linux-kernel - Re: [PATCH 1/2] mm/kasan: Fix KASAN poisoning in vrealloc()

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Message-ID: <38bcbe9c-5bc6-4bfa-b4ed-e187e048d600@gmail.com>
Date: Mon, 19 Jan 2026 15:43:02 +0100
From: Andrey Ryabinin <ryabinin.a.a@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
 Andrey Konovalov <andreyknvl@...il.com>
Cc: Maciej Żenczykowski <maze@...gle.com>,
 Maciej Wieczor-Retman <m.wieczorretman@...me>,
 Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>, kasan-dev@...glegroups.com,
 Uladzislau Rezki <urezki@...il.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, joonki.min@...sung-slsi.corp-partner.google.com,
 stable@...r.kernel.org
Subject: Re: [PATCH 1/2] mm/kasan: Fix KASAN poisoning in vrealloc()



On 1/19/26 1:48 AM, Andrew Morton wrote:
> On Sat, 17 Jan 2026 18:08:36 +0100 Andrey Konovalov <andreyknvl@...il.com> wrote:
> 
>> On Sat, Jan 17, 2026 at 2:16 AM Andrey Konovalov <andreyknvl@...il.com> wrote:
>>>
>>> On Fri, Jan 16, 2026 at 2:26 PM Andrey Ryabinin <ryabinin.a.a@...il.com> wrote:
>>>>
>>>> So something like bellow I guess.
>>>
>>> Yeah, looks good.
>>>
>>>> I think this would actually have the opposite effect and make the code harder to follow.
>>>> Introducing an extra wrapper adds another layer of indirection and more boilerplate, which
>>>> makes the control flow less obvious and the code harder to navigate and grep.
>>>>
>>>> And what's the benefit here? I don't clearly see it.
>>>
>>> One functional benefit is when HW_TAGS mode enabled in .config but
>>> disabled via command-line, we avoid a function call into KASAN
>>> runtime.
>>
>> Ah, and I just realized than kasan_vrealloc should go into common.c -
>> we also need it for HW_TAGS.
> 
> I think I'll send this cc:stable bugfix upstream as-is.
> 

Please, include follow-up fix before sending. We have to move kasan_vrealloc()
to common.c as shadow.c is not compiled for CONFIG_KASAN_HW_TAGS=y.
So without the fixup, CONFIG_KASAN_HW_TAGS=y will become broken.