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

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Date:   Thu, 23 Feb 2023 09:01:20 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Simon Horman <simon.horman@...igine.com>,
        Maxim Korotkov <korotkov.maxim.s@...il.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()

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