[libFuzzer] Disable len_control by default if LLVMFuzzerCustomMutator is used.
Summary:
Some custom mutators may not peform well when size restriction is
enforced by len_control. Because of that, it's safer to disable len_control
by default in such cases, but still allow users to enable it manually.
Bug example: https://bugs.chromium.org/p/chromium/issues/detail?id=919530.
Tested manually with LPM-based and regular fuzz targets.
Reviewers: kcc, vitalybuka, metzman
Reviewed By: kcc, metzman
Subscribers: delcypher, #sanitizers, llvm-commits
Tags: #llvm, #sanitizers
Differential Revision: https://reviews.llvm.org/D63334
llvm-svn: 363443
GitOrigin-RevId: 0784e01a98a01d30474655702051e9f4542ccc31
diff --git a/FuzzerDriver.cpp b/FuzzerDriver.cpp
index d55caf4..5458d6c 100644
--- a/FuzzerDriver.cpp
+++ b/FuzzerDriver.cpp
@@ -182,7 +182,8 @@
}
// We don't use any library to minimize dependencies.
-static void ParseFlags(const Vector<std::string> &Args) {
+static void ParseFlags(const Vector<std::string> &Args,
+ const ExternalFunctions *EF) {
for (size_t F = 0; F < kNumFlags; F++) {
if (FlagDescriptions[F].IntFlag)
*FlagDescriptions[F].IntFlag = FlagDescriptions[F].Default;
@@ -192,6 +193,11 @@
if (FlagDescriptions[F].StrFlag)
*FlagDescriptions[F].StrFlag = nullptr;
}
+
+ // Disable len_control by default, if LLVMFuzzerCustomMutator is used.
+ if (EF->LLVMFuzzerCustomMutator)
+ Flags.len_control = 0;
+
Inputs = new Vector<std::string>;
for (size_t A = 1; A < Args.size(); A++) {
if (ParseOneFlag(Args[A].c_str())) {
@@ -616,7 +622,7 @@
Printf("ERROR: argv[0] has been modified in LLVMFuzzerInitialize\n");
exit(1);
}
- ParseFlags(Args);
+ ParseFlags(Args, EF);
if (Flags.help) {
PrintHelp();
return 0;
diff --git a/FuzzerFlags.def b/FuzzerFlags.def
index 71f4990..6f0d5ad 100644
--- a/FuzzerFlags.def
+++ b/FuzzerFlags.def
@@ -19,7 +19,7 @@
FUZZER_FLAG_INT(len_control, 100, "Try generating small inputs first, "
"then try larger inputs over time. Specifies the rate at which the length "
"limit is increased (smaller == faster). If 0, immediately try inputs with "
- "size up to max_len.")
+ "size up to max_len. Default value is 0, if LLVMFuzzerCustomMutator is used.")
FUZZER_FLAG_STRING(seed_inputs, "A comma-separated list of input files "
"to use as an additional seed corpus. Alternatively, an \"@\" followed by "
"the name of a file containing the comma-seperated list.")
