syscall: add support for SysProcAttr.Pdeathsig on FreeBSD

Fixes #46258

Change-Id: I63f70e67274a9df39c757243b99b12e50a9e4784
Reviewed-on: https://go-review.googlesource.com/c/go/+/355570
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

5 files changed, 184 insertions, 119 deletions

diff --git a/src/syscall/exec_freebsd.go b/src/syscall/exec_freebsd.go
index 393b3d485b..a7410db4b6 100644
--- a/src/syscall/exec_freebsd.go
+++ b/src/syscall/exec_freebsd.go
@@ -5,6 +5,7 @@
 package syscall
 
 import (
+	"runtime"
 	"unsafe"
 )
 
@@ -29,9 +30,16 @@ type SysProcAttr struct {
 	// Unlike Setctty, in this case Ctty must be a descriptor
 	// number in the parent process.
 	Foreground bool
-	Pgid       int // Child's process group ID if Setpgid.
+	Pgid       int    // Child's process group ID if Setpgid.
+	Pdeathsig  Signal // Signal that the process will get when its parent dies (Linux and FreeBSD only)
 }
 
+const (
+	_P_PID = 0
+
+	_PROC_PDEATHSIG_CTL = 11
+)
+
 // Implemented in runtime package.
 func runtime_BeforeFork()
 func runtime_AfterFork()
@@ -57,6 +65,9 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		i      int
 	)
 
+	// Record parent PID so child can test if it has died.
+	ppid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
+
 	// guard against side effects of shuffling fds below.
 	// Make sure that nextfd is beyond any currently open files so
 	// that we can't run the risk of overwriting any of them.
@@ -175,6 +186,31 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
+	// Parent death signal
+	if sys.Pdeathsig != 0 {
+		switch runtime.GOARCH {
+		case "386", "arm":
+			_, _, err1 = RawSyscall6(SYS_PROCCTL, _P_PID, 0, 0, _PROC_PDEATHSIG_CTL, uintptr(unsafe.Pointer(&sys.Pdeathsig)), 0)
+		default:
+			_, _, err1 = RawSyscall6(SYS_PROCCTL, _P_PID, 0, _PROC_PDEATHSIG_CTL, uintptr(unsafe.Pointer(&sys.Pdeathsig)), 0, 0)
+		}
+		if err1 != 0 {
+			goto childerror
+		}
+
+		// Signal self if parent is already dead. This might cause a
+		// duplicate signal in rare cases, but it won't matter when
+		// using SIGKILL.
+		r1, _, _ = RawSyscall(SYS_GETPPID, 0, 0, 0)
+		if r1 != ppid {
+			pid, _, _ := RawSyscall(SYS_GETPID, 0, 0, 0)
+			_, _, err1 := RawSyscall(SYS_KILL, pid, uintptr(sys.Pdeathsig), 0)
+			if err1 != 0 {
+				goto childerror
+			}
+		}
+	}
+
 	// Pass 1: look for fd[i] < i and move those up above len(fd)
 	// so that pass 2 won't stomp on an fd it needs later.
 	if pipe < nextfd {
diff --git a/src/syscall/exec_linux.go b/src/syscall/exec_linux.go
index dfc5228545..e1506e1e2b 100644
--- a/src/syscall/exec_linux.go
+++ b/src/syscall/exec_linux.go
@@ -46,7 +46,7 @@ type SysProcAttr struct {
 	// number in the parent process.
 	Foreground   bool
 	Pgid         int            // Child's process group ID if Setpgid.
-	Pdeathsig    Signal         // Signal that the process will get when its parent dies (Linux only)
+	Pdeathsig    Signal         // Signal that the process will get when its parent dies (Linux and FreeBSD only)
 	Cloneflags   uintptr        // Flags for clone calls (Linux only)
 	Unshareflags uintptr        // Flags for unshare calls (Linux only)
 	UidMappings  []SysProcIDMap // User ID mappings for user namespaces.
diff --git a/src/syscall/exec_pdeathsig_test.go b/src/syscall/exec_pdeathsig_test.go
new file mode 100644
index 0000000000..6533d3a138
--- /dev/null
+++ b/src/syscall/exec_pdeathsig_test.go
@@ -0,0 +1,135 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build freebsd || linux
+// +build freebsd linux
+
+package syscall_test
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"os/signal"
+	"path/filepath"
+	"syscall"
+	"testing"
+	"time"
+)
+
+func TestDeathSignal(t *testing.T) {
+	if os.Getuid() != 0 {
+		t.Skip("skipping root only test")
+	}
+
+	// Copy the test binary to a location that a non-root user can read/execute
+	// after we drop privileges
+	tempDir, err := os.MkdirTemp("", "TestDeathSignal")
+	if err != nil {
+		t.Fatalf("cannot create temporary directory: %v", err)
+	}
+	defer os.RemoveAll(tempDir)
+	os.Chmod(tempDir, 0755)
+
+	tmpBinary := filepath.Join(tempDir, filepath.Base(os.Args[0]))
+
+	src, err := os.Open(os.Args[0])
+	if err != nil {
+		t.Fatalf("cannot open binary %q, %v", os.Args[0], err)
+	}
+	defer src.Close()
+
+	dst, err := os.OpenFile(tmpBinary, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0755)
+	if err != nil {
+		t.Fatalf("cannot create temporary binary %q, %v", tmpBinary, err)
+	}
+	if _, err := io.Copy(dst, src); err != nil {
+		t.Fatalf("failed to copy test binary to %q, %v", tmpBinary, err)
+	}
+	err = dst.Close()
+	if err != nil {
+		t.Fatalf("failed to close test binary %q, %v", tmpBinary, err)
+	}
+
+	cmd := exec.Command(tmpBinary)
+	cmd.Env = append(os.Environ(), "GO_DEATHSIG_PARENT=1")
+	chldStdin, err := cmd.StdinPipe()
+	if err != nil {
+		t.Fatalf("failed to create new stdin pipe: %v", err)
+	}
+	chldStdout, err := cmd.StdoutPipe()
+	if err != nil {
+		t.Fatalf("failed to create new stdout pipe: %v", err)
+	}
+	cmd.Stderr = os.Stderr
+
+	err = cmd.Start()
+	defer cmd.Wait()
+	if err != nil {
+		t.Fatalf("failed to start first child process: %v", err)
+	}
+
+	chldPipe := bufio.NewReader(chldStdout)
+
+	if got, err := chldPipe.ReadString('\n'); got == "start\n" {
+		syscall.Kill(cmd.Process.Pid, syscall.SIGTERM)
+
+		go func() {
+			time.Sleep(5 * time.Second)
+			chldStdin.Close()
+		}()
+
+		want := "ok\n"
+		if got, err = chldPipe.ReadString('\n'); got != want {
+			t.Fatalf("expected %q, received %q, %v", want, got, err)
+		}
+	} else {
+		t.Fatalf("did not receive start from child, received %q, %v", got, err)
+	}
+}
+
+func deathSignalParent() {
+	cmd := exec.Command(os.Args[0])
+	cmd.Env = append(os.Environ(),
+		"GO_DEATHSIG_PARENT=",
+		"GO_DEATHSIG_CHILD=1",
+	)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	attrs := syscall.SysProcAttr{
+		Pdeathsig: syscall.SIGUSR1,
+		// UID/GID 99 is the user/group "nobody" on RHEL/Fedora and is
+		// unused on Ubuntu
+		Credential: &syscall.Credential{Uid: 99, Gid: 99},
+	}
+	cmd.SysProcAttr = &attrs
+
+	err := cmd.Start()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "death signal parent error: %v\n", err)
+		os.Exit(1)
+	}
+	cmd.Wait()
+	os.Exit(0)
+}
+
+func deathSignalChild() {
+	c := make(chan os.Signal, 1)
+	signal.Notify(c, syscall.SIGUSR1)
+	go func() {
+		<-c
+		fmt.Println("ok")
+		os.Exit(0)
+	}()
+	fmt.Println("start")
+
+	buf := make([]byte, 32)
+	os.Stdin.Read(buf)
+
+	// We expected to be signaled before stdin closed
+	fmt.Println("not ok")
+	os.Exit(1)
+}
diff --git a/src/syscall/syscall_freebsd_test.go b/src/syscall/syscall_freebsd_test.go
index 89c7959d0c..72cd133b85 100644
--- a/src/syscall/syscall_freebsd_test.go
+++ b/src/syscall/syscall_freebsd_test.go
@@ -9,6 +9,7 @@ package syscall_test
 
 import (
 	"fmt"
+	"os"
 	"syscall"
 	"testing"
 	"unsafe"
@@ -53,3 +54,13 @@ func TestConvertFromDirent11(t *testing.T) {
 		}
 	}
 }
+
+func TestMain(m *testing.M) {
+	if os.Getenv("GO_DEATHSIG_PARENT") == "1" {
+		deathSignalParent()
+	} else if os.Getenv("GO_DEATHSIG_CHILD") == "1" {
+		deathSignalChild()
+	}
+
+	os.Exit(m.Run())
+}
diff --git a/src/syscall/syscall_linux_test.go b/src/syscall/syscall_linux_test.go
index 442dc9f10e..8d828be015 100644
--- a/src/syscall/syscall_linux_test.go
+++ b/src/syscall/syscall_linux_test.go
@@ -5,13 +5,11 @@
 package syscall_test
 
 import (
-	"bufio"
 	"fmt"
 	"io"
 	"io/fs"
 	"os"
 	"os/exec"
-	"os/signal"
 	"path/filepath"
 	"runtime"
 	"sort"
@@ -19,7 +17,6 @@ import (
 	"strings"
 	"syscall"
 	"testing"
-	"time"
 	"unsafe"
 )
 
@@ -153,120 +150,6 @@ func TestMain(m *testing.M) {
 	os.Exit(m.Run())
 }
 
-func TestLinuxDeathSignal(t *testing.T) {
-	if os.Getuid() != 0 {
-		t.Skip("skipping root only test")
-	}
-
-	// Copy the test binary to a location that a non-root user can read/execute
-	// after we drop privileges
-	tempDir, err := os.MkdirTemp("", "TestDeathSignal")
-	if err != nil {
-		t.Fatalf("cannot create temporary directory: %v", err)
-	}
-	defer os.RemoveAll(tempDir)
-	os.Chmod(tempDir, 0755)
-
-	tmpBinary := filepath.Join(tempDir, filepath.Base(os.Args[0]))
-
-	src, err := os.Open(os.Args[0])
-	if err != nil {
-		t.Fatalf("cannot open binary %q, %v", os.Args[0], err)
-	}
-	defer src.Close()
-
-	dst, err := os.OpenFile(tmpBinary, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0755)
-	if err != nil {
-		t.Fatalf("cannot create temporary binary %q, %v", tmpBinary, err)
-	}
-	if _, err := io.Copy(dst, src); err != nil {
-		t.Fatalf("failed to copy test binary to %q, %v", tmpBinary, err)
-	}
-	err = dst.Close()
-	if err != nil {
-		t.Fatalf("failed to close test binary %q, %v", tmpBinary, err)
-	}
-
-	cmd := exec.Command(tmpBinary)
-	cmd.Env = append(os.Environ(), "GO_DEATHSIG_PARENT=1")
-	chldStdin, err := cmd.StdinPipe()
-	if err != nil {
-		t.Fatalf("failed to create new stdin pipe: %v", err)
-	}
-	chldStdout, err := cmd.StdoutPipe()
-	if err != nil {
-		t.Fatalf("failed to create new stdout pipe: %v", err)
-	}
-	cmd.Stderr = os.Stderr
-
-	err = cmd.Start()
-	defer cmd.Wait()
-	if err != nil {
-		t.Fatalf("failed to start first child process: %v", err)
-	}
-
-	chldPipe := bufio.NewReader(chldStdout)
-
-	if got, err := chldPipe.ReadString('\n'); got == "start\n" {
-		syscall.Kill(cmd.Process.Pid, syscall.SIGTERM)
-
-		go func() {
-			time.Sleep(5 * time.Second)
-			chldStdin.Close()
-		}()
-
-		want := "ok\n"
-		if got, err = chldPipe.ReadString('\n'); got != want {
-			t.Fatalf("expected %q, received %q, %v", want, got, err)
-		}
-	} else {
-		t.Fatalf("did not receive start from child, received %q, %v", got, err)
-	}
-}
-
-func deathSignalParent() {
-	cmd := exec.Command(os.Args[0])
-	cmd.Env = append(os.Environ(),
-		"GO_DEATHSIG_PARENT=",
-		"GO_DEATHSIG_CHILD=1",
-	)
-	cmd.Stdin = os.Stdin
-	cmd.Stdout = os.Stdout
-	attrs := syscall.SysProcAttr{
-		Pdeathsig: syscall.SIGUSR1,
-		// UID/GID 99 is the user/group "nobody" on RHEL/Fedora and is
-		// unused on Ubuntu
-		Credential: &syscall.Credential{Uid: 99, Gid: 99},
-	}
-	cmd.SysProcAttr = &attrs
-
-	err := cmd.Start()
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "death signal parent error: %v\n", err)
-		os.Exit(1)
-	}
-	cmd.Wait()
-	os.Exit(0)
-}
-
-func deathSignalChild() {
-	c := make(chan os.Signal, 1)
-	signal.Notify(c, syscall.SIGUSR1)
-	go func() {
-		<-c
-		fmt.Println("ok")
-		os.Exit(0)
-	}()
-	fmt.Println("start")
-
-	buf := make([]byte, 32)
-	os.Stdin.Read(buf)
-
-	// We expected to be signaled before stdin closed
-	fmt.Println("not ok")
-	os.Exit(1)
-}
-
 func TestParseNetlinkMessage(t *testing.T) {
 	for i, b := range [][]byte{
 		{103, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 5, 8, 0, 3,