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Thu, 06 Aug 2026 11:22:42 -0700 (PDT) Received: from mtardy-friendly-lvh-runner.europe-west1-c.c.cilium-dev.internal ([2600:1900:4010:1a8::]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-4995420bd1csm82214425e9.3.2026.08.06.11.22.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Aug 2026 11:22:41 -0700 (PDT) From: Mahe Tardy To: bpf@vger.kernel.org Cc: 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, song@kernel.org, netdev@vger.kernel.org, sdf.kernel@gmail.com, ameryhung@gmail.com, kuniyu@google.com, memxor@gmail.com, Mahe Tardy Subject: [PATCH bpf-next v4 0/5] Introduce bpf_ksock Date: Thu, 6 Aug 2026 18:22:29 +0000 Message-Id: <20260806182234.380833-1-mahe.tardy@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This patch series introduces bpf_ksock, a set of BPF kfuncs to allow BPF programs to create UDP sockets and send data. This provides a mechanism for BPF LSM progs to emit telemetry over UDP independently of userspace. The main use case is to be able to completely dispense with agents/daemons for BPF programs after startup. In the case of Isovalent's Tetragon, the idea would be to be able to emit security alerts or export data from BPF even when the agent is down. For meta, according to Liam presentation[^2], this could replace logging via ringbuffers which created cross-binary versioning issues. The implementation follows the established kfunc lifecycle pattern (create/acquire/release with refcounting, kptr map storage, dtor registration), for example used by the network bpf_crypto kfuncs. For reference, this was discussed at LSF/MM/BPF 2025[^1] in Montreal, again at Plumbers 2025 in Tokyo. Liam Wisehart mentioned this work during his presentation of BpfJailer[^2]. Then it was also discussed during LSF/MM/BPF 2026 in Zagreb. A first version of it, called bpf_netpoll was submitted to the mailing list but eventually NACKED by Jakub Kicinski[^3]. The discussion eventually reached an agreement that we should use regular kernel sockets if we want to do network from BPF programs[^4]. This was fundamentally more complex to implement but here is a first proposition of how it could look like after several automated reviews using sashiko. For more details, here are some of the main adjustements I had to make during the preparation of these patches: Initially, the goal was to register the ksock_kfunc_set with BPF_PROG_TYPE_UNSPEC to allow send to be called from any programs. This introduces significant challenges (but might be doable). The limitation is still that the programs should be able to sleep but combining this with bpf workqueue allows to send from virtually anywhere. However, not by-passing LSM socket hooks make it impossible to be called from the workqueue context as the credential of the initial caller would not be preserved. Also, it would be easy for users to shoot themselves in the foot and attach a program that sends asynchronously over the network on a network hook. So the idea for now is to restrict the ksock_kfunc_set (which is acquire, release and send) to SYSCALL and LSM to make it simpler. Also to make the patch set easier to start with, the sockets are restricted to UDP. v4 updates: - drop the __sys_ prefix on connect_socket() (Song) - replace recursion protection with a verifier filter on calling bpf_ksock_send() on a program attached to the security_socket_sendmsg() LSM hook (Song) v3 updates: Simplifies bpf_ksock_connect arg by using a union (union bpf_ksock_addr) containing struct sockaddr_in and struct sockaddr_in6 to remove most of bpf_ksock_parse_addr() code (Stanislav). Note that I initially tried to put the union inside of struct bpf_ksock_addr_opts but we ended up with too much struct nesting depth from bpf, for example when trying to write the ipv4 address: addr_opts.addr.sin.sin_addr.s_addr = ipv4_remote; It resulted in: max struct nesting depth exceeded R2 pointer type STRUCT bpf_ksock_addr_opts must point to void, scalar, or struct with scalar v2 updates: This second version simplifies the patch set by removing bind, keeping connect + send for now (could be replaced per sendto if needed). It also removes the sysctl limit and the whole hashtable ksock_send guard with a single bit in task_struct. - remove bind from the API (Stanislav, Amery, Kuniyuki) - remove the bpf_ksock_max sysctl limit (Stanislav, Kuniyuki) - replace ksock_send_guard with a bit in task_struct (Kuniyuki) - remove unnecessary init struct sockaddr_storage addr = {}; (Kuniyuki) - remove redundant ASSERT_OK_FD (sashiko) - fix typos in ksock test patch commit log (bot+bpf-ci) - fix return statement in kfunc registration (bot+bpf-ci) v1 updates (from local sashiko iterations): - do not bypass the LSM and thus add send re-enter protection; - limit the number of socket creation through the kfunc per ns; - copy the arg values to avoid TOCTOU race since kfunc can sleep; - prevent calling bpf_ksock_create from workqueue with improper creds. [^1]: https://lwn.net/Articles/1022034/ [^2]: https://lpc.events/event/19/contributions/2159/ [^3]: https://lore.kernel.org/bpf/20260511182019.69ebc7c6@kernel.org/ [^4]: https://lore.kernel.org/bpf/CAPhsuW71P58XqsXrLbqsShgnozg66TA=T_c=fYrqSSzvL1tTWA@mail.gmail.com/ Link to v3: https://lore.kernel.org/bpf/20260804164652.296919-1-mahe.tardy@gmail.com/ Mahe Tardy (5): net: Add connect_socket() helper bpf: Add ksock kfuncs selftests/bpf: Add ksock kfunc test selftests/bpf: Test forbidden bpf_ksock_send() LSM attach selftests/bpf: Add ksock test for async callback guard include/linux/bpf_ksock.h | 36 ++ include/linux/socket.h | 2 + kernel/bpf/verifier.c | 3 + net/core/Makefile | 3 + net/core/bpf_ksock.c | 331 ++++++++++++++++++ net/socket.c | 32 +- .../testing/selftests/bpf/prog_tests/ksock.c | 133 +++++++ .../selftests/bpf/prog_tests/ksock_wq.c | 34 ++ .../selftests/bpf/progs/ksock_common.h | 58 +++ tools/testing/selftests/bpf/progs/ksock_lsm.c | 88 +++++ .../selftests/bpf/progs/ksock_lsm_verifier.c | 36 ++ tools/testing/selftests/bpf/progs/ksock_wq.c | 62 ++++ 12 files changed, 804 insertions(+), 14 deletions(-) create mode 100644 include/linux/bpf_ksock.h create mode 100644 net/core/bpf_ksock.c create mode 100644 tools/testing/selftests/bpf/prog_tests/ksock.c create mode 100644 tools/testing/selftests/bpf/prog_tests/ksock_wq.c create mode 100644 tools/testing/selftests/bpf/progs/ksock_common.h create mode 100644 tools/testing/selftests/bpf/progs/ksock_lsm.c create mode 100644 tools/testing/selftests/bpf/progs/ksock_lsm_verifier.c create mode 100644 tools/testing/selftests/bpf/progs/ksock_wq.c -- 2.34.1