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([2620:10d:c090:500::6:a7ca]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-34727be33dbsm14019503a91.8.2025.11.24.10.20.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Nov 2025 10:20:57 -0800 (PST) Message-ID: Subject: Re: [RFC PATCH v7 5/7] libbpf: Implement BTF type sorting validation for binary search optimization From: Eduard Zingerman To: Donglin Peng Cc: Andrii Nakryiko , ast@kernel.org, zhangxiaoqin@xiaomi.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Donglin Peng , Alan Maguire , Song Liu Date: Mon, 24 Nov 2025 10:20:55 -0800 In-Reply-To: References: <20251119031531.1817099-1-dolinux.peng@gmail.com> <20251119031531.1817099-6-dolinux.peng@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, 2025-11-22 at 16:38 +0800, Donglin Peng wrote: > On Sat, Nov 22, 2025 at 3:32=E2=80=AFPM Donglin Peng wrote: > >=20 > > On Sat, Nov 22, 2025 at 3:42=E2=80=AFAM Eduard Zingerman wrote: > > >=20 > > > On Thu, 2025-11-20 at 15:25 +0800, Donglin Peng wrote: > > >=20 > > > [...] > > >=20 > > > > Additionally, in the linear search branch, I saw there is a NULL ch= eck for > > > > the name returned by btf__name_by_offset. This suggests that checki= ng > > > > name_off =3D=3D 0 alone may not be sufficient to identify an anonym= ous type, > > > > which is why I used str_is_empty for a more robust check. > > >=20 > > > 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 al= l > > > types by btf_check_all_metas() called from btf_parse_base(), > > > btf_parse_module() and btf_parse_type_sec() -> btf_parse(). > > >=20 > > > So, it appears that kernel protects itself from invalid name_off > > > values at BTF load time. > >=20 > > 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. >=20 > Sorry =E2=80=94 my mistake. There=E2=80=99s no NULL check on the name fro= m > btf_str_by_offset in the kernel=E2=80=99s btf_find_by_name_kind. The > libbpf version has it. tools/lib/bpf/btf.c:btf_sanity_check() is called from btf_new(), it calls btf_validate_type(), which does btf_validate_str(). So, ignoring the NULL case on libbpf side should be safe as well. [...]