netdev - Re: [PATCH v2 1/4][next] uapi: socket: Introduce struct sockaddr

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Message-ID: <bc7d77fdbe97edc3481f9f73a438742651bd4b8b.camel@sipsolutions.net>
Date: Mon, 28 Oct 2024 21:47:08 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Andrew Lunn <andrew@...n.ch>, "Gustavo A. R. Silva"
 <gustavoars@...nel.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, David Ahern <dsahern@...nel.org>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-hardening@...r.kernel.org, Kees Cook <kees@...nel.org>, Simon Horman
 <horms@...nel.org>
Subject: Re: [PATCH v2 1/4][next] uapi: socket: Introduce struct
 sockaddr_legacy

On Mon, 2024-10-28 at 21:38 +0100, Andrew Lunn wrote:
> > As this new struct will live in UAPI, to avoid breaking user-space code
> > that expects `struct sockaddr`, the `__kernel_sockaddr_legacy` macro is
> > introduced. This macro allows us to use either `struct sockaddr` or
> > `struct sockaddr_legacy` depending on the context in which the code is
> > used: kernel-space or user-space.
> 
> Are there cases of userspace API structures where the flexiable array
> appears in the middle?

Clearly, it's the case for all the three other patches in this series.

> I assume this new compiler flag is not only for
> use in the kernel? When it gets turned on in user space, will the
> kernel headers will again produce warnings? Should we be considering
> allowing user space to opt in to using sockaddr_legacy?

For the userspace covered by patch 2 this will almost certainly never
happen, and I suspect that might also be true for the others (arp and
rtnetlink ioctls)? But it probably wouldn't be difficult either.

johannes