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portlist_linux.go
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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"
"path/filepath"
"runtime"
"strconv"
"strings"
"syscall"
"time"
"golang.org/x/sys/unix"
"tailscale.com/syncs"
)
// Reading the sockfiles on Linux is very fast, so we can do it often.
const pollInterval = 1 * time.Second
var sockfiles = []string{"/proc/net/tcp", "/proc/net/tcp6", "/proc/net/udp", "/proc/net/udp6"}
var sawProcNetPermissionErr syncs.AtomicBool
const (
v6Localhost = "00000000000000000000000001000000:"
v6Any = "00000000000000000000000000000000:0000"
v4Localhost = "0100007F:"
v4Any = "00000000:0000"
)
func listPorts() (List, error) {
if sawProcNetPermissionErr.Get() {
return nil, nil
}
l := []Port{}
for _, fname := range sockfiles {
proto := strings.TrimSuffix(filepath.Base(fname), "6")
// Android 10+ doesn't allow access to this anymore.
// https://developer.android.com/about/versions/10/privacy/changes#proc-net-filesystem
// Ignore it rather than have the system log about our violation.
if runtime.GOOS == "android" && syscall.Access(fname, unix.R_OK) != nil {
sawProcNetPermissionErr.Set(true)
return nil, nil
}
f, err := os.Open(fname)
if os.IsPermission(err) {
sawProcNetPermissionErr.Set(true)
return nil, nil
}
if err != nil {
return nil, fmt.Errorf("%s: %s", fname, err)
}
defer f.Close()
r := bufio.NewReader(f)
ports, err := parsePorts(r, proto)
if err != nil {
return nil, fmt.Errorf("parsing %q: %w", fname, err)
}
l = append(l, ports...)
}
return l, nil
}
func parsePorts(r *bufio.Reader, proto string) ([]Port, error) {
var ret []Port
// 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 localhost, ignore it.
// TODO: localhost is bigger than 1 IP, we need to ignore
// more things.
if strings.HasPrefix(local, v4Localhost) || strings.HasPrefix(local, v6Localhost) {
continue
}
if rem != v4Any && rem != v6Any {
// not a "listener" port
continue
}
// Don't use strings.Split here, because it causes
// allocations significant enough to show up in profiles.
i := strings.IndexByte(local, ':')
if i == -1 {
return nil, fmt.Errorf("%q unexpectedly didn't have a colon", local)
}
portv, err := strconv.ParseUint(local[i+1:], 16, 16)
if err != nil {
return nil, fmt.Errorf("%#v: %s", local[9:], err)
}
inodev := fmt.Sprintf("socket:[%s]", inode)
ret = append(ret, Port{
Proto: proto,
Port: uint16(portv),
inode: inodev,
})
}
return ret, 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 {
fdPath := fmt.Sprintf("/proc/%s/fd", pid)
// Android logs a bunch of audit violations in logcat
// if we try to open things we don't have access
// to. So on Android only, ask if we have permission
// rather than just trying it to determine whether we
// have permission.
if runtime.GOOS == "android" && syscall.Access(fdPath, unix.R_OK) != nil {
return nil
}
fdDir, err := os.Open(fdPath)
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
}
pe := pm[string(targetBuf[:n])] // m[string([]byte)] avoids alloc
if pe != nil {
bs, err := ioutil.ReadFile(fmt.Sprintf("/proc/%s/cmdline", pid))
if err != nil {
// Usually shouldn't happen. One possibility is
// the process has gone away, so let's skip it.
continue
}
argv := strings.Split(strings.TrimSuffix(string(bs), "\x00"), "\x00")
pe.Process = argvSubject(argv...)
}
}
}
})
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
}
}
}
}