linux-kernel - Re: [PATCH 1/2] btrfs: Prevent open-coded arithmetic in kmalloc

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Message-ID: <87jz1p4qd4.fsf@>
Date: Tue, 23 Sep 2025 08:47:35 +0200
From: Miquel Sabaté Solà <mssola@...ola.com>
To: David Sterba <dsterba@...e.cz>
Cc: linux-btrfs@...r.kernel.org,  clm@...com,  dsterba@...e.com,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] btrfs: Prevent open-coded arithmetic in kmalloc

David Sterba @ 2025-09-23 08:13 +02:

> On Mon, Sep 22, 2025 at 02:47:13PM +0200, Miquel Sabaté Solà wrote:
>> Hello,
>>
>> David Sterba @ 2025-09-22 12:28 +02:
>>
>> > On Fri, Sep 19, 2025 at 04:58:15PM +0200, Miquel Sabaté Solà wrote:
>> >> As pointed out in the documentation, calling 'kmalloc' with open-coded
>> >> arithmetic can lead to unfortunate overflows and this particular way of
>> >> using it has been deprecated. Instead, it's preferred to use
>> >> 'kmalloc_array' in cases where it might apply so an overflow check is
>> >> performed.
>> >
>> > So this is an API cleanup and it makes sense to use the checked
>> > multiplication but it should be also said that this is not fixing any
>> > overflow because in all cases the multipliers are bounded small numbers
>> > derived from number of items in leaves/nodes.
>>
>> Yes, it's just an API cleanup and I don't think it fixes any current bug
>> in the code base. So no need to CC stable or anything like that.
>
> Still the changelog should say explicitly that it's not a bug fix before
> somebody assigns a CVE to it because it mentions overflow.

Got it! I will submit a v2 and make this more explicit.

Thanks,
Miquel

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