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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 <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 = ReadFromFD(urandom_fd, reinterpret_cast<char*>(&number),
     50                             sizeof(number));
     51   CHECK(success);
     52 
     53   return number;
     54 }
     55 
     56 int GetUrandomFD(void) {
     57   return g_urandom_fd.Pointer()->fd();
     58 }
     59 
     60 }  // namespace base
     61