;
    return value;
  };

  auto mix = [&](uint32_t x, uint32_t y) {
    uint32_t result = kMixMulL * x - kMixMulR * y;
    result ^= result >> kShiftSize;
    return result;
  };

  for (const auto& seq_val : sequence) {
    for (auto& elem : seed_material) {
      elem = mix(elem, hash(seq_val));
    }
  }
}

absl::optional<uint32_t> GetSaltMaterial() {
  // Salt must be common for all generators within the same process so read it
  // only once and store in static variable.
  static const auto salt_material = []() -> absl::optional<uint32_t> {
    uint32_t salt_value = 0;

    if (random_internal::ReadSeedMaterialFromOSEntropy(
            MakeSpan(&salt_value, 1))) {
      return salt_value;
    }

    return absl::nullopt;
  }();

  return salt_material;
}

}  // namespace random_internal
ABSL_NAMESPACE_END
}  // namespace absl