blob: fe73b960f948222007fceafd0213eceadc526e3b [file] [log] [blame]
// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/rand_util.h"
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include "base/files/file_util.h"
#include "base/lazy_instance.h"
#include "base/logging.h"
namespace {
// We keep the file descriptor for /dev/urandom around so we don't need to
// reopen it (which is expensive), and since we may not even be able to reopen
// it if we are later put in a sandbox. This class wraps the file descriptor so
// we can use LazyInstance to handle opening it on the first access.
class URandomFd {
URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) {
DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
~URandomFd() { close(fd_); }
int fd() const { return fd_; }
const int fd_;
base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
} // namespace
namespace base {
// NOTE: This function must be cryptographically secure.
uint64 RandUint64() {
uint64 number;
RandBytes(&number, sizeof(number));
return number;
void RandBytes(void* output, size_t output_length) {
const int urandom_fd = g_urandom_fd.Pointer()->fd();
const bool success =
ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
int GetUrandomFD(void) {
return g_urandom_fd.Pointer()->fd();
} // namespace base