netdev - Re: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM

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Date: Mon, 22 May 2023 13:12:52 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Simon Horman <simon.horman@...igine.com>
Cc: Christian Brauner <brauner@...nel.org>, kernel test robot
 <lkp@...el.com>, Eric Dumazet <edumazet@...gle.com>, Alexander Mikhalitsyn
 <aleksandr.mikhalitsyn@...onical.com>, davem@...emloft.net,
 oe-kbuild-all@...ts.linux.dev, linux-kernel@...r.kernel.org,
 netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>, Leon Romanovsky
 <leon@...nel.org>, David Ahern <dsahern@...nel.org>, Arnd Bergmann
 <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Kuniyuki Iwashima
 <kuniyu@...zon.com>, Lennart Poettering <mzxreary@...inter.de>, Luca
 Boccassi <bluca@...ian.org>, linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next v5 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD

On Mon, 22 May 2023 15:19:17 +0200 Simon Horman wrote:
> > TLI, that AF_UNIX can be a kernel module...
> > I'm really not excited in exposing pidfd_prepare() to non-core kernel
> > code. Would it be possible to please simply refuse SO_PEERPIDFD and
> > SCM_PIDFD if AF_UNIX is compiled as a module? I feel that this must be
> > super rare because it risks breaking even simplistic userspace.  
> 
> It occurs to me that it may be simpler to not allow AF_UNIX to be a module.
> But perhaps that breaks something for someone...

Both of the two options (disable the feature with unix=m, make unix
bool) could lead to breakage, I reckon at least the latter makes
the breakage more obvious? So not allowing AF_UNIX as a module
gets my vote as well.

A mechanism of exporting symbols for core/internal use only would 
find a lot of use in networking :(