linux-kernel - Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets

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Date:   Wed, 28 Sep 2016 15:18:33 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     jhs@...atatu.com, eric.dumazet@...il.com, dsa@...ulusnetworks.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, avagin@...nvz.org, stephen@...workplumber.org
Subject: Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets

On Wed, Sep 28, 2016 at 08:07:01AM -0400, David Miller wrote:
...
> > 
> > I think you miss the point what I'm trying to say: currently end-user
> > may have reference to this member (for any reason) and his program
> > will compile and run. If we change the name the compilation procedure
> > fails and this will break API. Yes, referrning @pad is bad idea for
> > userspace code, and yes (!) better to simply rename it but lets do
> > that later, on top, so that if we break something in userspace
> > we could easily revert the oneline change.
> 
> Right, it would be legal for an existing user to have code that
> explicitly initializes every member of the structure, including 'pad'.
> So we have to keep that member around, at a minimum, for their sake.

+1

> 
> >> BTW: There is at least one major structure in inet diag has a hole
> >> today and doesnt have a padding indicator.
> >> 
> >> > If protocol goes over u8 then complete inet_diag_req_v2 structure will
> >> > have to be reworked becaue @sdiag_protocol is u8 as well. IOW, once
> >> > someone liftup IPPROTO_MAX > 255, he will notice the problem immediately
> >> > because diag for such module simply stop working properly.
> 
> Indeed, we need a 16-bit value here.

Yes, and we will need inet_diag_req_v3 for this sake ;) I think
we can even introduce it early and convert _v2 to _v3 transparently
inside kernel. I could start working on such change if people agreed
(but a bit latter, on the next week probably)