linux-kernel - Re: [PATCH v3 1/9] net: Add struct sockaddr

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Message-ID: <202510230929.7425CE38C4@keescook>
Date: Thu, 23 Oct 2025 09:31:17 -0700
From: Kees Cook <kees@...nel.org>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"Gustavo A. R. Silva" <gustavo@...eddedor.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Simon Horman <horms@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 1/9] net: Add struct sockaddr_unspec for sockaddr of
 unknown length

On Thu, Oct 23, 2025 at 12:43:06PM +0200, Paolo Abeni wrote:
> On 10/20/25 11:26 PM, Kees Cook wrote:
> > Add flexible sockaddr structure to support addresses longer than the
> > traditional 14-byte struct sockaddr::sa_data limitation without
> > requiring the full 128-byte sa_data of struct sockaddr_storage. This
> > allows the network APIs to pass around a pointer to an object that
> > isn't lying to the compiler about how big it is, but must be accompanied
> > by its actual size as an additional parameter.
> > 
> > It's possible we may way to migrate to including the size with the
> > struct in the future, e.g.:
> > 
> > struct sockaddr_unspec {
> > 	u16 sa_data_len;
> > 	u16 sa_family;
> > 	u8  sa_data[] __counted_by(sa_data_len);
> > };
> 
> Side note: sockaddr_unspec is possibly not the optimal name, as
> AF_UNSPEC has a specific meaning/semantic.
> 
> Name-wise, I think 'sockaddr_sized' would be better, but I agree with
> David the struct may cause unaligned access problems.

I'll go with sockaddr_unsized -- doing the sockaddr_sized variant is a
much more involved change. I just want to get us to where we are today
but with no lying to the compiler about sizes. :)

-- 
Kees Cook