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From:   Shankara Pailoor <sp3485@columbia.edu>
Date:   Sat, 20 Jan 2018 07:01:33 -0800
Message-ID: <CAASgV=uWyvLTdObEMO0oPGzeMuvTfOTssHKVbBkYNcocrWioPA@mail.gmail.com>
Subject: Re: Possible Memory Leak in KCOV Linux 4.15-rc1
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        syzkaller <syzkaller@googlegroups.com>
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Hi Dmitry,

I will try and get something to you tomorrow. Just wondering, but what
happens to the old struct kcov if a task opens /sys/kernel/debug/kcov
twice? I am looking here
https://elixir.free-electrons.com/linux/v4.15-rc8/source/kernel/kcov.c#L381
and I don't see where the previous struct would get freed.

Regards,
Shankara

On Sat, Jan 20, 2018 at 4:38 AM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Fri, Jan 19, 2018 at 8:29 PM, Shankara Pailoor <sp3485@columbia.edu> wrote:
>> Hi Dmitry,
>>
>> I added support for kcov in strace and I have been tracing a fairly
>> large program but after a little while, I notice that when I mmap a
>> new cover buffer, the call fails with ENOMEM. After killing the
>> program, I try and rerun and I notice that there is nearly no memory
>> on the system. When I do a kmemleak scan I get the following reports:
>>
>> I believe the problem occurs when I try and setup the kcov buffer
>> again after an exec. Instead of reusing the old file descriptor I open
>> kcov again within that process. In that case, I don't know what
>> happens to the old kcov struct.
>>
>> I don't see a maintainers list for kcov so I decided to email you
>> directly. Let me know what more information I can provide.
>
>
> Hi Shankara,
>
> Looks bad. Can you provide a reproducer?
> We extensively use kcov with syzkaller, but have not observed such
> leaks. Also I don't see anything obvious in the code.
>
> Thanks