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core/mount: use ptrace instead of go:linkname

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The Go runtime has started to [lock down future uses of linkname][1] since
go1.23. In the go source code, containerd project has been marked in the
comment, [hall of shame][2]. Well, the go:linkname is used to fork no-op
subprocess efficiently. However, since that comment, I would like to use
ptrace and remove go:linkname in the whole repository.

With go1.22 `go:linkname`:

```bash
$ go test -bench=.  -benchmem ./ -exec sudo
goos: linux
goarch: amd64
pkg: github.com/containerd/containerd/v2/core/mount
cpu: AMD Ryzen 7 5800H with Radeon Graphics
BenchmarkBatchRunGetUsernsFD_Concurrent1-16                 2440            533320 ns/op            1145 B/op         43 allocs/op
BenchmarkBatchRunGetUsernsFD_Concurrent10-16                 342           3661616 ns/op           11562 B/op        421 allocs/op
PASS
ok      github.com/containerd/containerd/v2/core/mount  2.983s
```

With go1.22 `ptrace`:

```bash
$ go test -bench=.  -benchmem ./ -exec sudo
goos: linux
goarch: amd64
pkg: github.com/containerd/containerd/v2/core/mount
cpu: AMD Ryzen 7 5800H with Radeon Graphics
BenchmarkBatchRunGetUsernsFD_Concurrent1-16                 1785            739557 ns/op            3948 B/op         68 allocs/op
BenchmarkBatchRunGetUsernsFD_Concurrent10-16                 328           4024300 ns/op           39601 B/op        671 allocs/op
PASS
ok      github.com/containerd/containerd/v2/core/mount  3.104s
```

With go1.23 `ptrace`:

```bash
$ go test -bench=.  -benchmem ./ -exec sudo
goos: linux
goarch: amd64
pkg: github.com/containerd/containerd/v2/core/mount
cpu: AMD Ryzen 7 5800H with Radeon Graphics
BenchmarkBatchRunGetUsernsFD_Concurrent1-16                 1815            723252 ns/op            4220 B/op         69 allocs/op
BenchmarkBatchRunGetUsernsFD_Concurrent10-16                 319           3957157 ns/op           42351 B/op        682 allocs/op
PASS
ok      github.com/containerd/containerd/v2/core/mount  3.051s
```

Diff:

The `ptrace` is slower than `go:linkname` mode. However, it's accepctable.

```
goos: linux
goarch: amd64
pkg: github.com/containerd/containerd/v2/core/mount
cpu: AMD Ryzen 7 5800H with Radeon Graphics
                                    │ go122-golinkname │             go122-ptrace              │             go123-ptrace              │
                                    │      sec/op      │    sec/op     vs base                 │    sec/op     vs base                 │
BatchRunGetUsernsFD_Concurrent1-16        533.3µ ± ∞ ¹   739.6µ ± ∞ ¹        ~ (p=1.000 n=1) ²   723.3µ ± ∞ ¹        ~ (p=1.000 n=1) ²
BatchRunGetUsernsFD_Concurrent10-16       3.662m ± ∞ ¹   4.024m ± ∞ ¹        ~ (p=1.000 n=1) ²   3.957m ± ∞ ¹        ~ (p=1.000 n=1) ²
geomean                                   1.397m         1.725m        +23.45%                   1.692m        +21.06%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05

                                    │ go122-golinkname │              go122-ptrace               │              go123-ptrace               │
                                    │       B/op       │     B/op       vs base                  │     B/op       vs base                  │
BatchRunGetUsernsFD_Concurrent1-16       1.118Ki ± ∞ ¹   3.855Ki ± ∞ ¹         ~ (p=1.000 n=1) ²   4.121Ki ± ∞ ¹         ~ (p=1.000 n=1) ²
BatchRunGetUsernsFD_Concurrent10-16      11.29Ki ± ∞ ¹   38.67Ki ± ∞ ¹         ~ (p=1.000 n=1) ²   41.36Ki ± ∞ ¹         ~ (p=1.000 n=1) ²
geomean                                  3.553Ki         12.21Ki        +243.65%                   13.06Ki        +267.43%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05

                                    │ go122-golinkname │             go122-ptrace             │             go123-ptrace             │
                                    │    allocs/op     │  allocs/op   vs base                 │  allocs/op   vs base                 │
BatchRunGetUsernsFD_Concurrent1-16         43.00 ± ∞ ¹   68.00 ± ∞ ¹        ~ (p=1.000 n=1) ²   69.00 ± ∞ ¹        ~ (p=1.000 n=1) ²
BatchRunGetUsernsFD_Concurrent10-16        421.0 ± ∞ ¹   671.0 ± ∞ ¹        ~ (p=1.000 n=1) ²   682.0 ± ∞ ¹        ~ (p=1.000 n=1) ²
geomean                                    134.5         213.6        +58.76%                   216.9        +61.23%
¹ need >= 6 samples for confidence interval at level 0.95
² need >= 4 samples to detect a difference at alpha level 0.05
```

[1]: <https://github.com/golang/go/issues/67401>
[2]: <https://github.com/golang/go/blob/release-branch.go1.23/src/runtime/proc.go#L4820>

Signed-off-by: Wei Fu <fuweid89@gmail.com>
This commit is contained in:
Wei Fu 2024-08-19 19:05:24 +08:00
parent bcdf507363
commit 3cd8f9734d
7 changed files with 280 additions and 332 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

100
core/mount/mount_idmapped_linux.go
View File

@ -19,15 +19,11 @@ package mount
import (
"fmt"
"os"
"runtime"
"strconv"
"strings"
"sync"
"syscall"
"golang.org/x/sys/unix"
"github.com/containerd/containerd/v2/pkg/sys"
)
// TODO: Support multiple mappings in future
@ -106,99 +102,3 @@ func GetUsernsFD(uidmap, gidmap string) (_usernsFD *os.File, _ error) {
}
return getUsernsFD(uidMaps, gidMaps)
}
func getUsernsFD(uidMaps, gidMaps []syscall.SysProcIDMap) (_usernsFD *os.File, retErr error) {
runtime.LockOSThread()
defer runtime.UnlockOSThread()
pid, pidfd, errno := sys.ForkUserns()
if errno != 0 {
return nil, errno
}
pidFD := os.NewFile(pidfd, "pidfd")
defer func() {
unix.PidfdSendSignal(int(pidFD.Fd()), unix.SIGKILL, nil, 0)
pidfdWaitid(pidFD)
pidFD.Close()
}()
// NOTE:
//
// The usernsFD will hold the userns reference in kernel. Even if the
// child process is reaped, the usernsFD is still valid.
usernsFD, err := os.Open(fmt.Sprintf("/proc/%d/ns/user", pid))
if err != nil {
return nil, fmt.Errorf("failed to get userns file descriptor for /proc/%d/user/ns: %w", pid, err)
}
defer func() {
if retErr != nil {
usernsFD.Close()
}
}()
uidmapFile, err := os.OpenFile(fmt.Sprintf("/proc/%d/%s", pid, "uid_map"), os.O_WRONLY, 0600)
if err != nil {
return nil, fmt.Errorf("failed to open /proc/%d/uid_map: %w", pid, err)
}
defer uidmapFile.Close()
gidmapFile, err := os.OpenFile(fmt.Sprintf("/proc/%d/%s", pid, "gid_map"), os.O_WRONLY, 0600)
if err != nil {
return nil, fmt.Errorf("failed to open /proc/%d/gid_map: %w", pid, err)
}
defer gidmapFile.Close()
testHookKillChildBeforePidfdSendSignal(pid, pidFD)
// Ensure the child process is still alive. If the err is ESRCH, we
// should return error because we can't guarantee the usernsFD and
// u[g]idmapFile are valid. It's safe to return error and retry.
if err := unix.PidfdSendSignal(int(pidFD.Fd()), 0, nil, 0); err != nil {
return nil, fmt.Errorf("failed to ensure child process is alive: %w", err)
}
testHookKillChildAfterPidfdSendSignal(pid, pidFD)
// NOTE:
//
// The u[g]id_map file descriptor is still valid if the child process
// is reaped.
writeMappings := func(f *os.File, idmap []syscall.SysProcIDMap) error {
mappings := ""
for _, m := range idmap {
mappings = fmt.Sprintf("%s%d %d %d\n", mappings, m.ContainerID, m.HostID, m.Size)
}
_, err := f.Write([]byte(mappings))
if err1 := f.Close(); err1 != nil && err == nil {
err = err1
}
return err
}
if err := writeMappings(uidmapFile, uidMaps); err != nil {
return nil, fmt.Errorf("failed to write uid_map: %w", err)
}
if err := writeMappings(gidmapFile, gidMaps); err != nil {
return nil, fmt.Errorf("failed to write gid_map: %w", err)
}
return usernsFD, nil
}
func pidfdWaitid(pidFD *os.File) error {
return sys.IgnoringEINTR(func() error {
return unix.Waitid(unix.P_PIDFD, int(pidFD.Fd()), nil, unix.WEXITED, nil)
})
}
var (
testHookLock sync.Mutex
testHookKillChildBeforePidfdSendSignal = func(_pid uintptr, _pidFD *os.File) {}
testHookKillChildAfterPidfdSendSignal = func(_pid uintptr, _pidFD *os.File) {}
)

125
core/mount/mount_idmapped_linux_test.go
View File

@ -27,7 +27,6 @@ import (
kernel "github.com/containerd/containerd/v2/pkg/kernelversion"
"github.com/containerd/continuity/testutil"
"github.com/stretchr/testify/require"
"golang.org/x/sys/unix"
)
func BenchmarkBatchRunGetUsernsFD_Concurrent1(b *testing.B) {
@ -72,7 +71,7 @@ var (
}
)
func TestGetUsernsFD(t *testing.T) {
func TestIdmappedMount(t *testing.T) {
testutil.RequiresRoot(t)
k512 := kernel.KernelVersion{Kernel: 5, Major: 12}
@ -82,15 +81,12 @@ func TestGetUsernsFD(t *testing.T) {
t.Skip("GetUsernsFD requires kernel >= 5.12")
}
t.Run("basic", testGetUsernsFDBasic)
t.Run("when kill child process before write u[g]id maps", testGetUsernsFDKillChildWhenWriteUGIDMaps)
t.Run("when kill child process after open u[g]id_map file", testGetUsernsFDKillChildAfterOpenUGIDMapFiles)
t.Run("GetUsernsFD", testGetUsernsFD)
t.Run("IDMapMount", testIDMapMount)
}
func testGetUsernsFDBasic(t *testing.T) {
func testGetUsernsFD(t *testing.T) {
for idx, tc := range []struct {
uidMaps string
gidMaps string
@ -128,108 +124,21 @@ func testGetUsernsFDBasic(t *testing.T) {
}
}
func testGetUsernsFDKillChildWhenWriteUGIDMaps(t *testing.T) {
hookFunc := func(reap bool) func(uintptr, *os.File) {
return func(_pid uintptr, pidFD *os.File) {
err := unix.PidfdSendSignal(int(pidFD.Fd()), unix.SIGKILL, nil, 0)
require.NoError(t, err)
func testIDMapMount(t *testing.T) {
usernsFD, err := getUsernsFD(testUIDMaps, testGIDMaps)
require.NoError(t, err)
defer usernsFD.Close()
if reap {
pidfdWaitid(pidFD)
}
}
}
srcDir, checkFunc := initIDMappedChecker(t, testUIDMaps, testGIDMaps)
destDir := t.TempDir()
defer func() {
require.NoError(t, UnmountAll(destDir, 0))
}()
for _, tcReap := range []bool{true, false} {
t.Run(fmt.Sprintf("#reap=%v", tcReap), func(t *testing.T) {
updateTestHookKillForGetUsernsFD(t, nil, hookFunc(tcReap))
usernsFD, err := getUsernsFD(testUIDMaps, testGIDMaps)
require.NoError(t, err)
defer usernsFD.Close()
srcDir, checkFunc := initIDMappedChecker(t, testUIDMaps, testGIDMaps)
destDir := t.TempDir()
defer func() {
require.NoError(t, UnmountAll(destDir, 0))
}()
err = IDMapMount(srcDir, destDir, int(usernsFD.Fd()))
usernsFD.Close()
require.NoError(t, err)
checkFunc(destDir)
})
}
}
func testGetUsernsFDKillChildAfterOpenUGIDMapFiles(t *testing.T) {
hookFunc := func(reap bool) func(uintptr, *os.File) {
return func(_pid uintptr, pidFD *os.File) {
err := unix.PidfdSendSignal(int(pidFD.Fd()), unix.SIGKILL, nil, 0)
require.NoError(t, err)
if reap {
pidfdWaitid(pidFD)
}
}
}
for _, tc := range []struct {
reap bool
expected error
}{
{
reap: false,
expected: nil,
},
{
reap: true,
expected: syscall.ESRCH,
},
} {
t.Run(fmt.Sprintf("#reap=%v", tc.reap), func(t *testing.T) {
updateTestHookKillForGetUsernsFD(t, hookFunc(tc.reap), nil)
usernsFD, err := getUsernsFD(testUIDMaps, testGIDMaps)
if tc.expected != nil {
require.Error(t, tc.expected, err)
return
}
require.NoError(t, err)
defer usernsFD.Close()
srcDir, checkFunc := initIDMappedChecker(t, testUIDMaps, testGIDMaps)
destDir := t.TempDir()
defer func() {
require.NoError(t, UnmountAll(destDir, 0))
}()
err = IDMapMount(srcDir, destDir, int(usernsFD.Fd()))
usernsFD.Close()
require.NoError(t, err)
checkFunc(destDir)
})
}
}
func updateTestHookKillForGetUsernsFD(t *testing.T, newBeforeFunc, newAfterFunc func(uintptr, *os.File)) {
testHookLock.Lock()
oldBefore := testHookKillChildBeforePidfdSendSignal
oldAfter := testHookKillChildAfterPidfdSendSignal
t.Cleanup(func() {
testHookKillChildBeforePidfdSendSignal = oldBefore
testHookKillChildAfterPidfdSendSignal = oldAfter
testHookLock.Unlock()
})
if newBeforeFunc != nil {
testHookKillChildBeforePidfdSendSignal = newBeforeFunc
}
if newAfterFunc != nil {
testHookKillChildAfterPidfdSendSignal = newAfterFunc
}
err = IDMapMount(srcDir, destDir, int(usernsFD.Fd()))
usernsFD.Close()
require.NoError(t, err)
checkFunc(destDir)
}
func initIDMappedChecker(t *testing.T, uidMaps, gidMaps []syscall.SysProcIDMap) (_srcDir string, _verifyFunc func(destDir string)) {

85
core/mount/mount_idmapped_utils_linux.go Normal file
View File

@ -0,0 +1,85 @@
//go:build go1.23 && linux
/*
Copyright The containerd Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package mount
import (
"fmt"
"os"
"syscall"
"github.com/containerd/containerd/v2/pkg/sys"
"golang.org/x/sys/unix"
)
// getUsernsFD returns pinnable user namespace's file descriptor.
//
// NOTE: The GO runtime uses pidfd to handle subprocess since go1.23. However,
// it has double close issue tracked by [1]. We can't use pidfd directly and
// the GO runtime doesn't export interface to show if it's using pidfd or not.
// So, we call `sys.SupportsPidFD` first and then use `os.Process` directly.
//
// [1]: https://github.com/golang/go/issues/68984
func getUsernsFD(uidMaps, gidMaps []syscall.SysProcIDMap) (_ *os.File, retErr error) {
if !sys.SupportsPidFD() {
return nil, fmt.Errorf("failed to prevent pid reused issue because pidfd isn't supported")
}
proc, err := os.StartProcess("/proc/self/exe", []string{"containerd[getUsernsFD]"}, &os.ProcAttr{
Sys: &syscall.SysProcAttr{
Cloneflags: unix.CLONE_NEWUSER,
UidMappings: uidMaps,
GidMappings: gidMaps,
// NOTE: It's reexec but it's not heavy because subprocess
// be in PTRACE_TRACEME mode before performing execve.
Ptrace: true,
Pdeathsig: syscall.SIGKILL,
},
})
if err != nil {
return nil, fmt.Errorf("failed to start noop process for unshare: %w", err)
}
defer func() {
proc.Kill()
proc.Wait()
}()
// NOTE:
//
// The usernsFD will hold the userns reference in kernel. Even if the
// child process is reaped, the usernsFD is still valid.
usernsFD, err := os.Open(fmt.Sprintf("/proc/%d/ns/user", proc.Pid))
if err != nil {
return nil, fmt.Errorf("failed to get userns file descriptor for /proc/%d/user/ns: %w", proc.Pid, err)
}
defer func() {
if retErr != nil {
usernsFD.Close()
}
}()
// Ensure the child process is still alive. If the err is ESRCH, we
// should return error because we can't guarantee the usernsFD and
// u[g]idmapFile are valid. It's safe to return error and retry.
if err := proc.Signal(syscall.Signal(0)); err != nil {
return nil, fmt.Errorf("failed to ensure child process is alive: %w", err)
}
return usernsFD, nil
}

93
core/mount/mount_idmapped_utils_linux_go122.go Normal file
View File

@ -0,0 +1,93 @@
//go:build !go1.23 && linux
/*
Copyright The containerd Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package mount
import (
"fmt"
"os"
"syscall"
"github.com/containerd/containerd/v2/pkg/sys"
"golang.org/x/sys/unix"
)
// getUsernsFD returns pinnable user namespace's file descriptor.
func getUsernsFD(uidMaps, gidMaps []syscall.SysProcIDMap) (_ *os.File, retErr error) {
var pidfd int
proc, err := os.StartProcess("/proc/self/exe", []string{"containerd[getUsernsFD]"}, &os.ProcAttr{
Sys: &syscall.SysProcAttr{
Cloneflags: unix.CLONE_NEWUSER,
UidMappings: uidMaps,
GidMappings: gidMaps,
// NOTE: It's reexec but it's not heavy because subprocess
// be in PTRACE_TRACEME mode before performing execve.
Ptrace: true,
Pdeathsig: syscall.SIGKILL,
PidFD: &pidfd,
},
})
if err != nil {
return nil, fmt.Errorf("failed to start noop process for unshare: %w", err)
}
if pidfd == -1 || !sys.SupportsPidFD() {
proc.Kill()
proc.Wait()
return nil, fmt.Errorf("failed to prevent pid reused issue because pidfd isn't supported")
}
pidFD := os.NewFile(uintptr(pidfd), "pidfd")
defer func() {
unix.PidfdSendSignal(int(pidFD.Fd()), unix.SIGKILL, nil, 0)
pidfdWaitid(pidFD)
pidFD.Close()
}()
// NOTE:
//
// The usernsFD will hold the userns reference in kernel. Even if the
// child process is reaped, the usernsFD is still valid.
usernsFD, err := os.Open(fmt.Sprintf("/proc/%d/ns/user", proc.Pid))
if err != nil {
return nil, fmt.Errorf("failed to get userns file descriptor for /proc/%d/user/ns: %w", proc.Pid, err)
}
defer func() {
if retErr != nil {
usernsFD.Close()
}
}()
// Ensure the child process is still alive. If the err is ESRCH, we
// should return error because we can't guarantee the usernsFD and
// u[g]idmapFile are valid. It's safe to return error and retry.
if err := unix.PidfdSendSignal(int(pidFD.Fd()), 0, nil, 0); err != nil {
return nil, fmt.Errorf("failed to ensure child process is alive: %w", err)
}
return usernsFD, nil
}
func pidfdWaitid(pidFD *os.File) error {
return sys.IgnoringEINTR(func() error {
return unix.Waitid(unix.P_PIDFD, int(pidFD.Fd()), nil, unix.WEXITED, nil)
})
}

85
pkg/sys/pidfd_linux.go Normal file
View File

@ -0,0 +1,85 @@
/*
Copyright The containerd Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package sys
import (
"context"
"errors"
"fmt"
"os"
"sync"
"github.com/containerd/log"
"golang.org/x/sys/unix"
)
var (
pidfdSupported bool
pidfdSupportedOnce sync.Once
)
// SupportsPidFD returns true if current kernel supports pidfd.
func SupportsPidFD() bool {
pidfdSupportedOnce.Do(func() {
logger := log.G(context.Background())
if err := checkPidFD(); err != nil {
logger.WithError(err).Error("failed to ensure the kernel supports pidfd")
pidfdSupported = false
return
}
pidfdSupported = true
})
return pidfdSupported
}
func checkPidFD() error {
// Linux kernel supports pidfd_open(2) since v5.3.
//
// https://man7.org/linux/man-pages/man2/pidfd_open.2.html
pidfd, err := unix.PidfdOpen(os.Getpid(), 0)
if err != nil {
return fmt.Errorf("failed to invoke pidfd_open: %w", err)
}
defer unix.Close(pidfd)
// Linux kernel supports pidfd_send_signal(2) since v5.1.
//
// https://man7.org/linux/man-pages/man2/pidfd_send_signal.2.html
if err := unix.PidfdSendSignal(pidfd, 0, nil, 0); err != nil {
return fmt.Errorf("failed to invoke pidfd_send_signal: %w", err)
}
// The waitid(2) supports P_PIDFD since Linux kernel v5.4.
//
// https://man7.org/linux/man-pages/man2/waitid.2.html
werr := IgnoringEINTR(func() error {
return unix.Waitid(unix.P_PIDFD, pidfd, nil, unix.WEXITED, nil)
})
// The waitid returns ECHILD since current process isn't the child of current process.
if !errors.Is(werr, unix.ECHILD) {
return fmt.Errorf("failed to invoke waitid with P_PIDFD: wanted error %v, but got %v",
unix.ECHILD, werr)
}
// NOTE: The CLONE_PIDFD flag has been supported since Linux kernel v5.2.
// So assumption is that if waitid(2) supports P_PIDFD, current kernel
// should support CLONE_PIDFD as well.
return nil
}

30
pkg/sys/subprocess_unsafe_linux.go
View File

@ -1,30 +0,0 @@
/*
Copyright The containerd Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package sys
import (
_ "unsafe" // required for go:linkname.
)
//go:linkname beforeFork syscall.runtime_BeforeFork
func beforeFork()
//go:linkname afterFork syscall.runtime_AfterFork
func afterFork()
//go:linkname afterForkInChild syscall.runtime_AfterForkInChild
func afterForkInChild()

94
pkg/sys/userns_unsafe_linux.go
View File

@ -1,94 +0,0 @@
/*
Copyright The containerd Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package sys
import (
"runtime"
"syscall"
"unsafe"
)
// ForkUserns is to fork child process with user namespace. It returns child
// process's pid and pidfd reference to the child process.
//
// Precondition: The runtime OS thread must be locked, which is GO runtime
// requirement.
//
// Beside this, the child process sets PR_SET_PDEATHSIG with SIGKILL so that
// the parent process's OS thread must be locked. Otherwise, the exit event of
// parent process's OS thread will send kill signal to the child process,
// even if parent process is still running.
//
//go:norace
//go:noinline
func ForkUserns() (_pid uintptr, _pidfd uintptr, _ syscall.Errno) {
var (
pidfd uintptr
pid, ppid uintptr
err syscall.Errno
)
ppid, _, err = syscall.RawSyscall(uintptr(syscall.SYS_GETPID), 0, 0, 0)
if err != 0 {
return 0, 0, err
}
beforeFork()
if runtime.GOARCH == "s390x" {
// NOTE:
//
// On the s390 architectures, the order of the first two
// arguments is reversed.
//
// REF: https://man7.org/linux/man-pages/man2/clone.2.html
pid, _, err = syscall.RawSyscall(syscall.SYS_CLONE,
0,
uintptr(syscall.CLONE_NEWUSER|syscall.SIGCHLD|syscall.CLONE_PIDFD),
uintptr(unsafe.Pointer(&pidfd)),
)
} else {
pid, _, err = syscall.RawSyscall(syscall.SYS_CLONE,
uintptr(syscall.CLONE_NEWUSER|syscall.SIGCHLD|syscall.CLONE_PIDFD),
0,
uintptr(unsafe.Pointer(&pidfd)),
)
}
if err != 0 || pid != 0 {
afterFork()
return pid, pidfd, err
}
afterForkInChild()
if _, _, err = syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGKILL), 0); err != 0 {
goto err
}
pid, _, err = syscall.RawSyscall(syscall.SYS_GETPPID, 0, 0, 0)
if err != 0 {
goto err
}
// exit if re-parent
if pid != ppid {
goto err
}
_, _, err = syscall.RawSyscall(syscall.SYS_PPOLL, 0, 0, 0)
err:
syscall.RawSyscall(syscall.SYS_EXIT, uintptr(err), 0, 0)
panic("unreachable")
}