netdev - Re: [PATCH net 3/3] wireguard: send: account for mtu=0 devices

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Message-ID: <CAHmME9qErQbU5Y36i=3L_R_PYw2Li_Vv2a9k7bSuMxpuLMcgsg@mail.gmail.com>
Date:   Fri, 14 Feb 2020 16:56:22 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 3/3] wireguard: send: account for mtu=0 devices

On Fri, Feb 14, 2020 at 4:18 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
> > However, while min_mtu=0 seems fine, it makes sense to restrict the
> > max_mtu. This commit also restricts the maximum MTU to the greatest
> > number for which rounding up to the padding multiple won't overflow a
> > signed integer. Packets this large were always rejected anyway
> > eventually, due to checks deeper in, but it seems more sound not to even
> > let the administrator configure something that won't work anyway.
> >
> If mtu is set to 0, the device must not send any payload.

Yes, but there's still internal keepalive messages.

>
> Are you sure this works ?
>
> Last statement :
>
> return padded_size - last_unit;
>
> will return a a ' negative number'

Woah nelly I don't know how I missed this. Thanks! Will send a v2 of
this patchset.