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Date:   Thu, 4 Jul 2019 19:21:28 +0800
From:   "liwei (GF)" <liwei391@...wei.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        <linux-kernel@...r.kernel.org>, <xiezhipeng1@...wei.com>
Subject: Re: [PATCH v2] fix use-after-free in perf_sched__lat

Hi Arnaldo,
I found this issue has not been fixed in mainline now, please take a glance at this.

On 2019/5/23 10:50, Namhyung Kim wrote:
> On Wed, May 22, 2019 at 08:08:23AM -0300, Arnaldo Carvalho de Melo wrote:
>> Em Wed, May 22, 2019 at 03:56:10PM +0900, Namhyung Kim escreveu:
>>> On Wed, May 08, 2019 at 10:36:48PM +0800, Wei Li wrote:
>>>> After thread is added to machine->threads[i].dead in
>>>> __machine__remove_thread, the machine->threads[i].dead is freed
>>>> when calling free(session) in perf_session__delete(). So it get a
>>>> Segmentation fault when accessing it in thread__put().
>>>>
>>>> In this patch, we delay the perf_session__delete until all threads
>>>> have been deleted.
>>>>
>>>> This can be reproduced by following steps:
>>>> 	ulimit -c unlimited
>>>> 	export MALLOC_MMAP_THRESHOLD_=0
>>>> 	perf sched record sleep 10
>>>> 	perf sched latency --sort max
>>>> 	Segmentation fault (core dumped)
>>>>
>>>> Signed-off-by: Zhipeng Xie <xiezhipeng1@...wei.com>
>>>> Signed-off-by: Wei Li <liwei391@...wei.com>
>>>
>>> Acked-by: Namhyung Kim <namhyung@...nel.org>
>>
>> I'll try to analyse this one soon, but my first impression was that we
>> should just grab reference counts when keeping a pointer to those
>> threads instead of keeping _all_ threads alive when supposedly we could
>> trow away unreferenced data structures.
>>
>> But this is just a first impression from just reading the patch
>> description, probably I'm missing something.
> 
> No, thread refcounting is fine.  We already did it and threads with the
> refcount will be accessed only.
> 
> But the problem is the head of the list.  After using the thread, the
> refcount is gone and thread is removed from the list and destroyed.
> However the head of list is in a struct machine which was freed with
> session already.
> 
> Thanks,
> Namhyung
> 
> 
>>
>> Thanks for providing instructions on readily triggering the segfault.
>>
>> - Arnaldo
> 
> .
> 

Thanks,
Wei

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