linux-kernel - Re: [PATCH] mm/kfence: Null check is added for return value of addr_to

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Date:   Fri, 24 Sep 2021 16:13:55 +0200
From:   Marco Elver <elver@...gle.com>
To:     Manjeet Pawar <manjeet.p@...sung.com>
Cc:     glider@...gle.com, dvyukov@...gle.com, akpm@...ux-foundation.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, r.thapliyal@...sung.com,
        a.sahrawat@...sung.com, v.narang@...sung.com
Subject: Re: [PATCH] mm/kfence: Null check is added for return value of addr_to_metadata

On Fri, 24 Sept 2021 at 15:55, Manjeet Pawar <manjeet.p@...sung.com> wrote:
> This patch add null check for return value of addr_to_metadata().
> currently 'meta' is geting accessed without any NULL check but it is
> usually checked for this function.
>
> Signed-off-by: Manjeet Pawar <manjeet.p@...sung.com>

Your commit message does not make sense -- what bug did you encounter?

"usually checked for this function" is not a reason to add the check.
Adding a check like this could also hide genuine bugs, as meta should
never be NULL in __kfence_free(). If it is, we'd like to see a crash.

Did you read kfence_free() in include/linux/kfence.h? It already
prevents __kfence_free() being called with a non-KFENCE address.

Without a more thorough explanation, Nack.

Thanks,
-- Marco