eBPF has been a powerful tools in the Linux kernel, offering safe and programmable hooks into low-level system behavior. I spent tonight reading about Qpoint. I dove deep into the socket.bpf.c file on their Git to understand how the QPoint is using eBPF to trace socket-level activity across the lifecycle of a connection. It monitors socket creation, data transmission, and teardown, while offering protocol-aware introspection—all from inside the kernel.

This is not just packet inspection. This is process-aware, syscall-correlated telemetry that bridges the user/kernel boundary with precision and intent.

What This Code Does

At its core, this eBPF program attaches to key syscall tracepoints (connect, accept, sendto, recvfrom, read, write, close, and others) and captures metadata and data buffers associated with socket usage. The major components include:

Socket Type Inference: At the sys_socket entry point, the code captures the domain, type, and protocol and stores it for use after the syscall returns.

Address and Connection Tracking: For syscalls like connect() and accept(), the destination or client address is captured and stored in per-FD maps. These addresses are then used to create per-connection identity tuples based on PID, FD, and time.

Data Path Inspection: As data flows through read, write, readv, writev, and their UDP counterparts, this code captures initial buffers—typically to fingerprint protocols like HTTP, TLS, or DNS—and submit structured events to a ring buffer.

TLS Detection: There’s a built-in handshake parser that looks for the ClientHello message to identify SSL traffic. TLS sessions are flagged and handled differently from plaintext traffic.

Process-Aware Filtering: Processes can be ignored dynamically via strategy maps (QP_IGNORE, QP_FORWARD, etc.), allowing selective inclusion or exclusion of connections based on runtime configuration.

Directional Filtering: The code differentiates between ingress and egress, loopback, internal vs. external traffic, and even proxies or management endpoints—giving the observer fine-grained control over what’s reported.

Design Strengths

• Kernel-resident efficiency: There’s no context switching overhead once the program is loaded. Everything is collected in-place, using verifier-safe memory access patterns and bounded loops.
• Structured telemetry: Events are explicitly typed (S_OPEN, S_DATA, S_CLOSE, S_PROTO, etc.) and correlated with per-connection state, offering clean semantics when consumed in user space.
• Protocol awareness: Unlike netfilter or raw packet sniffers, this code attempts to interpret the meaning of a connection—protocol, direction, and usage pattern—rather than just its headers.

While the implementation is technically sound, it raises deeper questions about Linux’s trust model and kernel-user space boundaries.

This code captures application-level data buffers at syscall entry and exit points, before encryption or masking occurs in user space. It can fingerprint plaintext HTTP requests, detect SSL handshakes, and correlate traffic with process metadata. While extremely powerful for observability and security tooling, this also opens the door to surveillance.

The kernel, historically, has not been a place for application-layer parsing. Doing so, even with the verifier’s constraints, represents a shift from a minimal trusted computing base to something more introspective—and potentially overreaching.

• What happens if this code misinterprets a protocol and causes false alerts?
• Should all eBPF observers be allowed to inspect TLS handshakes by default?
• Is it acceptable for an eBPF program to associate application data with PIDs and expose it externally?

These are not technical limitations—they’re design tradeoffs that need to be weighed carefully.

socket.bpf.c is a technical achievement. It showcases the full breadth of what modern eBPF tooling can do: real-time, low-overhead, semantically rich observability. But it also pushes on boundaries that Linux has historically tried to avoid—specifically, embedding high-level visibility logic in kernelspace.

The ability to introspect application behavior with this fidelity is powerful. But as with all power at the kernel level, it demands discipline, context-awareness, and a strong ethical hand.