runsc: Terminal resizing support.

Implements the TIOCGWINSZ and TIOCSWINSZ ioctls, which allow processes to resize
the terminal. This allows, for example, sshd to properly set the window size for
ssh sessions.

PiperOrigin-RevId: 210392504
Change-Id: I0d4789154d6d22f02509b31d71392e13ee4a50ba

pkg/abi/linux/tty.go

@@ -328,3 +328,13 @@ var DefaultSlaveTermios = KernelTermios{
 	InputSpeed:        38400,
 	OutputSpeed:       38400,
 }
+
+// WindowSize corresponds to struct winsize defined in
+// include/uapi/asm-generic/termios.h.
+//
+// +stateify savable
+type WindowSize struct {
+	Rows uint16
+	Cols uint16
+	_    [4]byte // Padding for 2 unused shorts.
+}

pkg/sentry/fs/tty/line_discipline.go

@@ -76,6 +76,12 @@ const (
 //
 // +stateify savable
 type lineDiscipline struct {
+	// sizeMu protects size.
+	sizeMu sync.Mutex `state:"nosave"`
+
+	// size is the terminal size (width and height).
+	size linux.WindowSize
+
 	// inQueue is the input queue of the terminal.
 	inQueue queue
 
@@ -142,6 +148,24 @@ func (l *lineDiscipline) setTermios(ctx context.Context, io usermem.IO, args arc
 	return 0, err
 }
 
+func (l *lineDiscipline) windowSize(ctx context.Context, io usermem.IO, args arch.SyscallArguments) error {
+	l.sizeMu.Lock()
+	defer l.sizeMu.Unlock()
+	_, err := usermem.CopyObjectOut(ctx, io, args[2].Pointer(), l.size, usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	return err
+}
+
+func (l *lineDiscipline) setWindowSize(ctx context.Context, io usermem.IO, args arch.SyscallArguments) error {
+	l.sizeMu.Lock()
+	defer l.sizeMu.Unlock()
+	_, err := usermem.CopyObjectIn(ctx, io, args[2].Pointer(), &l.size, usermem.IOOpts{
+		AddressSpaceActive: true,
+	})
+	return err
+}
+
 func (l *lineDiscipline) masterReadiness() waiter.EventMask {
 	// We don't have to lock a termios because the default master termios
 	// is immutable.

pkg/sentry/fs/tty/master.go

@@ -172,6 +172,10 @@ func (mf *masterFileOperations) Ioctl(ctx context.Context, io usermem.IO, args a
 	case linux.TIOCSPTLCK:
 		// TODO: Implement pty locking. For now just pretend we do.
 		return 0, nil
+	case linux.TIOCGWINSZ:
+		return 0, mf.t.ld.windowSize(ctx, io, args)
+	case linux.TIOCSWINSZ:
+		return 0, mf.t.ld.setWindowSize(ctx, io, args)
 	default:
 		return 0, syserror.ENOTTY
 	}

pkg/sentry/fs/tty/slave.go

@@ -150,6 +150,10 @@ func (sf *slaveFileOperations) Ioctl(ctx context.Context, io usermem.IO, args ar
 			AddressSpaceActive: true,
 		})
 		return 0, err
+	case linux.TIOCGWINSZ:
+		return 0, sf.si.t.ld.windowSize(ctx, io, args)
+	case linux.TIOCSWINSZ:
+		return 0, sf.si.t.ld.setWindowSize(ctx, io, args)
 	default:
 		return 0, syserror.ENOTTY
 	}