netdev - Re: [PATCH net] uapi: linux: restore IPPROTO

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Date:   Thu, 12 Jan 2023 11:54:21 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org,
        pabeni@...hat.com, edumazet@...gle.com
Subject: Re: [PATCH net] uapi: linux: restore IPPROTO_MAX to 256

On Wed, Jan 11, 2023 at 10:47:19PM +0100, Pablo Neira Ayuso wrote:
> IPPROTO_MAX used to be 256, but with the introduction of IPPROTO_MPTCP
> definition, IPPROTO_MAX was bumped to 263.
> 
> IPPROTO_MPTCP definition is used for the socket interface from
> userspace. It is never used in the layer 4 protocol field of
> IP headers.
> 
> IPPROTO_* definitions are used anywhere in the kernel as well as in
> userspace to set the layer 4 protocol field in IP headers.
> 
> At least in Netfilter, there is code in userspace that relies on
> IPPROTO_MAX (not inclusive) to check for the maximum layer 4 protocol.
> 
> This patch restores IPPROTO_MAX to 256.
> 
> Fixes: faf391c3826c ("tcp: Define IPPROTO_MPTCP")
> Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
> ---
> Alternatively, I can also define an internal __IPPROTO_MAX to 256 in
> userspace.  I understand an update on uapi at this stage might be
> complicated. Another possibility is to add a new definition
> IPPROTO_FIELD_MAX to uapi and set it to 256 that userspace could start
> using.

Scratch this.

This breaks inet_create() and inet6_create() which is going to break
MP-TCP with socket().

I'll post a v2 adding a new IPPROTO_FIELD_MAX definition 256.