linux-hardening - Re: [PATCH v3] bpf: Replace bpf_lpm_trie_key 0-length array with flexible array

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Date: Tue, 20 Feb 2024 10:52:56 -0800
From: Kees Cook <keescook@...omium.org>
To: Daniel Borkmann <daniel@...earbox.net>
Cc: Mark Rutland <mark.rutland@....com>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	Haowen Bai <baihaowen@...zu.com>, bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Yonghong Song <yonghong.song@...ux.dev>,
	Jonathan Corbet <corbet@....net>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Joanne Koong <joannelkoong@...il.com>,
	Yafang Shao <laoar.shao@...il.com>, Kui-Feng Lee <kuifeng@...a.com>,
	Anton Protopopov <aspsk@...valent.com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	netdev@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] bpf: Replace bpf_lpm_trie_key 0-length array with
 flexible array

On Tue, Feb 20, 2024 at 11:18:40AM +0100, Daniel Borkmann wrote:
> On 2/20/24 12:41 AM, Kees Cook wrote:
> > Replace deprecated 0-length array in struct bpf_lpm_trie_key with
> > flexible array. Found with GCC 13:
> [...]
> This fails the BPF CI :
> 
>   [...]
>     INSTALL /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/bpf/skel_internal.h
>     INSTALL /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/bpf/libbpf_version.h
>     INSTALL /tmp/work/bpf/bpf/tools/testing/selftests/bpf/tools/include/bpf/usdt.bpf.h
>   In file included from urandom_read_lib1.c:7:
>   In file included from /tmp/work/bpf/bpf/tools/lib/bpf/libbpf_internal.h:20:
>   In file included from /tmp/work/bpf/bpf/tools/lib/bpf/relo_core.h:7:
>   /tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:91:2: error: type name requires a specifier or qualifier
>      91 |         __struct_group(bpf_lpm_trie_key_hdr, hdr, /* no attrs */,
>         |         ^
>   /tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:91:58: error: expected identifier
>      91 |         __struct_group(bpf_lpm_trie_key_hdr, hdr, /* no attrs */,
>         |                                                                 ^
>   /tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:93:18: error: unexpected ';' before ')'
>      93 |                 __u32   prefixlen;
>         |                                  ^
>   /tmp/work/bpf/bpf/tools/include/uapi/linux/bpf.h:95:7: error: flexible array member 'data' not allowed in otherwise empty struct
>      95 |         __u8    data[];         /* Arbitrary size */
>         |                 ^

Ah-ha, my test build of cilium happened to cover up the lack of
stddef.h. Fixed now and sending a v4...

-- 
Kees Cook