linux-kernel - Re: [RFC] mm/kasan: Add Allocation, Free, Error timestamps to KASAN report

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Date:   Wed, 25 Oct 2023 21:22:53 +0200
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Juntong Deng <juntong.deng@...look.com>
Cc:     ryabinin.a.a@...il.com, glider@...gle.com, dvyukov@...gle.com,
        vincenzo.frascino@....com, akpm@...ux-foundation.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kernel-mentees@...ts.linuxfoundation.org" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [RFC] mm/kasan: Add Allocation, Free, Error timestamps to KASAN report

On Tue, Oct 17, 2023 at 9:40 PM Juntong Deng <juntong.deng@...look.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.