1
// Copyright (c) 2017-2022 Cloudflare, Inc.
2
// Licensed under the Apache 2.0 license found in the LICENSE file or at:
3
//     https://opensource.org/licenses/Apache-2.0
4
 
5
#include "entropy.h"
6
 
7
#include <ncrypto.h>
8
#include <openssl/crypto.h>
9
#include <openssl/rand.h>
10
 
11
#include <kj/debug.h>
12
#include <kj/exception.h>
13
 
14
#ifdef __unix__
15
#include <unistd.h>
16
#endif
17
 
18
namespace workerd {
19
 
20
void getEntropy(kj::ArrayPtr<kj::byte> output) {
21
  static constexpr size_t BUFFER_SIZE = 4096;
22
  struct BufferState {
23
    kj::FixedArray<kj::byte, BUFFER_SIZE> store;
24
    kj::ArrayPtr<kj::byte> data;  // Starts empty to trigger initial fill
25
#if defined(KJ_DEBUG) && defined(__unix__)
26
        // Track the PID separately to detect cross-fork usage.
27
    // This should be preserved across fork so we can detect PID changes.
28
    pid_t lastSeenPid = 0;
29
#endif
30
  };
31
 
32
  thread_local BufferState state{};
33
 
34
#if defined(KJ_DEBUG) && defined(__unix__)
35
  // Verify that getpid() hasn't changed. This code should be called strictly post-fork.
36
  // If we see crashes here in tests, it means there's some pre-fork call to getEntropy()
37
  // that needs to be removed.
38
  pid_t currentPid = getpid();
39
  if (state.lastSeenPid == 0) {
40
    state.lastSeenPid = currentPid;
41
  } else {
42
    KJ_ASSERT(state.lastSeenPid == currentPid,
43
        "PID changed from previous call to getEntropy() - this indicates a pre-fork call "
44
        "to getEntropy() that should be removed",
45
        state.lastSeenPid, currentPid);
46
  }
47
#endif
48
 
49
  while (output != nullptr) {
50
    if (state.data == nullptr) {
51
      ncrypto::ClearErrorOnReturn clearErrorOnReturn;
52
      if (RAND_bytes(state.store.begin(), BUFFER_SIZE) != 1) {
53
        KJ_FAIL_REQUIRE("RAND_bytes failed to generate random data");
54
      }
55
 
56
      state.data = state.store.asPtr();
57
    }
58
 
59
    size_t toCopy = kj::min(state.data.size(), output.size());
60
    output.first(toCopy).copyFrom(state.data.first(toCopy));
61
    // Zero out the source buffer after copying to prevent sensitive data from remaining in memory
62
    OPENSSL_cleanse(state.data.first(toCopy).begin(), toCopy);
63
    state.data = state.data.slice(toCopy);
64
    output = output.slice(toCopy);
65
  }
66
}
67
 
68
}  // namespace workerd