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

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Date:   Wed, 9 Oct 2019 16:06:18 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] bpf: switch to new usercopy helpers

On Wed, Oct 9, 2019 at 9:09 AM Christian Brauner
<christian.brauner@...ntu.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).