base/rand_util_posix.cc

   1 // Copyright (c) 2012 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 "base/rand_util.h"
   6
   7 #include <errno.h>
   8 #include <fcntl.h>
   9 #include <unistd.h>
  10
  11 #include "base/files/file_util.h"
  12 #include "base/lazy_instance.h"
  13 #include "base/logging.h"
  14
  15 namespace {
  16
  17 // We keep the file descriptor for /dev/urandom around so we don't need to
  18 // reopen it (which is expensive), and since we may not even be able to reopen
  19 // it if we are later put in a sandbox. This class wraps the file descriptor so
  20 // we can use LazyInstance to handle opening it on the first access.
  21 class URandomFd {
  22  public:
  23   URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) {
  24     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
  25   }
  26
  27   ~URandomFd() { close(fd_); }
  28
  29   int fd() const { return fd_; }
  30
  31  private:
  32   const int fd_;
  33 };
  34
  35 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
  36
  37 }  // namespace
  38
  39 namespace base {
  40
  41 // NOTE: This function must be cryptographically secure. http://crbug.com/140076
  42 uint64 RandUint64() {
  43   uint64 number;
  44   RandBytes(&number, sizeof(number));
  45   return number;
  46 }
  47
  48 void RandBytes(void* output, size_t output_length) {
  49   const int urandom_fd = g_urandom_fd.Pointer()->fd();
  50   const bool success =
  51       ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
  52   CHECK(success);
  53 }
  54
  55 int GetUrandomFD(void) {
  56   return g_urandom_fd.Pointer()->fd();
  57 }
  58
  59 }  // namespace base