linux-kernel - Re: [PATCH v2 1/3] bpf: Allow NULL buffers in bpf_dynptr_slice(

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Date:   Wed, 3 May 2023 11:49:14 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Rosenberg <drosen@...gle.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 v2 1/3] bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)

On Mon, May 1, 2023 at 5:52 PM Daniel Rosenberg <drosen@...gle.com> wrote:
>
> bpf_dynptr_slice(_rw) uses a user provided buffer if it can not provide
> a pointer to a block of contiguous memory. This buffer is unused in the
> case of local dynptrs, and may be unused in other cases as well. There
> is no need to require the buffer, as the kfunc can just return NULL if
> it was needed and not provided.
>
> This adds another kfunc annotation, __opt, which combines with __sz and
> __szk to allow the buffer associated with the size to be NULL. If the
> buffer is NULL, the verifier does not check that the buffer is of
> sufficient size.
>
> Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> ---

LGTM

Acked-by: Andrii Nakryiko <andrii@...nel.org>

>  Documentation/bpf/kfuncs.rst | 23 ++++++++++++++++++++++-
>  include/linux/skbuff.h       |  2 +-
>  kernel/bpf/helpers.c         | 30 ++++++++++++++++++------------
>  kernel/bpf/verifier.c        | 17 +++++++++++++----
>  4 files changed, 54 insertions(+), 18 deletions(-)
>

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