syscall: restore signal mask after setting foreground process group

Fixes #37217

Change-Id: I0151bb77fc4c4552d1b19c31d784943b72f84b80
Reviewed-on: https://go-review.googlesource.com/c/go/+/313653
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/syscall/exec_bsd.go

@@ -90,8 +90,6 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 
 	// Fork succeeded, now in child.
 
-	runtime_AfterForkInChild()
-
 	// Enable tracing if requested.
 	if sys.Ptrace {
 		_, _, err1 = RawSyscall(SYS_PTRACE, uintptr(PTRACE_TRACEME), 0, 0)
@@ -137,6 +135,10 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
+	// Restore the signal mask. We do this after TIOCSPGRP to avoid
+	// having the kernel send a SIGTTOU signal to the process group.
+	runtime_AfterForkInChild()
+
 	// Chroot
 	if chroot != nil {
 		_, _, err1 = RawSyscall(SYS_CHROOT, uintptr(unsafe.Pointer(chroot)), 0, 0)

src/syscall/exec_libc.go

@@ -116,8 +116,6 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 
 	// Fork succeeded, now in child.
 
-	runtime_AfterForkInChild()
-
 	// Session ID
 	if sys.Setsid {
 		_, err1 = setsid()
@@ -153,6 +151,10 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
+	// Restore the signal mask. We do this after TIOCSPGRP to avoid
+	// having the kernel send a SIGTTOU signal to the process group.
+	runtime_AfterForkInChild()
+
 	// Chroot
 	if chroot != nil {
 		err1 = chroot1(uintptr(unsafe.Pointer(chroot)))

src/syscall/exec_libc2.go

@@ -91,8 +91,6 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 
 	// Fork succeeded, now in child.
 
-	runtime_AfterForkInChild()
-
 	// Enable tracing if requested.
 	if sys.Ptrace {
 		if err := ptrace(PTRACE_TRACEME, 0, 0, 0); err != nil {
@@ -136,6 +134,10 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
+	// Restore the signal mask. We do this after TIOCSPGRP to avoid
+	// having the kernel send a SIGTTOU signal to the process group.
+	runtime_AfterForkInChild()
+
 	// Chroot
 	if chroot != nil {
 		_, _, err1 = rawSyscall(abi.FuncPCABI0(libc_chroot_trampoline), uintptr(unsafe.Pointer(chroot)), 0, 0)

src/syscall/exec_linux.go

@@ -233,8 +233,6 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 
 	// Fork succeeded, now in child.
 
-	runtime_AfterForkInChild()
-
 	// Enable the "keep capabilities" flag to set ambient capabilities later.
 	if len(sys.AmbientCaps) > 0 {
 		_, _, err1 = RawSyscall6(SYS_PRCTL, PR_SET_KEEPCAPS, 1, 0, 0, 0, 0)
@@ -294,6 +292,10 @@ func forkAndExecInChild1(argv0 *byte, argv, envv []*byte, chroot, dir *byte, att
 		}
 	}
 
+	// Restore the signal mask. We do this after TIOCSPGRP to avoid
+	// having the kernel send a SIGTTOU signal to the process group.
+	runtime_AfterForkInChild()
+
 	// Unshare
 	if sys.Unshareflags != 0 {
 		_, _, err1 = RawSyscall(SYS_UNSHARE, sys.Unshareflags, 0, 0)

src/syscall/exec_unix_test.go

@@ -167,11 +167,13 @@ func TestPgid(t *testing.T) {
 
 func TestForeground(t *testing.T) {
 	signal.Ignore(syscall.SIGTTIN, syscall.SIGTTOU)
+	defer signal.Reset()
 
 	tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0)
 	if err != nil {
 		t.Skipf("Can't test Foreground. Couldn't open /dev/tty: %s", err)
 	}
+	defer tty.Close()
 
 	// This should really be pid_t, however _C_int (aka int32) is generally
 	// equivalent.
@@ -216,8 +218,45 @@ func TestForeground(t *testing.T) {
 	if errno != 0 {
 		t.Fatalf("TIOCSPGRP failed with error code: %s", errno)
 	}
+}
 
-	signal.Reset()
+func TestForegroundSignal(t *testing.T) {
+	tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("couldn't open /dev/tty: %s", err)
+	}
+	defer tty.Close()
+
+	ch1 := make(chan os.Signal, 1)
+	ch2 := make(chan bool)
+
+	signal.Notify(ch1, syscall.SIGTTIN, syscall.SIGTTOU)
+	defer signal.Stop(ch1)
+
+	go func() {
+		cmd := create(t)
+		cmd.proc.SysProcAttr = &syscall.SysProcAttr{
+			Ctty:       int(tty.Fd()),
+			Foreground: true,
+		}
+		cmd.Start()
+		cmd.Stop()
+		close(ch2)
+	}()
+
+	timer := time.NewTimer(30 * time.Second)
+	defer timer.Stop()
+	for {
+		select {
+		case sig := <-ch1:
+			t.Errorf("unexpected signal %v", sig)
+		case <-ch2:
+			// Success.
+			return
+		case <-timer.C:
+			t.Fatal("timed out waiting for child process")
+		}
+	}
 }
 
 // Test a couple of cases that SysProcAttr can't handle. Issue 29458.