1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
|
package main
import (
"crypto/rand"
"encoding/json"
"fmt"
"io"
"log"
"os"
"os/exec"
"os/signal"
"path/filepath"
"syscall"
"github.com/kardianos/osext"
)
const daemonRunProgram = "gitlab-pages-unprivileged"
func daemonMain() {
if os.Args[0] != daemonRunProgram {
return
}
log.Printf("Starting the daemon as unprivileged user (uid: %d, gid: %d)...", syscall.Getuid(), syscall.Getgid())
// read the configuration from the pipe "ExtraFiles"
var config appConfig
if err := json.NewDecoder(os.NewFile(3, "options")).Decode(&config); err != nil {
log.Fatalln(err)
}
runApp(config)
os.Exit(0)
}
func daemonReexec(uid, gid uint, args ...string) (cmd *exec.Cmd, err error) {
path, err := osext.Executable()
if err != nil {
return
}
cmd = &exec.Cmd{
Path: path,
Args: args,
Stdin: os.Stdin,
Stdout: os.Stdout,
Stderr: os.Stderr,
SysProcAttr: &syscall.SysProcAttr{
Credential: &syscall.Credential{
Uid: uint32(uid),
Gid: uint32(gid),
},
Setsid: true,
},
}
return
}
func daemonUpdateFd(cmd *exec.Cmd, fd *uintptr) {
if *fd == 0 {
return
}
file := os.NewFile(*fd, "[socket]")
// we add 3 since, we have a 3 predefined FDs
*fd = uintptr(3 + len(cmd.ExtraFiles))
cmd.ExtraFiles = append(cmd.ExtraFiles, file)
}
func killProcess(cmd *exec.Cmd) {
if cmd.Process != nil {
cmd.Process.Kill()
}
cmd.Wait()
for _, file := range cmd.ExtraFiles {
file.Close()
}
}
func passSignals(cmd *exec.Cmd) {
if cmd.Process == nil {
return
}
s := make(chan os.Signal)
signal.Notify(s, syscall.SIGTERM, os.Interrupt, os.Kill)
go func() {
for cmd.Process != nil {
cmd.Process.Signal(<-s)
}
}()
}
func copyFile(dest, src string, perm os.FileMode) (err error) {
srcFile, err := os.Open(src)
if err != nil {
return
}
defer srcFile.Close()
destFile, err := os.OpenFile(dest, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
if err != nil {
return
}
defer destFile.Close()
_, err = io.Copy(destFile, srcFile)
return
}
func daemonCreateExecutable(name string, perm os.FileMode) (file *os.File, err error) {
// We assume that crypto random generates true random, non-colliding hash
b := make([]byte, 16)
_, err = rand.Read(b)
if err != nil {
return
}
path := fmt.Sprintf("%s.%x", name, b)
file, err = os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_EXCL, perm)
if err != nil {
return
}
return
}
func daemonChroot(cmd *exec.Cmd) (path string, err error) {
wd, err := os.Getwd()
if err != nil {
return
}
// Generate temporary file
temporaryExecutable, err := daemonCreateExecutable(".daemon", 0755)
if err != nil {
return
}
defer temporaryExecutable.Close()
defer func() {
// Remove the temporary file in case of failure
if err != nil {
os.Remove(temporaryExecutable.Name())
}
}()
// Open current executable
executableFile, err := os.Open(cmd.Path)
if err != nil {
return
}
defer executableFile.Close()
// Copy the executable content
_, err = io.Copy(temporaryExecutable, executableFile)
if err != nil {
return
}
// Update command to use chroot
cmd.SysProcAttr.Chroot = wd
cmd.Path = temporaryExecutable.Name()
cmd.Dir = "/"
path = filepath.Join(wd, temporaryExecutable.Name())
return
}
func daemonize(config appConfig, uid, gid uint) {
var err error
defer func() {
if err != nil {
log.Fatalln(err)
}
}()
log.Printf("Running the daemon as unprivileged user (uid:%d, gid: %d)...", uid, gid)
cmd, err := daemonReexec(uid, gid, daemonRunProgram)
if err != nil {
return
}
defer killProcess(cmd)
// Run daemon in chroot environment
temporaryExecutable, err := daemonChroot(cmd)
if err != nil {
println("Chroot failed", err)
return
}
defer os.Remove(temporaryExecutable)
// Create a pipe to pass the configuration
configReader, configWriter, err := os.Pipe()
if err != nil {
return
}
defer configWriter.Close()
cmd.ExtraFiles = append(cmd.ExtraFiles, configReader)
// Create a new file and store the FD
daemonUpdateFd(cmd, &config.ListenHTTP)
daemonUpdateFd(cmd, &config.ListenHTTPS)
daemonUpdateFd(cmd, &config.listenProxy)
// Start the process
if err = cmd.Start(); err != nil {
println("Start failed", err)
return
}
// Write the configuration
if err = json.NewEncoder(configWriter).Encode(config); err != nil {
return
}
configWriter.Close()
// Remove executable
os.Remove(temporaryExecutable)
// Pass through signals
passSignals(cmd)
// Wait for process to exit
err = cmd.Wait()
}
|