netdev - Re: [PATCH net-next] net: Add options as a flexible array to struct ip_tunnel

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Message-ID: <20250211162851.4409b61a@kernel.org>
Date: Tue, 11 Feb 2025 16:28:51 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Gal Pressman <gal@...dia.com>
Cc: Kees Cook <kees@...nel.org>, netdev@...r.kernel.org, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>, Tariq Toukan
 <tariqt@...dia.com>, Louis Peens <louis.peens@...igine.com>, Simon Horman
 <horms@...nel.org>, David Ahern <dsahern@...nel.org>, Pravin B Shelar
 <pshelar@....org>, Yotam Gigi <yotam.gi@...il.com>, Jamal Hadi Salim
 <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko
 <jiri@...nulli.us>, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 dev@...nvswitch.org, linux-hardening@...r.kernel.org, Cosmin Ratiu
 <cratiu@...dia.com>
Subject: Re: [PATCH net-next] net: Add options as a flexible array to struct
 ip_tunnel_info

On Tue, 11 Feb 2025 20:59:24 +0200 Gal Pressman wrote:
> > Everything else looks very good, though, yes, I would agree with the
> > alignment comments made down-thread. This was "accidentally correct"
> > before in the sense that the end of the struct would be padded for
> > alignment, but isn't guaranteed to be true with an explicit u8 array.
> > The output of "pahole -C struct ip_tunnel_info" before/after should
> > answer any questions, though.  
> 
> Thanks, I will attach pahole's output in the commit message.

Why not slap an __aligned(sizeof(void *)) or just __aligned(8) 
on the new option field? That should give us the same behavior 
as we have today implicitly.