Re: [PATCH v7 1/7] fuzz: accelerate non-crash detection

[Alexander Bulekov]

On 210110 2119, Qiuhao Li wrote:
> We spend much time waiting for the timeout program during the minimization
> process until it passes a time limit. This patch hacks the CLOSED (indicates
> the redirection file closed) notification in QTest's output if it doesn't
> crash.
> 
> Test with quadrupled trace input at:
>   https://bugs.launchpad.net/qemu/+bug/1890333/comments/1
> 
> Original version:
>   real        1m37.246s
>   user        0m13.069s
>   sys 0m8.399s
> 
> Refined version:
>   real        0m45.904s
>   user        0m16.874s
>   sys 0m10.042s
> 
> Note:
> 
> Sometimes the mutated or the same trace may trigger a different crash
> summary (second-to-last line) but indicates the same bug. For example, Bug
> 1910826 [1], which will trigger a stack overflow, may output summaries
> like:
> 
> SUMMARY: AddressSanitizer: stack-overflow
> /home/qiuhao/hack/qemu/build/../softmmu/physmem.c:488 in
> flatview_do_translate
> 
> or
> 
> SUMMARY: AddressSanitizer: stack-overflow
> (/home/qiuhao/hack/qemu/build/qemu-system-i386+0x27ca049) in __asan_memcpy
> 
> Etc.
> 
> If we use the whole summary line as the token, we may be prevented from
> further minimization. So in this patch, we only use the first three words
> which indicate the type of crash:
> 
> SUMMARY: AddressSanitizer: stack-overflow
> 
> [1] https://bugs.launchpad.net/qemu/+bug/1910826
> 
> Signed-off-by: Qiuhao Li <Qiuhao.Li@outlook.com>

Reviewed-by: Alexander Bulekov <alxndr@bu.edu>

Thanks

> ---
>  scripts/oss-fuzz/minimize_qtest_trace.py | 43 +++++++++++++++++-------
>  1 file changed, 31 insertions(+), 12 deletions(-)
> 
> diff --git a/scripts/oss-fuzz/minimize_qtest_trace.py 
> b/scripts/oss-fuzz/minimize_qtest_trace.py
> index 5e405a0d5f..97f1201747 100755
> --- a/scripts/oss-fuzz/minimize_qtest_trace.py
> +++ b/scripts/oss-fuzz/minimize_qtest_trace.py
> @@ -29,8 +29,14 @@ whether the crash occred. Optionally, manually set a 
> string that idenitifes the
>  crash by setting CRASH_TOKEN=
>  """.format((sys.argv[0])))
>  
> +deduplication_note = """\n\
> +Note: While trimming the input, sometimes the mutated trace triggers a 
> different
> +type crash but indicates the same bug. Under this situation, our minimizer is
> +incapable of recognizing and stopped from removing it. In the future, we may
> +use a more sophisticated crash case deduplication method.
> +\n"""
> +
>  def check_if_trace_crashes(trace, path):
> -    global CRASH_TOKEN
>      with open(path, "w") as tracefile:
>          tracefile.write("".join(trace))
>  
> @@ -41,18 +47,32 @@ def check_if_trace_crashes(trace, path):
>                             trace_path=path),
>                            shell=True,
>                            stdin=subprocess.PIPE,
> -                          stdout=subprocess.PIPE)
> -    stdo = rc.communicate()[0]
> -    output = stdo.decode('unicode_escape')
> -    if rc.returncode == 137:    # Timed Out
> -        return False
> -    if len(output.splitlines()) < 2:
> -        return False
> -
> +                          stdout=subprocess.PIPE,
> +                          encoding="utf-8")
> +    global CRASH_TOKEN
>      if CRASH_TOKEN is None:
> -        CRASH_TOKEN = output.splitlines()[-2]
> +        try:
> +            outs, _ = rc.communicate(timeout=5)
> +            CRASH_TOKEN = " ".join(outs.splitlines()[-2].split()[0:3])
> +        except subprocess.TimeoutExpired:
> +            print("subprocess.TimeoutExpired")
> +            return False
> +        print("Identifying Crashes by this string: {}".format(CRASH_TOKEN))
> +        global deduplication_note
> +        print(deduplication_note)
> +        return True
>  
> -    return CRASH_TOKEN in output
> +    for line in iter(rc.stdout.readline, b''):
> +        if "CLOSED" in line:
> +            return False
> +        if CRASH_TOKEN in line:
> +            return True
> +        # We reach the end of stdout and there is no "CLOSED" or CRASH_TOKEN
> +        # Usually this is caused by a different type of crash
> +        if line == "":
> +            return False
> +
> +    return False
>  
>  
>  def minimize_trace(inpath, outpath):
> @@ -66,7 +86,6 @@ def minimize_trace(inpath, outpath):
>      print("Crashed in {} seconds".format(end-start))
>      TIMEOUT = (end-start)*5
>      print("Setting the timeout for {} seconds".format(TIMEOUT))
> -    print("Identifying Crashes by this string: {}".format(CRASH_TOKEN))
>  
>      i = 0
>      newtrace = trace[:]
> -- 
> 2.25.1
>