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Mon, 16 Mar 2026 04:29:37 -0700 (PDT) From: Chengkaitao To: martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, shuah@kernel.org, chengkaitao@kylinos.cn, linux-kselftest@vger.kernel.org Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next v8 6/8] bpf: allow bpf_list_front/back result as the prev argument of bpf_list_add_impl Date: Mon, 16 Mar 2026 19:28:41 +0800 Message-ID: <20260316112843.78657-7-pilgrimtao@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260316112843.78657-1-pilgrimtao@gmail.com> References: <20260316112843.78657-1-pilgrimtao@gmail.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kaitao Cheng KF_ARG_PTR_TO_LIST_NODE normally requires an owning reference (PTR_TO_BTF_ID | MEM_ALLOC and ref_obj_id). For bpf_list_add_impl's third argument (prev), allow a non-owning reference with ref_obj_id==0 so that the result of bpf_list_front() or bpf_list_back() can be passed as the insertion point. When prev is such a non-owning ref, skip the MEM_ALLOC/ref_obj_id checks and jump to the shared list-node processing. Owning refs (e.g. from pop + refcount_acquire) still pass the existing checks and reach the same label. Signed-off-by: Kaitao Cheng --- kernel/bpf/verifier.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 98ddb370feb5..0a6f2e6a5d28 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13737,6 +13737,14 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ return ret; break; case KF_ARG_PTR_TO_LIST_NODE: + if (meta->func_id == special_kfunc_list[KF_bpf_list_add_impl] + && i == 2 && type_is_non_owning_ref(reg->type) + && !reg->ref_obj_id) { + /* Allow bpf_list_front/back return value as + * list_add_impl's third arg (R3). + */ + goto check_ok; + } if (reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) { verbose(env, "arg#%d expected pointer to allocated object\n", i); return -EINVAL; @@ -13745,6 +13753,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_ verbose(env, "allocated object must be referenced\n"); return -EINVAL; } +check_ok: ret = process_kf_arg_ptr_to_list_node(env, reg, regno, meta); if (ret < 0) return ret; -- 2.50.1 (Apple Git-155)