linux-kernel - Re: [PATCH 2/3] bpf: Allow NULL buffers in bpf_dynptr_slice(

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Date:   Fri, 28 Apr 2023 18:57:48 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Joanne Koong <joannelkoong@...il.com>,
        Mykola Lysenko <mykolal@...com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 2/3] bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)

On Thu, Apr 6, 2023 at 2:09 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> would this work correctly if someone passes a non-null buffer with too
> small size? Can you please add a test for this use case.
>
Working on a test case for this, but the test case I wrote fails
without my patches.
I'm just declaring a buffer of size 9 on the stack, and then passing
in bpf_dynptr_slice that buffer, and size 10. That's passing the
verifier just fine. In fact, it loads successfully up to size 16. I'm
guessing that's adjusting for alignment? Still feels very strange. Is
that expected behavior?