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Date:   Wed, 31 Jan 2018 19:07:49 -0600
Message-ID: <20180131190749.Horde.bsc7GhewsZwdnkmDtMlSwWO@gator4166.hostgator.com>
From:   "Gustavo A. R. Silva" <garsilva@embeddedor.com>
To:     Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc:     "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        "Wong Hoi Sing, Edison" <hswong3i@gmail.com>,
        "Hung Hing Lun, Mike" <hlhung3i@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit
References: <20180201002407.GA1608@embeddedgus>
 <20180201003236.06143fd0@alans-desktop>
In-Reply-To: <20180201003236.06143fd0@alans-desktop>
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Hi Alan,

Quoting Alan Cox <gnomes@lxorguk.ukuu.org.uk>:

> On Wed, 31 Jan 2018 18:24:07 -0600
> "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:
>
>> Cast to s64 some variables and a macro in order to give the
>> compiler complete information about the proper arithmetic to
>> use. Notice that these elements are used in contexts that
>> expect expressions of type s64 (64 bits, signed).
>>
>> Currently such expression are being evaluated using 32-bit
>> arithmetic.
>
> The question you need to ask is 'can it overflow 32bit maths', otherwise
> you are potentially making the system do extra work for no reason.
>

Yeah, I get your point and it seems that in this particular case there  
is no risk of a 32bit overflow, but in general and IMHO as the code  
evolves, the use of incorrect arithmetic may have security  
implications in the future, so I advocate for code correctness in this  
case.

Thanks
--
Gustavo