Subject: Re: [PATCH v6 4/7] pidfd: Replace open-coded partial receive_fd()

From: Kees Cook <[email-masked]>
Date: Wed, 8 Jul 2020 23:35:39 -0700

On Tue, Jul 07, 2020 at 02:22:20PM +0200, Christian Brauner wrote:
> So while the patch is correct it leaves 5.6 and 5.7 with a bug in the
> pidfd_getfd() implementation and that just doesn't seem right. I'm
> wondering whether we should introduce:
> 
> void sock_update(struct file *file)
> {
> 	struct socket *sock;
> 	int error;
> 
> 	sock = sock_from_file(file, &error);
> 	if (sock) {
> 		sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> 		sock_update_classid(&sock->sk->sk_cgrp_data);
> 	}
> }
> 
> and switch pidfd_getfd() over to:
> 
> diff --git a/kernel/pid.c b/kernel/pid.c
> index f1496b757162..c26bba822be3 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -642,10 +642,12 @@ static int pidfd_getfd(struct pid *pid, int fd)
>         }
> 
>         ret = get_unused_fd_flags(O_CLOEXEC);
> -       if (ret < 0)
> +       if (ret < 0) {
>                 fput(file);
> -       else
> +       } else {
> +               sock_update(file);
>                 fd_install(ret, file);
> +       }
> 
>         return ret;
>  }
> 
> first thing in the series and then all of the other patches on top of it
> so that we can Cc stable for this and that can get it backported to 5.6,
> 5.7, and 5.8.
> 
> Alternatively, I can make this a separate bugfix patch series which I'll
> send upstream soonish. Or we have specific patches just for 5.6, 5.7,
> and 5.8. Thoughts?

Okay, I looked at hch's clean-ups again and I'm reminded why they
don't make great -stable material. :) The compat bug (also missing the
sock_update()) needs a similar fix (going back to 3.6...), so, yeah,
for ease of backport, probably an explicit sock_update() implementation
(with compat and native scm using it), and a second patch for pidfd.

Let me see what I looks best...

-- 
Kees Cook