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

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Message-ID: <20230718082615.08448806@kernel.org>
Date:   Tue, 18 Jul 2023 08:26:15 -0700
From:   Jakub Kicinski <kuba@...nel.org>
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,  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, int offset, int len,
>  	if (likely(hlen - offset >= 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.