base/rand_util_posix.cc

   1 // Copyright (c) 2011 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 #include "base/rand_util_c.h"
   7
   8 #include <errno.h>
   9 #include <fcntl.h>
  10 #include <unistd.h>
  11
  12 #include "base/file_util.h"
  13 #include "base/lazy_instance.h"
  14 #include "base/logging.h"
  15
  16 namespace {
  17
  18 // We keep the file descriptor for /dev/urandom around so we don't need to
  19 // reopen it (which is expensive), and since we may not even be able to reopen
  20 // it if we are later put in a sandbox. This class wraps the file descriptor so
  21 // we can use LazyInstance to handle opening it on the first access.
  22 class URandomFd {
  23  public:
  24   URandomFd() {
  25     fd_ = open("/dev/urandom", O_RDONLY);
  26     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
  27   }
  28
  29   ~URandomFd() {
  30     close(fd_);
  31   }
  32
  33   int fd() const { return fd_; }
  34
  35  private:
  36   int fd_;
  37 };
  38
  39 base::LazyInstance<URandomFd> g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
  40
  41 }  // namespace
  42
  43 namespace base {
  44
  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 }  // namespace base
  58
  59 int GetUrandomFD(void) {
  60   return g_urandom_fd.Pointer()->fd();
  61 }