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We have several use cases where a pod injects traffic into the datapath of another so that the traffic appears to have originated from that pod. One such use case is a synthetic flow generator which injects synthetic traffic into a pod's datapath to enable dynamic probing and debugging. Another is a transparent proxy where connections originating from one pod are redirected towards another which proxies that connection. The new connection is bound to the IP of the original pod using IP_TRANSPARENT and its traffic is injected into that pod's datapath and handled as if it had originated there. This can be used for mTLS, etc. We use bpf_redirect(BPF_F_INGRESS) to direct traffic leaving the proxy, flow generator, etc. towards the target pod, ensuring that eBPF programs that are meant to intercept traffic leaving that pod are executed. However, this doesn't work with netkit. With netkit, an ingress redirection from proxy to workload skips eBPF programs that are meant to intercept traffic leaving the pod, since they reside on the netkit peer device. One workaround is to attach the same program to both the netkit peer device and the TCX ingress hook for the netkit pair's primary interface, but a) This seems hacky and we need to be careful not to run the same program twice for the same skb in cases where we want to pass that traffic to the host stack. b) We're trying to keep the proxy redirection / traffic injection systems as modular and separated from Cilium as possible, the system that manages netkit setup and core eBPF programming. It would be handy if instead we could redirect traffic directly from one netkit peer device to another. This patch proposes an extension to bpf_redirect_peer to allow us to do just that. With this patch, the BPF_F_EGRESS flag tells bpf_redirect_peer to emit the skb in the egress direction of the target interface's peer device While the main use case is netkit, I suppose you could also use this mode with veth as well if, e.g., there were some eBPF programs attached to that side of the veth pair that needed to intercept traffic. +---------------------------------------------------------------------+ | +-------------------------+ 6. bpf_redirect_neigh(eth0) | | | pod (10.244.0.10) | ------------------------ | | | | | | | | | +--------+ | | +---------+ | | | | 1. packet -->| | | | | | | | | | leaves ^ | netkit |<===========|======| netkit | | | | | | | peer |=======(eBPF)=====>| primary | | | | | | | | | | | | | | | | | +--------+ | | +---------+ | | | | | | | 2. bpf_redirect v | | +-----------|-------------+ |___________________ +-------| | | | | eth0 | | | 5. bpf_redirect_peer(BPF_F_EGRESS) | +-------| | |________________________ | | | +-------------------------+ | | | | | proxy (10.244.0.11) | | | | | | IP_TRANSPARENT | | | | | | +--------+ | | +---------+ | | | | 3. packet <--| | | | | |<-- | | | enters | netkit |<===========|======| netkit | | | | [proxy] | peer |=======(eBPF)=====>| primary | | | | 4. packet -->| | | | | | | | leaves +--------+ | +---------+ | | | sip=10.244.0.10 | | | +-------------------------+ | +---------------------------------------------------------------------+ Using the proxy use case as an example, in step 5 we would redirect traffic leaving the proxy towards the pod's peer device using bpf_redirect_peer(BPF_F_EGRESS). As a bonus, since the skb doesn't have to go through the backlog queue it can take full advantage of netkit's performance benefits. I set up a test where outgoing iperf3 traffic is injected into the datapath of another pod using either bpf_redirect_peer(BPF_F_EGRESS) or bpf_redirect(BPF_F_INGRESS). I used Cilium's eBPF host routing mode which skips the host stack and uses BPF redirect helpers to do all the routing. (net.ipv4.tcp_congestion_control=cubic,mtu=1500,100GiB link,Cilium eBPF host routing mode) BASELINE [bpf_redirect(BPF_F_INGRESS)] 1. [iperf pod] ==bpf_redirect([pod b], BPF_F_INGRESS)==> [pod b] 2. [pod b] ==bpf_redirect_neigh([eth0])==> eth0 3. eth0 ==over network==> [host b] [ ID] Interval Transfer Bitrate Retr [ 5] 0.00-60.00 sec 231 GBytes 33.0 Gbits/sec 12060 sender [ 5] 0.00-60.00 sec 230 GBytes 33.0 Gbits/sec receiver TEST [bpf_redirect_peer(BPF_F_EGRESS)] 1. [iperf pod] ==bpf_redirect_peer([pod b], BPF_F_EGRESS)==> [pod b] 2. [pod b] ==bpf_redirect_neigh([eth0])==> eth0 3. eth0 ==over network==> [host b] [ ID] Interval Transfer Bitrate Retr [ 5] 0.00-60.00 sec 272 GBytes 38.9 Gbits/sec 0 sender [ 5] 0.00-60.00 sec 272 GBytes 38.9 Gbits/sec receiver In this test, using bpf_redirect_peer(BPF_F_EGRESS) for the hop from [iperf pod] to [pod b] led to ~18% more throughput compared to bpf_redirect(BPF_F_INGRESS). Signed-off-by: Jordan Rife <jordan@jrife.io> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Paul Chaignon <paul.chaignon@gmail.com> Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev> Link: https://lore.kernel.org/r/20260618182035.43811-2-jordan@jrife.io Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst