src/entropy.cpp

   1 /*
   2  * Copyright (c) 2000-2004 Apple Computer, Inc. All Rights Reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
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  18  * Please see the License for the specific language governing rights and
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  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24
  25 //
  26 // EntropyManager - manage entropy on the system.
  27 //
  28 // Here is our mission:
  29 // (1) On startup, read the entropy file and seed it into the RNG for initial use
  30 // (2) Periodically, collect entropy from the system and seed it into the RNG
  31 // (3) Once in a while, take entropy from the RNG and write it to the entropy file
  32 //   for use across reboots.
  33 //
  34 // This class will fail to operate if the process has (and retains) root privileges.
  35 // We re-open the entropy file on each use so that we don't work with a "phantom"
  36 // file that some fool administrator removed yesterday.
  37 //
  38 #include "entropy.h"
  39 #include <sys/sysctl.h>
  40 #include <mach/clock_types.h>
  41 #include <errno.h>
  42 #include <security_utilities/logging.h>
  43 #include <sys/sysctl.h>
  44 #include <security_utilities/debugging.h>
  45
  46 /* when true, action() called every 15 seconds */
  47 #define ENTROPY_QUICK_UPDATE    0
  48 #if             ENTROPY_QUICK_UPDATE
  49 #define COLLECT_INTERVAL                15
  50 #else
  51 #define COLLECT_INTERVAL                collectInterval
  52 #endif  //ENTROPY_QUICK_UPDATE
  53
  54 using namespace UnixPlusPlus;
  55
  56
  57 //
  58 // During construction, we perform initial entropy file recovery.
  59 //
  60 EntropyManager::EntropyManager(MachPlusPlus::MachServer &srv, const char *entropyFile)
  61     : DevRandomGenerator(true), server(srv),
  62     mEntropyFilePath(entropyFile), mNextUpdate(Time::now())
  63 {
  64     // Read the entropy file and seed the RNG. It is not an error if we can't find one.
  65     try {
  66         AutoFileDesc oldEntropyFile(entropyFile, O_RDONLY);
  67         char buffer[entropyFileSize];
  68         if (size_t size = oldEntropyFile.read(buffer))
  69             addEntropy(buffer, size);
  70     } catch (...) { }
  71
  72     // go through a collect/update/reschedule cycle immediately
  73     action();
  74 }
  75
  76
  77 //
  78 // Timer action
  79 //
  80 void EntropyManager::action()
  81 {
  82     collectEntropy();
  83     updateEntropyFile();
  84
  85     server.setTimer(this, Time::Interval(COLLECT_INTERVAL));    // drifting reschedule (desired)
  86 }
  87
  88
  89 //
  90 // Collect system timings and seed into the RNG.
  91 // Note that the sysctl will block until the buffer is full or the timeout expires.
  92 // We currently use a 1ms timeout, which almost always fills the buffer and
  93 // does not provide enough of a delay to worry about it. If we ever get worried,
  94 // we could call longTermActivity on the server object to get another thread going.
  95 //
  96 void EntropyManager::collectEntropy()
  97 {
  98     int mib[4];
  99     mib[0] = CTL_KERN;
 100     mib[1] = KERN_KDEBUG;
 101     mib[2] = KERN_KDGETENTROPY;
 102     mib[3] = 1; // milliseconds maximum delay
 103     mach_timespec_t timings[timingsToCollect];
 104     size_t size = sizeof(timings);
 105     int ret = sysctl(mib, 4, timings, &size, NULL, 0);
 106     if (ret == -1) {
 107         Syslog::alert("entropy collection failed (errno=%d)", errno);
 108         return;
 109     }
 110     char buffer[timingsToCollect];
 111     for (unsigned n = 0; n < size; n++)
 112         buffer[n] = timings[n].tv_nsec; // truncating to LSB
 113         secdebug("entropy", "Entropy size %d: %02x %02x %02x %02x %02x %02x %02x %02x...",
 114                 (int)size,
 115                 (unsigned char)buffer[0], (unsigned char)buffer[1], (unsigned char)buffer[2],
 116                 (unsigned char)buffer[3], (unsigned char)buffer[4], (unsigned char)buffer[5],
 117                 (unsigned char)buffer[6], (unsigned char)buffer[7]);
 118     addEntropy(buffer, size);
 119 }
 120
 121
 122 //
 123 // (Re)write the entropy file with random data pulled from the RNG
 124 //
 125 void EntropyManager::updateEntropyFile()
 126 {
 127     if (Time::now() >= mNextUpdate) {
 128         try {
 129                         mNextUpdate = Time::now() + Time::Interval(updateInterval);
 130             secdebug("entropy", "updating %s", mEntropyFilePath.c_str());
 131                 char buffer[entropyFileSize];
 132                         random(buffer, entropyFileSize);
 133             AutoFileDesc entropyFile(mEntropyFilePath.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0600);
 134             if (entropyFile.write(buffer) != entropyFileSize)
 135                 Syslog::warning("short write on entropy file %s", mEntropyFilePath.c_str());
 136         } catch (...) {
 137             Syslog::warning("error writing entropy file %s", mEntropyFilePath.c_str());
 138         }
 139     }
 140 }
 141