From 3742f7f0dbfe66a9d6d0ffd1e30130fb15e1dca8 Mon Sep 17 00:00:00 2001 From: Wei Fu Date: Thu, 12 Oct 2023 21:58:56 +0800 Subject: [PATCH] idmapped: use pidfd to avoid pid reuse issue MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit It's followup for #5890. The containerd-shim process depends on the mount package to init rootfs for container. For the container enable user namespace, the mount package needs to fork child process to get the brand-new user namespace. However, there are two reapers in one process (described by the following list) and there are race-condition cases. 1. mount package 2. sys.Reaper as global one which watch all the SIGCHLD. === [kill(2)][kill] the wrong process === Currently, we use pipe to ensure that child process is alive. However, the pide file descriptor can be hold by other process, which the child process cannot exit by self. We should use [kill(2)][kill] to ensure the child process. But we might kill the wrong process if the child process might be reaped by containerd-shim and the PID might be reused by other process. === [waitid(2)][waitid] on the wrong child process === ``` containerd-shim process: Goroutine 1(GetUsernsFD): Goroutine 2(Reaper) 1. Ready to wait for child process X 2. Received SIGCHLD from X 3. Reaped the zombie child process X (X has been reused by other child process) 4. Wait on process X The goroutine 1 will be stuck until the process X has been terminated. ``` === open `/proc/X/ns/user` on the wrong child process === There is also pid-reused risk between opening `/proc/$pid/ns/user` and writing `/proc/$pid/u[g]id_map`. ``` containerd-shim process: Goroutine 1(GetUsernsFD): Goroutine 2(Reaper) 1. Fork child process X 2. Write /proc/X/uid_map,gid_map 3. Received SIGCHLD from X 4. Reaped the zombie child process X (X has been reused by other process) 5. Open /proc/X/ns/user file as usernsFD The usernsFD links to the wrong X!!! ``` In order to fix the race-condition, we should use [CLONE_PIDFD][clone2] (Since Linux v5.2). When we fork child process `X`, the kernel will return a process file descriptor `X_PIDFD` referencing to child process `X`. With the pidfd, we can use [pidfd_send_signal(2)][pidfd_send_signal] (Since Linux v5.1) to send signal(0) to ensure the child process `X` is alive. If the `X` has terminated and its PID has been recycled for another process. The pidfd_send_signal fails with the error ESRCH. Therefore, we can open `/proc/X/{ns/user,uid_map,gid_map}` file descriptors as first and then use pidfd_send_signal to check the process is still alive. If so, we can ensure the file descriptors are valid and reference to the child process `X`. Even if the `X` PID has been reused after pidfd_send_signal call, the file descriptors are still valid. ```code X, pidfd = clone2(CLONE_PIDFD) usernsFD = open /proc/X/ns/user uidmapFD = open /proc/X/uid_map gidmapFD = open /proc/X/gid_map pidfd_send_signal pidfd, signal(0) return err if no such process == When we arrive here, we can ensure usernsFD/uidmapFD/gidmapFD are correct == even if X has been reused after pidfd_send_signal call. update uid/gid mapping by uidmapFD/gidmapFD return usernsFD ``` And the [waitid(2)][waitid] also supports pidfd type (Since Linux 5.4). We can use pidfd type waitid to ensure we are waiting for the correct process. All the PID related race-condition issues can be resolved by pidfd. ```bash ➜ mount git:(followup-idmapped) pwd /home/fuwei/go/src/github.com/containerd/containerd/mount ➜ mount git:(followup-idmapped) sudo go test -test.root -run TestGetUsernsFD -count=1000 -failfast -p 100 ./... PASS ok github.com/containerd/containerd/mount 3.446s ``` [kill]: [clone2]: [pidfd_send_signal]: [waitid]: Signed-off-by: Wei Fu --- mount/mount_idmapped_linux.go | 172 ++++++++++------- mount/mount_idmapped_linux_test.go | 235 ++++++++++++++++++++++++ mount/mount_linux.go | 13 +- snapshots/overlay/overlayutils/check.go | 6 +- sys/userns_unsafe_linux.go | 79 +++++--- 5 files changed, 406 insertions(+), 99 deletions(-) create mode 100644 mount/mount_idmapped_linux_test.go diff --git a/mount/mount_idmapped_linux.go b/mount/mount_idmapped_linux.go index 92208771e..930070e7f 100644 --- a/mount/mount_idmapped_linux.go +++ b/mount/mount_idmapped_linux.go @@ -19,15 +19,15 @@ package mount import ( "fmt" "os" + "runtime" "strconv" "strings" + "sync" "syscall" - "unsafe" "golang.org/x/sys/unix" "github.com/containerd/containerd/sys" - "github.com/sirupsen/logrus" ) // TODO: Support multiple mappings in future @@ -36,21 +36,26 @@ func parseIDMapping(mapping string) ([]syscall.SysProcIDMap, error) { if len(parts) != 3 { return nil, fmt.Errorf("user namespace mappings require the format `container-id:host-id:size`") } + cID, err := strconv.Atoi(parts[0]) if err != nil { return nil, fmt.Errorf("invalid container id for user namespace remapping, %w", err) } + hID, err := strconv.Atoi(parts[1]) if err != nil { return nil, fmt.Errorf("invalid host id for user namespace remapping, %w", err) } + size, err := strconv.Atoi(parts[2]) if err != nil { return nil, fmt.Errorf("invalid size for user namespace remapping, %w", err) } - if cID != 0 || hID < 0 || size < 0 { - return nil, fmt.Errorf("invalid mapping %s, all IDs and size must be positive integers (container ID of 0 is only supported)", mapping) + + if cID < 0 || hID < 0 || size < 0 { + return nil, fmt.Errorf("invalid mapping %s, all IDs and size must be positive integers", mapping) } + return []syscall.SysProcIDMap{ { ContainerID: cID, @@ -87,80 +92,121 @@ func IDMapMount(source, target string, usernsFd int) (err error) { return nil } -// GetUsernsFD forks the current process and creates a user namespace using the specified -// mappings. -// -// It returns: -// 1. The file descriptor of the /proc/[pid]/ns/user of the newly -// created mapping. -// 2. "Clean up" function that should be called once user namespace -// file descriptor is no longer needed. -// 3. Usual error. -func GetUsernsFD(uidmap, gidmap string) (_ int, _ func(), err error) { - var ( - usernsFile *os.File - pipeMap [2]int - pid uintptr - errno syscall.Errno - uidMaps, gidMaps []syscall.SysProcIDMap - ) - - if uidMaps, err = parseIDMapping(uidmap); err != nil { - return -1, nil, err - } - if gidMaps, err = parseIDMapping(gidmap); err != nil { - return -1, nil, err +// GetUsernsFD forks the current process and creates a user namespace using +// the specified mappings. +func GetUsernsFD(uidmap, gidmap string) (_usernsFD *os.File, _ error) { + uidMaps, err := parseIDMapping(uidmap) + if err != nil { + return nil, err } - syscall.ForkLock.Lock() - if err = syscall.Pipe2(pipeMap[:], syscall.O_CLOEXEC); err != nil { - syscall.ForkLock.Unlock() - return -1, nil, err + gidMaps, err := parseIDMapping(gidmap) + if err != nil { + return nil, err } + return getUsernsFD(uidMaps, gidMaps) +} - pid, errno = sys.ForkUserns(pipeMap) - syscall.ForkLock.Unlock() +func getUsernsFD(uidMaps, gidMaps []syscall.SysProcIDMap) (_usernsFD *os.File, retErr error) { + runtime.LockOSThread() + defer runtime.UnlockOSThread() + + pid, pidfd, errno := sys.ForkUserns() if errno != 0 { - syscall.Close(pipeMap[0]) - syscall.Close(pipeMap[1]) - return -1, nil, errno + return nil, errno } - syscall.Close(pipeMap[0]) + pidFD := os.NewFile(pidfd, "pidfd") + defer func() { + unix.PidfdSendSignal(int(pidFD.Fd()), unix.SIGKILL, nil, 0) - writeMappings := func(fname string, idmap []syscall.SysProcIDMap) error { + 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("%d %d %d\n", m.ContainerID, m.HostID, m.Size) + mappings = fmt.Sprintf("%s%d %d %d\n", mappings, m.ContainerID, m.HostID, m.Size) } - return os.WriteFile(fmt.Sprintf("/proc/%d/%s", pid, fname), []byte(mappings), 0600) - } - cleanUpChild := func() { - sync := sys.ProcSyncExit - if _, _, errno := syscall.Syscall6(syscall.SYS_WRITE, uintptr(pipeMap[1]), uintptr(unsafe.Pointer(&sync)), unsafe.Sizeof(sync), 0, 0, 0); errno != 0 { - logrus.WithError(errno).Warnf("failed to sync with child (ProcSyncExit)") + _, err := f.Write([]byte(mappings)) + if err1 := f.Close(); err1 != nil && err == nil { + err = err1 } - syscall.Close(pipeMap[1]) - - if _, err := unix.Wait4(int(pid), nil, 0, nil); err != nil { - logrus.WithError(err).Warnf("failed to wait for child process; the SIGHLD might be received by shim reaper") - } - } - defer cleanUpChild() - - if err := writeMappings("uid_map", uidMaps); err != nil { - return -1, nil, err - } - if err := writeMappings("gid_map", gidMaps); err != nil { - return -1, nil, err + return err } - if usernsFile, err = os.Open(fmt.Sprintf("/proc/%d/ns/user", pid)); err != nil { - return -1, nil, fmt.Errorf("failed to get user ns file descriptor for - /proc/%d/user/ns: %w", pid, err) + if err := writeMappings(uidmapFile, uidMaps); err != nil { + return nil, fmt.Errorf("failed to write uid_map: %w", err) } - return int(usernsFile.Fd()), func() { - usernsFile.Close() - }, nil + 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 { + // https://elixir.bootlin.com/linux/v5.4.258/source/include/uapi/linux/wait.h#L20 + const PPidFD = 3 + + var e syscall.Errno + for { + _, _, e = syscall.Syscall6(syscall.SYS_WAITID, PPidFD, pidFD.Fd(), 0, syscall.WEXITED, 0, 0) + if e != syscall.EINTR { + break + } + } + return e +} + +var ( + testHookLock sync.Mutex + + testHookKillChildBeforePidfdSendSignal = func(_pid uintptr, _pidFD *os.File) {} + + testHookKillChildAfterPidfdSendSignal = func(_pid uintptr, _pidFD *os.File) {} +) diff --git a/mount/mount_idmapped_linux_test.go b/mount/mount_idmapped_linux_test.go new file mode 100644 index 000000000..1b21b9492 --- /dev/null +++ b/mount/mount_idmapped_linux_test.go @@ -0,0 +1,235 @@ +/* + 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" + "path/filepath" + "syscall" + "testing" + + "github.com/containerd/continuity/testutil" + "github.com/stretchr/testify/require" + "golang.org/x/sys/unix" +) + +var ( + testUIDMaps = []syscall.SysProcIDMap{ + {ContainerID: 1000, HostID: 0, Size: 100}, + {ContainerID: 5000, HostID: 2000, Size: 100}, + {ContainerID: 10000, HostID: 3000, Size: 100}, + } + + testGIDMaps = []syscall.SysProcIDMap{ + {ContainerID: 1000, HostID: 0, Size: 100}, + {ContainerID: 5000, HostID: 2000, Size: 100}, + {ContainerID: 10000, HostID: 3000, Size: 100}, + } +) + +func TestGetUsernsFD(t *testing.T) { + testutil.RequiresRoot(t) + + 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) + +} + +func testGetUsernsFDBasic(t *testing.T) { + for idx, tc := range []struct { + uidMaps string + gidMaps string + hasErr bool + }{ + { + uidMaps: "0:1000:100", + gidMaps: "0:1000:100", + hasErr: false, + }, + { + uidMaps: "100:1000:100", + gidMaps: "0:-1:100", + hasErr: true, + }, + { + uidMaps: "100:1000:100", + gidMaps: "-1:1000:100", + hasErr: true, + }, + { + uidMaps: "100:1000:100", + gidMaps: "0:1000:-1", + hasErr: true, + }, + } { + t.Run(fmt.Sprintf("#%v", idx), func(t *testing.T) { + _, err := GetUsernsFD(tc.uidMaps, tc.gidMaps) + if tc.hasErr { + require.Error(t, err) + } else { + require.NoError(t, err) + } + }) + } +} + +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) + + if reap { + pidfdWaitid(pidFD) + } + } + } + + 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 + } +} + +func initIDMappedChecker(t *testing.T, uidMaps, gidMaps []syscall.SysProcIDMap) (_srcDir string, _verifyFunc func(destDir string)) { + testutil.RequiresRoot(t) + + srcDir := t.TempDir() + + require.Equal(t, len(uidMaps), len(gidMaps)) + for idx := range uidMaps { + file := filepath.Join(srcDir, fmt.Sprintf("%v", idx)) + + f, err := os.Create(file) + require.NoError(t, err, fmt.Sprintf("create file %s", file)) + defer f.Close() + + uid, gid := uidMaps[idx].ContainerID, gidMaps[idx].ContainerID + err = f.Chown(uid, gid) + require.NoError(t, err, fmt.Sprintf("chown %v:%v for file %s", uid, gid, file)) + } + + return srcDir, func(destDir string) { + for idx := range uidMaps { + file := filepath.Join(destDir, fmt.Sprintf("%v", idx)) + + f, err := os.Open(file) + require.NoError(t, err, fmt.Sprintf("open file %s", file)) + defer f.Close() + + stat, err := f.Stat() + require.NoError(t, err, fmt.Sprintf("stat file %s", file)) + + sysStat := stat.Sys().(*syscall.Stat_t) + + uid, gid := uidMaps[idx].HostID, gidMaps[idx].HostID + require.Equal(t, uint32(uid), sysStat.Uid, fmt.Sprintf("check file %s uid", file)) + require.Equal(t, uint32(gid), sysStat.Gid, fmt.Sprintf("check file %s gid", file)) + t.Logf("IDMapped File %s uid=%v, gid=%v", file, uid, gid) + } + } +} diff --git a/mount/mount_linux.go b/mount/mount_linux.go index 837d9b802..69a032b9f 100644 --- a/mount/mount_linux.go +++ b/mount/mount_linux.go @@ -93,26 +93,23 @@ func (m *Mount) mount(target string) (err error) { var ( chdir string recalcOpt bool - usernsFd int + usernsFd *os.File options = m.Options ) opt := parseMountOptions(options) // The only remapping of both GID and UID is supported if opt.uidmap != "" && opt.gidmap != "" { - var ( - childProcCleanUp func() - ) - if usernsFd, childProcCleanUp, err = GetUsernsFD(opt.uidmap, opt.gidmap); err != nil { + if usernsFd, err = GetUsernsFD(opt.uidmap, opt.gidmap); err != nil { return err } - defer childProcCleanUp() + defer usernsFd.Close() // overlay expects lowerdir's to be remapped instead if m.Type == "overlay" { var ( userNsCleanUp func() ) - options, userNsCleanUp, err = prepareIDMappedOverlay(usernsFd, options) + options, userNsCleanUp, err = prepareIDMappedOverlay(int(usernsFd.Fd()), options) defer userNsCleanUp() if err != nil { @@ -196,7 +193,7 @@ func (m *Mount) mount(target string) (err error) { // remap non-overlay mount point if opt.uidmap != "" && opt.gidmap != "" && m.Type != "overlay" { - if err := IDMapMount(target, target, usernsFd); err != nil { + if err := IDMapMount(target, target, int(usernsFd.Fd())); err != nil { return err } } diff --git a/snapshots/overlay/overlayutils/check.go b/snapshots/overlay/overlayutils/check.go index e94c95a88..678a7e1cb 100644 --- a/snapshots/overlay/overlayutils/check.go +++ b/snapshots/overlay/overlayutils/check.go @@ -255,13 +255,13 @@ func SupportsIDMappedMounts() (bool, error) { uidmap := fmt.Sprintf("%d:%d:%d", uidMap.ContainerID, uidMap.HostID, uidMap.Size) gidmap := fmt.Sprintf("%d:%d:%d", gidMap.ContainerID, gidMap.HostID, gidMap.Size) - usernsFd, childProcCleanUp, err := mount.GetUsernsFD(uidmap, gidmap) + usernsFd, err := mount.GetUsernsFD(uidmap, gidmap) if err != nil { return false, err } - defer childProcCleanUp() + defer usernsFd.Close() - if err = mount.IDMapMount(lowerDir, lowerDir, usernsFd); err != nil { + if err = mount.IDMapMount(lowerDir, lowerDir, int(usernsFd.Fd())); err != nil { return false, fmt.Errorf("failed to remap lowerdir %s: %w", lowerDir, err) } defer func() { diff --git a/sys/userns_unsafe_linux.go b/sys/userns_unsafe_linux.go index bedf8943c..4ebe46c32 100644 --- a/sys/userns_unsafe_linux.go +++ b/sys/userns_unsafe_linux.go @@ -22,44 +22,73 @@ import ( "unsafe" ) -// ProcSyncType is used for synchronization -// between parent and child processes. -type ProcSyncType uint8 - -const ( - // ProcSyncExit tells child "it's time to exit". - ProcSyncExit ProcSyncType = 0x1 -) - +// 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(pipeMap [2]int) (pid uintptr, errno syscall.Errno) { - var sync ProcSyncType +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" { - pid, _, errno = syscall.RawSyscall6(uintptr(syscall.SYS_CLONE), 0, syscall.CLONE_NEWUSER|uintptr(syscall.SIGCHLD), 0, 0, 0, 0) + // 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, _, errno = syscall.RawSyscall6(uintptr(syscall.SYS_CLONE), syscall.CLONE_NEWUSER|uintptr(syscall.SIGCHLD), 0, 0, 0, 0, 0) + pid, _, err = syscall.RawSyscall(syscall.SYS_CLONE, + uintptr(syscall.CLONE_NEWUSER|syscall.SIGCHLD|syscall.CLONE_PIDFD), + 0, + uintptr(unsafe.Pointer(&pidfd)), + ) } - if errno != 0 || pid != 0 { + if err != 0 || pid != 0 { afterFork() - return pid, errno + return pid, pidfd, err } - afterForkInChild() - if _, _, errno = syscall.RawSyscall(syscall.SYS_CLOSE, uintptr(pipeMap[1]), 0, 0); errno != 0 { - goto err - } - if _, _, errno = syscall.RawSyscall6(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGKILL), 0, 0, 0, 0); errno != 0 { - goto err - } - // wait for parent's signal - if _, _, errno = syscall.RawSyscall6(syscall.SYS_READ, uintptr(pipeMap[0]), uintptr(unsafe.Pointer(&sync)), unsafe.Sizeof(sync), 0, 0, 0); errno != 0 || sync != ProcSyncExit { + + 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.RawSyscall6(syscall.SYS_EXIT, uintptr(errno), 0, 0, 0, 0, 0) + syscall.RawSyscall(syscall.SYS_EXIT, uintptr(err), 0, 0) panic("unreachable") }