netdev - Re: [PATCH bpf-next v4 06/10] bpf: Track provenance for pointers formed from referenced PTR_TO_BTF

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Date:   Sat, 18 Dec 2021 21:05:18 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        netfilter-devel <netfilter-devel@...r.kernel.org>,
        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>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: [PATCH bpf-next v4 06/10] bpf: Track provenance for pointers
 formed from referenced PTR_TO_BTF_ID

On Sat, Dec 18, 2021 at 8:33 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:
>
> It is, but into parent_ref_obj_id, to match during release_reference.
>
> > Shouldn't r2 get a different ref_obj_id after r2 = r1->next ?
>
> It's ref_obj_id is still 0.
>
> Thinking about this more, we actually only need 1 extra bit of information in
> reg_state, not even a new member. We can simply copy ref_obj_id and set this
> bit, then we can reject this register during release but consider it during
> release_reference.

It seems to me that this patch created the problem and it's trying
to fix it at the same time.

mark_btf_ld_reg() shouldn't be copying ref_obj_id.
If it keeps it as zero the problem will not happen, no?