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: URandomFd()25 URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) { 26 DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno; 27 } 28 ~URandomFd()29 ~URandomFd() { close(fd_); } 30 fd() const31 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 RandUint64()44uint64_t RandUint64() { 45 uint64_t number; 46 RandBytes(&number, sizeof(number)); 47 return number; 48 } 49 RandBytes(void * output,size_t output_length)50void 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 GetUrandomFD(void)57int GetUrandomFD(void) { 58 return g_urandom_fd.Pointer()->fd(); 59 } 60 61 } // namespace base 62