tailscale/portlist/portlist_linux.go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package portlist

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"sort"
	"strconv"
	"strings"
)

// Reading the sockfiles on Linux is very fast, so we can do it often.
const POLL_SECONDS = 1

// TODO(apenwarr): Include IPv6 ports eventually.
// Right now we don't route IPv6 anyway so it's better to exclude them.
var sockfiles = []string{"/proc/net/tcp", "/proc/net/udp"}

func listPorts() (List, error) {
	l := []Port{}

	for pi, fname := range sockfiles {
		proto := protos[pi]

		f, err := os.Open(fname)
		if err != nil {
			return nil, fmt.Errorf("%s: %s", fname, err)
		}
		defer f.Close()
		r := bufio.NewReader(f)

		// skip header row
		_, err = r.ReadString('\n')
		if err != nil {
			return nil, err
		}

		for err == nil {
			line, err := r.ReadString('\n')
			if err == io.EOF {
				break
			}
			if err != nil {
				return nil, err
			}

			// sl local rem ... inode
			words := strings.Fields(line)
			local := words[1]
			rem := words[2]
			inode := words[9]

			if rem != "00000000:0000" {
				// not a "listener" port
				continue
			}

			portv, err := strconv.ParseUint(local[9:], 16, 16)
			if err != nil {
				return nil, fmt.Errorf("%#v: %s", local[9:], err)
			}
			inodev := fmt.Sprintf("socket:[%s]", inode)
			l = append(l, Port{
				Proto: proto,
				Port:  uint16(portv),
				inode: inodev,
			})
		}
	}

	sort.Slice(l, func(i, j int) bool {
		return (&l[i]).lessThan(&l[j])
	})

	return l, nil
}

func addProcesses(pl []Port) ([]Port, error) {
	pm := map[string]*Port{}
	for k := range pl {
		pm[pl[k].inode] = &pl[k]
	}

	pdir, err := os.Open("/proc")
	if err != nil {
		return nil, fmt.Errorf("/proc: %s", err)
	}
	defer pdir.Close()

	for {
		pids, err := pdir.Readdirnames(100)
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("/proc: %s", err)
		}

		for _, pid := range pids {
			_, err := strconv.ParseInt(pid, 10, 64)
			if err != nil {
				// not a pid, ignore it.
				// /proc has lots of non-pid stuff in it.
				continue
			}
			fddir, err := os.Open(fmt.Sprintf("/proc/%s/fd", pid))
			if err != nil {
				// Can't open fd list for this pid. Maybe
				// don't have access. Ignore it.
				continue
			}
			defer fddir.Close()

			for {
				fds, err := fddir.Readdirnames(100)
				if err == io.EOF {
					break
				}
				if err != nil {
					return nil, fmt.Errorf("readdir: %s", err)
				}
				for _, fd := range fds {
					target, err := os.Readlink(fmt.Sprintf("/proc/%s/fd/%s", pid, fd))
					if err != nil {
						// Not a symlink or no permission.
						// Skip it.
						continue
					}

					// TODO(apenwarr): use /proc/*/cmdline instead of /comm?
					// Unsure right now whether users will want the extra detail
					// or not.
					pe := pm[target]
					if pe != nil {
						comm, err := ioutil.ReadFile(fmt.Sprintf("/proc/%s/comm", pid))
						if err != nil {
							// Usually shouldn't happen. One possibility is
							// the process has gone away, so let's skip it.
							continue
						}
						pe.Process = strings.TrimSpace(string(comm))
					}
				}
			}
		}
	}

	return pl, nil
}