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/files/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() : fd_(open("/dev/urandom", O_RDONLY)) { 24 DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno; 25 } 26 27 ~URandomFd() { close(fd_); } 28 29 int fd() const { return fd_; } 30 31 private: 32 const int fd_; 33 }; 34 35 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER; 36 37 } // namespace 38 39 namespace base { 40 41 // NOTE: This function must be cryptographically secure. http://crbug.com/140076 42 uint64 RandUint64() { 43 uint64 number; 44 RandBytes(&number, sizeof(number)); 45 return number; 46 } 47 48 void RandBytes(void* output, size_t output_length) { 49 const int urandom_fd = g_urandom_fd.Pointer()->fd(); 50 const bool success = 51 ReadFromFD(urandom_fd, static_cast<char*>(output), output_length); 52 CHECK(success); 53 } 54 55 int GetUrandomFD(void) { 56 return g_urandom_fd.Pointer()->fd(); 57 } 58 59 } // namespace base 60
