linux-kernel - Re: [RFC PATCH v7 5/7] libbpf: Implement BTF type sorting validation for binary search optimization

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Message-ID: <CAErzpmsCDmGvne4+TCbm09RNhfcUYVdsk_X7uoS_tSDKG=0Kqg@mail.gmail.com>
Date: Sat, 22 Nov 2025 16:38:45 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>
Cc: Andrii Nakryiko <andrii.nakryiko@...il.com>, ast@...nel.org, zhangxiaoqin@...omi.com, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org, 
	Donglin Peng <pengdonglin@...omi.com>, Alan Maguire <alan.maguire@...cle.com>, 
	Song Liu <song@...nel.org>
Subject: Re: [RFC PATCH v7 5/7] libbpf: Implement BTF type sorting validation
 for binary search optimization

On Sat, Nov 22, 2025 at 3:32 PM Donglin Peng <dolinux.peng@...il.com> wrote:
>
> On Sat, Nov 22, 2025 at 3:42 AM Eduard Zingerman <eddyz87@...il.com> wrote:
> >
> > On Thu, 2025-11-20 at 15:25 +0800, Donglin Peng wrote:
> >
> > [...]
> >
> > > Additionally, in the linear search branch, I saw there is a NULL check for
> > > the name returned by btf__name_by_offset. This suggests that checking
> > > name_off == 0 alone may not be sufficient to identify an anonymous type,
> > > which is why I used str_is_empty for a more robust check.
> >
> > btf_str_by_offset(btf, offset) returns NULL only when 'offset' is
> > larger then 'btf->hdr.str_len'. However, function btf_check_meta()
> > verifies that this shall not happen by invoking
> > btf_name_offset_valid() check. The btf_check_meta() is invoked for all
> > types by btf_check_all_metas() called from btf_parse_base(),
> > btf_parse_module() and btf_parse_type_sec() -> btf_parse().
> >
> > So, it appears that kernel protects itself from invalid name_off
> > values at BTF load time.
>
> Right. The kernel guarantees that btf_str_by_offsetnever returns NULL,
> and there is no NULL check performed on the name returned by
> btf_find_by_name_kind. The NULL check is included in the libbpf version
> of the function.

Sorry — my mistake. There’s no NULL check on the name from
btf_str_by_offset in the kernel’s btf_find_by_name_kind. The
libbpf version has it.

>
> >
> > [...]