Hands-On Tutorial: Writing Production eBPF Security Programs in C & Rust with libbpf (2026 Masterclass)

Originally published on Andrax Pentester by Syed Zada Abrar.

eBPF (Extended Berkeley Packet Filter) LSM (Linux Security Module) enables developers and security engineers to attach sandboxed, verifier-checked C or Rust programs directly to Linux kernel LSM hooks (such as bprm_check_security, file_open, and task_alloc) without modifying kernel source code or loading unsafe kernel modules (kmods).

Compared to traditional tracepoints and kprobes (which provide passive visibility), BPF LSM allows active policy enforcement by returning error codes (such as -EACCES or -EPERM) directly to syscall dispatchers.

+-------------------------------------------------------------------------+
|                              USERSPACE                                  |
|  +------------------------+             +----------------------------+  |
|  | C Loader (libbpf)      |             | Rust Loader (Aya)          |  |
|  | - Opens BPF Skeleton   |             | - Loads ELF Bytecode       |  |
|  | - Polls BPF RingBuffer |             | - Manages Async RingBuffer |  |
|  +-----------+------------+             +-------------+--------------+  |
+--------------|----------------------------------------|-----------------+
               | syscall bpf()                          | syscall bpf()
+--------------v----------------------------------------v-----------------+
|                              KERNEL SPACE                               |
|  +-------------------------------------------------------------------+  |
|  |                         eBPF VERIFIER                             |  |
|  | - Checks Memory Safety | - Verifies Bounded Loops | - Enforces CO-RE |  |
|  +-----------------------------------+-------------------------------+  |
|                                      | JIT Compilation                  |
|  +-----------------------------------v-------------------------------+  |
|  |                         BPF LSM ENGINE                            |  |
|  |  SEC("lsm/bprm_check_security")  --> Blocks execution from /tmp   |  |
|  |  SEC("lsm/file_open")            --> Audits /etc/shadow access   |  |
|  +-----------------------------------+-------------------------------+  |
|                                      | Events                           |  |
|  +-----------------------------------v-------------------------------+  |
|  |                     BPF_MAP_TYPE_RINGBUF                          |  |
|  +-------------------------------------------------------------------+  |
+-------------------------------------------------------------------------+

Key Technical Takeaways

CO-RE (Compile Once, Run Everywhere) relies on BTF (BPF Type Format) to dynamically relocate kernel struct field offsets at runtime across different kernel versions.
Ring Buffers (BPF_MAP_TYPE_RINGBUF) supersede legacy Perf Event Buffers (BPF_MAP_TYPE_PERF_EVENT_ARRAY) by offering single-memory-region ring allocation, lower CPU overhead, and atomic memory reservations (bpf_ringbuf_reserve / bpf_ringbuf_submit).
Security Enforcement: Returning -EPERM or -EACCES from an LSM hook immediately aborts the corresponding kernel operation before side effects occur.

Complete Masterclass & Working Source Code

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