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pcap_linux.go
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pcap_linux.go
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package pcap
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
"sync/atomic"
"time"
"unsafe"
"golang.org/x/net/bpf"
syscall "golang.org/x/sys/unix"
"github.com/google/gopacket"
log "github.com/sirupsen/logrus"
)
const (
//defaultFrameSize = 4096
defaultFrameSize = 65632 //nolint:unused
//defaultBlockNumbers = 128
defaultBlockNumbers = 32
//defaultBlockSize = defaultFrameSize * defaultBlockNumbers
defaultBlockSize = 131072 //nolint:unused
//defaultFramesPerBlock = defaultBlockSize / defaultFrameSize
defaultFramesPerBlock = 32
EthHlen = 0x10
// defaultSyscalls default setting for using syscalls
defaultSyscalls = false
offsetToBlockStatus = 4 + 4
)
var (
packetRALLSize int32
alignedTpacketHdrSize int32
alignedTpacketRALLSize int32
alignedTpacketAllHdrSize int32
)
type blockHeader struct {
Version uint32
OffsetToPriv uint32
H1 syscall.TpacketHdrV1
}
type captured struct {
data []byte
ci gopacket.CaptureInfo
}
type Handle struct {
// this must be first for atomic to behave nicely
isOpen uint32
syscalls bool
promiscuous bool
index int
iface string
snaplen int32
fd int
ring []byte
framePtr int
framesPerBuffer uint32
frameIndex uint32 //nolint:unused
frameSize uint32
frameNumbers uint32
blockNumbers int
blockSize int
pollfd []syscall.PollFd
endian binary.ByteOrder
filter []bpf.RawInstruction
cache []captured
}
func (h *Handle) ReadPacketData() (data []byte, ci gopacket.CaptureInfo, err error) {
if atomic.LoadUint32(&h.isOpen) == 0 {
return data, ci, io.EOF
}
if h.syscalls {
return h.readPacketDataSyscall()
}
// mmap can return multiple packets, so we can cache extras, and return if there are
// if there already was one in the cache, return it
if len(h.cache) > 0 {
cap := h.cache[0]
h.cache = h.cache[1:]
return cap.data, cap.ci, nil
}
// there was not, so read a new one
caps, err := h.readPacketDataMmap()
if err != nil {
return nil, ci, err
}
switch len(caps) {
case 0:
return nil, ci, nil
case 1:
return caps[0].data, caps[0].ci, nil
}
h.cache = caps
cap := h.cache[0]
h.cache = h.cache[1:]
return cap.data, cap.ci, nil
}
func (h *Handle) readPacketDataSyscall() (data []byte, ci gopacket.CaptureInfo, err error) {
b := make([]byte, h.snaplen)
read, _, err := syscall.Recvfrom(h.fd, b, 0)
if err != nil {
return nil, ci, fmt.Errorf("error reading: %v", err)
}
// TODO: add CaptureInfo, specifically:
// capture timestamp
// original packet length
ci = gopacket.CaptureInfo{
CaptureLength: read,
InterfaceIndex: h.index,
}
return b, ci, nil
}
func (h *Handle) readPacketDataMmap() ([]captured, error) {
logger := log.WithFields(log.Fields{
"method": "mmap",
"iface": h.iface,
})
logger.Debugf("started: framesPerBuffer %d, blockSize %d, frameSize %d, frameNumbers %d, blockNumbers %d", h.framesPerBuffer, h.blockSize, h.frameSize, h.frameNumbers, h.blockNumbers)
// we check the bit setting on the pointer
blockBase := h.framePtr * h.blockSize
// add a loop, so that we do not just rely on the polling, but instead the actual flag bit
flagIndex := blockBase + offsetToBlockStatus
for atomic.LoadUint32(&h.isOpen) > 0 {
logger.Debugf("checking for packet at block %d, buffer starting position %d, flagIndex %d ring pointer %p", h.framePtr, blockBase, flagIndex, h.ring)
if h.ring[flagIndex]&syscall.TP_STATUS_USER == syscall.TP_STATUS_USER {
return h.processMmapPackets(blockBase, flagIndex)
}
logger.Debugf("packet not ready at block %d position %d, polling via %#v", h.framePtr, blockBase, h.pollfd)
val, err := syscall.Poll(h.pollfd, -1)
logger.Debugf("poll returned val %v with pollfd %#v", val, h.pollfd)
switch {
case err != nil && err == syscall.EINTR:
logger.Debug("poll returned with EINTR, continuing")
continue
case err != nil:
logger.Errorf("error polling socket: %v", err)
return nil, fmt.Errorf("error polling socket: %v", err)
case val < 0:
logger.Error("negative return value from polling socket")
return nil, errors.New("negative return value from polling socket")
case h.pollfd[0].Revents&syscall.POLLIN == syscall.POLLIN:
continue
case h.pollfd[0].Revents&syscall.POLLERR == syscall.POLLERR:
// unknown error; we need to check the socket itself to find out
logger.Debug("received POLLERR, checking actual error from socket")
sockOptVal, err := syscall.GetsockoptInt(h.fd, syscall.SOL_SOCKET, syscall.SO_ERROR)
if err != nil {
logger.Errorf("could not get sockopt to check poll error; sockopt error: %v", err)
return nil, fmt.Errorf("could not get sockopt to check poll error; sockopt error: %v", err)
}
if sockOptVal == int(syscall.ENETDOWN) {
logger.Errorf("interface %s is down, marking as closed and returning", h.iface)
atomic.StoreUint32(&h.isOpen, 0)
return nil, nil
}
// we have no idea what it was, so just return
logger.Error("unknown error returned from socket")
return nil, errors.New("unknown error returned from socket")
case h.pollfd[0].Revents&syscall.POLLNVAL == syscall.POLLNVAL:
logger.Error("socket closed")
atomic.StoreUint32(&h.isOpen, 0)
return nil, io.EOF
}
}
// if we got here, it was not 0, so EOF
return nil, io.EOF
}
func (h *Handle) processMmapPackets(blockBase, flagIndex int) ([]captured, error) {
logger := log.WithFields(log.Fields{
"method": "mmap-process",
"iface": h.iface,
})
// read the header
logger.Debugf("reading block header into b slice from position %d to position %d", blockBase, blockBase+h.blockSize)
b := h.ring[blockBase : blockBase+h.blockSize]
buf := bytes.NewBuffer(b[:])
bHdr := blockHeader{}
logger.Debugf("binary parsing block header of size %d", buf.Len())
if err := binary.Read(buf, h.endian, &bHdr); err != nil {
logger.Errorf("error reading block header: %v", err)
return nil, fmt.Errorf("error reading block header: %v", err)
}
logger.Debugf("block header %#v", bHdr)
// now we need to get the packets themselves
numPkts := int(bHdr.H1.Num_pkts)
packets := make([]captured, numPkts)
nextOffset := bHdr.H1.Offset_to_first_pkt
for i := 0; i < numPkts; i++ {
hdr := syscall.Tpacket3Hdr{}
logger.Debugf("packet number %d/%d at position %d in block", i, numPkts, nextOffset)
b = b[nextOffset:]
buf := bytes.NewBuffer(b[:alignedTpacketHdrSize])
logger.Debugf("binary parsing packet header of size %d", buf.Len())
if err := binary.Read(buf, h.endian, &hdr); err != nil {
msg := fmt.Sprintf("error reading tpacket3 header on byte %d: %v", i, err)
logger.Errorf(msg)
return nil, fmt.Errorf(msg)
}
logger.Debugf("tpacket3 header %#v", hdr)
nextOffset = hdr.Next_offset
logger.Debugf("setting next offset to %d", nextOffset)
// read the sockaddr_ll
// unfortunately, we cannot do binary.Read() because syscall.SockaddrLinklayer has an embedded slice
// so we have to read it manually
// use b[hdr.Mac:hdr.Mac+alignedTpacketRALLSize] instead?
sall, err := parseSocketAddrLinkLayer(b[alignedTpacketHdrSize:alignedTpacketAllHdrSize], h.endian)
if err != nil {
logger.Errorf("error parsing sockaddr_ll: %v", err)
return nil, fmt.Errorf("error parsing sockaddr_ll for packet %d: %v", i, err)
}
ci := gopacket.CaptureInfo{
Length: int(hdr.Len),
CaptureLength: int(hdr.Snaplen),
Timestamp: time.Unix(int64(hdr.Sec), int64(hdr.Nsec)),
InterfaceIndex: int(sall.Ifindex),
}
data := b[hdr.Mac : uint32(hdr.Mac)+hdr.Snaplen]
packets[i] = captured{
ci: ci,
data: data,
}
logger.Debugf("raw packet for packet %d: %d\n ", i, data)
}
// indicate we are done with this frame, send back to the kernel
logger.Debugf("returning block at pos %d to kernel", h.framePtr)
h.ring[flagIndex] = syscall.TP_STATUS_KERNEL
h.framePtr = (h.framePtr + 1) % h.blockNumbers
logger.Debugf("final block: %d", h.framePtr)
return packets, nil
}
// Close close sockets and release resources
func (h *Handle) Close() {
logger := log.WithFields(log.Fields{
"iface": h.iface,
})
atomic.StoreUint32(&h.isOpen, 0)
if h.ring != nil {
if err := syscall.Munmap(h.ring); err != nil {
logger.Errorf("error unmapping mmap at %p ; nothing to do", h.ring)
}
}
// close the socket
if err := syscall.Close(h.fd); err != nil {
logger.Errorf("error closing file descriptor %d ; nothing to do", h.fd)
}
}
// set a classic BPF filter on the listener. filter must be compliant with
// tcpdump syntax.
func (h *Handle) setFilter() error {
/*
* Try to install the kernel filter.
*/
prog := syscall.SockFprog{
Len: uint16(len(h.filter)),
Filter: (*syscall.SockFilter)(unsafe.Pointer(&h.filter[0])),
}
if err := syscall.SetsockoptSockFprog(h.fd, syscall.SOL_SOCKET, syscall.SO_ATTACH_FILTER, &prog); err != nil {
return fmt.Errorf("unable to set filter: %v", err)
}
return nil
}
func tpacketAlign(base int32) int32 {
return (base + syscall.TPACKET_ALIGNMENT - 1) &^ (syscall.TPACKET_ALIGNMENT - 1)
}
func openLive(iface string, snaplen int32, promiscuous bool, timeout time.Duration, syscalls bool) (handle *Handle, _ error) {
logger := log.WithFields(log.Fields{
"iface": iface,
"snaplen": snaplen,
"promiscuous": promiscuous,
"timeout": timeout,
"syscalls": syscalls,
})
logger.Debug("started")
h := Handle{
// we start with it not open
isOpen: 0,
snaplen: snaplen,
syscalls: syscalls,
iface: iface,
}
// we need to know our endianness
endianness, err := getEndianness()
if err != nil {
return nil, err
}
h.endian = endianness
// because syscall package does not provide this
rall := syscall.RawSockaddrLinklayer{}
packetRALLSize = int32(unsafe.Sizeof(rall))
alignedTpacketHdrSize = tpacketAlign(syscall.SizeofTpacket3Hdr)
alignedTpacketRALLSize = tpacketAlign(packetRALLSize)
alignedTpacketAllHdrSize = alignedTpacketHdrSize + alignedTpacketRALLSize
// set up the socket - remember to switch to network socket order for the protocol int
fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, int(htons(syscall.ETH_P_ALL)))
if err != nil {
logger.Errorf("failed opening raw socket: %v", err)
return nil, fmt.Errorf("failed opening raw socket: %v", err)
}
h.fd = fd
h.pollfd = []syscall.PollFd{{Fd: int32(h.fd), Events: syscall.POLLIN}}
if err := syscall.SetNonblock(fd, false); err != nil {
return nil, fmt.Errorf("failed to set socket as blocking: %v", err)
}
if iface != "" {
// get our interface
in, err := net.InterfaceByName(iface)
if err != nil {
logger.Errorf("unknown interface %s: %v", iface, err)
return nil, fmt.Errorf("unknown interface %s: %v", iface, err)
}
// check the interface is up
if in.Flags&net.FlagUp != net.FlagUp {
logger.Errorf("interface %s is not up", iface)
return nil, fmt.Errorf("interface %s is not up", iface)
}
h.index = in.Index
// create the sockaddr_ll
sa := syscall.SockaddrLinklayer{
Protocol: htons(syscall.ETH_P_ALL),
Ifindex: in.Index,
}
// bind to it
if err = syscall.Bind(fd, &sa); err != nil {
return nil, fmt.Errorf("failed to bind")
}
if promiscuous {
h.promiscuous = true
mreq := syscall.PacketMreq{
Ifindex: int32(in.Index),
Type: syscall.PACKET_MR_PROMISC,
}
if err = syscall.SetsockoptPacketMreq(fd, syscall.SOL_PACKET, syscall.PACKET_ADD_MEMBERSHIP, &mreq); err != nil {
logger.Errorf("failed to set promiscuous for %s: %v", iface, err)
return nil, fmt.Errorf("failed to set promiscuous for %s: %v", iface, err)
}
}
}
if !syscalls {
if err = syscall.SetsockoptInt(fd, syscall.SOL_PACKET, syscall.PACKET_VERSION, syscall.TPACKET_V3); err != nil {
logger.Errorf("failed to set TPACKET_V3: %v", err)
return nil, fmt.Errorf("failed to set TPACKET_V3: %v", err)
}
// set up the ring
var (
frameSize = uint32(tpacketAlign(syscall.SizeofTpacket3Hdr+EthHlen) + tpacketAlign(snaplen))
pageSize = syscall.Getpagesize()
blockSize = uint32(pageSize)
blockNumbers uint32 = defaultBlockNumbers
)
for {
if blockSize > frameSize {
break
}
blockSize = blockSize << 1
}
// we use the default - for now
framesPerBuffer := blockSize / frameSize
frameNumbers := blockNumbers * framesPerBuffer
tpreq := syscall.TpacketReq3{
Block_size: blockSize,
Block_nr: blockNumbers,
Frame_size: frameSize,
Frame_nr: frameNumbers,
}
logger.Debugf("creating mmap buffer with tpreq %#v", tpreq)
if err = syscall.SetsockoptTpacketReq3(fd, syscall.SOL_PACKET, syscall.PACKET_RX_RING, &tpreq); err != nil {
logger.Errorf("failed to set tpacket req: %v", err)
return nil, fmt.Errorf("failed to set tpacket req: %v", err)
}
totalSize := int(tpreq.Block_size * tpreq.Block_nr)
data, err := syscall.Mmap(fd, 0, totalSize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
if err != nil {
logger.Errorf("error mmapping: %v", err)
return nil, fmt.Errorf("error mmapping: %v", err)
}
logger.Infof("mmap buffer created at %p with size %d", data, len(data))
h.framesPerBuffer = framesPerBuffer
h.blockSize = int(blockSize)
h.frameSize = frameSize
h.frameNumbers = frameNumbers
h.blockNumbers = int(blockNumbers)
h.ring = data
h.cache = make([]captured, 0, blockSize/frameSize)
}
atomic.StoreUint32(&h.isOpen, 1)
return &h, nil
}
// parseSocketAddrLinkLayer parse byte data to get a RawSockAddrLinkLayer
func parseSocketAddrLinkLayer(b []byte, endian binary.ByteOrder) (*syscall.RawSockaddrLinklayer, error) {
if len(b) < int(packetRALLSize) {
return nil, fmt.Errorf("bytes of length %d shorter than mandated %d", len(b), packetRALLSize)
}
var addr [8]byte
copy(addr[:], b[11:19])
sall := syscall.RawSockaddrLinklayer{
Family: endian.Uint16(b[0:2]),
Protocol: endian.Uint16(b[2:4]),
Ifindex: int32(endian.Uint32(b[4:8])),
Hatype: endian.Uint16(b[8:10]),
Pkttype: b[10],
Halen: b[11],
Addr: addr,
}
return &sall, nil
}