netdev - RE: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

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Message-ID: <ef625a4f15144822a037ddabc33a4134@AcuMS.aculab.com>
Date:   Thu, 1 Feb 2018 10:14:29 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Gustavo A. R. Silva'" <garsilva@...eddedor.com>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>
CC:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Wong Hoi Sing, Edison" <hswong3i@...il.com>,
        "Hung Hing Lun, Mike" <hlhung3i@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] tcp_lp: use 64-bit arithmetic instead of 32-bit

> > 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.

	David