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: URandomFd()23 URandomFd() { 24 fd_ = open("/dev/urandom", O_RDONLY); 25 DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno; 26 } 27 ~URandomFd()28 ~URandomFd() { 29 close(fd_); 30 } 31 fd() const32 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 RandUint64()45uint64 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 GetUrandomFD(void)56int GetUrandomFD(void) { 57 return g_urandom_fd.Pointer()->fd(); 58 } 59 60 } // namespace base 61