tailscale/portlist/portlist_linux.go

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// 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"
"time"
"golang.org/x/sys/unix"
)
// Reading the sockfiles on Linux is very fast, so we can do it often.
const pollInterval = 1 * time.Second
// 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"}
var protos = []string{"tcp", "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 a port is bound to 127.0.0.1, ignore it.
if strings.HasPrefix(local, "0100007F:") {
continue
}
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{} // by Port.inode
for i := range pl {
pm[pl[i].inode] = &pl[i]
}
err := foreachPID(func(pid string) error {
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.
return nil
}
defer fdDir.Close()
targetBuf := make([]byte, 64) // plenty big for "socket:[165614651]"
for {
fds, err := fdDir.Readdirnames(100)
if err == io.EOF {
return nil
}
if os.IsNotExist(err) {
// This can happen if the directory we're
// reading disappears during the run. No big
// deal.
return nil
}
if err != nil {
return fmt.Errorf("addProcesses.readDir: %w", err)
}
for _, fd := range fds {
n, err := unix.Readlink(fmt.Sprintf("/proc/%s/fd/%s", pid, fd), targetBuf)
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[string(targetBuf[:n])] // m[string([]byte)] avoids alloc
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))
}
}
}
})
if err != nil {
return nil, err
}
return pl, nil
}
func foreachPID(fn func(pidStr string) error) error {
pdir, err := os.Open("/proc")
if err != nil {
return err
}
defer pdir.Close()
for {
pids, err := pdir.Readdirnames(100)
if err == io.EOF {
return nil
}
if os.IsNotExist(err) {
// This can happen if the directory we're
// reading disappears during the run. No big
// deal.
return nil
}
if err != nil {
return fmt.Errorf("foreachPID.readdir: %w", 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
}
if err := fn(pid); err != nil {
return err
}
}
}
}