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([2620:10d:c090:500::4:d279]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-14365b97994sm2152282c88.12.2026.09.10.15.01.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Sep 2026 15:01:21 -0700 (PDT) Message-ID: <9b3ca4f410cf1f2af0464df282fe017ae801bbd4.camel@gmail.com> Subject: Re: [PATCH bpf 2/2] selftests/bpf: Test BTF walk into a flexible array of zero-sized elements From: Eduard Zingerman To: Jiayuan Chen , bpf@vger.kernel.org Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Kumar Kartikeya Dwivedi , Martin KaFai Lau , Song Liu , Yonghong Song , Jiri Olsa , Emil Tsalapatis , Ihor Solodrai , Shuah Khan , Yazhou Tang , Amery Hung , Matt Bobrowski , Tejun Heo , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Date: Thu, 10 Sep 2026 15:01:18 -0700 In-Reply-To: <20260910122316.186384-2-jiayuan.chen@linux.dev> References: <20260910122316.186384-1-jiayuan.chen@linux.dev> <20260910122316.186384-2-jiayuan.chen@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, 2026-09-10 at 20:22 +0800, Jiayuan Chen wrote: > The program stashes a bpf_obj_new() object whose type ends with a flexibl= e > array of empty structs, then reads it back as an untrusted kptr. Without > the previous patch this divides by zero in btf_struct_walk() instead of > being rejected. >=20 > # ./test_progs -t verifier_btf_flex_array > ... > #602 verifier_btf_flex_array:OK > Summary: 1/1 PASSED, 0 SKIPPED, 0/0 FAILED >=20 > Signed-off-by: Jiayuan Chen > --- Please simplify test case as follows: SEC("syscall") __failure __msg("access beyond struct test_flex_batch at off 4 size 1") int stash_and_peek(void *ctx) { struct map_value *v; int key =3D 0; v =3D bpf_map_lookup_elem(&batches, &key); if (!v || !v->batch) return 0; return *(char *)&v->batch->events[0]; } Also, aren't there already test cases for flex arrays somewhere? Probably no need to add a new file. ...