netdev - Re: [PATCH net-next 2/3] ipv6: save dontfrag in cork

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Message-ID: <CANn89iJrj7LUz5bxB0Kk-=OM8m6_++279ganNJBPUoSszxUjjQ@mail.gmail.com>
Date: Fri, 7 Mar 2025 11:07:40 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, horms@...nel.org, 
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next 2/3] ipv6: save dontfrag in cork

On Fri, Mar 7, 2025 at 4:36 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> From: Willem de Bruijn <willemb@...gle.com>
>
> When spanning datagram construction over multiple send calls using
> MSG_MORE, per datagram settings are configured on the first send.
>
> That is when ip(6)_setup_cork stores these settings for subsequent use
> in __ip(6)_append_data and others.
>
> The only flag that escaped this was dontfrag. As a result, a datagram
> could be constructed with df=0 on the first sendmsg, but df=1 on a
> next. Which is what cmsg_ip.sh does in an upcoming MSG_MORE test in
> the "diff" scenario.
>
> Changing datagram conditions in the middle of constructing an skb
> makes this already complex code path even more convoluted. It is here
> unintentional. Bring this flag in line with expected sockopt/cmsg
> behavior.
>
> And stop passing ipc6 to __ip6_append_data, to avoid such issues
> in the future. This is already the case for __ip_append_data.
>
> inet6_cork had a 6 byte hole, so the 1B flag has no impact.
>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>