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From:   Andrey Konovalov <andreyknvl@gmail.com>
Date:   Wed, 25 Oct 2023 21:22:53 +0200
Message-ID: <CA+fCnZfn0RnnhifNxctrUaLEptE=z9L=e3BY_8tRH2UXZWAO6Q@mail.gmail.com>
Subject: Re: [RFC] mm/kasan: Add Allocation, Free, Error timestamps to KASAN report
To:     Juntong Deng <juntong.deng@outlook.com>
Cc:     ryabinin.a.a@gmail.com, glider@google.com, dvyukov@google.com,
        vincenzo.frascino@arm.com, akpm@linux-foundation.org,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-kernel-mentees@lists.linuxfoundation.org" 
        <linux-kernel-mentees@lists.linuxfoundation.org>
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On Tue, Oct 17, 2023 at 9:40=E2=80=AFPM Juntong Deng <juntong.deng@outlook.=
com> wrote:
>
> The idea came from the bug I was fixing recently,
> 'KASAN: slab-use-after-free Read in tls_encrypt_done'.
>
> This bug is caused by subtle race condition, where the data structure
> is freed early on another CPU, resulting in use-after-free.
>
> Like this bug, some of the use-after-free bugs are caused by race
> condition, but it is not easy to quickly conclude that the cause of the
> use-after-free is race condition if only looking at the stack trace.
>
> I did not think this use-after-free was caused by race condition at the
> beginning, it took me some time to read the source code carefully and
> think about it to determine that it was caused by race condition.
>
> By adding timestamps for Allocation, Free, and Error to the KASAN
> report, it will be much easier to determine if use-after-free is
> caused by race condition.

An alternative would be to add the CPU number to the alloc/free stack
traces. Something like:

Allocated by task 42 on CPU 2:
(stack trace)

The bad access stack trace already prints the CPU number.