[fuzzer] Create user provided fuzzer writeable directories when requested if they dont exist

Currently, libFuzzer will exit with an error message if a non-existent
directory is provided for any of the appropriate arguments. For cases
where libFuzzer is used in a specialized embedded environment, it would
be much easier to have libFuzzer create the directories for the user.

This patch accommodates for this scenario by allowing the user to provide
the argument `-create_missing_dirs=1` which makes libFuzzer attempt to
create the `artifact_prefix`, `exact_artifact_path`,
`features_dir` and/or corpus directory if they don't already exist rather
than throw an error and exit.

Split off from D84808 as requested [here](https://reviews.llvm.org/D84808#2208546).

Reviewed By: morehouse

Differential Revision: https://reviews.llvm.org/D86733

compiler-rt/lib/fuzzer/FuzzerDriver.cpp

@@ -250,11 +250,26 @@ static void WorkerThread(const Command &BaseCmd, std::atomic<unsigned> *Counter,
   }
 }
 
-static void ValidateDirectoryExists(const std::string &Path) {
-  if (!Path.empty() && !IsDirectory(Path)) {
-    Printf("ERROR: The required directory \"%s\" does not exist\n", Path.c_str());
+static void ValidateDirectoryExists(const std::string &Path,
+                                    bool CreateDirectory) {
+  if (Path.empty()) {
+    Printf("ERROR: Provided directory path is an empty string\n");
     exit(1);
   }
+
+  if (IsDirectory(Path))
+    return;
+
+  if (CreateDirectory) {
+    if (!MkDirRecursive(Path)) {
+      Printf("ERROR: Failed to create directory \"%s\"\n", Path.c_str());
+      exit(1);
+    }
+    return;
+  }
+
+  Printf("ERROR: The required directory \"%s\" does not exist\n", Path.c_str());
+  exit(1);
 }
 
 std::string CloneArgsWithoutX(const Vector<std::string> &Args,
@@ -691,7 +706,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
     std::string OutputCorpusDir = (*Inputs)[0];
     if (!IsFile(OutputCorpusDir)) {
       Options.OutputCorpus = OutputCorpusDir;
-      ValidateDirectoryExists(Options.OutputCorpus);
+      ValidateDirectoryExists(Options.OutputCorpus, Flags.create_missing_dirs);
     }
   }
   Options.ReportSlowUnits = Flags.report_slow_units;
@@ -705,11 +720,12 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
     if (!IsSeparator(ArtifactPathDir[ArtifactPathDir.length() - 1])) {
       ArtifactPathDir = DirName(ArtifactPathDir);
     }
-    ValidateDirectoryExists(ArtifactPathDir);
+    ValidateDirectoryExists(ArtifactPathDir, Flags.create_missing_dirs);
   }
   if (Flags.exact_artifact_path) {
     Options.ExactArtifactPath = Flags.exact_artifact_path;
-    ValidateDirectoryExists(DirName(Options.ExactArtifactPath));
+    ValidateDirectoryExists(DirName(Options.ExactArtifactPath),
+                            Flags.create_missing_dirs);
   }
   Vector<Unit> Dictionary;
   if (Flags.dict)
@@ -735,7 +751,7 @@ int FuzzerDriver(int *argc, char ***argv, UserCallback Callback) {
     Options.DataFlowTrace = Flags.data_flow_trace;
   if (Flags.features_dir) {
     Options.FeaturesDir = Flags.features_dir;
-    ValidateDirectoryExists(Options.FeaturesDir);
+    ValidateDirectoryExists(Options.FeaturesDir, Flags.create_missing_dirs);
   }
   if (Flags.collect_data_flow)
     Options.CollectDataFlow = Flags.collect_data_flow;

compiler-rt/lib/fuzzer/FuzzerFlags.def

@@ -167,3 +167,7 @@ FUZZER_DEPRECATED_FLAG(use_clang_coverage)
 FUZZER_FLAG_STRING(data_flow_trace, "Experimental: use the data flow trace")
 FUZZER_FLAG_STRING(collect_data_flow,
                    "Experimental: collect the data flow trace")
+
+FUZZER_FLAG_INT(create_missing_dirs, 0, "Automatically attempt to create "
+     "directories for arguments that would normally expect them to already "
+     "exist (i.e. artifact_prefix, exact_artifact_path, features_dir, corpus)")

compiler-rt/lib/fuzzer/FuzzerIO.cpp

@@ -144,6 +144,38 @@ void VPrintf(bool Verbose, const char *Fmt, ...) {
   fflush(OutputFile);
 }
 
+static bool MkDirRecursiveInner(const std::string &Leaf) {
+  // Prevent chance of potential infinite recursion
+  if (Leaf == ".")
+    return true;
+
+  const std::string &Dir = DirName(Leaf);
+
+  if (IsDirectory(Dir)) {
+    MkDir(Leaf);
+    return IsDirectory(Leaf);
+  }
+
+  bool ret = MkDirRecursiveInner(Dir);
+  if (!ret) {
+    // Give up early if a previous MkDir failed
+    return ret;
+  }
+
+  MkDir(Leaf);
+  return IsDirectory(Leaf);
+}
+
+bool MkDirRecursive(const std::string &Dir) {
+  if (Dir.empty())
+    return false;
+
+  if (IsDirectory(Dir))
+    return true;
+
+  return MkDirRecursiveInner(Dir);
+}
+
 void RmDirRecursive(const std::string &Dir) {
   IterateDirRecursive(
       Dir, [](const std::string &Path) {},

compiler-rt/lib/fuzzer/FuzzerIO.h

@@ -64,6 +64,7 @@ size_t FileSize(const std::string &Path);
 void ListFilesInDirRecursive(const std::string &Dir, long *Epoch,
                              Vector<std::string> *V, bool TopDir);
 
+bool MkDirRecursive(const std::string &Dir);
 void RmDirRecursive(const std::string &Dir);
 
 // Iterate files and dirs inside Dir, recursively.

compiler-rt/test/fuzzer/fuzzer-dirs.test

@@ -16,6 +16,7 @@ RUN: %run %t-SimpleTest %t/SUB1 -runs=0 2>&1 | FileCheck %s --check-prefix=LONG
 LONG: INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 8192 bytes
 RUN: rm -rf %t/SUB1
 
+# Verify error message prints to console when directory does not exist
 RUN: rm -rf %t.dir && mkdir -p %t.dir
 RUN: not %run %t-SimpleTest -artifact_prefix=%t.dir/NONEXISTENT_DIR/ 2>&1 | FileCheck %s --check-prefix=NONEXISTENT_DIR_RGX
 RUN: not %run %t-SimpleTest -artifact_prefix=%t.dir/NONEXISTENT_DIR/myprefix 2>&1 | FileCheck %s --check-prefix=NONEXISTENT_DIR_RGX
@@ -23,3 +24,39 @@ RUN: not %run %t-SimpleTest -features_dir=%t.dir/NONEXISTENT_DIR/ 2>&1 | FileChe
 RUN: not %run %t-SimpleTest %t.dir/NONEXISTENT_DIR 2>&1 | FileCheck %s --check-prefix=NONEXISTENT_DIR_RGX
 RUN: not %run %t-SimpleTest -exact_artifact_path=%t.dir/NONEXISTENT_DIR/myprefix 2>&1 | FileCheck %s --check-prefix=NONEXISTENT_DIR_RGX
 NONEXISTENT_DIR_RGX: ERROR: The required directory "{{.*/NONEXISTENT_DIR/?}}" does not exist
+
+# Verify error message prints to console when given directory is an empty
+# string
+RUN: not %run %t-SimpleTest "" 2>&1 | FileCheck %s --check-prefix=INVALID_DIR_RGX
+INVALID_DIR_RGX: ERROR: Provided directory path is an empty string
+
+# Verify error message prints to console when directory creation fails
+# For platforms without functioning chmod (i.e. Windows), use a forbidden
+# character in the directory name.
+RUN: rm -rf %t.dir && mkdir -p %t.dir/access_restricted && (chmod u-w %t.dir/access_restricted || true)
+RUN: not %run %t-SimpleTest -create_missing_dirs=1 %t.dir/access_restricted/?corpus? 2>&1 | FileCheck %s --check-prefix=DIR_CREATION_FAILURE
+DIR_CREATION_FAILURE: ERROR: Failed to create directory "{{.*/access_restricted/\?corpus\?}}"
+
+# Verify directories and sub-directories are created when -create_missing_dirs=1
+RUN: not %run %t-SimpleTest -create_missing_dirs=1 -artifact_prefix=%t.dir/subdira/./././artifacts/ -features_dir=%t.dir/subdirb/../dummy_dir/././../subdirb/features/ %t.dir/subdirc/corpus
+RUN: test -e %t.dir/subdira/artifacts/
+RUN: test -e %t.dir/subdirb/features/
+RUN: test -e %t.dir/subdirc/corpus/
+RUN: test -e %t.dir/dummy_dir
+
+# Verify directories and sub-directories are created for exact_artifact_path
+# when -create_missing_dirs=1
+RUN: not %run %t-SimpleTest -create_missing_dirs=1 -exact_artifact_path=%t.dir/subdird/exact_artifacts/abc
+RUN: test -e %t.dir/subdird/exact_artifacts/abc
+
+# Verify directories and sub-directories are created for artifact_prefix when
+# it's referring to a file name prefix and -create_missing_dirs=1
+RUN: not %run %t-SimpleTest -create_missing_dirs=1 -artifact_prefix=%t.dir/subdire/myprefix
+RUN: test -e %t.dir/subdire/ && not test -e %t.dir/subdire/myprefix
+
+# Verify directories are created when referring to relative paths and
+# -create_missing_dirs=1
+RUN: cd %t.dir && not %run %t-SimpleTest -create_missing_dirs=1 -artifact_prefix=cwd_artifacts/ -features_dir=cwd_features/subdirtest/ ./cwd_corpus
+RUN: test -e %t.dir/cwd_artifacts/
+RUN: test -e %t.dir/cwd_features/subdirtest/
+RUN: test -e %t.dir/cwd_corpus/