netdev - RE: [PATCH net] datagram: When peeking datagrams with offset

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Date:   Thu, 17 Aug 2017 09:15:11 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Willem de Bruijn' <willemdebruijn.kernel@...il.com>,
        Paolo Abeni <pabeni@...hat.com>
CC:     Matthew Dawson <matthew@...systems.ca>,
        Network Development <netdev@...r.kernel.org>,
        "Macieira, Thiago" <thiago.macieira@...el.com>
Subject: RE: [PATCH net] datagram: When peeking datagrams with offset < 0
 don't skip empty skbs

From: Willem de Bruijn
> Sent: 17 August 2017 00:27
> Actually, it is safe even without the check. Overflow of the signed integer
> is benign here.

IIRC the C language states that 'signed integer overflow' is undefined.
So 'MAXINT + 1' doesn't have to equal '-MAXINT - 1' (as one would
expect on a 2's compliment system).

While the linux kernel probably won't run on systems where this isn't true
(eg where signed arithmetic saturates) gcc will assume it can't happen
and optimise code with that assumption.

This may not matter here ...

	David