iovisor/bcc

helper for memmem()

Open

#471 opened on Mar 31, 2016

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enhancementhelp wantedprio:medium

Description

Protocol such as DNS or IPv6 are hard to filter with cBPF because important parts are relative to floating offset, since BPF disallows loops and has relatively narrow registers, we have to unroll them and scan message with a lot of branches, burning the instruction limit.

Proposal

Provide kernel helper such as memmem(off_from, off_to, pattern) where offsets (R0, R1) are relative to packet payload, and pattern (R2) is a b/h/w/dw, and returned value would be offset in packet where the match occured or packet length (no occurence).

Contributor guide

Tech stack
c
Domain
backendinfrastructureperformance
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
understanding of BPF internalskernel programming experienceC proficiency
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
10
Research direction
This issue proposes a new kernel helper `memmem()` for BPF to scan packet payloads for patterns. Research should focus on existing BPF helper patterns in the kernel (e.g., `bpf skb load bytes`), the BPF verifier constraints on loops, and how offset calculations are handled. Look at the kernel's BPF helper API in `include/uapi/linux/bpf.h` and existing helpers in `net/core/filter.c`. Consider discussing with the BPF mailing list or reviewing similar feature requests in the kernel bug tracker.
helper for memmem() · iovisor/bcc#471 | Good First Issue