Tweak settings for AFL++ (#2208)

- Change fuzz duration to 4 hr.
- Use AFL_EXPAND_HAVOC_NOW as per Marc's recommendation since we
  are working on saturated corpus most of the time.
  "Setting AFL_EXPAND_HAVOC_NOW will start in the extended havoc mode
  that includes costly mutations."

src/local/butler/scripts/setup.py

@@ -48,8 +48,8 @@
 """
 
 AFL_TEMPLATE = """MAX_FUZZ_THREADS = 1
-MAX_TESTCASES = 4
-FUZZ_TEST_TIMEOUT = 4800
+MAX_TESTCASES = 1
+FUZZ_TEST_TIMEOUT = 14400
 TEST_TIMEOUT = 30
 WARMUP_TIMEOUT = 30
 BAD_BUILD_CHECK = False

src/python/bot/fuzzers/afl/constants.py

@@ -45,6 +45,8 @@
 
 CLOSE_FD_MASK_ENV_VAR = 'AFL_DRIVER_CLOSE_FD_MASK'
 
+EXPAND_HAVOC_NOW_VAR = 'AFL_EXPAND_HAVOC_NOW'
+
 MAX_FILE_BYTES = 2**20  # 1 MB
 
 # This should be as high as possible, otherwise AFL will restart the binary too

src/python/bot/fuzzers/afl/launcher.py

@@ -670,6 +670,7 @@ def set_environment_variables(self):
     environment.set_value(constants.SKIP_CRASHES_ENV_VAR, 1)
     environment.set_value(constants.SKIP_CPUFREQ_ENV_VAR, 1)
     environment.set_value(constants.BENCH_UNTIL_CRASH_ENV_VAR, 1)
+    environment.set_value(constants.EXPAND_HAVOC_NOW_VAR, 1)
     environment.set_value(constants.STDERR_FILENAME_ENV_VAR,
                           self.stderr_file_path)