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[bugfix] Fix handling of mock snaplen field in pktHdr for packets smaller than snaplen #86

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merged 2 commits into from
May 7, 2024
Merged

[bugfix] Fix handling of mock snaplen field in pktHdr for packets smaller than snaplen #86

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e9e9703
Fix handling of snaplen field in pktHdr for packets smaller than snaplen
fako1024 May 6, 2024
cb4ba29
Fix comment
fako1024 May 6, 2024
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2 changes: 1 addition & 1 deletion capture/afpacket/afring/afring.go
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Original file line number Diff line number Diff line change
Expand Up @@ -121,7 +121,7 @@ func NewSourceFromLink(link *link.Link, options ...Option) (*Source, error) {
// NextIPPacket() methods (the latter two by calling .Payload() / .IPLayer() on the created buffer). It ensures
// that a valid packet of appropriate structure / length is created
func (s *Source) NewPacket() capture.Packet {
p := make(capture.Packet, 6+s.snapLen)
p := make(capture.Packet, capture.PacketHdrOffset+s.snapLen)
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Drive-by code cleanup (uses newly introduced const).

return p
}

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2 changes: 1 addition & 1 deletion capture/afpacket/afring/afring_mock.go
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Expand Up @@ -141,7 +141,7 @@ func (m *MockSource) addPacket(payload []byte, totalLen uint32, pktType, ipLayer
block := m.ringBuffer.ring[thisBlock*m.blockSize : thisBlock*m.blockSize+m.blockSize]

*(*tPacketHeaderV3Mock)(unsafe.Pointer(&block[m.curBlockPos+12])) = tPacketHeaderV3Mock{
snaplen: min(uint32(m.snapLen), totalLen), // The snaplen is set to the totalLen if a packet is shorter
snaplen: min(uint32(m.snapLen), uint32(len(payload))), // The snaplen is set to the actual payload length if a packet is shorter
pktLen: totalLen,
pktMac: mac,
pktNet: mac + uint16(m.ipLayerOffset),
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25 changes: 18 additions & 7 deletions capture/capture.go
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Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,13 @@ import (
"golang.org/x/net/ipv6"
)

var (
const (

// PacketHdrOffset denotes the header offset / length for storing information about the packet
PacketHdrOffset = 6
)

var (

// ErrCaptureStopped denotes that the capture was stopped
ErrCaptureStopped = errors.New("capture was stopped")
Expand Down Expand Up @@ -85,8 +88,12 @@ func (i IPLayer) String() (res string) {
if ipLayerType == 4 {
protocol := i[9]
if protocol == 6 || protocol == 17 {
dport = binary.BigEndian.Uint16(i[ipv4.HeaderLen+2 : ipv4.HeaderLen+4])
sport = binary.BigEndian.Uint16(i[ipv4.HeaderLen : ipv4.HeaderLen+2])
if len(i) >= ipv4.HeaderLen+4 {
dport = binary.BigEndian.Uint16(i[ipv4.HeaderLen+2 : ipv4.HeaderLen+4])
}
if len(i) >= ipv4.HeaderLen+2 {
sport = binary.BigEndian.Uint16(i[ipv4.HeaderLen : ipv4.HeaderLen+2])
}
}
return fmt.Sprintf("%s:%d => %s:%d (proto: %d)",
net.IP(i[12:16]).String(),
Expand All @@ -98,8 +105,12 @@ func (i IPLayer) String() (res string) {
} else if ipLayerType == 6 {
protocol := i[6]
if protocol == 6 || protocol == 17 {
dport = binary.BigEndian.Uint16(i[ipv6.HeaderLen+2 : ipv6.HeaderLen+4])
sport = binary.BigEndian.Uint16(i[ipv6.HeaderLen : ipv6.HeaderLen+2])
if len(i) >= ipv6.HeaderLen+4 {
dport = binary.BigEndian.Uint16(i[ipv6.HeaderLen+2 : ipv6.HeaderLen+4])
}
if len(i) >= ipv6.HeaderLen+2 {
sport = binary.BigEndian.Uint16(i[ipv6.HeaderLen : ipv6.HeaderLen+2])
}
}
return fmt.Sprintf("%s:%d => %s:%d (proto: %d)",
net.IP(i[8:24]).String(),
Expand Down Expand Up @@ -188,9 +199,9 @@ func NewIPPacket(buf Packet, payload []byte, pktType PacketType, totalLen int, i
buf[0] = pktType
buf[1] = ipLayerOffset
*(*uint32)(unsafe.Pointer(&buf[2])) = uint32(totalLen) // #nosec G103
copy(buf[PacketHdrOffset:], payload)
n := copy(buf[PacketHdrOffset:], payload)

return buf
return buf[:PacketHdrOffset+n]
}

// TotalLen returnsthe total packet length, including all headers
Expand Down
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