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Re: [PATCH v4 1/7] fuzz: accelerate non-crash detection
From: |
Alexander Bulekov |
Subject: |
Re: [PATCH v4 1/7] fuzz: accelerate non-crash detection |
Date: |
Sun, 10 Jan 2021 11:00:40 -0500 |
On 210110 2110, Qiuhao Li wrote:
> On Wed, 2021-01-06 at 23:18 -0500, Alexander Bulekov wrote:
> > On 201229 1240, 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
> > >
> > > Signed-off-by: Qiuhao Li <Qiuhao.Li@outlook.com>
> > > ---
> > > scripts/oss-fuzz/minimize_qtest_trace.py | 41 ++++++++++++++++--
> > > ------
> > > 1 file changed, 28 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/scripts/oss-fuzz/minimize_qtest_trace.py
> > > b/scripts/oss-fuzz/minimize_qtest_trace.py
> > > index 5e405a0d5f..aa69c7963e 100755
> > > --- a/scripts/oss-fuzz/minimize_qtest_trace.py
> > > +++ b/scripts/oss-fuzz/minimize_qtest_trace.py
> > > @@ -29,30 +29,46 @@ 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
> > > +crash output 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))
> > >
> > > - rc = subprocess.Popen("timeout -s 9 {timeout}s {qemu_path}
> > > {qemu_args} 2>&1\
> > > + proc = subprocess.Popen("timeout {timeout}s {qemu_path}
> > > {qemu_args} 2>&1\
> >
> > Why remove the -s 9 here? I ran into a case where the minimizer got
> > stuck on one iteration. Adding back "sigkill" to the timeout can be a
> > safety net to catch those bad cases.
> > -Alex
>
> Hi Alex,
>
> After reviewed this patch again, I think this get-stuck bug may be
> caused by code:
>
> - return CRASH_TOKEN in output
Hi,
Thanks for fixing this. Strangely, I was able to fix it by swapping
the b'' for a ' ' when I was stuck on a testcase a few days ago.
vvv
> + for line in iter(rc.stdout.readline, b''):
> + if "CLOSED" in line:
> + return False
> + if CRASH_TOKEN in line:
> + return True
>
I think your proposed change essentially does the same?
-Alex
> I assumed there are only two end cases in lines of stdout, but while we
> are trimming the trace input, the crash output (second-to-last line)
> may changes, in which case we will go through the output and fail to
> find "CLOSED" and CRASH_TOKEN, thus get stuck in the loop above.
>
> To fix this bug and get a more trimmed input trace, we can:
>
> Use the first three words of the second-to-last line instead of the
> whole string, which indicate the type of crash as the token.
>
> - CRASH_TOKEN = output.splitlines()[-2]
> + CRASH_TOKEN = " ".join(outs.splitlines()[-2].split()[0:3])
>
> If we reach the end of a subprocess' output, return False.
>
> + if line == "":
> + return False
>
> I fix it in [PATCH v7 1/7] and give an example. Could you review again?
> Thanks :-)
>
> FYI, I mentioned this situation firstly in [PATCH 1/4], where I gave a
> more detailed example:
>
> https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg05888.html
>
> >
> > > < {trace_path}".format(timeout=TIMEOUT,
> > > qemu_path=QEMU_PATH,
> > > qemu_args=QEMU_ARGS,
> > > 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, _ = proc.communicate(timeout=5)
> > > + CRASH_TOKEN = outs.splitlines()[-2]
> > > + 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(proc.stdout.readline, b''):
> > > + if "CLOSED" in line:
> > > + return False
> > > + if CRASH_TOKEN in line:
> > > + return True
> > > +
> > > + return False
> > >
> > >
> > > def minimize_trace(inpath, outpath):
> > > @@ -66,7 +82,6 @@ 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
> > >
>