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
|
package shim
import (
"context"
"encoding/gob"
"errors"
"os"
"os/exec"
"strconv"
"strings"
"syscall"
"time"
"git.gensokyo.uk/security/fortify/internal"
"git.gensokyo.uk/security/fortify/internal/fmsg"
"git.gensokyo.uk/security/fortify/sandbox"
)
// used by the parent process
type Shim struct {
// user switcher process
cmd *exec.Cmd
// fallback exit notifier with error returned killing the process
killFallback chan error
// monitor to shim encoder
encoder *gob.Encoder
}
func (s *Shim) Unwrap() *exec.Cmd { return s.cmd }
func (s *Shim) Fallback() chan error { return s.killFallback }
func (s *Shim) String() string {
if s.cmd == nil {
return "(unused shim manager)"
}
return s.cmd.String()
}
func (s *Shim) Start(
aid string,
supp []string,
) (*time.Time, error) {
// prepare user switcher invocation
fsuPath := internal.MustFsuPath()
s.cmd = exec.Command(fsuPath)
// pass shim setup pipe
if fd, e, err := sandbox.Setup(&s.cmd.ExtraFiles); err != nil {
return nil, fmsg.WrapErrorSuffix(err,
"cannot create shim setup pipe:")
} else {
s.encoder = e
s.cmd.Env = []string{
Env + "=" + strconv.Itoa(fd),
"FORTIFY_APP_ID=" + aid,
}
}
// format fsu supplementary groups
if len(supp) > 0 {
fmsg.Verbosef("attaching supplementary group ids %s", supp)
s.cmd.Env = append(s.cmd.Env, "FORTIFY_GROUPS="+strings.Join(supp, " "))
}
s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
s.cmd.Dir = "/"
fmsg.Verbose("starting shim via fsu:", s.cmd)
// withhold messages to stderr
fmsg.Suspend()
if err := s.cmd.Start(); err != nil {
return nil, fmsg.WrapErrorSuffix(err,
"cannot start fsu:")
}
startTime := time.Now().UTC()
return &startTime, nil
}
func (s *Shim) Serve(ctx context.Context, params *Params) error {
// kill shim if something goes wrong and an error is returned
s.killFallback = make(chan error, 1)
killShim := func() {
if err := s.cmd.Process.Signal(os.Interrupt); err != nil {
s.killFallback <- err
}
}
defer func() { killShim() }()
encodeErr := make(chan error)
go func() { encodeErr <- s.encoder.Encode(params) }()
select {
// encode return indicates setup completion
case err := <-encodeErr:
if err != nil {
return fmsg.WrapErrorSuffix(err,
"cannot transmit shim config:")
}
killShim = func() {}
return nil
// setup canceled before payload was accepted
case <-ctx.Done():
err := ctx.Err()
if errors.Is(err, context.Canceled) {
return fmsg.WrapError(syscall.ECANCELED,
"shim setup canceled")
}
if errors.Is(err, context.DeadlineExceeded) {
return fmsg.WrapError(syscall.ETIMEDOUT,
"deadline exceeded waiting for shim")
}
// unreachable
return err
}
}
|
