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package portscan
import (
"bufio"
"errors"
"fmt"
"io"
"os"
"path/filepath"
"strconv"
"strings"
)
const tcpListen = "0A"
const udpBound = "07"
type listenSocket struct {
Port int
Inode uint64
}
func parseProcNetTCP(r io.Reader) ([]listenSocket, error) {
return parseProcNet(r, tcpListen)
}
func parseProcNetUDP(r io.Reader) ([]listenSocket, error) {
return parseProcNet(r, udpBound)
}
func parseProcNet(r io.Reader, state string) ([]listenSocket, error) {
sc := bufio.NewScanner(r)
var out []listenSocket
for sc.Scan() {
fields := strings.Fields(sc.Text())
if len(fields) == 0 || fields[0] == "sl" {
continue
}
if len(fields) < 10 {
return nil, fmt.Errorf("portscan: %q is not a socket-table row", sc.Text())
}
if fields[3] != state {
continue
}
_, portHex, ok := strings.Cut(fields[1], ":")
if !ok {
return nil, fmt.Errorf("portscan: local_address %q has no port", fields[1])
}
port, err := strconv.ParseUint(portHex, 16, 16)
if err != nil {
return nil, fmt.Errorf("portscan: local port %q: %w", portHex, err)
}
inode, err := strconv.ParseUint(fields[9], 10, 64)
if err != nil {
return nil, fmt.Errorf("portscan: inode %q: %w", fields[9], err)
}
out = append(out, listenSocket{Port: int(port), Inode: inode})
}
if err := sc.Err(); err != nil {
return nil, fmt.Errorf("portscan: reading the socket table: %w", err)
}
return out, nil
}
func socketInode(link string) (uint64, bool) {
rest, ok := strings.CutPrefix(link, "socket:[")
if !ok {
return 0, false
}
rest, ok = strings.CutSuffix(rest, "]")
if !ok {
return 0, false
}
inode, err := strconv.ParseUint(rest, 10, 64)
if err != nil {
return 0, false
}
return inode, true
}
func walkInodeOwners(root string, want map[uint64]bool) (map[uint64][]int, error) {
entries, err := os.ReadDir(root)
if err != nil {
return nil, fmt.Errorf("portscan: reading the process table %s: %w", root, err)
}
out := map[uint64][]int{}
for _, entry := range entries {
pid, err := strconv.Atoi(entry.Name())
if err != nil {
continue
}
fdDir := filepath.Join(root, entry.Name(), "fd")
fds, err := os.ReadDir(fdDir)
if err != nil {
continue
}
for _, fd := range fds {
target, err := os.Readlink(filepath.Join(fdDir, fd.Name()))
if err != nil {
continue
}
inode, ok := socketInode(target)
if !ok || !want[inode] {
continue
}
out[inode] = append(out[inode], pid)
}
}
return out, nil
}
func listenersIn(root string) (map[int][]int, error) {
return ownersIn(root, "tcp", parseProcNetTCP)
}
func datagramListenersIn(root string) (map[int][]int, error) {
return ownersIn(root, "udp", parseProcNetUDP)
}
func ownersIn(root, table string, parse func(io.Reader) ([]listenSocket, error)) (map[int][]int, error) {
socks, err := readTable(filepath.Join(root, "net", table), true, parse)
if err != nil {
return nil, err
}
six, err := readTable(filepath.Join(root, "net", table+"6"), false, parse)
if err != nil {
return nil, err
}
socks = append(socks, six...)
want := make(map[uint64]bool, len(socks))
for _, s := range socks {
want[s.Inode] = true
}
owners, err := walkInodeOwners(root, want)
if err != nil {
return nil, err
}
byPort := map[int][]int{}
for _, s := range socks {
if len(owners[s.Inode]) == 0 {
continue
}
byPort[s.Port] = append(byPort[s.Port], owners[s.Inode]...)
}
return byPort, nil
}
func readTable(path string, required bool, parse func(io.Reader) ([]listenSocket, error)) ([]listenSocket, error) {
f, err := os.Open(path)
if err != nil {
if !required && errors.Is(err, os.ErrNotExist) {
return nil, nil
}
return nil, fmt.Errorf("portscan: opening %s: %w", path, err)
}
defer f.Close()
return parse(f)
}
