Re: [PATCH net-next v6 1/3] scm: add SO_PASSPIDFD and SCM_PIDFD

[Christian Brauner <brauner@kernel.org>]

On Mon, May 22, 2023 at 01:34:09PM -0700, Jakub Kicinski wrote:
> On Mon, 22 May 2023 15:24:37 +0200 Alexander Mikhalitsyn wrote:
> > v6:
> > 	- disable feature when CONFIG_UNIX=n/m (pidfd_prepare API is not exported to modules)
> 
> IMHO hiding the code under #if IS_BUILTIN(CONFIG_UNRELATED) is
> surprising to the user and.. ugly?
> 
> Can we move scm_pidfd_recv() into a C source and export that?
> That should be less controversial than exporting pidfd_prepare()
> directly?

I really would like to avoid that because it will just mean that someone
else will abuse that function and then make an argument why we should
export the other function.

I think it would be ok if we required that unix support is built in
because it's not unprecedented either and we're not breaking anything.
Bpf has the same requirement:

  #if IS_BUILTIN(CONFIG_UNIX) && defined(CONFIG_BPF_SYSCALL)
  struct bpf_unix_iter_state {
          struct seq_net_private p;
          unsigned int cur_sk;
          unsigned int end_sk;
          unsigned int max_sk;
          struct sock **batch;
          bool st_bucket_done;
  };

and

  #if IS_BUILTIN(CONFIG_UNIX) && defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
  DEFINE_BPF_ITER_FUNC(unix, struct bpf_iter_meta *meta,
                       struct unix_sock *unix_sk, uid_t uid)