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/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() {
  24     fd_ = open("/dev/urandom", O_RDONLY);
  25     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
  26   }
  27
  28   ~URandomFd() {
  29     close(fd_);
  30   }
  31
  32   int fd() const { return fd_; }
  33
  34  private:
  35   int fd_;
  36 };
  37
  38 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
  39
  40 }  // namespace
  41
  42 namespace base {
  43
  44 // NOTE: This function must be cryptographically secure. http://crbug.com/140076
  45 uint64 RandUint64() {
  46   uint64 number;
  47
  48   int urandom_fd = g_urandom_fd.Pointer()->fd();
  49   bool success = file_util::ReadFromFD(urandom_fd,
  50                                        reinterpret_cast<char*>(&number),
  51                                        sizeof(number));
  52   CHECK(success);
  53
  54   return number;
  55 }
  56
  57 int GetUrandomFD(void) {
  58   return g_urandom_fd.Pointer()->fd();
  59 }
  60
  61 }  // namespace base