Re: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier

[Kees Cook]

On Sat, May 30, 2020 at 03:58:27PM +0200, Christian Brauner wrote:
> On Sat, May 30, 2020 at 05:17:24AM +0200, Jann Horn wrote:
> > On Sat, May 30, 2020 at 4:43 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > I mean, yes, that's certainly better, but it just seems a shame that
> > > everyone has to do the get_unused/put_unused dance just because of how
> > > SCM_RIGHTS does this weird put_user() in the middle.
> > >
> > > Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we
> > > move the put_user() after instead?
> > 
> > Honestly, I think trying to remove file descriptors and such after
> > -EFAULT is a waste of time. If userspace runs into -EFAULT, userspace
> [...]
> 
> There's really no point in trying to save a broken scm message imho.

Right -- my concern is about stuffing a fd into a process without it
knowing (this is likely an overly paranoid concern, given that if the
process is getting EFAULT at the end of a list of fds, all the prior
ones will be installed too..)

-- 
Kees Cook