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 #include "base/posix/eintr_wrapper.h" 17 18 namespace { 19 20 // We keep the file descriptor for /dev/urandom around so we don't need to 21 // reopen it (which is expensive), and since we may not even be able to reopen 22 // it if we are later put in a sandbox. This class wraps the file descriptor so 23 // we can use LazyInstance to handle opening it on the first access. 24 class URandomFd { 25 public: 26 URandomFd() : fd_(HANDLE_EINTR(open("/dev/urandom", O_RDONLY | O_CLOEXEC))) { 27 DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno; 28 } 29 30 ~URandomFd() { close(fd_); } 31 32 int fd() const { return fd_; } 33 34 private: 35 const 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_t RandUint64() { 46 uint64_t number; 47 RandBytes(&number, sizeof(number)); 48 return number; 49 } 50 51 void RandBytes(void* output, size_t output_length) { 52 const int urandom_fd = g_urandom_fd.Pointer()->fd(); 53 const bool success = 54 ReadFromFD(urandom_fd, static_cast<char*>(output), output_length); 55 CHECK(success); 56 } 57 58 int GetUrandomFD(void) { 59 return g_urandom_fd.Pointer()->fd(); 60 } 61 62 } // namespace base 63
