linux-kernel - Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf

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Date:   Tue, 30 Mar 2021 16:16:44 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Pedro Tammela <pctammela@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Joe Stringer <joe@...ium.io>,
        Quentin Monnet <quentin@...valent.com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <bpf@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>,
        Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()'
 and 'bpf_ringbuf_submit()'

On Tue, Mar 30, 2021 at 3:54 PM Pedro Tammela <pctammela@...il.com> wrote:
>
>  BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
>  {
> +       if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
> +               return -EINVAL;
> +
>         bpf_ringbuf_commit(sample, flags, false /* discard */);
> +
>         return 0;

I think ringbuf design was meant for bpf_ringbuf_submit to never fail.
If we do flag validation it probably should be done at the verifier time.