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      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 <stddef.h>
     10 #include <stdint.h>
     11 #include <unistd.h>
     12 
     13 #include "base/files/file_util.h"
     14 #include "base/lazy_instance.h"
     15 #include "base/logging.h"
     16 
     17 namespace {
     18 
     19 // We keep the file descriptor for /dev/urandom around so we don't need to
     20 // reopen it (which is expensive), and since we may not even be able to reopen
     21 // it if we are later put in a sandbox. This class wraps the file descriptor so
     22 // we can use LazyInstance to handle opening it on the first access.
     23 class URandomFd {
     24  public:
     25   URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) {
     26     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
     27   }
     28 
     29   ~URandomFd() { close(fd_); }
     30 
     31   int fd() const { return fd_; }
     32 
     33  private:
     34   const int fd_;
     35 };
     36 
     37 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
     38 
     39 }  // namespace
     40 
     41 namespace base {
     42 
     43 // NOTE: This function must be cryptographically secure. http://crbug.com/140076
     44 uint64_t RandUint64() {
     45   uint64_t number;
     46   RandBytes(&number, sizeof(number));
     47   return number;
     48 }
     49 
     50 void RandBytes(void* output, size_t output_length) {
     51   const int urandom_fd = g_urandom_fd.Pointer()->fd();
     52   const bool success =
     53       ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
     54   CHECK(success);
     55 }
     56 
     57 int GetUrandomFD(void) {
     58   return g_urandom_fd.Pointer()->fd();
     59 }
     60 
     61 }  // namespace base
     62