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[195.134.167.217]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4995bb9093asm1622265e9.2.2026.08.06.10.21.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 10:21:32 -0700 (PDT) Date: Thu, 6 Aug 2026 19:21:30 +0200 From: Mahe Tardy To: Song Liu Cc: Kumar Kartikeya Dwivedi , bpf@vger.kernel.org, andrew+netdev@lunn.ch, andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net, eddyz87@gmail.com, edumazet@google.com, john.fastabend@gmail.com, kuba@kernel.org, liamwisehart@meta.com, martin.lau@linux.dev, pabeni@redhat.com, netdev@vger.kernel.org, sdf.kernel@gmail.com, ameryhung@gmail.com, kuniyu@google.com Subject: Re: [PATCH bpf-next v3 2/5] bpf: Add ksock kfuncs Message-ID: References: <20260804164652.296919-1-mahe.tardy@gmail.com> <20260804164652.296919-3-mahe.tardy@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Aug 04, 2026 at 09:55:44PM -0700, Song Liu wrote: > On Tue, Aug 4, 2026 at 9:47 AM Mahe Tardy wrote: > [...] > > +__bpf_kfunc int bpf_ksock_send(struct bpf_ksock *ks, const void *data, > > + u32 data__sz) > > +{ > > + struct msghdr msg = { > > + .msg_flags = MSG_DONTWAIT, > > + }; > > + struct kvec iov = { > > + .iov_base = (void *)data, > > + .iov_len = data__sz, > > + }; > > + int ret; > > + > > + if (!bpf_ksock_has_user_task_context()) > > + return -EOPNOTSUPP; > > + > > + /* Early check for UDP. Exact limits enforced by kernel_sendmsg(). */ > > + if (data__sz > IP_MAX_MTU) > > + return -EMSGSIZE; > > + > > + if (current->in_bpf_ksock_send) > > + return -EBUSY; > > Returning EBUSY is not ideal. Can we avoid recursion by disallowing > calling bpf_ksock_send from certain hooks? You can find examples > check_kfunc_call() or check_special_kfunc(). This probably means > we need to grow special_kfunc_list, which is not ideal. This is actually a really nice feedback. I didn't know we could add a filter per attach BTF ID. This resolves the issue that the send kfunc calls security_socket_sendmsg so we can remove all the recursion protection and struggles, it's rejected at verifier time. The filter now looks like this, I'd send this in the next version: BTF_ID_LIST_SINGLE(bpf_lsm_socket_sendmsg_id, func, bpf_lsm_socket_sendmsg) static int bpf_ksock_kfunc_filter(const struct bpf_prog *prog, u32 kfunc_id) { if (!btf_id_set8_contains(&ksock_kfunc_btf_ids, kfunc_id)) return 0; if (prog->type == BPF_PROG_TYPE_SYSCALL) return 0; if (prog->type == BPF_PROG_TYPE_LSM && prog->aux->attach_btf_id != bpf_lsm_socket_sendmsg_id[0]) return 0; return -EACCES; } I don't think I need to touch anything else. I'll adjust the tests according to this. Thanks Song. > > @Kumar, do you have strong objection that we grow special_kfunc_list > for this use case? > > Thanks, > Song > > > > + > > + current->in_bpf_ksock_send = true; > > + ret = kernel_sendmsg(ks->sock, &msg, &iov, 1, data__sz); > > + current->in_bpf_ksock_send = false; > > + > > + return ret; > > +} > > + > > +__bpf_kfunc_end_defs();