linux-kernel - Re: [PATCH v2] bnxt: avoid overflow in bnxt_get_nvram

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Date:   Fri, 24 Feb 2023 09:32:15 +0300
From:   Maxim Korotkov <korotkov.maxim.s@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>,
        Simon Horman <simon.horman@...igine.com>
Cc:     Michael Chan <michael.chan@...adcom.com>,
        Pavan Chebbi <pavan.chebbi@...adcom.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, lvc-project@...uxtesting.org
Subject: Re: [PATCH v2] bnxt: avoid overflow in bnxt_get_nvram_directory()

23.02.2023 11:01, Paolo Abeni wrote:
> On Tue, 2023-02-21 at 10:34 +0100, Paolo Abeni wrote:
>> On Sun, 2023-02-19 at 15:14 +0100, Simon Horman wrote:
>>> On Sun, Feb 19, 2023 at 11:46:56AM +0300, Maxim Korotkov wrote:
>>>> The value of an arithmetic expression is subject
>>>> of possible overflow due to a failure to cast operands to a larger data
>>>> type before performing arithmetic. Used macro for multiplication instead
>>>> operator for avoiding overflow.
>>>>
>>>> Found by Security Code and Linux Verification
>>>> Center (linuxtesting.org) with SVACE.
>>>>
>>>> Fixes: c0c050c58d84 ("bnxt_en: New Broadcom ethernet driver.")
>>>> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@...il.com>
>>>> Reviewed-by: Pavan Chebbi <pavan.chebbi@...adcom.com>
>>>
>>> I agree that it is correct to use mul_u32_u32() for multiplication
>>> of two u32 entities where the result is 64bit, avoiding overflow.
>>>
>>> And I agree that the fixes tag indicates the commit where the code
>>> in question was introduced.
>>>
>>> However, it is not clear to me if this is a theoretical bug
>>> or one that can manifest in practice - I think it implies that
>>> buflen really can be > 4Gbytes.
>>>
>>> And thus it is not clear to me if this patch should be for 'net' or
>>> 'net-next'.
>>
>> ... especially considered that both 'dir_entries' and 'entry_length'
>> are copied back to the user-space using a single byte each.
> 
> To be clear: if this is really a bug you should update the commit
> message stating how the bug could happen. Otherwise you could repost
> for net-next stripping the fixes tag.
> 
> Thanks,
> 
> Paolo
> 
This is more of a hypothetical issue in my opinion. At least I don't 
have proof of concept. I'll resend this patch when net-next tree be open.
Best regards, Max