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Date:   Thu, 01 Feb 2018 20:33:52 -0600
Message-ID: <20180201203352.Horde.xv5XUdiSqNDHlFujzwjX6S0@gator4166.hostgator.com>
From:   "Gustavo A. R. Silva" <garsilva@embeddedor.com>
To:     David Laight <David.Laight@aculab.com>
Cc:     Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
        "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>
 <20180131190749.Horde.bsc7GhewsZwdnkmDtMlSwWO@gator4166.hostgator.com>
 <ef625a4f15144822a037ddabc33a4134@AcuMS.aculab.com>
In-Reply-To: <ef625a4f15144822a037ddabc33a4134@AcuMS.aculab.com>
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Hi David,

Quoting David Laight <David.Laight@aculab.com>:

>> > 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.
>
> Even if the variable are 64bit you still need to worry (maybe less)
> about arithmetic overflow.
> The only real way to avoid overflow is to understand the domain
> of the values being used.
>

Yep, that's correct.

Thanks for the feedback.
--
Gustavo