Re: [PATCH 0/3] bpf: switch to new usercopy helpers

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	Network Development <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/3] bpf: switch to new usercopy helpers
Date: Tue, 15 Oct 2019 15:45:54 -0700	[thread overview]
Message-ID: <CAADnVQJ6t+HQBRhN3mZrz4qhzGybsY2g-26mc2kQARkbLxqzTA@mail.gmail.com> (raw)
In-Reply-To: <20191010092647.cpxh7neqgabq36gt@wittgenstein>

On Thu, Oct 10, 2019 at 2:26 AM Christian Brauner
<christian.brauner@ubuntu.com> wrote:
>
> On Wed, Oct 09, 2019 at 04:06:18PM -0700, Alexei Starovoitov wrote:
> > On Wed, Oct 9, 2019 at 9:09 AM Christian Brauner
> > <christian.brauner@ubuntu.com> wrote:
> > >
> > > Hey everyone,
> > >
> > > In v5.4-rc2 we added two new helpers check_zeroed_user() and
> > > copy_struct_from_user() including selftests (cf. [1]). It is a generic
> > > interface designed to copy a struct from userspace. The helpers will be
> > > especially useful for structs versioned by size of which we have quite a
> > > few.
> > >
> > > The most obvious benefit is that this helper lets us get rid of
> > > duplicate code. We've already switched over sched_setattr(), perf_event_open(),
> > > and clone3(). More importantly it will also help to ensure that users
> > > implementing versioning-by-size end up with the same core semantics.
> > >
> > > This point is especially crucial since we have at least one case where
> > > versioning-by-size is used but with slighly different semantics:
> > > sched_setattr(), perf_event_open(), and clone3() all do do similar
> > > checks to copy_struct_from_user() while rt_sigprocmask(2) always rejects
> > > differently-sized struct arguments.
> > >
> > > This little series switches over bpf codepaths that have hand-rolled
> > > implementations of these helpers.
> >
> > check_zeroed_user() is not in bpf-next.
> > we will let this set sit in patchworks for some time until bpf-next
> > is merged back into net-next and we fast forward it.
> > Then we can apply it (assuming no conflicts).
>
> Sounds good to me. Just ping me when you need me to resend rebase onto
> bpf-next.

-rc1 is now in bpf-next.
I took a look at patches and they look good overall.

In patches 2 and 3 the zero init via "= {};"
should be unnecessary anymore due to
copy_struct_from_user() logic, right?

Could you also convert all other case in kernel/bpf/,
so bpf_check_uarg_tail_zero() can be removed ?
Otherwise the half-way conversion will look odd.