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

[Christian Brauner]

On Wed, Jul 08, 2020 at 11:35:39PM -0700, Kees Cook wrote:
> 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...

Yeah, it'd be quite some code. I've written some patches for this before
I sent this mail, just so you know. We likely need a 5.6 and 5.7 patch
and a 5.8 patch after Christoph's changes. The 5.8 fixes I'd like to get
in during this merge window. So either I can do this or you can send me
the patches for this?

Christian