1 //===- FuzzerLoop.cpp - Fuzzer's main loop --------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 // Fuzzer's main loop.
9 //===----------------------------------------------------------------------===//
10 
11 #include "FuzzerCorpus.h"
12 #include "FuzzerIO.h"
13 #include "FuzzerInternal.h"
14 #include "FuzzerMutate.h"
15 #include "FuzzerPlatform.h"
16 #include "FuzzerRandom.h"
17 #include "FuzzerTracePC.h"
18 #include <algorithm>
19 #include <cstring>
20 #include <memory>
21 #include <mutex>
22 #include <set>
23 
24 #if defined(__has_include)
25 #if __has_include(<sanitizer / lsan_interface.h>)
26 #include <sanitizer/lsan_interface.h>
27 #endif
28 #endif
29 
30 #define NO_SANITIZE_MEMORY
31 #if defined(__has_feature)
32 #if __has_feature(memory_sanitizer)
33 #undef NO_SANITIZE_MEMORY
34 #define NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory))
35 #endif
36 #endif
37 
38 namespace fuzzer {
39 static const size_t kMaxUnitSizeToPrint = 256;
40 
41 thread_local bool Fuzzer::IsMyThread;
42 
43 bool RunningUserCallback = false;
44 
45 // Only one Fuzzer per process.
46 static Fuzzer *F;
47 
48 // Leak detection is expensive, so we first check if there were more mallocs
49 // than frees (using the sanitizer malloc hooks) and only then try to call lsan.
50 struct MallocFreeTracer {
51   void Start(int TraceLevel) {
52     this->TraceLevel = TraceLevel;
53     if (TraceLevel)
54       Printf("MallocFreeTracer: START\n");
55     Mallocs = 0;
56     Frees = 0;
57   }
58   // Returns true if there were more mallocs than frees.
59   bool Stop() {
60     if (TraceLevel)
61       Printf("MallocFreeTracer: STOP %zd %zd (%s)\n", Mallocs.load(),
62              Frees.load(), Mallocs == Frees ? "same" : "DIFFERENT");
63     bool Result = Mallocs > Frees;
64     Mallocs = 0;
65     Frees = 0;
66     TraceLevel = 0;
67     return Result;
68   }
69   std::atomic<size_t> Mallocs;
70   std::atomic<size_t> Frees;
71   int TraceLevel = 0;
72 
73   std::recursive_mutex TraceMutex;
74   bool TraceDisabled = false;
75 };
76 
77 static MallocFreeTracer AllocTracer;
78 
79 // Locks printing and avoids nested hooks triggered from mallocs/frees in
80 // sanitizer.
81 class TraceLock {
82 public:
83   TraceLock() : Lock(AllocTracer.TraceMutex) {
84     AllocTracer.TraceDisabled = !AllocTracer.TraceDisabled;
85   }
86   ~TraceLock() { AllocTracer.TraceDisabled = !AllocTracer.TraceDisabled; }
87 
88   bool IsDisabled() const {
89     // This is already inverted value.
90     return !AllocTracer.TraceDisabled;
91   }
92 
93 private:
94   std::lock_guard<std::recursive_mutex> Lock;
95 };
96 
97 ATTRIBUTE_NO_SANITIZE_MEMORY
98 void MallocHook(const volatile void *ptr, size_t size) {
99   size_t N = AllocTracer.Mallocs++;
100   F->HandleMalloc(size);
101   if (int TraceLevel = AllocTracer.TraceLevel) {
102     TraceLock Lock;
103     if (Lock.IsDisabled())
104       return;
105     Printf("MALLOC[%zd] %p %zd\n", N, ptr, size);
106     if (TraceLevel >= 2 && EF)
107       PrintStackTrace();
108   }
109 }
110 
111 ATTRIBUTE_NO_SANITIZE_MEMORY
112 void FreeHook(const volatile void *ptr) {
113   size_t N = AllocTracer.Frees++;
114   if (int TraceLevel = AllocTracer.TraceLevel) {
115     TraceLock Lock;
116     if (Lock.IsDisabled())
117       return;
118     Printf("FREE[%zd]   %p\n", N, ptr);
119     if (TraceLevel >= 2 && EF)
120       PrintStackTrace();
121   }
122 }
123 
124 // Crash on a single malloc that exceeds the rss limit.
125 void Fuzzer::HandleMalloc(size_t Size) {
126   if (!Options.MallocLimitMb || (Size >> 20) < (size_t)Options.MallocLimitMb)
127     return;
128   Printf("==%d== ERROR: libFuzzer: out-of-memory (malloc(%zd))\n", GetPid(),
129          Size);
130   Printf("   To change the out-of-memory limit use -rss_limit_mb=<N>\n\n");
131   PrintStackTrace();
132   DumpCurrentUnit("oom-");
133   Printf("SUMMARY: libFuzzer: out-of-memory\n");
134   PrintFinalStats();
135   _Exit(Options.OOMExitCode); // Stop right now.
136 }
137 
138 Fuzzer::Fuzzer(UserCallback CB, InputCorpus &Corpus, MutationDispatcher &MD,
139                FuzzingOptions Options)
140     : CB(CB), Corpus(Corpus), MD(MD), Options(Options) {
141   if (EF->__sanitizer_set_death_callback)
142     EF->__sanitizer_set_death_callback(StaticDeathCallback);
143   assert(!F);
144   F = this;
145   TPC.ResetMaps();
146   IsMyThread = true;
147   if (Options.DetectLeaks && EF->__sanitizer_install_malloc_and_free_hooks)
148     EF->__sanitizer_install_malloc_and_free_hooks(MallocHook, FreeHook);
149   TPC.SetUseCounters(Options.UseCounters);
150   TPC.SetUseValueProfileMask(Options.UseValueProfile);
151 
152   if (Options.Verbosity)
153     TPC.PrintModuleInfo();
154   if (!Options.OutputCorpus.empty() && Options.ReloadIntervalSec)
155     EpochOfLastReadOfOutputCorpus = GetEpoch(Options.OutputCorpus);
156   MaxInputLen = MaxMutationLen = Options.MaxLen;
157   TmpMaxMutationLen = 0;  // Will be set once we load the corpus.
158   AllocateCurrentUnitData();
159   CurrentUnitSize = 0;
160   memset(BaseSha1, 0, sizeof(BaseSha1));
161 }
162 
163 Fuzzer::~Fuzzer() {}
164 
165 void Fuzzer::AllocateCurrentUnitData() {
166   if (CurrentUnitData || MaxInputLen == 0)
167     return;
168   CurrentUnitData = new uint8_t[MaxInputLen];
169 }
170 
171 void Fuzzer::StaticDeathCallback() {
172   assert(F);
173   F->DeathCallback();
174 }
175 
176 void Fuzzer::DumpCurrentUnit(const char *Prefix) {
177   if (!CurrentUnitData)
178     return; // Happens when running individual inputs.
179   ScopedDisableMsanInterceptorChecks S;
180   MD.PrintMutationSequence();
181   Printf("; base unit: %s\n", Sha1ToString(BaseSha1).c_str());
182   size_t UnitSize = CurrentUnitSize;
183   if (UnitSize <= kMaxUnitSizeToPrint) {
184     PrintHexArray(CurrentUnitData, UnitSize, "\n");
185     PrintASCII(CurrentUnitData, UnitSize, "\n");
186   }
187   WriteUnitToFileWithPrefix({CurrentUnitData, CurrentUnitData + UnitSize},
188                             Prefix);
189 }
190 
191 NO_SANITIZE_MEMORY
192 void Fuzzer::DeathCallback() {
193   DumpCurrentUnit("crash-");
194   PrintFinalStats();
195 }
196 
197 void Fuzzer::StaticAlarmCallback() {
198   assert(F);
199   F->AlarmCallback();
200 }
201 
202 void Fuzzer::StaticCrashSignalCallback() {
203   assert(F);
204   F->CrashCallback();
205 }
206 
207 void Fuzzer::StaticExitCallback() {
208   assert(F);
209   F->ExitCallback();
210 }
211 
212 void Fuzzer::StaticInterruptCallback() {
213   assert(F);
214   F->InterruptCallback();
215 }
216 
217 void Fuzzer::StaticGracefulExitCallback() {
218   assert(F);
219   F->GracefulExitRequested = true;
220   Printf("INFO: signal received, trying to exit gracefully\n");
221 }
222 
223 void Fuzzer::StaticFileSizeExceedCallback() {
224   Printf("==%lu== ERROR: libFuzzer: file size exceeded\n", GetPid());
225   exit(1);
226 }
227 
228 void Fuzzer::CrashCallback() {
229   if (EF->__sanitizer_acquire_crash_state &&
230       !EF->__sanitizer_acquire_crash_state())
231     return;
232   Printf("==%lu== ERROR: libFuzzer: deadly signal\n", GetPid());
233   PrintStackTrace();
234   Printf("NOTE: libFuzzer has rudimentary signal handlers.\n"
235          "      Combine libFuzzer with AddressSanitizer or similar for better "
236          "crash reports.\n");
237   Printf("SUMMARY: libFuzzer: deadly signal\n");
238   DumpCurrentUnit("crash-");
239   PrintFinalStats();
240   _Exit(Options.ErrorExitCode); // Stop right now.
241 }
242 
243 void Fuzzer::ExitCallback() {
244   if (!RunningUserCallback)
245     return; // This exit did not come from the user callback
246   if (EF->__sanitizer_acquire_crash_state &&
247       !EF->__sanitizer_acquire_crash_state())
248     return;
249   Printf("==%lu== ERROR: libFuzzer: fuzz target exited\n", GetPid());
250   PrintStackTrace();
251   Printf("SUMMARY: libFuzzer: fuzz target exited\n");
252   DumpCurrentUnit("crash-");
253   PrintFinalStats();
254   _Exit(Options.ErrorExitCode);
255 }
256 
257 void Fuzzer::MaybeExitGracefully() {
258   if (!F->GracefulExitRequested) return;
259   Printf("==%lu== INFO: libFuzzer: exiting as requested\n", GetPid());
260   RmDirRecursive(TempPath("FuzzWithFork", ".dir"));
261   F->PrintFinalStats();
262   _Exit(0);
263 }
264 
265 void Fuzzer::InterruptCallback() {
266   Printf("==%lu== libFuzzer: run interrupted; exiting\n", GetPid());
267   PrintFinalStats();
268   ScopedDisableMsanInterceptorChecks S; // RmDirRecursive may call opendir().
269   RmDirRecursive(TempPath("FuzzWithFork", ".dir"));
270   // Stop right now, don't perform any at-exit actions.
271   _Exit(Options.InterruptExitCode);
272 }
273 
274 NO_SANITIZE_MEMORY
275 void Fuzzer::AlarmCallback() {
276   assert(Options.UnitTimeoutSec > 0);
277   // In Windows and Fuchsia, Alarm callback is executed by a different thread.
278   // NetBSD's current behavior needs this change too.
279 #if !LIBFUZZER_WINDOWS && !LIBFUZZER_NETBSD && !LIBFUZZER_FUCHSIA
280   if (!InFuzzingThread())
281     return;
282 #endif
283   if (!RunningUserCallback)
284     return; // We have not started running units yet.
285   size_t Seconds =
286       duration_cast<seconds>(system_clock::now() - UnitStartTime).count();
287   if (Seconds == 0)
288     return;
289   if (Options.Verbosity >= 2)
290     Printf("AlarmCallback %zd\n", Seconds);
291   if (Seconds >= (size_t)Options.UnitTimeoutSec) {
292     if (EF->__sanitizer_acquire_crash_state &&
293         !EF->__sanitizer_acquire_crash_state())
294       return;
295     Printf("ALARM: working on the last Unit for %zd seconds\n", Seconds);
296     Printf("       and the timeout value is %d (use -timeout=N to change)\n",
297            Options.UnitTimeoutSec);
298     DumpCurrentUnit("timeout-");
299     Printf("==%lu== ERROR: libFuzzer: timeout after %d seconds\n", GetPid(),
300            Seconds);
301     PrintStackTrace();
302     Printf("SUMMARY: libFuzzer: timeout\n");
303     PrintFinalStats();
304     _Exit(Options.TimeoutExitCode); // Stop right now.
305   }
306 }
307 
308 void Fuzzer::RssLimitCallback() {
309   if (EF->__sanitizer_acquire_crash_state &&
310       !EF->__sanitizer_acquire_crash_state())
311     return;
312   Printf(
313       "==%lu== ERROR: libFuzzer: out-of-memory (used: %zdMb; limit: %zdMb)\n",
314       GetPid(), GetPeakRSSMb(), Options.RssLimitMb);
315   Printf("   To change the out-of-memory limit use -rss_limit_mb=<N>\n\n");
316   PrintMemoryProfile();
317   DumpCurrentUnit("oom-");
318   Printf("SUMMARY: libFuzzer: out-of-memory\n");
319   PrintFinalStats();
320   _Exit(Options.OOMExitCode); // Stop right now.
321 }
322 
323 void Fuzzer::PrintStats(const char *Where, const char *End, size_t Units,
324                         size_t Features) {
325   size_t ExecPerSec = execPerSec();
326   if (!Options.Verbosity)
327     return;
328   Printf("#%zd\t%s", TotalNumberOfRuns, Where);
329   if (size_t N = TPC.GetTotalPCCoverage())
330     Printf(" cov: %zd", N);
331   if (size_t N = Features ? Features : Corpus.NumFeatures())
332     Printf(" ft: %zd", N);
333   if (!Corpus.empty()) {
334     Printf(" corp: %zd", Corpus.NumActiveUnits());
335     if (size_t N = Corpus.SizeInBytes()) {
336       if (N < (1 << 14))
337         Printf("/%zdb", N);
338       else if (N < (1 << 24))
339         Printf("/%zdKb", N >> 10);
340       else
341         Printf("/%zdMb", N >> 20);
342     }
343     if (size_t FF = Corpus.NumInputsThatTouchFocusFunction())
344       Printf(" focus: %zd", FF);
345   }
346   if (TmpMaxMutationLen)
347     Printf(" lim: %zd", TmpMaxMutationLen);
348   if (Units)
349     Printf(" units: %zd", Units);
350 
351   Printf(" exec/s: %zd", ExecPerSec);
352   Printf(" rss: %zdMb", GetPeakRSSMb());
353   Printf("%s", End);
354 }
355 
356 void Fuzzer::PrintFinalStats() {
357   if (Options.PrintFullCoverage)
358     TPC.PrintCoverage(/*PrintAllCounters=*/true);
359   if (Options.PrintCoverage)
360     TPC.PrintCoverage(/*PrintAllCounters=*/false);
361   if (Options.PrintCorpusStats)
362     Corpus.PrintStats();
363   if (!Options.PrintFinalStats)
364     return;
365   size_t ExecPerSec = execPerSec();
366   Printf("stat::number_of_executed_units: %zd\n", TotalNumberOfRuns);
367   Printf("stat::average_exec_per_sec:     %zd\n", ExecPerSec);
368   Printf("stat::new_units_added:          %zd\n", NumberOfNewUnitsAdded);
369   Printf("stat::slowest_unit_time_sec:    %zd\n", TimeOfLongestUnitInSeconds);
370   Printf("stat::peak_rss_mb:              %zd\n", GetPeakRSSMb());
371 }
372 
373 void Fuzzer::SetMaxInputLen(size_t MaxInputLen) {
374   assert(this->MaxInputLen == 0); // Can only reset MaxInputLen from 0 to non-0.
375   assert(MaxInputLen);
376   this->MaxInputLen = MaxInputLen;
377   this->MaxMutationLen = MaxInputLen;
378   AllocateCurrentUnitData();
379   Printf("INFO: -max_len is not provided; "
380          "libFuzzer will not generate inputs larger than %zd bytes\n",
381          MaxInputLen);
382 }
383 
384 void Fuzzer::SetMaxMutationLen(size_t MaxMutationLen) {
385   assert(MaxMutationLen && MaxMutationLen <= MaxInputLen);
386   this->MaxMutationLen = MaxMutationLen;
387 }
388 
389 void Fuzzer::CheckExitOnSrcPosOrItem() {
390   if (!Options.ExitOnSrcPos.empty()) {
391     static auto *PCsSet = new Set<uintptr_t>;
392     auto HandlePC = [&](const TracePC::PCTableEntry *TE) {
393       if (!PCsSet->insert(TE->PC).second)
394         return;
395       std::string Descr = DescribePC("%F %L", TE->PC + 1);
396       if (Descr.find(Options.ExitOnSrcPos) != std::string::npos) {
397         Printf("INFO: found line matching '%s', exiting.\n",
398                Options.ExitOnSrcPos.c_str());
399         _Exit(0);
400       }
401     };
402     TPC.ForEachObservedPC(HandlePC);
403   }
404   if (!Options.ExitOnItem.empty()) {
405     if (Corpus.HasUnit(Options.ExitOnItem)) {
406       Printf("INFO: found item with checksum '%s', exiting.\n",
407              Options.ExitOnItem.c_str());
408       _Exit(0);
409     }
410   }
411 }
412 
413 void Fuzzer::RereadOutputCorpus(size_t MaxSize) {
414   if (Options.OutputCorpus.empty() || !Options.ReloadIntervalSec)
415     return;
416   Vector<Unit> AdditionalCorpus;
417   ReadDirToVectorOfUnits(Options.OutputCorpus.c_str(), &AdditionalCorpus,
418                          &EpochOfLastReadOfOutputCorpus, MaxSize,
419                          /*ExitOnError*/ false);
420   if (Options.Verbosity >= 2)
421     Printf("Reload: read %zd new units.\n", AdditionalCorpus.size());
422   bool Reloaded = false;
423   for (auto &U : AdditionalCorpus) {
424     if (U.size() > MaxSize)
425       U.resize(MaxSize);
426     if (!Corpus.HasUnit(U)) {
427       if (RunOne(U.data(), U.size())) {
428         CheckExitOnSrcPosOrItem();
429         Reloaded = true;
430       }
431     }
432   }
433   if (Reloaded)
434     PrintStats("RELOAD");
435 }
436 
437 void Fuzzer::PrintPulseAndReportSlowInput(const uint8_t *Data, size_t Size) {
438   auto TimeOfUnit =
439       duration_cast<seconds>(UnitStopTime - UnitStartTime).count();
440   if (!(TotalNumberOfRuns & (TotalNumberOfRuns - 1)) &&
441       secondsSinceProcessStartUp() >= 2)
442     PrintStats("pulse ");
443   auto Threshhold =
444       static_cast<long>(static_cast<double>(TimeOfLongestUnitInSeconds) * 1.1);
445   if (TimeOfUnit > Threshhold && TimeOfUnit >= Options.ReportSlowUnits) {
446     TimeOfLongestUnitInSeconds = TimeOfUnit;
447     Printf("Slowest unit: %zd s:\n", TimeOfLongestUnitInSeconds);
448     WriteUnitToFileWithPrefix({Data, Data + Size}, "slow-unit-");
449   }
450 }
451 
452 static void WriteFeatureSetToFile(const std::string &FeaturesDir,
453                                   const std::string &FileName,
454                                   const Vector<uint32_t> &FeatureSet) {
455   if (FeaturesDir.empty() || FeatureSet.empty()) return;
456   WriteToFile(reinterpret_cast<const uint8_t *>(FeatureSet.data()),
457               FeatureSet.size() * sizeof(FeatureSet[0]),
458               DirPlusFile(FeaturesDir, FileName));
459 }
460 
461 static void RenameFeatureSetFile(const std::string &FeaturesDir,
462                                  const std::string &OldFile,
463                                  const std::string &NewFile) {
464   if (FeaturesDir.empty()) return;
465   RenameFile(DirPlusFile(FeaturesDir, OldFile),
466              DirPlusFile(FeaturesDir, NewFile));
467 }
468 
469 static void WriteEdgeToMutationGraphFile(const std::string &MutationGraphFile,
470                                          const InputInfo *II,
471                                          const InputInfo *BaseII,
472                                          const std::string &MS) {
473   if (MutationGraphFile.empty())
474     return;
475 
476   std::string Sha1 = Sha1ToString(II->Sha1);
477 
478   std::string OutputString;
479 
480   // Add a new vertex.
481   OutputString.append("\"");
482   OutputString.append(Sha1);
483   OutputString.append("\"\n");
484 
485   // Add a new edge if there is base input.
486   if (BaseII) {
487     std::string BaseSha1 = Sha1ToString(BaseII->Sha1);
488     OutputString.append("\"");
489     OutputString.append(BaseSha1);
490     OutputString.append("\" -> \"");
491     OutputString.append(Sha1);
492     OutputString.append("\" [label=\"");
493     OutputString.append(MS);
494     OutputString.append("\"];\n");
495   }
496 
497   AppendToFile(OutputString, MutationGraphFile);
498 }
499 
500 bool Fuzzer::RunOne(const uint8_t *Data, size_t Size, bool MayDeleteFile,
501                     InputInfo *II, bool ForceAddToCorpus,
502                     bool *FoundUniqFeatures) {
503   if (!Size)
504     return false;
505   // Largest input length should be INT_MAX.
506   assert(Size < std::numeric_limits<uint32_t>::max());
507 
508   ExecuteCallback(Data, Size);
509   auto TimeOfUnit = duration_cast<microseconds>(UnitStopTime - UnitStartTime);
510 
511   UniqFeatureSetTmp.clear();
512   size_t FoundUniqFeaturesOfII = 0;
513   size_t NumUpdatesBefore = Corpus.NumFeatureUpdates();
514   TPC.CollectFeatures([&](uint32_t Feature) {
515     if (Corpus.AddFeature(Feature, static_cast<uint32_t>(Size), Options.Shrink))
516       UniqFeatureSetTmp.push_back(Feature);
517     if (Options.Entropic)
518       Corpus.UpdateFeatureFrequency(II, Feature);
519     if (Options.ReduceInputs && II && !II->NeverReduce)
520       if (std::binary_search(II->UniqFeatureSet.begin(),
521                              II->UniqFeatureSet.end(), Feature))
522         FoundUniqFeaturesOfII++;
523   });
524   if (FoundUniqFeatures)
525     *FoundUniqFeatures = FoundUniqFeaturesOfII;
526   PrintPulseAndReportSlowInput(Data, Size);
527   size_t NumNewFeatures = Corpus.NumFeatureUpdates() - NumUpdatesBefore;
528   if (NumNewFeatures || ForceAddToCorpus) {
529     TPC.UpdateObservedPCs();
530     auto NewII =
531         Corpus.AddToCorpus({Data, Data + Size}, NumNewFeatures, MayDeleteFile,
532                            TPC.ObservedFocusFunction(), ForceAddToCorpus,
533                            TimeOfUnit, UniqFeatureSetTmp, DFT, II);
534     WriteFeatureSetToFile(Options.FeaturesDir, Sha1ToString(NewII->Sha1),
535                           NewII->UniqFeatureSet);
536     WriteEdgeToMutationGraphFile(Options.MutationGraphFile, NewII, II,
537                                  MD.MutationSequence());
538     return true;
539   }
540   if (II && FoundUniqFeaturesOfII &&
541       II->DataFlowTraceForFocusFunction.empty() &&
542       FoundUniqFeaturesOfII == II->UniqFeatureSet.size() &&
543       II->U.size() > Size) {
544     auto OldFeaturesFile = Sha1ToString(II->Sha1);
545     Corpus.Replace(II, {Data, Data + Size});
546     RenameFeatureSetFile(Options.FeaturesDir, OldFeaturesFile,
547                          Sha1ToString(II->Sha1));
548     return true;
549   }
550   return false;
551 }
552 
553 void Fuzzer::TPCUpdateObservedPCs() { TPC.UpdateObservedPCs(); }
554 
555 size_t Fuzzer::GetCurrentUnitInFuzzingThead(const uint8_t **Data) const {
556   assert(InFuzzingThread());
557   *Data = CurrentUnitData;
558   return CurrentUnitSize;
559 }
560 
561 void Fuzzer::CrashOnOverwrittenData() {
562   Printf("==%d== ERROR: libFuzzer: fuzz target overwrites its const input\n",
563          GetPid());
564   PrintStackTrace();
565   Printf("SUMMARY: libFuzzer: overwrites-const-input\n");
566   DumpCurrentUnit("crash-");
567   PrintFinalStats();
568   _Exit(Options.ErrorExitCode); // Stop right now.
569 }
570 
571 // Compare two arrays, but not all bytes if the arrays are large.
572 static bool LooseMemeq(const uint8_t *A, const uint8_t *B, size_t Size) {
573   const size_t Limit = 64;
574   if (Size <= 64)
575     return !memcmp(A, B, Size);
576   // Compare first and last Limit/2 bytes.
577   return !memcmp(A, B, Limit / 2) &&
578          !memcmp(A + Size - Limit / 2, B + Size - Limit / 2, Limit / 2);
579 }
580 
581 void Fuzzer::ExecuteCallback(const uint8_t *Data, size_t Size) {
582   TPC.RecordInitialStack();
583   TotalNumberOfRuns++;
584   assert(InFuzzingThread());
585   // We copy the contents of Unit into a separate heap buffer
586   // so that we reliably find buffer overflows in it.
587   uint8_t *DataCopy = new uint8_t[Size];
588   memcpy(DataCopy, Data, Size);
589   if (EF->__msan_unpoison)
590     EF->__msan_unpoison(DataCopy, Size);
591   if (EF->__msan_unpoison_param)
592     EF->__msan_unpoison_param(2);
593   if (CurrentUnitData && CurrentUnitData != Data)
594     memcpy(CurrentUnitData, Data, Size);
595   CurrentUnitSize = Size;
596   {
597     ScopedEnableMsanInterceptorChecks S;
598     AllocTracer.Start(Options.TraceMalloc);
599     UnitStartTime = system_clock::now();
600     TPC.ResetMaps();
601     RunningUserCallback = true;
602     int Res = CB(DataCopy, Size);
603     RunningUserCallback = false;
604     UnitStopTime = system_clock::now();
605     (void)Res;
606     assert(Res == 0);
607     HasMoreMallocsThanFrees = AllocTracer.Stop();
608   }
609   if (!LooseMemeq(DataCopy, Data, Size))
610     CrashOnOverwrittenData();
611   CurrentUnitSize = 0;
612   delete[] DataCopy;
613 }
614 
615 std::string Fuzzer::WriteToOutputCorpus(const Unit &U) {
616   if (Options.OnlyASCII)
617     assert(IsASCII(U));
618   if (Options.OutputCorpus.empty())
619     return "";
620   std::string Path = DirPlusFile(Options.OutputCorpus, Hash(U));
621   WriteToFile(U, Path);
622   if (Options.Verbosity >= 2)
623     Printf("Written %zd bytes to %s\n", U.size(), Path.c_str());
624   return Path;
625 }
626 
627 void Fuzzer::WriteUnitToFileWithPrefix(const Unit &U, const char *Prefix) {
628   if (!Options.SaveArtifacts)
629     return;
630   std::string Path = Options.ArtifactPrefix + Prefix + Hash(U);
631   if (!Options.ExactArtifactPath.empty())
632     Path = Options.ExactArtifactPath; // Overrides ArtifactPrefix.
633   WriteToFile(U, Path);
634   Printf("artifact_prefix='%s'; Test unit written to %s\n",
635          Options.ArtifactPrefix.c_str(), Path.c_str());
636   if (U.size() <= kMaxUnitSizeToPrint)
637     Printf("Base64: %s\n", Base64(U).c_str());
638 }
639 
640 void Fuzzer::PrintStatusForNewUnit(const Unit &U, const char *Text) {
641   if (!Options.PrintNEW)
642     return;
643   PrintStats(Text, "");
644   if (Options.Verbosity) {
645     Printf(" L: %zd/%zd ", U.size(), Corpus.MaxInputSize());
646     MD.PrintMutationSequence(Options.Verbosity >= 2);
647     Printf("\n");
648   }
649 }
650 
651 void Fuzzer::ReportNewCoverage(InputInfo *II, const Unit &U) {
652   II->NumSuccessfullMutations++;
653   MD.RecordSuccessfulMutationSequence();
654   PrintStatusForNewUnit(U, II->Reduced ? "REDUCE" : "NEW   ");
655   WriteToOutputCorpus(U);
656   NumberOfNewUnitsAdded++;
657   CheckExitOnSrcPosOrItem(); // Check only after the unit is saved to corpus.
658   LastCorpusUpdateRun = TotalNumberOfRuns;
659 }
660 
661 // Tries detecting a memory leak on the particular input that we have just
662 // executed before calling this function.
663 void Fuzzer::TryDetectingAMemoryLeak(const uint8_t *Data, size_t Size,
664                                      bool DuringInitialCorpusExecution) {
665   if (!HasMoreMallocsThanFrees)
666     return; // mallocs==frees, a leak is unlikely.
667   if (!Options.DetectLeaks)
668     return;
669   if (!DuringInitialCorpusExecution &&
670       TotalNumberOfRuns >= Options.MaxNumberOfRuns)
671     return;
672   if (!&(EF->__lsan_enable) || !&(EF->__lsan_disable) ||
673       !(EF->__lsan_do_recoverable_leak_check))
674     return; // No lsan.
675   // Run the target once again, but with lsan disabled so that if there is
676   // a real leak we do not report it twice.
677   EF->__lsan_disable();
678   ExecuteCallback(Data, Size);
679   EF->__lsan_enable();
680   if (!HasMoreMallocsThanFrees)
681     return; // a leak is unlikely.
682   if (NumberOfLeakDetectionAttempts++ > 1000) {
683     Options.DetectLeaks = false;
684     Printf("INFO: libFuzzer disabled leak detection after every mutation.\n"
685            "      Most likely the target function accumulates allocated\n"
686            "      memory in a global state w/o actually leaking it.\n"
687            "      You may try running this binary with -trace_malloc=[12]"
688            "      to get a trace of mallocs and frees.\n"
689            "      If LeakSanitizer is enabled in this process it will still\n"
690            "      run on the process shutdown.\n");
691     return;
692   }
693   // Now perform the actual lsan pass. This is expensive and we must ensure
694   // we don't call it too often.
695   if (EF->__lsan_do_recoverable_leak_check()) { // Leak is found, report it.
696     if (DuringInitialCorpusExecution)
697       Printf("\nINFO: a leak has been found in the initial corpus.\n\n");
698     Printf("INFO: to ignore leaks on libFuzzer side use -detect_leaks=0.\n\n");
699     CurrentUnitSize = Size;
700     DumpCurrentUnit("leak-");
701     PrintFinalStats();
702     _Exit(Options.ErrorExitCode); // not exit() to disable lsan further on.
703   }
704 }
705 
706 void Fuzzer::MutateAndTestOne() {
707   MD.StartMutationSequence();
708 
709   auto &II = Corpus.ChooseUnitToMutate(MD.GetRand());
710   if (Options.DoCrossOver) {
711     auto &CrossOverII = Corpus.ChooseUnitToCrossOverWith(
712         MD.GetRand(), Options.CrossOverUniformDist);
713     MD.SetCrossOverWith(&CrossOverII.U);
714   }
715   const auto &U = II.U;
716   memcpy(BaseSha1, II.Sha1, sizeof(BaseSha1));
717   assert(CurrentUnitData);
718   size_t Size = U.size();
719   assert(Size <= MaxInputLen && "Oversized Unit");
720   memcpy(CurrentUnitData, U.data(), Size);
721 
722   assert(MaxMutationLen > 0);
723 
724   size_t CurrentMaxMutationLen =
725       Min(MaxMutationLen, Max(U.size(), TmpMaxMutationLen));
726   assert(CurrentMaxMutationLen > 0);
727 
728   for (int i = 0; i < Options.MutateDepth; i++) {
729     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
730       break;
731     MaybeExitGracefully();
732     size_t NewSize = 0;
733     if (II.HasFocusFunction && !II.DataFlowTraceForFocusFunction.empty() &&
734         Size <= CurrentMaxMutationLen)
735       NewSize = MD.MutateWithMask(CurrentUnitData, Size, Size,
736                                   II.DataFlowTraceForFocusFunction);
737 
738     // If MutateWithMask either failed or wasn't called, call default Mutate.
739     if (!NewSize)
740       NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
741     assert(NewSize > 0 && "Mutator returned empty unit");
742     assert(NewSize <= CurrentMaxMutationLen && "Mutator return oversized unit");
743     Size = NewSize;
744     II.NumExecutedMutations++;
745     Corpus.IncrementNumExecutedMutations();
746 
747     bool FoundUniqFeatures = false;
748     bool NewCov = RunOne(CurrentUnitData, Size, /*MayDeleteFile=*/true, &II,
749                          /*ForceAddToCorpus*/ false, &FoundUniqFeatures);
750     TryDetectingAMemoryLeak(CurrentUnitData, Size,
751                             /*DuringInitialCorpusExecution*/ false);
752     if (NewCov) {
753       ReportNewCoverage(&II, {CurrentUnitData, CurrentUnitData + Size});
754       break;  // We will mutate this input more in the next rounds.
755     }
756     if (Options.ReduceDepth && !FoundUniqFeatures)
757       break;
758   }
759 
760   II.NeedsEnergyUpdate = true;
761 }
762 
763 void Fuzzer::PurgeAllocator() {
764   if (Options.PurgeAllocatorIntervalSec < 0 || !EF->__sanitizer_purge_allocator)
765     return;
766   if (duration_cast<seconds>(system_clock::now() -
767                              LastAllocatorPurgeAttemptTime)
768           .count() < Options.PurgeAllocatorIntervalSec)
769     return;
770 
771   if (Options.RssLimitMb <= 0 ||
772       GetPeakRSSMb() > static_cast<size_t>(Options.RssLimitMb) / 2)
773     EF->__sanitizer_purge_allocator();
774 
775   LastAllocatorPurgeAttemptTime = system_clock::now();
776 }
777 
778 void Fuzzer::ReadAndExecuteSeedCorpora(Vector<SizedFile> &CorporaFiles) {
779   const size_t kMaxSaneLen = 1 << 20;
780   const size_t kMinDefaultLen = 4096;
781   size_t MaxSize = 0;
782   size_t MinSize = -1;
783   size_t TotalSize = 0;
784   for (auto &File : CorporaFiles) {
785     MaxSize = Max(File.Size, MaxSize);
786     MinSize = Min(File.Size, MinSize);
787     TotalSize += File.Size;
788   }
789   if (Options.MaxLen == 0)
790     SetMaxInputLen(std::min(std::max(kMinDefaultLen, MaxSize), kMaxSaneLen));
791   assert(MaxInputLen > 0);
792 
793   // Test the callback with empty input and never try it again.
794   uint8_t dummy = 0;
795   ExecuteCallback(&dummy, 0);
796 
797   if (CorporaFiles.empty()) {
798     Printf("INFO: A corpus is not provided, starting from an empty corpus\n");
799     Unit U({'\n'}); // Valid ASCII input.
800     RunOne(U.data(), U.size());
801   } else {
802     Printf("INFO: seed corpus: files: %zd min: %zdb max: %zdb total: %zdb"
803            " rss: %zdMb\n",
804            CorporaFiles.size(), MinSize, MaxSize, TotalSize, GetPeakRSSMb());
805     if (Options.ShuffleAtStartUp)
806       std::shuffle(CorporaFiles.begin(), CorporaFiles.end(), MD.GetRand());
807 
808     if (Options.PreferSmall) {
809       std::stable_sort(CorporaFiles.begin(), CorporaFiles.end());
810       assert(CorporaFiles.front().Size <= CorporaFiles.back().Size);
811     }
812 
813     // Load and execute inputs one by one.
814     for (auto &SF : CorporaFiles) {
815       auto U = FileToVector(SF.File, MaxInputLen, /*ExitOnError=*/false);
816       assert(U.size() <= MaxInputLen);
817       RunOne(U.data(), U.size(), /*MayDeleteFile*/ false, /*II*/ nullptr,
818              /*ForceAddToCorpus*/ Options.KeepSeed,
819              /*FoundUniqFeatures*/ nullptr);
820       CheckExitOnSrcPosOrItem();
821       TryDetectingAMemoryLeak(U.data(), U.size(),
822                               /*DuringInitialCorpusExecution*/ true);
823     }
824   }
825 
826   PrintStats("INITED");
827   if (!Options.FocusFunction.empty()) {
828     Printf("INFO: %zd/%zd inputs touch the focus function\n",
829            Corpus.NumInputsThatTouchFocusFunction(), Corpus.size());
830     if (!Options.DataFlowTrace.empty())
831       Printf("INFO: %zd/%zd inputs have the Data Flow Trace\n",
832              Corpus.NumInputsWithDataFlowTrace(),
833              Corpus.NumInputsThatTouchFocusFunction());
834   }
835 
836   if (Corpus.empty() && Options.MaxNumberOfRuns) {
837     Printf("ERROR: no interesting inputs were found. "
838            "Is the code instrumented for coverage? Exiting.\n");
839     exit(1);
840   }
841 }
842 
843 void Fuzzer::Loop(Vector<SizedFile> &CorporaFiles) {
844   auto FocusFunctionOrAuto = Options.FocusFunction;
845   DFT.Init(Options.DataFlowTrace, &FocusFunctionOrAuto, CorporaFiles,
846            MD.GetRand());
847   TPC.SetFocusFunction(FocusFunctionOrAuto);
848   ReadAndExecuteSeedCorpora(CorporaFiles);
849   DFT.Clear();  // No need for DFT any more.
850   TPC.SetPrintNewPCs(Options.PrintNewCovPcs);
851   TPC.SetPrintNewFuncs(Options.PrintNewCovFuncs);
852   system_clock::time_point LastCorpusReload = system_clock::now();
853 
854   TmpMaxMutationLen =
855       Min(MaxMutationLen, Max(size_t(4), Corpus.MaxInputSize()));
856 
857   while (true) {
858     auto Now = system_clock::now();
859     if (!Options.StopFile.empty() &&
860         !FileToVector(Options.StopFile, 1, false).empty())
861       break;
862     if (duration_cast<seconds>(Now - LastCorpusReload).count() >=
863         Options.ReloadIntervalSec) {
864       RereadOutputCorpus(MaxInputLen);
865       LastCorpusReload = system_clock::now();
866     }
867     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
868       break;
869     if (TimedOut())
870       break;
871 
872     // Update TmpMaxMutationLen
873     if (Options.LenControl) {
874       if (TmpMaxMutationLen < MaxMutationLen &&
875           TotalNumberOfRuns - LastCorpusUpdateRun >
876               Options.LenControl * Log(TmpMaxMutationLen)) {
877         TmpMaxMutationLen =
878             Min(MaxMutationLen, TmpMaxMutationLen + Log(TmpMaxMutationLen));
879         LastCorpusUpdateRun = TotalNumberOfRuns;
880       }
881     } else {
882       TmpMaxMutationLen = MaxMutationLen;
883     }
884 
885     // Perform several mutations and runs.
886     MutateAndTestOne();
887 
888     PurgeAllocator();
889   }
890 
891   PrintStats("DONE  ", "\n");
892   MD.PrintRecommendedDictionary();
893 }
894 
895 void Fuzzer::MinimizeCrashLoop(const Unit &U) {
896   if (U.size() <= 1)
897     return;
898   while (!TimedOut() && TotalNumberOfRuns < Options.MaxNumberOfRuns) {
899     MD.StartMutationSequence();
900     memcpy(CurrentUnitData, U.data(), U.size());
901     for (int i = 0; i < Options.MutateDepth; i++) {
902       size_t NewSize = MD.Mutate(CurrentUnitData, U.size(), MaxMutationLen);
903       assert(NewSize > 0 && NewSize <= MaxMutationLen);
904       ExecuteCallback(CurrentUnitData, NewSize);
905       PrintPulseAndReportSlowInput(CurrentUnitData, NewSize);
906       TryDetectingAMemoryLeak(CurrentUnitData, NewSize,
907                               /*DuringInitialCorpusExecution*/ false);
908     }
909   }
910 }
911 
912 } // namespace fuzzer
913 
914 extern "C" {
915 
916 ATTRIBUTE_INTERFACE size_t
917 LLVMFuzzerMutate(uint8_t *Data, size_t Size, size_t MaxSize) {
918   assert(fuzzer::F);
919   return fuzzer::F->GetMD().DefaultMutate(Data, Size, MaxSize);
920 }
921 
922 } // extern "C"
923