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bpf.go
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bpf.go
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// +build linux
/*
* Copyright (C) 2017 Red Hat, Inc.
*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*
*/
package flow
import (
"fmt"
"github.com/google/gopacket/layers"
"github.com/google/gopacket/pcap"
"golang.org/x/net/bpf"
)
// BPF describes a filter
type BPF struct {
vm *bpf.VM
}
// BPFFilterToRaw creates a raw binary filter from a BPF expression
func BPFFilterToRaw(linkType layers.LinkType, captureLength uint32, filter string) ([]bpf.RawInstruction, error) {
// use pcap bpf compiler to get raw bpf instruction
pcapBPF, err := pcap.CompileBPFFilter(linkType, int(captureLength), filter)
if err != nil {
return nil, err
}
rawBPF := make([]bpf.RawInstruction, len(pcapBPF))
for i, ri := range pcapBPF {
rawBPF[i] = bpf.RawInstruction{Op: ri.Code, Jt: ri.Jt, Jf: ri.Jf, K: ri.K}
}
return rawBPF, nil
}
// Matches returns true data match the filter
func (b *BPF) Matches(data []byte) bool {
if b.vm == nil {
return true
}
if n, err := b.vm.Run(data); err != nil || n == 0 {
return false
}
return true
}
// NewBPF creates a new BPF filter
func NewBPF(linkType layers.LinkType, captureLength uint32, filter string) (*BPF, error) {
if filter == "" {
return &BPF{}, nil
}
rawBPF, err := BPFFilterToRaw(linkType, captureLength, filter)
if err != nil {
return nil, err
}
instBPF, ok := bpf.Disassemble(rawBPF)
if !ok {
return nil, fmt.Errorf("BPF expression not correctly decoded: %s", filter)
}
vm, err := bpf.NewVM(instBPF)
if err != nil {
return nil, err
}
return &BPF{
vm: vm,
}, nil
}