netdev - Re: [RFC] CDC-NCM: avoid overflow in sanity checking

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Message-ID: <393ec81c-52b4-842b-1ecd-4ffc29743665@suse.com>
Date:   Mon, 14 Feb 2022 20:30:02 +0100
From:   Oliver Neukum <oneukum@...e.com>
To:     Bjørn Mork <bjorn@...k.no>,
        Alan Stern <stern@...land.harvard.edu>
CC:     Hans Petter Selasky <hps@...asky.org>,
        Oliver Neukum <oneukum@...e.com>, linux-usb@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [RFC] CDC-NCM: avoid overflow in sanity checking


On 11.02.22 08:17, Bjørn Mork wrote:
> Alan Stern <stern@...land.harvard.edu> writes:
>
>
> Only  is that the existing code wants the inverted result:
>
>  	if (offset > skb_in->len || len > skb_in->len - offset) ...
>
> with all values unsigned.

Its logic is

if (!sane(fragment))
    continue;
process(fragment);

rather than

if (sane(fragment))
    process(fragment);

A simple matter of inversion.

> And there you point out my problem:  discipline :-)
>
Do we still agree that unsigned integers are the better option?

    Regards
        Oliver