Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230502005218.3627530-1-drosen@google.com> <20230718082615.08448806@kernel.org>
In-Reply-To: <20230718082615.08448806@kernel.org>
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Tue, 18 Jul 2023 08:52:55 -0700
Message-ID: <CAADnVQJEEF=nqxo6jHKK=Tn3M_NVXHQjhY=_sry=tE8X4ss25A@mail.gmail.com>
Subject: Re: [PATCH v2 1/3] bpf: Allow NULL buffers in bpf_dynptr_slice(_rw)
To:     Jakub Kicinski <kuba@kernel.org>
Cc:     Daniel Rosenberg <drosen@google.com>, bpf <bpf@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        John Fastabend <john.fastabend@gmail.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Shuah Khan <shuah@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Joanne Koong <joannelkoong@gmail.com>,
        Mykola Lysenko <mykolal@fb.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Jul 18, 2023 at 8:26=E2=80=AFAM Jakub Kicinski <kuba@kernel.org> wr=
ote:
>
> On Mon,  1 May 2023 17:52:16 -0700 Daniel Rosenberg wrote:
> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -4033,7 +4033,7 @@ __skb_header_pointer(const struct sk_buff *skb, i=
nt offset, int len,
> >       if (likely(hlen - offset >=3D len))
> >               return (void *)data + offset;
> >
> > -     if (!skb || unlikely(skb_copy_bits(skb, offset, buffer, len) < 0)=
)
> > +     if (!skb || !buffer || unlikely(skb_copy_bits(skb, offset, buffer=
, len) < 0))
> >               return NULL;
>
> First off - please make sure you CC netdev on changes to networking!
>
> Please do not add stupid error checks to core code for BPF safety.
> Wrap the call if you can't guarantee that value is sane, this is
> a very bad precedent.

This is NOT for safety. You misread the code.